actomyosin ring

{{short description|Cellular formation during cytokinesis}}

File:Cell cycle with images.jpg

In molecular biology, an actomyosin ring or contractile ring, is a prominent structure during cytokinesis.{{cite journal | pmid = 27505246 | year = 2016 | last1 = Cheffings | first1 = T. H. | last2 = Burroughs | first2 = N. J. | last3 = Balasubramanian | first3 = M. K. | title = Actomyosin Ring Formation and Tension Generation in Eukaryotic Cytokinesis | journal = Current Biology | volume = 26 | issue = 15 | pages = R719–R737 | doi = 10.1016/j.cub.2016.06.071 | s2cid = 3908927 | doi-access = free }} It forms perpendicular to the axis of the spindle apparatus{{cite book | doi = 10.1007/978-1-4419-9863-7_779 | chapter = Actomyosin Ring | title = Encyclopedia of Systems Biology | year = 2013 | last1 = Mana-Capelli | first1 = Sebastian | last2 = McCollum | first2 = Dannel | page = 8 | isbn = 978-1-4419-9862-0 }} towards the end of telophase, in which sister chromatids are identically separated at the opposite sides of the spindle forming nuclei (Figure 1). The actomyosin ring follows an orderly sequence of events: identification of the active division site, formation of the ring, constriction of the ring, and disassembly of the ring. It is composed of actin and myosin II bundles, thus the term actomyosin. The actomyosin ring operates in contractile motion,{{cite journal | pmid = 24757001 | year = 2014 | last1 = Munjal | first1 = A. | last2 = Lecuit | first2 = T. | title = Actomyosin networks and tissue morphogenesis | journal = Development | volume = 141 | issue = 9 | pages = 1789–1793 | doi = 10.1242/dev.091645 | s2cid = 5257808 | doi-access = free }} although the mechanism on how or what triggers the constriction is still an evolving topic.{{cite journal | pmid = 23931302 | year = 2013 | last1 = Mendes Pinto | first1 = I. | last2 = Rubinstein | first2 = B. | last3 = Li | first3 = R. | title = Force to divide: Structural and mechanical requirements for actomyosin ring contraction | journal = Biophysical Journal | volume = 105 | issue = 3 | pages = 547–554 | doi = 10.1016/j.bpj.2013.06.033 | pmc = 3736747 }} Other cytoskeletal proteins are also involved in maintaining the stability of the ring{{cite journal | pmid = 27799371 | year = 2016 | last1 = Martin | first1 = A. C. | title = Embryonic ring closure: Actomyosin rings do the two-step | journal = The Journal of Cell Biology | volume = 215 | issue = 3 | pages = 301–303 | doi = 10.1083/jcb.201610061 | pmc = 5100299 }} and driving its constriction.{{cite journal|last1=Kucera| first1=Ondrej| last2=Siahaan| first2=Valerie| last3=Janda| first3=Daniel| last4=Dijkstra| first4=Sietske H| last5=Pilatova| first5=Eliska | last6=Zatecka| first6=Eva | last7=Diez| first7=Stefan | last8=Braun| first8=Marcus | last9=Lansky| first9=Zdenek |date=2021| title=Anillin propels myosin-independent constriction of actin rings | journal=Nature Communications| volume=12| issue=1| pages=4595| doi=10.1038/s41467-021-24474-1| pmid=34321459| pmc=8319318}} Apart from cytokinesis, in which the ring constricts as the cells divide (Figure 2), actomyosin ring constriction has also been found to activate during wound closure.{{cite journal | pmid = 27326928 | year = 2016 | last1 = Schwayer | first1 = C. | last2 = Sikora | first2 = M. | last3 = Slováková | first3 = J. | last4 = Kardos | first4 = R. | last5 = Heisenberg | first5 = C. P. | title = Actin Rings of Power | journal = Developmental Cell | volume = 37 | issue = 6 | pages = 493–506 | doi = 10.1016/j.devcel.2016.05.024 | doi-access = free }} During this process, actin filaments are degraded, preserving the thickness of the ring. After cytokinesis is complete, one of the two daughter cells inherits a remnant known as the midbody ring.{{cite journal | pmid = 22683192 | year = 2012 | last1 = Pelletier | first1 = L. | last2 = Yamashita | first2 = Y. M. | title = Centrosome asymmetry and inheritance during animal development | journal = Current Opinion in Cell Biology | volume = 24 | issue = 4 | pages = 541–546 | doi = 10.1016/j.ceb.2012.05.005 | pmc = 3425708 }}

Activation of the cell-cycle kinase (e.g. Rho-kinases) during telophase initiates constriction of the actomyosin ring by creating a groove that migrates in an inward motion. Rho-kinases such as ROCK1 has been found to regulate actomyosin contraction through phosphorylation of the myosin light chain (MLC).{{cite journal | pmid = 23598717 | year = 2013 | last1 = Shi | first1 = J. | last2 = Surma | first2 = M. | last3 = Zhang | first3 = L. | last4 = Wei | first4 = L. | title = Dissecting the roles of ROCK isoforms in stress-induced cell detachment | journal = Cell Cycle | volume = 12 | issue = 10 | pages = 1492–1900 | doi = 10.4161/cc.24699 | pmc = 3680529 }} This mechanism promotes cell-cell contacts and integrity leading to adhesion formation.