Caenorhabditis elegans

File:CrawlingCelegans.gif

C.{{nbsp}}elegans is unsegmented, vermiform, and bilaterally symmetrical. It has a cuticle (a strong outer covering, as an exoskeleton), four main epidermal cords, and a fluid-filled pseudocoelom (body cavity). It also has some of the same organ systems as larger animals. About one in a thousand individuals is male and the rest are hermaphrodites.{{cite book | vauthors = Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P | year = 2007 | title = Molecular Biology of the Cell | edition = 5th | page = 1321 | publisher = Garland Science | isbn = 978-0-8153-4105-5 }} The basic anatomy of C.{{nbsp}}elegans includes a mouth, pharynx, intestine, gonad, and collagenous cuticle. Like all nematodes, they have neither a circulatory nor a respiratory system. The four bands of muscles that run the length of the body are connected to a neural system that allows the muscles to move the animal's body only as dorsal bending or ventral bending, but not left or right, except for the head, where the four muscle quadrants are wired independently from one another. When a wave of dorsal/ventral muscle contractions proceeds from the back to the front of the animal, the animal is propelled backwards. When a wave of contractions is initiated at the front and proceeds posteriorly along the body, the animal is propelled forwards. Because of this dorsal/ventral bias in body bends, any normal living, moving individual tends to lie on either its left side or its right side when observed crossing a horizontal surface. A set of ridges on the lateral sides of the body cuticle, the alae, is believed to give the animal added traction during these bending motions.

File:Caenorhabditis elegans hermaphrodite adult-en.svg

File:C_elegans_tissues.svg

File:C_elegans_cell_and_nucleus_sizes.svg

In relation to lipid metabolism, C.{{nbsp}}elegans does not have any specialized adipose tissues, a pancreas, a liver, or even blood to deliver nutrients compared to mammals. Neutral lipids are instead stored in the intestine, epidermis, and embryos. The epidermis corresponds to the mammalian adipocytes by being the main triglyceride depot.{{cite journal | vauthors = Lemieux GA, Ashrafi K | title = Investigating Connections between Metabolism, Longevity, and Behavior in Caenorhabditis elegans | journal = Trends in Endocrinology and Metabolism | volume = 27 | issue = 8 | pages = 586–596 | date = August 2016 | pmid = 27289335 | pmc = 4958586 | doi = 10.1016/j.tem.2016.05.004 }}

The pharynx is a muscular food pump in the head of C.{{nbsp}}elegans, which is triangular in cross-section. This grinds food and transports it directly to the intestine. A set of "valve cells" connects the pharynx to the intestine, but how this valve operates is not understood. After digestion, the contents of the intestine are released via the rectum, as is the case with all other nematodes.{{Cite web|url=http://www.wormbook.org/chapters/www_organformation/organformation.html|title=The C. elegans pharynx: a model for organogenesis|website=www.wormbook.org|access-date=2017-03-15}} No direct connection exists between the pharynx and the excretory canal, which functions in the release of liquid urine.

Males have a single-lobed gonad, a vas deferens, and a tail specialized for mating, which incorporates spicules. Hermaphrodites have two ovaries, oviducts, and spermatheca, and a single uterus.

File:C elegans male.svg

File:C. elegans with pencil for scale.webm

There are 302 neurons in C.{{nbsp}}elegans, approximately one-third of all the somatic cells in the whole body.{{cite book | vauthors=Soares FA, Fagundez DA, Avila DS | chapter=Neurodegeneration Induced by Metals in Caenorhabditis elegans | series=Advances in Neurobiology | title=Neurotoxicity of Metals | volume=18 | pages=55–383 | year=2017 | doi = 10.1007/978-3-319-60189-2_18 | pmid=28889277| isbn=978-3-319-60188-5 }} Many neurons contain dendrites which extend from the cell to receive neurotransmitters or other signals, and a process that extends to the nerve ring (the "brain") for a synaptic connection with other neurons.Nonet, M. (2004) [https://web.archive.org/web/20150302133204/http://thalamus.wustl.edu/nonetlab/ResearchF/elegans.html About the nematode Caenorhabdtis elegans] C.{{nbsp}}elegans has excitatory cholinergic and inhibitory GABAergic motor neurons which connect with body wall muscles to regulate movement. In addition, these neurons and other neurons such as interneurons use a variety of neurotransmitters to control behaviors.{{Cite journal |doi=10.1895/wormbook.1.12.1|pmid=18050401|pmc=4781215|title=Specification of the nervous system|journal=WormBook|pages=1–19|year=2005|last1=Hobert|first1=Oliver}}

File:Nematode Caenorhabditis Elegans (cropped).jpg

Numerous gut granules are present in the intestine of C.{{nbsp}}elegans, the functions of which are still not fully known, as are many other aspects of this nematode, despite the many years that it has been studied. These gut granules are found in all of the Rhabditida orders. They are very similar to lysosomes in that they feature an acidic interior and the capacity for endocytosis, but they are considerably larger, reinforcing the view of their being storage organelles.

A particular feature of the granules is that when they are observed under ultraviolet light, they react by emitting an intense blue fluorescence. Another phenomenon seen is termed 'death fluorescence'. As the worms die, a dramatic burst of blue fluorescence is emitted. This death fluorescence typically takes place in an anterior to posterior wave that moves along the intestine, and is seen in both young and old worms, whether subjected to lethal injury or peacefully dying of old age.

Many theories have been posited on the functions of the gut granules, with earlier ones being eliminated by later findings. They are thought to store zinc as one of their functions. Recent chemical analysis has identified the blue fluorescent material they contain as a glycosylated form of anthranilic acid (AA). The need for the large amounts of AA the many gut granules contain is questioned. One possibility is that the AA is antibacterial and used in defense against invading pathogens. Another possibility is that the granules provide photoprotection; the bursts of AA fluorescence entail the conversion of damaging UV light to relatively harmless visible light. This is seen as a possible link to the melanin–containing melanosomes.

{{cite journal | vauthors = Coburn C, Gems D | title = The mysterious case of the C. elegans gut granule: death fluorescence, anthranilic acid and the kynurenine pathway | journal = Frontiers in Genetics | volume = 4 | pages = 151 | year = 2013 | pmid = 23967012 | pmc = 3735983 | doi = 10.3389/fgene.2013.00151 | doi-access = free }}

The hermaphroditic worm is considered to be a specialized form of self-fertile female, as its soma is female. The hermaphroditic germline produces male gametes first, and lays eggs through its uterus after internal fertilization. Hermaphrodites produce all their sperm in the L4 stage (150 sperm cells per gonadal arm) and then produce only oocytes. The hermaphroditic gonad acts as an ovotestis with sperm cells being stored in the same area of the gonad as the oocytes until the first oocyte pushes the sperm into the spermatheca (a chamber wherein the oocytes become fertilized by the sperm).

{{cite journal | vauthors = Nayak S, Goree J, Schedl T | title = fog-2 and the evolution of self-fertile hermaphroditism in Caenorhabditis | journal = PLOS Biology | volume = 3 | issue = 1 | pages = e6 | date = January 2005 | pmid = 15630478 | pmc = 539060 | doi = 10.1371/journal.pbio.0030006 | doi-access = free }}

The male can inseminate the hermaphrodite, which will preferentially use male sperm (both types of sperm are stored in the spermatheca).

File:Male Mating.gif The sperm of C. elegans is amoeboid, lacking flagella and acrosomes.{{cite journal | vauthors = Ma X, Zhao Y, Sun W, Shimabukuro K, Miao L | title = Transformation: how do nematode sperm become activated and crawl? | journal = Protein & Cell | volume = 3 | issue = 10 | pages = 755–61 | date = October 2012 | pmid = 22903434 | pmc = 4875351 | doi = 10.1007/s13238-012-2936-2 }} When self-inseminated, the wild-type worm lays about 300 eggs. When inseminated by a male, the number of progeny can exceed 1,000. Hermaphrodites do not typically mate with other hermaphrodites. At 20 °C, the laboratory strain of C. elegans (N2) has an average lifespan around 2–3 weeks and a generation time of 3 to 4 days.

C. elegans has five pairs of autosomes and one pair of sex chromosomes. Sex in C. elegans is based on an X0 sex-determination system. Hermaphrodites of C. elegans have a matched pair of sex chromosomes (XX); the rare males have only one sex chromosome (X0).

C. elegans are mostly hermaphroditic organisms, producing both sperms and oocytes.{{cite journal | vauthors = Starostina NG, Lim JM, Schvarzstein M, Wells L, Spence AM, Kipreos ET | title = A CUL-2 ubiquitin ligase containing three FEM proteins degrades TRA-1 to regulate C. elegans sex determination | journal = Developmental Cell | volume = 13 | issue = 1 | pages = 127–39 | date = July 2007 | pmid = 17609115 | doi = 10.1016/j.devcel.2007.05.008 | pmc = 2064902 }} Males do occur in the population in a rate of approximately 1 in 200 hermaphrodites, but the two sexes are highly differentiated.{{Cite web|title=Handbook - Male Introduction|url=https://www.wormatlas.org/male/introduction/mainframe.htm|access-date=2021-03-30|website=www.wormatlas.org}} Males differ from their hermaphroditic counterparts in that they are smaller and can be identified through the shape of their tail. C.elegans reproduce through a process called androdioecy. This means that they can reproduce in two ways: either through self-fertilization in hermaphrodites or through hermaphrodites breeding with males. Males are produced through non-disjunction of the X chromosomes during meiosis. The worms that reproduce through self-fertilization are at risk for high linkage disequilibrium, which leads to lower genetic diversity in populations and an increase in accumulation of deleterious alleles.{{cite journal | vauthors = Frézal L, Félix MA | title = C. elegans outside the Petri dish | journal = eLife | volume = 4 | pages = e05849 | date = March 2015 | pmid = 25822066 | doi = 10.7554/eLife.05849 | pmc = 4373675 | doi-access = free }} In C. elegans, somatic sex determination is attributed to the tra-1 gene.{{Cite journal|date=1999-08-06|title=The TRA-1A Sex Determination Protein of C. elegans Regulates Sexually Dimorphic Cell Deaths by Repressing the egl-1 Cell Death Activator Gene|journal=Cell|language=en|volume=98|issue=3|pages=317–327|doi=10.1016/S0092-8674(00)81961-3|issn=0092-8674|last1=Conradt|first1=Barbara|last2=Horvitz|first2=H.Robert|pmid=10458607|s2cid=14951719|doi-access=free}} The tra-1 is a gene within the TRA-1 transcription factor sex determination pathway that is regulated post-transcriptionally and works by promoting female development. In hermaphrodites (XX), there are high levels of tra-1 activity, which produces the female reproductive system and inhibits male development. At a certain time in their life cycle, one day before adulthood, hermaphrodites can be identified through the addition of a vulva near their tail. In males (XO), there are low levels of tra-1 activity, resulting in a male reproductive system. Recent research has shown that there are three other genes, fem-1, fem-2, and fem-3, that negatively regulate the TRA-1 pathway and act as the final determiner of sex in C. elegans.

The sex determination system in C. elegans is a topic that has been of interest to scientists for years.{{cite journal | vauthors = Haag ES | title = The evolution of nematode sex determination: C. elegans as a reference point for comparative biology | journal = WormBook: The Online Review of C. Elegans Biology | volume = | issue = | pages = 1–14 | date = December 2005 | pmid = 18050417 | pmc = 4781019 | doi = 10.1895/wormbook.1.120.1 }} Since they are used as a model organism, any information discovered about the way their sex determination system might have evolved could further the same evolutionary biology research in other organisms. After almost 30 years of research, scientists have begun to put together the pieces in the evolution of such a system. What they have discovered is that there is a complex pathway involved that has several layers of regulation. The closely related organism Caenorhabditis briggsae has been studied extensively and its whole genome sequence has helped put together the missing pieces in the evolution of C. elegans sex determination. It has been discovered that two genes have assimilated, leading to the proteins XOL-1 and MIX-1 having an effect on sex determination in C. elegans as well. Mutations in the XOL-1 pathway leads to feminization in C. elegans .{{cite journal | vauthors = Miller LM, Plenefisch JD, Casson LP, Meyer BJ | title = xol-1: a gene that controls the male modes of both sex determination and X chromosome dosage compensation in C. elegans | language = English | journal = Cell | volume = 55 | issue = 1 | pages = 167–83 | date = October 1988 | pmid = 3167975 | doi = 10.1016/0092-8674(88)90019-0 | s2cid = 5005906 }} The mix-1 gene is known to hypoactivate the X chromosome and regulates the morphology of the male tail in C. elegans.{{Cite web|title=mix-1 (gene) - WormBase : Nematode Information Resource|url=https://wormbase.org/species/c_elegans/gene/WBGene00003367#0-9f-10|access-date=2021-04-23|website=wormbase.org}} Looking at the nematode as a whole, the male and hermaphrodite sex likely evolved from parallel evolution. Parallel evolution is defined as similar traits evolving from an ancestor in similar conditions; simply put, the two species evolve in similar ways over time. An example of this would be marsupial and placental mammals. Scientists have also hypothesized that hermaphrodite asexual reproduction, or "selfing", could have evolved convergently by studying species similar to C. elegans Other studies on the sex determination evolution suggest that genes involving sperm evolve at the faster rate than female genes.{{cite journal | vauthors = Cutter AD, Ward S | title = Sexual and temporal dynamics of molecular evolution in C. elegans development | journal = Molecular Biology and Evolution | volume = 22 | issue = 1 | pages = 178–88 | date = January 2005 | pmid = 15371532 | doi = 10.1093/molbev/msh267 | doi-access = free }} However, sperm genes on the X chromosome have reduced evolution rates. Sperm genes have short coding sequences, high codon bias, and disproportionate representation among orphan genes. These characteristics of sperm genes may be the reason for their high rates of evolution and may also suggest how sperm genes evolved out of hermaphrodite worms. Overall, scientists have a general idea of the sex determination pathway in C. elegans, however, the evolution of how this pathway came to be is not yet well defined.

File:C._elegans_embryo_development.tif

The fertilized zygote undergoes rotational holoblastic cleavage.

Sperm entry into the oocyte commences formation of an anterior-posterior axis.{{cite journal | vauthors = Goldstein B, Hird SN | title = Specification of the anteroposterior axis in Caenorhabditis elegans | journal = Development | volume = 122 | issue = 5 | pages = 1467–74 | date = May 1996 | pmid = 8625834 | doi = 10.1242/dev.122.5.1467 | url = https://pubmed.ncbi.nlm.nih.gov/8625834/ }} The sperm microtubule organizing center directs the movement of the sperm pronucleus to the future posterior pole of the embryo, while also inciting the movement of PAR proteins, a group of cytoplasmic determination factors, to their proper respective locations.{{cite book | title=Developmental biology| edition=11th| author=Gilbert SF| year=2016| pages=268| publisher=Sinauer| isbn=9781605354705}} As a result of the difference in PAR protein distribution, the first cell division is highly asymmetric.{{cite journal | vauthors = Guo S, Kemphues KJ | title = par-1, a gene required for establishing polarity in C. elegans embryos, encodes a putative Ser/Thr kinase that is asymmetrically distributed | journal = Cell | volume = 81 | issue = 4 | pages = 611–20 | date = May 1995 | pmid = 7758115 | doi = 10.1016/0092-8674(95)90082-9 | doi-access = free }} C. elegans embryogenesis is among the best understood examples of asymmetric cell division.{{cite journal | vauthors = Gönczy P, Rose LS | title = Asymmetric cell division and axis formation in the embryo | journal = WormBook | pages = 1–20 | date = October 2005 | pmid = 18050411 | pmc = 4780927 | doi = 10.1895/wormbook.1.30.1 }}

All cells of the germline arise from a single primordial germ cell, called the P4 cell, established early in embryogenesis.Kimble J, Crittenden SL. Germline proliferation and its control. 2005 Aug 15. In: WormBook: The Online Review of C. elegans Biology [Internet]. Pasadena (CA): WormBook; 2005-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK19769/{{cite encyclopedia | title=WBbt:0006773 (anatomy term) | encyclopedia=WormBase |edition=WS242 |id=WBbt:0006773 |date=May 14, 2014}} This primordial cell divides to generate two germline precursors that do not divide further until after hatching.

The resulting daughter cells of the first cell division are called the AB cell (containing PAR-6 and PAR-3) and the P1 cell (containing PAR-1 and PAR-2). A second cell division produces the ABp and ABa cells from the AB cell, and the EMS and P2 cells from the P1 cell. This division establishes the dorsal-ventral axis, with the ABp cell forming the dorsal side and the EMS cell marking the ventral side.{{cite book | title=Developmental biology| edition=11th| author=Gilbert SF| year=2016| pages=272| publisher=Sinauer| isbn=9781605354705}} Through Wnt signaling, the P2 cell instructs the EMS cell to divide along the anterior-posterior axis.{{cite journal | vauthors = Thorpe CJ, Schlesinger A, Carter JC, Bowerman B | title = Wnt signaling polarizes an early C. elegans blastomere to distinguish endoderm from mesoderm | journal = Cell | volume = 90 | issue = 4 | pages = 695–705 | date = August 1997 | pmid = 9288749 | doi = 10.1016/s0092-8674(00)80530-9 | doi-access = free }} Through Notch signaling, the P2 cell differentially specifies the ABp and ABa cells, which further defines the dorsal-ventral axis. The left-right axis also becomes apparent early in embryogenesis, although it is unclear exactly when specifically the axis is determined. However, most theories of the L-R axis development involve some kind of differences in cells derived from the AB cell.{{cite journal | vauthors = Pohl C, Bao Z | title = Chiral forces organize left-right patterning in C. elegans by uncoupling midline and anteroposterior axis | journal = Developmental Cell | volume = 19 | issue = 3 | pages = 402–12 | date = September 2010 | pmid = 20833362 | pmc = 2952354 | doi = 10.1016/j.devcel.2010.08.014 }} {{cite journal | pmid = 3073266 | volume=16 | title=[Quantification of sebaceous excretion in volunteers: influence of chronological age, sex and race] | year=1988 | journal=Med Cutan Ibero Lat Am | pages=439–44 | vauthors=Villares JC, Carlini EA| issue=6 }} {{cite book | title=Developmental biology| edition=11th| author=Gilbert SF| year=2016| pages=269| publisher=Sinauer| isbn=9781605354705}}

Gastrulation occurs after the embryo reaches the 24-cell stage.{{cite journal | vauthors = Skiba F, Schierenberg E | title = Cell lineages, developmental timing, and spatial pattern formation in embryos of free-living soil nematodes | journal = Developmental Biology | volume = 151 | issue = 2 | pages = 597–610 | date = June 1992 | pmid = 1601187 | doi = 10.1016/0012-1606(92)90197-o | url = https://pubmed.ncbi.nlm.nih.gov/1601187 }} C. elegans are a species of protostomes, so the blastopore eventually forms the mouth. Involution into the blastopore begins with movement of the endoderm cells and subsequent formation of the gut, followed by the P4 germline precursor, and finally the mesoderm cells, including the cells that eventually form the pharynx. Gastrulation ends when epiboly of the hypoblasts closes the blastopore.{{cite book | title=Developmental biology| edition=11th| author=Gilbert SF| year=2016| pages=273| publisher=Sinauer| isbn=9781605354705}}

File:C_elegans_developmental_stages.svg

File:C_elegans_life_cycle.svg

Under environmental conditions favourable for reproduction, hatched larvae develop through four larval stages - L1, L2, L3, and L4 - in just 3 days at 20 °C. When conditions are stressed, as in food insufficiency, excessive population density or high temperature, C. elegans can enter an alternative third larval stage, L2d, called the dauer stage (Dauer is German for permanent). A specific dauer pheromone regulates entry into the dauer state. This pheromone is composed of similar derivatives of the 3,6-dideoxy sugar, ascarylose. Ascarosides, named after the ascarylose base, are involved in many sex-specific and social behaviors.{{Cite journal|last1=Ludewig|first1=Andreas H.|last2=Schroeder|first2=Frank C.|date=2013-01-18|title=Ascaroside signaling in C. elegans|journal=WormBook|pages=1–22|doi=10.1895/wormbook.1.155.1|issn=1551-8507|pmc=3758900|pmid=23355522}} In this way, they constitute a chemical language that C. elegans uses to modulate various phenotypes. Dauer larvae are stress-resistant; they are thin and their mouths are sealed with a characteristic dauer cuticle and cannot take in food. They can remain in this stage for a few months.{{cite web |title=Introduction to C. Elegans |url=http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html |work=C. Elegans as a model organism |publisher=Rutgers University |url-status=dead |archive-url=https://web.archive.org/web/20020818213550/http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html |archive-date=2002-08-18 |access-date=August 15, 2014}}{{Cite web|url=http://www.wormatlas.org/hermaphrodite/introduction/mainframe.htm|title = Handbook - Introduction}} The stage ends when conditions improve favour further growth of the larva, now moulting into the L4 stage, even though the gonad development is arrested at the L2 stage.{{Cite web|url=http://www.wormbook.org/chapters/www_dauer/dauer.html|title=Dauer|website=www.wormbook.org|access-date=2018-09-27}}

Each stage transition is punctuated by a molt of the worm's transparent cuticle. Transitions through these stages are controlled by genes of the heterochronic pathway, an evolutionarily conserved set of regulatory factors.{{cite journal | vauthors = Resnick TD, McCulloch KA, Rougvie AE | title = miRNAs give worms the time of their lives: small RNAs and temporal control in Caenorhabditis elegans | journal = Developmental Dynamics | volume = 239 | issue = 5 | pages = 1477–89 | date = May 2010 | pmid = 20232378 | pmc = 4698981 | doi = 10.1002/dvdy.22260 }} Many heterochronic genes code for microRNAs, which repress the expression of heterochronic transcription factors and other heterochronic miRNAs.{{Cite book | vauthors = Rougvie AE, Moss EG | title = Developmental transitions in C. elegans larval stages | chapter = Developmental Transitions in C. Elegans Larval Stages | journal = Current Topics in Developmental Biology | series = Developmental Timing | volume = 105 | pages = 153–80 | year = 2013 | publisher = Academic Press | pmid = 23962842 | doi = 10.1016/B978-0-12-396968-2.00006-3 | url = https://pubmed.ncbi.nlm.nih.gov/23962842 | isbn = 9780123969682 }} miRNAs were originally discovered in C. elegans.{{cite journal | vauthors = Lee RC, Feinbaum RL, Ambros V | title = The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14 | journal = Cell | volume = 75 | issue = 5 | pages = 843–54 | date = December 1993 | pmid = 8252621 | doi = 10.1016/0092-8674(93)90529-y | doi-access = free }} Important developmental events controlled by heterochronic genes include the division and eventual syncitial fusion of the hypodermic seam cells, and their subsequent secretion of the alae in young adults. It is believed that the heterochronic pathway represents an evolutionarily conserved predecessor to circadian clocks.{{cite journal | vauthors = Banerjee D, Kwok A, Lin SY, Slack FJ | title = Developmental timing in C. elegans is regulated by kin-20 and tim-1, homologs of core circadian clock genes | journal = Developmental Cell | volume = 8 | issue = 2 | pages = 287–95 | date = February 2005 | pmid = 15691769 | doi = 10.1016/j.devcel.2004.12.006 | doi-access = free }}

Some nematodes have a fixed, genetically determined number of cells, a phenomenon known as eutely. The adult C. elegans hermaphrodite has 959 somatic cells and the male has 1033 cells,{{Cite journal|last1=Sulston|first1=J.E.|last2=Horvitz|first2=H.R.|date=March 1977|title=Post-embryonic cell lineages of the nematode, Caenorhabditis elegans|url=https://linkinghub.elsevier.com/retrieve/pii/0012160677901580|journal=Developmental Biology|language=en|volume=56|issue=1|pages=110–156|doi=10.1016/0012-1606(77)90158-0|pmid=838129}}{{Cite journal|last1=Sulston|first1=J.E.|last2=Schierenberg|first2=E.|last3=White|first3=J.G.|last4=Thomson|first4=J.N.|date=November 1983|title=The embryonic cell lineage of the nematode Caenorhabditis elegans|url=https://linkinghub.elsevier.com/retrieve/pii/0012160683902014|journal=Developmental Biology|language=en|volume=100|issue=1|pages=64–119|doi=10.1016/0012-1606(83)90201-4|pmid=6684600}}{{Cite journal|last1=Sammut|first1=Michele|last2=Cook|first2=Steven J.|last3=Nguyen|first3=Ken C. Q.|last4=Felton|first4=Terry|last5=Hall|first5=David H.|last6=Emmons|first6=Scott W.|last7=Poole|first7=Richard J.|last8=Barrios|first8=Arantza|date=October 2015|title=Glia-derived neurons are required for sex-specific learning in C. elegans|journal=Nature|language=en|volume=526|issue=7573|pages=385–390|doi=10.1038/nature15700|issn=0028-0836|pmc=4650210|pmid=26469050|bibcode=2015Natur.526..385S}} although it has been suggested that the number of their intestinal cells can increase by one to three in response to gut microbes experienced by mothers.{{Cite journal|last1=Ohno|first1=Hayao|last2=Bao|first2=Zhirong|date=2020-11-14|title=Small RNAs couple embryonic developmental programs to gut microbes|journal=bioRxiv|url=http://biorxiv.org/lookup/doi/10.1101/2020.11.13.381830|language=en|doi=10.1101/2020.11.13.381830|s2cid=227060212}} Much of the literature describes the cell number in males as 1031, but the discovery of a pair of left and right MCM neurons increased the number by two in 2015. The number of cells does not change after cell division ceases at the end of the larval period, and subsequent growth is due solely to an increase in the size of individual cells.{{cite book |title=Invertebrate Zoology |edition=7th |last1=Ruppert |first1=Edward E. |last2=Fox | first2=Richard S. |last3=Barnes |first3=Robert D. | name-list-style = vanc |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=753 }}

{{Main|Host microbe interactions in Caenorhabditis elegans}}

The different Caenorhabditis species occupy various nutrient- and bacteria-rich environments. They feed on the bacteria that develop in decaying organic matter (microbivory). They possess chemosensory receptors which enable the detection of bacteria and bacterial-secreted metabolites (such as iron siderophores), so that they can migrate towards their bacterial prey.{{Cite journal |last1=Hu |first1=Minqi |last2=Ma |first2=Yeping |last3=Chua |first3=Song Lin |date=2024-01-16 |title=Bacterivorous nematodes decipher microbial iron siderophores as prey cue in predator–prey interactions |journal=Proceedings of the National Academy of Sciences |language=en |volume=121 |issue=3 |pages=e2314077121 |doi=10.1073/pnas.2314077121 |issn=0027-8424|doi-access=free |pmid=38190542 |pmc=10801909 |bibcode=2024PNAS..12114077H }} Soil lacks enough organic matter to support self-sustaining populations. C. elegans can survive on a diet of a variety of bacteria, but its wild ecology is largely unknown. Most laboratory strains were taken from artificial environments such as gardens and compost piles. More recently, C. elegans has been found to thrive in other kinds of organic matter, particularly rotting fruit.

{{cite journal | vauthors = Félix MA, Braendle C | title = The natural history of Caenorhabditis elegans | journal = Current Biology | volume = 20 | issue = 22 | pages = R965–9 | date = November 2010 | pmid = 21093785 | doi = 10.1016/j.cub.2010.09.050 | doi-access = free | bibcode = 2010CBio...20.R965F }}

C. elegans can also ingest pollutants, especially tiny nanoplastics, which could enable the association with antibiotic-resistant bacteria, resulting in the dissemination of nanoplastics and antibiotic-resistant bacteria by C. elegans across the soil.{{Cite journal |last1=Chan |first1=Shepherd Yuen |last2=Liu |first2=Sylvia Yang |last3=Wu |first3=Rongben |last4=Wei |first4=Wei |last5=Fang |first5=James Kar-Hei |last6=Chua |first6=Song Lin |date=2023-06-02 |title=Simultaneous Dissemination of Nanoplastics and Antibiotic Resistance by Nematode Couriers |url=https://pubs.acs.org/doi/10.1021/acs.est.2c07129 |journal=Environmental Science & Technology |volume=57 |issue=23 |pages=8719–8727 |language=en |doi=10.1021/acs.est.2c07129 |pmid=37267481 |bibcode=2023EnST...57.8719C |s2cid=259047038 |issn=0013-936X}}
C. elegans can also use different species of yeast, including Cryptococcus laurentii and C. kuetzingii, as sole sources of food.{{cite journal | vauthors = Mylonakis E, Ausubel FM, Perfect JR, Heitman J, Calderwood SB | title = Killing of Caenorhabditis elegans by Cryptococcus neoformans as a model of yeast pathogenesis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 24 | pages = 15675–80 | date = November 2002 | pmid = 12438649 | pmc = 137775 | doi = 10.1073/pnas.232568599 | bibcode = 2002PNAS...9915675M | doi-access = free }} Although a bacterivore, C. elegans can be killed by a number of pathogenic bacteria, including human pathogens such as Staphylococcus aureus,{{cite journal | vauthors = Sifri CD, Begun J, Ausubel FM, Calderwood SB | title = Caenorhabditis elegans as a model host for Staphylococcus aureus pathogenesis | journal = Infection and Immunity | volume = 71 | issue = 4 | pages = 2208–17 | date = April 2003 | pmid = 12654843 | pmc = 152095 | doi = 10.1128/IAI.71.4.2208-2217.2003 }} Pseudomonas aeruginosa,{{cite journal | vauthors = Tan MW, Mahajan-Miklos S, Ausubel FM | title = Killing of Caenorhabditis elegans by Pseudomonas aeruginosa used to model mammalian bacterial pathogenesis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 96 | issue = 2 | pages = 715–20 | date = January 1999 | pmid = 9892699 | pmc = 15202 | doi = 10.1073/pnas.96.2.715 | bibcode = 1999PNAS...96..715T | doi-access = free }} Salmonella enterica or Enterococcus faecalis.{{cite journal | vauthors = Garsin DA, Villanueva JM, Begun J, Kim DH, Sifri CD, Calderwood SB, Ruvkun G, Ausubel FM | display-authors = 6 | title = Long-lived C. elegans daf-2 mutants are resistant to bacterial pathogens | journal = Science | volume = 300 | issue = 5627 | pages = 1921 | date = June 2003 | pmid = 12817143 | doi = 10.1126/science.1080147 | s2cid = 37703980 }} Pathogenic bacteria can also form biofilms, whose sticky exopolymer matrix could impede C. elegans motility {{Cite journal |last1=Chan |first1=Shepherd Yuen |last2=Liu |first2=Sylvia Yang |last3=Seng |first3=Zijing |last4=Chua |first4=Song Lin |date=January 2021 |title=Biofilm matrix disrupts nematode motility and predatory behavior |journal=The ISME Journal |language=en |volume=15 |issue=1 |pages=260–269 |doi=10.1038/s41396-020-00779-9 |pmid=32958848 |pmc=7852553 |bibcode=2021ISMEJ..15..260C |issn=1751-7370}} and cloaks bacterial quorum sensing chemoattractants from predator detection.{{Cite journal |last1=Li |first1=Shaoyang |last2=Liu |first2=Sylvia Yang |last3=Chan |first3=Shepherd Yuen |last4=Chua |first4=Song Lin |date=May 2022 |title=Biofilm matrix cloaks bacterial quorum sensing chemoattractants from predator detection |journal=The ISME Journal |language=en |volume=16 |issue=5 |pages=1388–1396 |doi=10.1038/s41396-022-01190-2 |pmid=35034106 |pmc=9038794 |bibcode=2022ISMEJ..16.1388L |issn=1751-7370}}

Invertebrates such as millipedes, insects, isopods, and gastropods can transport dauer larvae to various suitable locations. The larvae have also been seen to feed on their hosts when they die.

{{cite journal | vauthors = Kiontke K, Sudhaus W | title = Ecology of Caenorhabditis species | journal = WormBook | pages = 1–14 | date = January 2006 | pmid = 18050464 | pmc = 4780885 | doi = 10.1895/wormbook.1.37.1 }}

Nematodes can survive desiccation, and in C. elegans, the mechanism for this capability has been demonstrated to be late embryogenesis abundant proteins.

{{cite journal | vauthors = Gal TZ, Glazer I, Koltai H | title = An LEA group 3 family member is involved in survival of C. elegans during exposure to stress | journal = FEBS Letters | volume = 577 | issue = 1–2 | pages = 21–6 | date = November 2004 | pmid = 15527756 | doi = 10.1016/j.febslet.2004.09.049 | s2cid = 21960486 | doi-access = free | bibcode = 2004FEBSL.577...21G }}

C. elegans, as other nematodes, can be eaten by predator nematodes and other omnivores, including some insects.Elaine R. Ingham [https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/biology/ Soil biology primer] USDA

The Orsay virus is a virus that affects C. elegans, as well as the Caenorhabditis elegans Cer1 virus{{Cite journal |doi=10.1101/gr.9.10.924|pmid=10523521|title=Genomic Analysis of Caenorhabditis elegans Reveals Ancient Families of Retroviral-like Elements|journal=Genome Research|volume=9|issue=10|pages=924–935|year=1999|last1=Bowen|first1=N. J.|doi-access=free}} and the Caenorhabditis elegans Cer13 virus.

; Interactions with fungi

Wild isolates of Caenorhabditis elegans are regularly found with infections by Microsporidia fungi. One such species, Nematocida parisii, replicates in the intestines of C. elegans.{{cite journal | vauthors = Cuomo CA, Desjardins CA, Bakowski MA, Goldberg J, Ma AT, Becnel JJ, Didier ES, Fan L, Heiman DI, Levin JZ, Young S, Zeng Q, Troemel ER | title = Microsporidian genome analysis reveals evolutionary strategies for obligate intracellular growth | journal = Genome Research | volume = 22 | issue = 12 | pages = 2478–88 | date = December 2012 | pmid = 22813931 | pmc = 3514677 | doi = 10.1101/gr.142802.112 }}

Arthrobotrys oligospora is the model organism for interactions between fungi and nematodes.{{Cite journal |doi=10.1080/21501203.2011.562559|title=Arthrobotrys oligospora: A model organism for understanding the interaction between fungi and nematodes|journal=Mycology|volume=2|issue=2|pages=59–78|year=2011|last1=Niu|first1=Xue-Mei|last2=Zhang|first2=Ke-Qin | name-list-style = vanc |doi-access=free}} It is the most common and widespread nematode capturing fungus.

{{Further|History of research on Caenorhabditis elegans}}

File:Epigenetic-Regulation-of-Histone-H3-Serine-10-Phosphorylation-Status-by-HCF-1-Proteins-in-C.-pone.0001213.s003.ogv

In 1963, Sydney Brenner proposed using C. elegans as a model organism for the investigation primarily of neural development in animals. It is one of the simplest organisms with a nervous system. The neurons do not fire action potentials, and do not express any voltage-gated sodium channels.{{cite journal | vauthors = Clare JJ, Tate SN, Nobbs M, Romanos MA | title = Voltage-gated sodium channels as therapeutic targets | journal = Drug Discovery Today | volume = 5 | issue = 11 | pages = 506–520 | date = November 2000 | pmid = 11084387 | doi = 10.1016/S1359-6446(00)01570-1 }} In the hermaphrodite, this system comprises 302 neurons{{cite journal |bibcode=2007AcPPB..38.2201K |title=Dynamics of the Model of the Caenorhabditis Elegans Neural Network |journal=Acta Physica Polonica B |volume=38 |issue=6 |pages=2201 | vauthors = Kosinski RA, Zaremba M |year=2007 }} the pattern of which has been comprehensively mapped,

{{cite journal

|title=Whole-animal connectomes of both Caenorhabditis elegans sexes

|last1=Cook

|first1=SJ

|last2=Jarrell

|first2=TA

|last3=Brittin

|first3=CA

|last4=Wang

|first4=Y

|last5=Bloniarz

|first5=AE

|last6=Yakovlev

|first6=MA

|last7=Nguyen

|first7=KCQ

|last8=Tang

|first8=Lt-H

|last9=Bayer

|first9=EA

|last10=Duerr

|first10=JS

|last11=Bulow

|first11=HE

|last12=Hobert

|first12=O

|last13=Hall

|first13=DH

|last14=Emmons

|first14=SW

|journal=Nature

|date=3 December 2019

|volume=571

|issue=7763

|pages=63–71

|publisher= US National Library of Medicine, National Institutes of Health

|doi=10.1038/s41586-019-1352-7

|pmc=6889226

|pmid=31270481

|bibcode=2019Natur.571...63C

}} in what is known as a connectome,{{cite journal |last1=Brouillette |first1=Monique |title=Mapping the brain to understand the mind |journal=Knowable Magazine |date=21 April 2022 |doi=10.1146/knowable-042122-1|doi-access=free |url=https://knowablemagazine.org/article/mind/2022/mapping-brain-understand-mind |language=en}} and shown to be a small-world network.{{cite journal | vauthors = Watts DJ, Strogatz SH | title = Collective dynamics of 'small-world' networks | journal = Nature | volume = 393 | issue = 6684 | pages = 440–2 | date = June 1998 | pmid = 9623998 | doi = 10.1038/30918 | bibcode = 1998Natur.393..440W | s2cid = 4429113 }}

Research has explored the neural and molecular mechanisms that control several behaviors of C. elegans, including chemotaxis, thermotaxis, mechanotransduction, learning, memory, and mating behaviour.{{cite journal | vauthors = Schafer WR | title = Deciphering the neural and molecular mechanisms of C. elegans behavior | journal = Current Biology | volume = 15 | issue = 17 | pages = R723–9 | date = September 2005 | pmid = 16139205 | doi = 10.1016/j.cub.2005.08.020 | author-link1 = William Schafer (neuroscientist) | doi-access = free | bibcode = 2005CBio...15.R723S }} In 2019 the connectome of the male was published using a technique distinct from that used for the hermaphrodite. The same paper used the new technique to redo the hermaphrodite connectome, finding 1,500 new synapses.{{cite journal | vauthors = Cook SJ, Jarrell TA, Brittin CA, Wang Y, Bloniarz AE, Yakovlev MA, Nguyen KC, Tang LT, Bayer EA, Duerr JS, Bülow HE, Hobert O, Hall DH, Emmons SW | display-authors = 6 | title = Whole-animal connectomes of both Caenorhabditis elegans sexes | journal = Nature | volume = 571 | issue = 7763 | pages = 63–71 | date = July 2019 | pmid = 31270481 | pmc = 6889226 | doi = 10.1038/s41586-019-1352-7 | bibcode = 2019Natur.571...63C }}

It has been used as a model organism to study molecular mechanisms in metabolic diseases.{{cite journal | vauthors = Alcántar-Fernández J, Navarro RE, Salazar-Martínez AM, Pérez-Andrade ME, Miranda-Ríos J | title = Caenorhabditis elegans respond to high-glucose diets through a network of stress-responsive transcription factors | journal = PLOS ONE | volume = 13 | issue = 7 | pages = e0199888 | date = 2018 | pmid = 29990370 | pmc = 6039004 | doi = 10.1371/journal.pone.0199888 | bibcode = 2018PLoSO..1399888A | doi-access = free }}

Brenner also chose it as it is easy to grow in bulk populations, and convenient for genetic analysis.{{cite web |last=Avery |first=L |title=Sydney Brenner |url=http://elegans.swmed.edu/Sydney.html |publisher=Southwestern Medical Center |url-status=dead |archive-url=https://web.archive.org/web/20110815143145/http://elegans.swmed.edu/Sydney.html |archive-date=August 15, 2011 }} [http://elegans.som.vcu.edu/Sydney.html Alt. URL] {{Webarchive|url=https://web.archive.org/web/20131208060434/http://elegans.som.vcu.edu/Sydney.html |date=2013-12-08 }} It is a multicellular eukaryotic organism, yet simple enough to be studied in great detail. The transparency of C. elegans facilitates the study of cellular differentiation and other developmental processes in the intact organism. The spicules in the male clearly distinguish males from females. Strains are cheap to breed and can be frozen. When subsequently thawed, they remain viable, allowing long-term storage. Maintenance is easy when compared to other multicellular model organisms. A few hundred nematodes can be kept on a single agar plate and suitable growth medium. Brenner described the use of a mutant of E. coli – OP50. OP50 is a uracil-requiring organism and its deficiency in the plate prevents the overgrowth of bacteria which would obscure the worms.{{cite journal | last1 = Brenner | first1 = S | year = 1974 | title = The genetics of Caenorhabditis elegans. | journal = Genetics | volume = 77 | issue = 1| pages = 71–94 | doi = 10.1093/genetics/77.1.71 | pmc = 1213120 | pmid = 4366476 }} The use of OP50 does not demand any major laboratory safety measures, since it is non-pathogenic and easily grown in Luria-Bertani (LB) media overnight.{{Cite web|url=http://www.wormbook.org/chapters/www_behavior/behavior.html#sec1|title=Behavior|website=www.wormbook.org|access-date=2018-09-26}}

The developmental fate of every single somatic cell (959 in the adult hermaphrodite; 1031 in the adult male) has been mapped.

{{cite journal | vauthors = Sulston JE, Horvitz HR | title = Post-embryonic cell lineages of the nematode, Caenorhabditis elegans | journal = Developmental Biology | volume = 56 | issue = 1 | pages = 110–56 | date = March 1977 | pmid = 838129 | doi = 10.1016/0012-1606(77)90158-0 }}

{{cite journal | vauthors = Kimble J, Hirsh D | title = The postembryonic cell lineages of the hermaphrodite and male gonads in Caenorhabditis elegans | journal = Developmental Biology | volume = 70 | issue = 2 | pages = 396–417 | date = June 1979 | pmid = 478167 | doi = 10.1016/0012-1606(79)90035-6 }} These patterns of cell lineage are largely invariant between individuals, whereas in mammals, cell development is more dependent on cellular cues from the embryo.

As mentioned previously, the first cell divisions of early embryogenesis in C. elegans are among the best understood examples of asymmetric cell divisions, and the worm is a very popular model system for studying developmental biology.

Programmed cell death (apoptosis) eliminates many additional cells (131 in the hermaphrodite, most of which would otherwise become neurons); this "apoptotic predictability" has contributed to the elucidation of some apoptotic genes. Cell death-promoting genes and a single cell-death inhibitor have been identified.{{cite journal | vauthors = Peden E, Killian DJ, Xue D | title = Cell death specification in C. elegans | journal = Cell Cycle | volume = 7 | issue = 16 | pages = 2479–84 | date = August 2008 | pmid = 18719375 | pmc = 2651394 | doi = 10.4161/cc.7.16.6479 }}

File:C elegans stained.jpg to highlight the nuclei of all cells]]

RNA interference (RNAi) is a relatively straightforward method of disrupting the function of specific genes. Silencing the function of a gene can sometimes allow a researcher to infer its possible function. The nematode can be soaked in, injected with,{{Cite web|url=https://www.youtube.com/watch?v=Wam-kw4xwZc| archive-url=https://ghostarchive.org/varchive/youtube/20211117/Wam-kw4xwZc| archive-date=2021-11-17 | url-status=live|title=Injection of C. elegans Gonads|last=NIDDK|first=National Institute of Diabetes and Digestive and Kidney Diseases|website=YouTube|date=March 5, 2015|access-date=March 21, 2020}}{{cbignore}} or fed with genetically transformed bacteria that express the double-stranded RNA of interest, the sequence of which complements the sequence of the gene that the researcher wishes to disable.

{{cite journal | vauthors = Kamath RS, Fraser AG, Dong Y, Poulin G, Durbin R, Gotta M, Kanapin A, Le Bot N, Moreno S, Sohrmann M, Welchman DP, Zipperlen P, Ahringer J | title = Systematic functional analysis of the Caenorhabditis elegans genome using RNAi | journal = Nature | volume = 421 | issue = 6920 | pages = 231–7 | date = January 2003 | pmid = 12529635 | doi = 10.1038/nature01278 | bibcode = 2003Natur.421..231K | hdl = 10261/63159 | s2cid = 15745225 }}

RNAi has emerged as a powerful tool in the study of functional genomics. C. elegans has been used to analyse gene functions and claim the promise of future findings in the systematic genetic interactions.{{cite journal | vauthors = Fortunato A, Fraser AG | title = Uncover genetic interactions in Caenorhabditis elegans by RNA interference | journal = Bioscience Reports | volume = 25 | issue = 5–6 | pages = 299–307 | date = 2005 | pmid = 16307378 | doi = 10.1007/s10540-005-2892-7 | s2cid = 6983519 }}

Environmental RNAi uptake is much worse in other species of worms in the genus Caenorhabditis. Although injecting RNA into the body cavity of the animal induces gene silencing in most species, only C. elegans and a few other distantly related nematodes can take up RNA from the bacteria they eat for RNAi.

{{cite journal | vauthors = Félix MA | title = RNA interference in nematodes and the chance that favored Sydney Brenner | journal = Journal of Biology | volume = 7 | issue = 9 | pages = 34 | date = November 2008 | pmid = 19014674 | pmc = 2776389 | doi = 10.1186/jbiol97 | doi-access = free }} This ability has been mapped down to a single gene, sid-2, which, when inserted as a transgene in other species, allows them to take up RNA for RNAi as C. elegans does.

{{cite journal | vauthors = Winston WM, Sutherlin M, Wright AJ, Feinberg EH, Hunter CP | title = Caenorhabditis elegans SID-2 is required for environmental RNA interference | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 25 | pages = 10565–70 | date = June 2007 | pmid = 17563372 | pmc = 1965553 | doi = 10.1073/pnas.0611282104 | bibcode = 2007PNAS..10410565W | doi-access = free }}

Research into meiosis has been considerably simplified since every germ cell nucleus is at the same given position as it moves down the gonad, so is at the same stage in meiosis. In an early phase of meiosis, the oocytes become extremely resistant to radiation and this resistance depends on expression of genes rad51 and atm that have key roles in recombinational repair.{{cite journal | vauthors = Takanami T, Mori A, Takahashi H, Higashitani A | title = Hyper-resistance of meiotic cells to radiation due to a strong expression of a single recA-like gene in Caenorhabditis elegans | journal = Nucleic Acids Research | volume = 28 | issue = 21 | pages = 4232–6 | date = November 2000 | pmid = 11058122 | pmc = 113154 | doi = 10.1093/nar/28.21.4232 }}{{cite journal | vauthors = Takanami T, Zhang Y, Aoki H, Abe T, Yoshida S, Takahashi H, Horiuchi S, Higashitani A | title = Efficient repair of DNA damage induced by heavy ion particles in meiotic prophase I nuclei of Caenorhabditis elegans | journal = Journal of Radiation Research | volume = 44 | issue = 3 | pages = 271–6 | date = September 2003 | pmid = 14646232 | doi = 10.1269/jrr.44.271 | bibcode = 2003JRadR..44..271T | doi-access = free }} Gene mre-11 also plays a crucial role in recombinational repair of DNA damage during meiosis.{{cite journal | vauthors = Chin GM, Villeneuve AM | title = C. elegans mre-11 is required for meiotic recombination and DNA repair but is dispensable for the meiotic G(2) DNA damage checkpoint | journal = Genes & Development | volume = 15 | issue = 5 | pages = 522–34 | date = March 2001 | pmid = 11238374 | pmc = 312651 | doi = 10.1101/gad.864101 }} Furthermore, during meiosis in C. elegans the tumor suppressor BRCA1/BRC-1 and the structural maintenance of chromosomes SMC5/SMC6 protein complex interact to promote high fidelity repair of DNA double-strand breaks.{{cite journal |vauthors=Toraason E, Salagean A, Almanzar DE, Brown JE, Richter CM, Kurhanewicz NA, Rog O, Libuda DE |title=BRCA1/BRC-1 and SMC-5/6 regulate DNA repair pathway engagement during Caenorhabditis elegans meiosis |journal=eLife |volume=13 |issue= |pages= |date=August 2024 |pmid=39115289 |pmc=11368404 |doi=10.7554/eLife.80687 |doi-access=free |url=}}

A study of the frequency of outcrossing in natural populations showed that selfing is the predominant mode of reproduction in C. elegans, but that infrequent outcrossing events occur at a rate around 1%.{{cite journal | vauthors = Barrière A, Félix MA | title = High local genetic diversity and low outcrossing rate in Caenorhabditis elegans natural populations | journal = Current Biology | volume = 15 | issue = 13 | pages = 1176–84 | date = July 2005 | pmid = 16005289 | doi = 10.1016/j.cub.2005.06.022 | arxiv = q-bio/0508003 | bibcode = 2005CBio...15.1176B | s2cid = 2229622 }} Meioses that result in selfing are unlikely to contribute significantly to beneficial genetic variability, but these meioses may provide the adaptive benefit of recombinational repair of DNA damages that arise, especially under stressful conditions.Bernstein H, Bernstein C (July 2010) "Evolutionary Origin of Recombination during Meiosis," BioScience 60(7), 498-505. https://doi.org/10.1525/bio.2010.60.7.5

Nicotine dependence can also be studied using C. elegans because it exhibits behavioral responses to nicotine that parallel those of mammals. These responses include acute response, tolerance, withdrawal, and sensitization.{{cite journal | vauthors = Feng Z, Li W, Ward A, Piggott BJ, Larkspur ER, Sternberg PW, Xu XZ | title = A C. elegans model of nicotine-dependent behavior: regulation by TRP-family channels | journal = Cell | volume = 127 | issue = 3 | pages = 621–33 | date = November 2006 | pmid = 17081982 | pmc = 2859215 | doi = 10.1016/j.cell.2006.09.035 }}

As for most model organisms, scientists that work in the field curate a dedicated online database and WormBase is that for C. elegans. The WormBase attempts to collate all published information on C. elegans and other related nematodes. Information on C. elegans is included with data on other model organisms in the Alliance of Genome Resources.{{Cite web |title=Alliance of Genome Resources Community Forum |url=https://community.alliancegenome.org/ |access-date=2024-08-01 |website=Alliance of Genome Resources Community Forum |language=en}}

C. elegans has been a model organism for research into ageing; for example, the inhibition of an insulin-like growth factor signaling pathway has been shown to increase adult lifespan threefold;{{cite journal | vauthors = Wolkow CA, Kimura KD, Lee MS, Ruvkun G | title = Regulation of C. elegans life-span by insulinlike signaling in the nervous system | journal = Science | volume = 290 | issue = 5489 | pages = 147–50 | date = October 2000 | pmid = 11021802 | doi = 10.1126/science.290.5489.147 | bibcode = 2000Sci...290..147W }}{{cite journal | vauthors = Ewald CY, Landis JN, Porter Abate J, Murphy CT, Blackwell TK | title = Dauer-independent insulin/IGF-1-signalling implicates collagen remodelling in longevity | language = En | journal = Nature | volume = 519 | issue = 7541 | pages = 97–101 | date = March 2015 | pmid = 25517099 | pmc = 4352135 | doi = 10.1038/nature14021 | bibcode = 2015Natur.519...97E }} while glucose feeding promotes oxidative stress and reduces adult lifespan by a half. Similarly, induced degradation of an insulin/IGF-1 receptor late in life extended life expectancy of worms dramatically.{{Cite journal|last1=Venz|first1=Richard|last2=Pekec|first2=Tina|last3=Katic|first3=Iskra|last4=Ciosk|first4=Rafal|author5-link=Collin Y. Ewald|last5=Ewald|first5=Collin Yvès|date=2021-09-10|editor-last=Leiser|editor-first=Scott F|editor2-last=Kaeberlein|editor2-first=Matt|editor3-last=Alcedo|editor3-first=Joy|title=End-of-life targeted degradation of DAF-2 insulin/IGF-1 receptor promotes longevity free from growth-related pathologies|journal=eLife|volume=10|pages=e71335|doi=10.7554/eLife.71335|pmid=34505574|pmc=8492056|issn=2050-084X |doi-access=free }}

Long-lived mutants of C. elegans were demonstrated to be resistant to oxidative stress and UV light.{{Cite journal |doi=10.1093/nar/gkm1161 |pmc=2275101 |pmid=18203746|title=Longevity and resistance to stress correlate with DNA repair capacity in Caenorhabditis elegans |year=2008 |last1=Hyun |first1=Moonjung |last2=Lee |first2=Jihyun |last3=Lee |first3=Kyungjin |last4=May |first4=Alfred |last5=Bohr |first5=Vilhelm A. |last6=Ahn |first6=Byungchan |journal=Nucleic Acids Research |volume=36 |issue=4 |pages=1380–1389 }} These long-lived mutants had a higher DNA repair capability than wild-type C. elegans. Knockdown of the nucleotide excision repair gene Xpa-1 increased sensitivity to UV and reduced the life span of the long-lived mutants. These findings indicate that DNA repair capability underlies longevity. Consistent with the idea that oxidative DNA damage causes aging, it was found that in C. elegans, exosome-mediated delivery of superoxide dismutase (SOD) reduces the level of reactive oxygen species (ROS) and significantly extends lifespan, i.e. delays aging under normal, as well as hostile conditions.{{cite journal |vauthors=Shao X, Zhang M, Chen Y, Sun S, Yang S, Li Q |title=Exosome-mediated delivery of superoxide dismutase for anti-aging studies in Caenorhabditis elegans |journal=Int J Pharm |volume=641 |issue= |pages=123090 |date=June 2023 |pmid=37268030 |doi=10.1016/j.ijpharm.2023.123090 |url=}}

The capacity to repair DNA damage by the process of nucleotide excision repair declines with age.{{Cite journal |doi=10.1186/gb-2007-8-5-r70 |pmc=1929140 |pmid=17472752|title=Decline of nucleotide excision repair capacity in aging Caenorhabditis elegans |year=2007 |last1=Meyer |first1=Joel N. |last2=Boyd |first2=Windy A. |last3=Azzam |first3=Gregory A. |last4=Haugen |first4=Astrid C. |last5=Freedman |first5=Jonathan H. |last6=Van Houten |first6=Bennett |journal=Genome Biology |volume=8 |issue=5 |pages=R70 |doi-access=free }}

C. elegans exposed to 5mM lithium chloride (LiCl) showed lengthened life spans.{{cite journal | vauthors = McColl G, Killilea DW, Hubbard AE, Vantipalli MC, Melov S, Lithgow GJ | title = Pharmacogenetic analysis of lithium-induced delayed aging in Caenorhabditis elegans | journal = The Journal of Biological Chemistry | volume = 283 | issue = 1 | pages = 350–7 | date = January 2008 | pmid = 17959600 | pmc = 2739662 | doi = 10.1074/jbc.M705028200 | doi-access = free }} When exposed to 10μM LiCl, reduced mortality was observed, but not with 1μM.{{cite journal | vauthors = Zarse K, Terao T, Tian J, Iwata N, Ishii N, Ristow M | title = Low-dose lithium uptake promotes longevity in humans and metazoans | journal = European Journal of Nutrition | volume = 50 | issue = 5 | pages = 387–9 | date = August 2011 | pmid = 21301855 | pmc = 3151375 | doi = 10.1007/s00394-011-0171-x }}

C. elegans has been instrumental in the identification of the functions of genes implicated in Alzheimer's disease, such as presenilin.{{cite journal | vauthors = Ewald CY, Li C | title = Understanding the molecular basis of Alzheimer's disease using a Caenorhabditis elegans model system | journal = Brain Structure & Function | volume = 214 | issue = 2–3 | pages = 263–83 | date = March 2010 | pmid = 20012092 | pmc = 3902020 | doi = 10.1007/s00429-009-0235-3 }} Moreover, extensive research on C. elegans has identified RNA-binding proteins as essential factors during germline and early embryonic development.{{cite journal | vauthors = Hanazawa M, Yonetani M, Sugimoto A | title = PGL proteins self associate and bind RNPs to mediate germ granule assembly in C. elegans | journal = The Journal of Cell Biology | volume = 192 | issue = 6 | pages = 929–37 | date = March 2011 | pmid = 21402787 | pmc = 3063142 | doi = 10.1083/jcb.201010106 }}

Telomeres, the length of which have been shown to correlate with increased lifespan and delayed onset of senescence in a multitude of organisms, from C. elegans{{Cite journal|last1=Coutts|first1=Fiona|last2=Palmos|first2=Alish B.|last3=Duarte|first3=Rodrigo R. R.|last4=de Jong|first4=Simone|last5=Lewis|first5=Cathryn M.|last6=Dima|first6=Danai|last7=Powell|first7=Timothy R.|date=March 2019|title=The polygenic nature of telomere length and the anti-ageing properties of lithium|journal=Neuropsychopharmacology|volume=44|issue=4|pages=757–765|doi=10.1038/s41386-018-0289-0|issn=1740-634X|pmc=6372618|pmid=30559463}}{{Cite journal|last1=Raices|first1=Marcela|last2=Maruyama|first2=Hugo|last3=Dillin|first3=Andrew|last4=Karlseder|first4=Jan|date=September 2005|title=Uncoupling of longevity and telomere length in C. elegans|journal=PLOS Genetics|volume=1|issue=3|pages=e30|doi=10.1371/journal.pgen.0010030|issn=1553-7404|pmc=1200426|pmid=16151516 |doi-access=free }} to humans,{{Cite journal|last1=Lulkiewicz|first1=M.|last2=Bajsert|first2=J.|last3=Kopczynski|first3=P.|last4=Barczak|first4=W.|last5=Rubis|first5=B.|date=September 2020|title=Telomere length: how the length makes a difference|journal=Molecular Biology Reports|volume=47|issue=9|pages=7181–7188|doi=10.1007/s11033-020-05551-y|issn=1573-4978|pmc=7561533|pmid=32876842}} show an interesting behaviour in C. elegans. While C. elegans maintains its telomeres in a canonical way similar to other eukaryotes, in contrast Drosophila melanogaster is noteworthy in its use of retrotransposons to maintain its telomeres,{{Cite journal|last1=Pardue|first1=Mary-Lou|last2=DeBaryshe|first2=P. G.|date=2011-12-20|title=Retrotransposons that maintain chromosome ends|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=108|issue=51|pages=20317–20324|doi=10.1073/pnas.1100278108|issn=1091-6490|pmc=3251079|pmid=21821789|doi-access=free}} during knock-out of the catalytic subunit of the telomerase (trt-1) C. elegans can gain the ability of alternative telomere lengthening (ALT). C. elegans was the first eukaryote to gain ALT functionality after knock-out of the canonical telomerase pathway.{{Cite journal|last1=Meier|first1=Bettina|last2=Clejan|first2=Iuval|last3=Liu|first3=Yan|last4=Lowden|first4=Mia|last5=Gartner|first5=Anton|last6=Hodgkin|first6=Jonathan|last7=Ahmed|first7=Shawn|date=February 2006|title=trt-1 is the Caenorhabditis elegans catalytic subunit of telomerase|journal=PLOS Genetics|volume=2|issue=2|pages=e18|doi=10.1371/journal.pgen.0020018|issn=1553-7404|pmc=1361356|pmid=16477310 |doi-access=free }} ALT is also observed in about 10-15% of all clinical cancers.{{Cite journal|last1=Cesare|first1=Anthony J.|last2=Reddel|first2=Roger R.|date=May 2010|title=Alternative lengthening of telomeres: models, mechanisms and implications|url=https://pubmed.ncbi.nlm.nih.gov/20351727|journal=Nature Reviews. Genetics|volume=11|issue=5|pages=319–330|doi=10.1038/nrg2763|issn=1471-0064|pmid=20351727|s2cid=19224032}} Thus C. elegans is a prime candidate for ALT research.{{Cite journal|last1=Ijomone|first1=Omamuyovwi M.|last2=Miah|first2=Mahfuzur R.|last3=Peres|first3=Tanara V.|last4=Nwoha|first4=Polycarp U.|last5=Aschner|first5=Michael|date=December 2016|title=Null allele mutants of trt-1, the catalytic subunit of telomerase in Caenorhabditis elegans, are less sensitive to Mn-induced toxicity and DAergic degeneration|url=https://pubmed.ncbi.nlm.nih.gov/27593554|journal=Neurotoxicology|volume=57|pages=54–60|doi=10.1016/j.neuro.2016.08.016|issn=1872-9711|pmid=27593554|bibcode=2016NeuTx..57...54I }}{{Cite journal|last1=Shtessel|first1=Ludmila|last2=Lowden|first2=Mia Rochelle|last3=Cheng|first3=Chen|last4=Simon|first4=Matt|last5=Wang|first5=Kyle|last6=Ahmed|first6=Shawn|date=February 2013|title=Caenorhabditis elegans POT-1 and POT-2 repress telomere maintenance pathways|journal=G3: Genes, Genomes, Genetics|volume=3|issue=2|pages=305–313|doi=10.1534/g3.112.004440|issn=2160-1836|pmc=3564990|pmid=23390606}}{{Cite journal|last1=Kwon|first1=Mi-Sun|last2=Min|first2=Jaewon|last3=Jeon|first3=Hee-Yeon|last4=Hwang|first4=Kwangwoo|last5=Kim|first5=Chuna|last6=Lee|first6=Junho|last7=Joung|first7=Je-Gun|last8=Park|first8=Woong-Yang|last9=Lee|first9=Hyunsook|date=October 2016|title=Paradoxical delay of senescence upon depletion of BRCA2 in telomerase-deficient worms|journal=FEBS Open Bio|volume=6|issue=10|pages=1016–1024|doi=10.1002/2211-5463.12109|issn=2211-5463|pmc=5055038|pmid=27761361}} Bayat et al. showed the paradoxical shortening of telomeres during trt-1 over-expression which lead to near sterility while the worms even exhibited a slight increase in lifespan, despite shortened telomeres.{{Cite journal|last1=Bayat|first1=Melih|last2=Tanny|first2=Robyn E.|last3=Wang|first3=Ye|last4=Herden|first4=Carla|last5=Daniel|first5=Jens|last6=Andersen|first6=Erik C.|last7=Liebau|first7=Eva|last8=Waschk|first8=Daniel E. J.|date=2020-03-30|title=Effects of telomerase overexpression in the model organism Caenorhabditis elegans|url=https://pubmed.ncbi.nlm.nih.gov/31954861|journal=Gene|volume=732|pages=144367|doi=10.1016/j.gene.2020.144367|issn=1879-0038|pmid=31954861|s2cid=210829489}}

C. elegans is notable in animal sleep studies as the most primitive organism to display sleep-like states. In C. elegans, a lethargus phase occurs shortly before each moult.{{cite journal | vauthors = Iwanir S, Tramm N, Nagy S, Wright C, Ish D, Biron D | title = The microarchitecture of C. elegans behavior during lethargus: homeostatic bout dynamics, a typical body posture, and regulation by a central neuron | journal = Sleep | volume = 36 | issue = 3 | pages = 385–95 | date = March 2013 | pmid = 23449971 | pmc = 3571756 | doi = 10.5665/Sleep.2456 }} C. elegans has also been demonstrated to sleep after exposure to physical stress, including heat shock, UV radiation, and bacterial toxins.{{cite journal | vauthors = Hill AJ, Mansfield R, Lopez JM, Raizen DM, Van Buskirk C | title = Cellular stress induces a protective sleep-like state in C. elegans | journal = Current Biology | volume = 24 | issue = 20 | pages = 2399–405 | date = October 2014 | pmid = 25264259 | pmc = 4254280 | doi = 10.1016/j.cub.2014.08.040 | bibcode = 2014CBio...24.2399H }}

While the worm has no eyes, it has been found to be sensitive to light due to a third type of light-sensitive animal photoreceptor protein, LITE-1, which is 10 to 100 times more efficient at absorbing light than the other two types of photopigments (opsins and cryptochromes) found in the animal kingdom.[https://www.livescience.com/56913-new-photoreceptor-found-in-worms.html Teensy, Eyeless Worms Have Completely New Light-Detecting Cells]

C. elegans is remarkably adept at tolerating acceleration. It can withstand 400,000 g's, according to geneticists at the University of São Paulo in Brazil. In an experiment, 96% of them were still alive without adverse effects after an hour in an ultracentrifuge.Scientific American, August 2018, page 14

Having a small size and short life cycle, C. elegans is one of the few organisms that can enable in vivo high throughput screening (HTS) platforms for the evaluation of chemical libraries of drugs and toxins in a multicellular organism.{{cite journal | title = In vivo quantitative high-throughput screening for drug discovery and comparative toxicology.|author1 = Dranchak, P.K.|author2 = Oliphant, E.|author3 = Queme, B. |author4 = Lamy, L. |author5 = Wang, Y.|author6 = Huang, R. |author7 = Xia, M. |author8 = Tao, D.|author9 = Inglese, J.| journal = Dis Model Mech|date = 2023 |volume = 16| issue=3 | pages=dmm049863 |doi = 10.1242/dmm.049863| pmid=36786055 |pmc = 10067442}} Orthologous phenotypes observable in C. elegans for human diseases have the potential to enable profiling of drug library profiling that can inform potential repurposing of existing approved drugs for therapeutic indications in humans.{{cite journal | title = Caenorhabditis elegans for rare disease modeling and drug discovery: strategies and strengths. |author1 = Kropp, P.A. |author2 = Bauer, R.|author3 = Zafra, I. |author4 = Graham, C. |author5 = Golden, A.| journal = Dis Model Mech|date = 2021 |volume = 14|issue = 8 | pages = dmm049010|doi = 10.1242/dmm.049010|pmid = 34370008 |pmc = 8380043}}

C. elegans made news when specimens were discovered to have survived the Space Shuttle Columbia disaster in February 2003.

{{cite news

|date=1 May 2003

|title=Worms survived Columbia disaster

|url=http://news.bbc.co.uk/1/hi/sci/tech/2992123.stm

|work=BBC News

|access-date=2008-07-11

}} Later, in January 2009, live samples of C. elegans from the University of Nottingham were announced to be spending two weeks on the International Space Station that October, in a space research project to explore the effects of zero gravity on muscle development and physiology. The research was primarily about genetic basis of muscle atrophy, which relates to spaceflight or being bed-ridden, geriatric, or diabetic.

{{cite news

|date=17 January 2009

|title=University sends worms into space

|url=http://news.bbc.co.uk/1/hi/england/nottinghamshire/7835020.stm

|work=BBC News

|access-date=2009-07-09

}} Descendants of the worms aboard Columbia in 2003 were launched into space on Endeavour for the STS-134 mission.{{cite news

|last1=Klotz

|first1=I

|date=16 May 2011

|title=Legacy Space Worms Flying on Shuttle

|url=http://news.discovery.com/space/legacy-space-worms-flying-on-shuttle-110516.html

|work=Discovery News

|access-date=2011-05-17

|archive-date=2012-06-16

|archive-url=https://web.archive.org/web/20120616014937/http://news.discovery.com/space/legacy-space-worms-flying-on-shuttle-110516.html

|url-status=dead

}} Additional experiments on muscle dystrophy during spaceflight were carried on board the ISS starting in 2018.{{Cite journal |last1=Soni |first1=Purushottam |last2=Anupom |first2=Taslim |last3=Lesanpezeshki |first3=Leila |last4=Rahman |first4=Mizanur |last5=Hewitt |first5=Jennifer E. |last6=Vellone |first6=Matthew |last7=Stodieck |first7=Louis |last8=Blawzdziewicz |first8=Jerzy |last9=Szewczyk |first9=Nathaniel J. |last10=Vanapalli |first10=Siva A. |date=2022-11-07 |title=Microfluidics-integrated spaceflight hardware for measuring muscle strength of Caenorhabditis elegans on the International Space Station |journal=npj Microgravity |volume=8 |issue=1 |pages=50 |doi=10.1038/s41526-022-00241-4 |issn=2373-8065 |pmc=9640571 |pmid=36344513|bibcode=2022npjMG...8...50S }} It was shown that the genes affecting muscles attachment were expressed less in space. However, it has yet to be seen if this affects muscle strength.

{{Infobox genome

| image = Karyotype of Caenorhabditis elegans.png

| caption = Karyotype of C. elegans
{{hidden|explanation of colors|Mitotic chromosomes of C. elegans. DNA (red)/ Kinetochores (green). Holocentric organisms, including C. elegans, assemble diffuse kinetochores along the entire poleward face of each sister chromatid.}}

| taxId = 41

| ploidy = diploid

| chromosomes = 5 pairs of autosomes (I, II, III, IV and V) + 1 or 2 sex chromosomes (X{{cite journal | vauthors = Strome S, Kelly WG, Ercan S, Lieb JD | title = Regulation of the X chromosomes in Caenorhabditis elegans | journal = Cold Spring Harbor Perspectives in Biology | volume = 6 | issue = 3 | pages = a018366 | date = March 2014 | pmid = 24591522 | pmc = 3942922 | doi = 10.1101/cshperspect.a018366 }})

| size = 101.169 Mb (haploid)

| year = 1998

| organelle = mitochondrion

| organelle-size = 0,01 Mb

| organelle-year =

}}

File:CelegansGoldsteinLabUNC.jpg

C. elegans was the first multicellular organism to have its whole genome sequenced. The sequence was published in 1998,

{{cite journal |author=The C. elegans Sequencing Consortium | title = Genome sequence of the nematode C. elegans: a platform for investigating biology | journal = Science | volume = 282 | issue = 5396 | pages = 2012–8 | date = December 1998 | pmid = 9851916 | doi = 10.1126/science.282.5396.2012 | bibcode = 1998Sci...282.2012. }} although some small gaps were present; the last gap was finished by October 2002.{{citation needed|date=January 2022}} In the run up to the whole genome the C. elegans Sequencing Consortium/C. elegans Genome Project released several partial scans including Wilson et al. 1994.{{cite journal | last=Sadler | first=J. Evan | title=Biochemistry and genetics of von Willebrand factor | journal=Annual Review of Biochemistry | publisher=Annual Reviews | volume=67 | issue=1 | year=1998 | issn=0066-4154 | doi=10.1146/annurev.biochem.67.1.395 | pages=395–424| pmid=9759493 | doi-access=free }}{{cite journal | last=Hahn | first=Mark E. | title=Aryl hydrocarbon receptors: diversity and evolution | journal=Chemico-Biological Interactions | publisher=Elsevier | volume=141 | issue=1–2 | year=2002 | issn=0009-2797 | doi=10.1016/s0009-2797(02)00070-4 | pages=131–160| pmid=12213389 | bibcode=2002CBI...141..131H }}{{cite journal | last=Bustelo | first=Xosé R. | title=Regulatory and Signaling Properties of the Vav Family | journal=Molecular and Cellular Biology | publisher=American Society for Microbiology | volume=20 | issue=5 | year=2000 | issn=0270-7306 | doi=10.1128/mcb.20.5.1461-1477.2000 | pages=1461–1477| pmid=10669724 | pmc=85310 }}

The C. elegans genome is about 100 million base pairs long and consists of six pairs of chromosomes in hermaphrodites or five pairs of autosomes with XO chromosome in male C. elegans and a mitochondrial genome. Its gene density is about one gene per five kilo-base pairs. Introns make up 26% and intergenic regions 47% of the genome. Many genes are arranged in clusters and how many of these are operons is unclear.{{cite journal | vauthors = Blumenthal T, Evans D, Link CD, Guffanti A, Lawson D, Thierry-Mieg J, Thierry-Mieg D, Chiu WL, Duke K, Kiraly M, Kim SK | title = A global analysis of Caenorhabditis elegans operons | journal = Nature | volume = 417 | issue = 6891 | pages = 851–4 | date = June 2002 | pmid = 12075352 | doi = 10.1038/nature00831 | bibcode = 2002Natur.417..851B | s2cid = 4351788 }} C. elegans and other nematodes are among the few eukaryotes currently known to have operons; these include trypanosomes, flatworms (notably the trematode Schistosoma mansoni), and a primitive chordate tunicate Oikopleura dioica. Many more organisms are likely to be shown to have these operons.{{cite journal | vauthors = Blumenthal T | title = Operons in eukaryotes | journal = Briefings in Functional Genomics & Proteomics | volume = 3 | issue = 3 | pages = 199–211 | date = November 2004 | pmid = 15642184 | doi = 10.1093/bfgp/3.3.199 | doi-access = free }}

The genome contains an estimated 20,470 protein-coding genes.{{cite web

|date=10 August 2011

|title=WS227 Release Letter

|url=http://www.wormbase.org/wiki/index.php/WS227

|publisher=WormBase

|access-date=2013-11-19

|archive-url=https://archive.today/20131128221823/http://www.wormbase.org/wiki/index.php/WS227

|archive-date=28 November 2013

|url-status=dead

}} About 35% of C. elegans genes have human homologs. Remarkably, human genes have been shown repeatedly to replace their C. elegans homologs when introduced into C. elegans. Conversely, many C. elegans genes can function similarly to mammalian genes.

The number of known RNA genes in the genome has increased greatly due to the 2006 discovery of a new class called 21U-RNA genes,{{cite journal | vauthors = Ruby JG, Jan C, Player C, Axtell MJ, Lee W, Nusbaum C, Ge H, Bartel DP | title = Large-scale sequencing reveals 21U-RNAs and additional microRNAs and endogenous siRNAs in C. elegans | journal = Cell | volume = 127 | issue = 6 | pages = 1193–207 | date = December 2006 | pmid = 17174894 | doi = 10.1016/j.cell.2006.10.040 | doi-access = free }} and the genome is now believed to contain more than 16,000 RNA genes, up from as few as 1,300 in 2005.{{cite journal | vauthors = Stricklin SL, Griffiths-Jones S, Eddy SR | title = C. elegans noncoding RNA genes | journal = WormBook | pages = 1–7 | date = June 2005 | pmid = 18023116 | pmc = 4781554 | doi = 10.1895/wormbook.1.1.1 }}

Scientific curators continue to appraise the set of known genes; new gene models continue to be added and incorrect ones modified or removed.

The reference C. elegans genome sequence continues to change as new evidence reveals errors in the original sequencing. Most changes are minor, adding or removing only a few base pairs of DNA. For example, the WS202 release of WormBase (April 2009) added two base pairs to the genome sequence.{{cite web

|date=29 May 2009

|title=WS202 Release Letter

|url=http://www.wormbase.org/wiki/index.php/WS202

|archive-url=https://archive.today/20131201022934/http://www.wormbase.org/wiki/index.php/WS202

|url-status=dead

|archive-date=December 1, 2013

|publisher=WormBase

|access-date=2013-11-19

}} Sometimes, more extensive changes are made as noted in the WS197 release of December 2008, which added a region of over 4,300 bp to the sequence.{{cite web

|date=27 November 2008

|title=WS197 Release Letter

|url=http://www.wormbase.org/wiki/index.php/WS197

|publisher=WormBase

|access-date=2013-11-19

|archive-url=https://web.archive.org/web/20191017232138/https://wiki.wormbase.org/index.php/WS197

|archive-date=17 October 2019

|url-status=dead

}}{{cite web

|date=15 June 2011

|title=Genome sequence changes

|url=http://www.wormbase.org/wiki/index.php/Genome_sequence_changes

|access-date=2011-08-13

|publisher=WormBase

|archive-url=https://web.archive.org/web/20191017232140/https://wiki.wormbase.org/index.php/Genome_sequence_changes

|archive-date=17 October 2019

|url-status=dead

}}

The C. elegans Genome Project's Wilson et al. 1994 found CelVav and a von Willebrand factor A domain and with Wilson et al. 1998 provides the first credible evidence for an aryl hydrocarbon receptor (AHR) homolog outside of vertebrates. 2

In 2003, the genome sequence of the related nematode C. briggsae was also determined, allowing researchers to study the comparative genomics of these two organisms.{{cite journal | vauthors = Stein LD, Bao Z, Blasiar D, Blumenthal T, Brent MR, Chen N, Chinwalla A, Clarke L, Clee C, Coghlan A, Coulson A, D'Eustachio P, Fitch DH, Fulton LA, Fulton RE, Griffiths-Jones S, Harris TW, Hillier LW, Kamath R, Kuwabara PE, Mardis ER, Marra MA, Miner TL, Minx P, Mullikin JC, Plumb RW, Rogers J, Schein JE, Sohrmann M, Spieth J, Stajich JE, Wei C, Willey D, Wilson RK, Durbin R, Waterston RH | title = The genome sequence of Caenorhabditis briggsae: a platform for comparative genomics | journal = PLOS Biology | volume = 1 | issue = 2 | pages = E45 | date = November 2003 | pmid = 14624247 | pmc = 261899 | doi = 10.1371/journal.pbio.0000045 | doi-access = free }} The genome sequences of more nematodes from the same genus e.g., C. remanei,{{cite web |url=http://genome.wustl.edu/genome.cgi?GENOME=Caenorhabditis%20remanei |author=Genome Sequencing Center |title=Caenorhabditis remanei: Background |access-date=2008-07-11 |publisher=Washington University School of Medicine |archive-url=https://web.archive.org/web/20080616091639/http://genome.wustl.edu/genome.cgi?GENOME=Caenorhabditis+remanei |archive-date=2008-06-16}} C. japonica{{cite web |url=http://genome.wustl.edu/genome.cgi?GENOME=Caenorhabditis%20japonica |author=Genome Sequencing Center |title=Caenorhabditis japonica: Background |access-date=2008-07-11 |publisher=Washington University School of Medicine |archive-url=https://web.archive.org/web/20080626053444/http://genome.wustl.edu/genome.cgi?GENOME=Caenorhabditis+japonica |archive-date=2008-06-26}} and C. brenneri (named after Brenner), have also been studied using the shotgun sequencing technique.{{cite journal | vauthors = Staden R | title = A strategy of DNA sequencing employing computer programs | journal = Nucleic Acids Research | volume = 6 | issue = 7 | pages = 2601–10 | date = June 1979 | pmid = 461197 | pmc = 327874 | doi = 10.1093/nar/6.7.2601 }} These sequences have now been completed.{{cite web|url=http://genome.ucsc.edu |title=UCSC genome browser |access-date=8 July 2014}}{{cite journal | vauthors = Kuhn RM, Karolchik D, Zweig AS, Wang T, Smith KE, Rosenbloom KR, Rhead B, Raney BJ, Pohl A, Pheasant M, Meyer L, Hsu F, Hinrichs AS, Harte RA, Giardine B, Fujita P, Diekhans M, Dreszer T, Clawson H, Barber GP, Haussler D, Kent WJ | title = The UCSC Genome Browser Database: update 2009 | journal = Nucleic Acids Research | volume = 37 | issue = Database issue | pages = D755–61 | date = January 2009 | pmid = 18996895 | pmc = 2686463 | doi = 10.1093/nar/gkn875 }}

File:C. elegans.jpg

As of 2014, C. elegans is the most basal species in the 'Elegans' group (10 species) of the 'Elegans' supergroup (17 species) in phylogenetic studies. It forms a branch of its own distinct to any other species of the group.{{cite journal | vauthors = Félix MA, Braendle C, Cutter AD | title = A streamlined system for species diagnosis in Caenorhabditis (Nematoda: Rhabditidae) with name designations for 15 distinct biological species | journal = PLOS ONE | volume = 9 | issue = 4 | pages = e94723 | year = 2014 | pmid = 24727800 | pmc = 3984244 | doi = 10.1371/journal.pone.0094723 | bibcode = 2014PLoSO...994723F | doi-access = free }}

Tc1 transposon is a DNA transposon active in C. elegans.

Several scientists have won the Nobel Prize in Physiology or Medicine for scientific discoveries made working with C. elegans. It was awarded in 2002 to Sydney Brenner, H. Robert Horvitz, and John Sulston for their work on the genetics of organ development and programmed cell death, in 2006 to Andrew Fire and Craig C. Mello for their discovery of RNA interference, and in 2024 to Victor Ambros and Gary Ruvkun for their discovery of microRNA and its role in gene regulation.{{cite journal | vauthors = Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC | title = Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans | journal = Nature | volume = 391 | issue = 6669 | pages = 806–11 | date = February 1998 | pmid = 9486653 | doi = 10.1038/35888 | bibcode = 1998Natur.391..806F | s2cid = 4355692 | url = http://www.dspace.cam.ac.uk/handle/1810/238264 }}{{cite journal | last1=Callaway | first1=Ewen | last2=Sanderson | first2=Katharine | title=Medicine Nobel awarded for gene-regulating 'microRNAs' | journal=Nature | publisher=Nature Publishing Group | date=2024-10-07 | volume=634 | issue=8034 | pages=524–525 | doi=10.1038/d41586-024-03212-9 | pmid=39375555 | url=https://www.nature.com/articles/d41586-024-03212-9 | access-date=2024-10-08}}

In 2008, Martin Chalfie shared a Nobel Prize in Chemistry for his work on green fluorescent protein; some of the research involved the use of C. elegans.

Many scientists who research C. elegans closely connect to Sydney Brenner, with whom almost all research in this field began in the 1970s; they have worked as either a postdoctoral or a postgraduate researcher in Brenner's lab or in the lab of someone who previously worked with Brenner. Most who worked in his lab later established their own worm research labs, thereby creating a fairly well-documented "lineage" of C. elegans scientists, which was recorded into the WormBase database in some detail at the 2003 International Worm Meeting.{{cite journal | vauthors = Harris TW, Antoshechkin I, Bieri T, Blasiar D, Chan J, Chen WJ, De La Cruz N, Davis P, Duesbury M, Fang R, Fernandes J, Han M, Kishore R, Lee R, Müller HM, Nakamura C, Ozersky P, Petcherski A, Rangarajan A, Rogers A, Schindelman G, Schwarz EM, Tuli MA, Van Auken K, Wang D, Wang X, Williams G, Yook K, Durbin R, Stein LD, Spieth J, Sternberg PW | display-authors = 6 | title = WormBase: a comprehensive resource for nematode research | journal = Nucleic Acids Research | volume = 38 | issue = Database issue | pages = D463-7 | date = January 2010 | pmid = 19910365 | pmc = 2808986 | doi = 10.1093/nar/gkp952 }}

• Animal testing on invertebrates
• Bioluminescence
• Eileen Southgate
• Intronerator
• OpenWorm
• WormBook

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• {{cite book | vauthors = Bird J, Bird AC | title = The structure of nematodes | publisher = Academic Press | year = 1991 | isbn = 978-0-12-099651-3 | pages = 1, 69–70, 152–153, 165, 224–225 }}
• {{cite book |last1=Hope |first1=IA |title=C. elegans: a practical approach |publisher=Oxford University Press |year=1999 |pages=1–6 |isbn=978-0-19-963738-6}}
• {{cite book | vauthors = Riddle DL, Blumenthal T, Meyer RJ, Priess JR |year=1997 |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=ce2 |title=C. elegans II |publisher=Cold Spring Harbor Laboratory Press |pages=1–4, 679–683 |pmid=21413221 |isbn=978-0-87969-532-3}}

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• Brenner S (2002) Nature's Gift to Science. In. http://nobelprize.org/nobel_prizes/medicine/laureates/2002/brenner-lecture.pdf (also Horvitz and Sulston lectures)
• [https://web.archive.org/web/20170420234209/http://www.wormbase.org/ WormBase] – an extensive online database covering the biology and genomics of C. elegans and other nematodes
• [http://www.wormatlas.org WormAtlas] – online database on all aspects of C. elegans anatomy with detailed explanations and high-quality images
• [http://www.wormbook.org WormBook] – online review of C. elegans biology
• [https://www.ncbi.nlm.nih.gov/IEB/Research/Acembly/index.html?worm AceView WormGenes] – another genome database for C. elegans, maintained at the NCBI
• [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=ce2.TOC C. elegans II] – a free online textbook.
• [http://www.wormweb.org/neuralnet WormWeb Neural Network] – an online tool for visualizing and navigating the connectome of C. elegans
• [http://labs.bio.unc.edu/Goldstein/movies.html C. elegans movies] – a visual introduction to C. elegans
• {{UCSC genomes|ce11}}
• [https://gd.eppo.int/taxon/CAEOEL Caenorhabditis elegans at eppo.int] (EPPO code CAEOEL)
• {{ Cite journal | title=Using C. elegans to study anesthesia | year=2022| doi=10.6084/m9.figshare.20963590.v1| url=https://visualiseyourthesis.figshare.com/articles/presentation/Neural_Correlates_of_Behavioural_Changes_During_Propofol_General_Anaesthesia_in_Caenorhabditis_Elegans/20963590| last1=Cylinder| first1=Drew}}

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Category:Nematodes described in 1900

Category:Articles containing video clips

Category:Animal models in neuroscience