sex cords

{{Infobox embryology

| Name = Sex cords

| Latin = chorda sexualis primordialis gonadalis

| Image =

| Caption =

| Image2 =

| Caption2 =

| CarnegieStage =

| Precursor = Genital ridge

| GivesRiseTo = Testis cords, cortical cords

| System = Reproductive system

}}Once the genital ridge has committed to becoming male sex cords, Sertoli cells develop. These cells then induce the production and organisation of cells making up the testicular cords. These cords will eventually become the testes, which in turn produce hormones, in particular testosterone.{{Cite book |url=https://www.cambridge.org/core/product/identifier/9781139192736/type/book |title=Textbook of Clinical Embryology |date=2013-10-31 |publisher=Cambridge University Press |isbn=978-1-139-19273-6 |editor-last=Coward |editor-first=Kevin |edition=1 |doi=10.1017/cbo9781139192736 |editor-last2=Wells |editor-first2=Dagan}} These hormones drive the formation of the other male sex characteristics, and induce testicular descent out of the abdomen. These hormones also cause the development of the male reproductive tract. Embryos are formed with Wolffian and Mullerian ducts, which will either become the male or female reproductive tract, respectively. In a male embryo, the testicular cords will induce the development of the Wolffian duct into the vas deferens, epididymis and the seminal vesicle and cause the repression and regression of the Mullerian duct. The other male sex organs (ex. the prostate) as well as external genitalia are also formed under the influence of testosterone.

Female sex cord development depends on specific genes being expressed, where multiple pro-ovarian genes (including Wnt4, FoxL2, and Rsp01){{Cite journal |last1=Chassot |first1=Anne-Amandine |last2=Gillot |first2=Isabelle |last3=Chaboissier |first3=Marie-Christine |date=December 2014 |title=R-spondin1, WNT4, and the CTNNB1 signaling pathway: strict control over ovarian differentiation |url=https://rep.bioscientifica.com/view/journals/rep/148/6/R97.xml |journal=Reproduction |volume=148 |issue=6 |pages=R97–R110 |doi=10.1530/REP-14-0177 |pmid=25187620 |issn=1470-1626|doi-access=free }}{{Cite journal |last1=Ottolenghi |first1=Chris |last2=Omari |first2=Shakib |last3=Garcia-Ortiz |first3=J. Elias |last4=Uda |first4=Manuela |last5=Crisponi |first5=Laura |last6=Forabosco |first6=Antonino |last7=Pilia |first7=Giuseppe |last8=Schlessinger |first8=David |date=2005-06-08 |title=Foxl2 is required for commitment to ovary differentiation |journal=Human Molecular Genetics |volume=14 |issue=14 |pages=2053–2062 |doi=10.1093/hmg/ddi210 |pmid=15944199 |issn=1460-2083|doi-access=free }}{{Cite journal |last1=Chassot |first1=A.-A. |last2=Ranc |first2=F. |last3=Gregoire |first3=E. P. |last4=Roepers-Gajadien |first4=H. L. |last5=Taketo |first5=M. M. |last6=Camerino |first6=G. |last7=de Rooij |first7=D. G. |last8=Schedl |first8=A. |last9=Chaboissier |first9=M.-C. |date=2008-01-18 |title=Activation of -catenin signaling by Rspo1 controls differentiation of the mammalian ovary |journal=Human Molecular Genetics |language=en |volume=17 |issue=9 |pages=1264–1277 |doi=10.1093/hmg/ddn016 |issn=0964-6906|doi-access=free }} and the lack of Sry gene expression are responsible. The lack of testosterone allows for Müllerian duct proliferation, and Wolffian duct repression. The lack of male sex hormones gives rise to female sex cords and subsequent genitalia differentiation, rather than a presence of female sex hormones. After inducing female sex cord formation, coordination between multiple genes (Bmp, Pax2, Lim1, and Wnt4 in mice) is required for Müllerian duct development. Once the Müllerian ducts are determined, genes contributing to cell identity and positioning (specifically, Hox genes) play a key role in developing female reproductive structures.{{Cite journal |last1=Duverger |first1=Olivier |last2=Morasso |first2=Maria I. |date=2008 |title=Role of homeobox genes in the patterning, specification, and differentiation of ectodermal appendages in mammals |journal=Journal of Cellular Physiology |language=en |volume=216 |issue=2 |pages=337–346 |doi=10.1002/jcp.21491 |pmid=18459147 |issn=0021-9541|pmc=2561923 }} The Hox genes are expressed in specific combinations to give rise to the fallopian tubes, uterus, and upper region of the vagina.{{Citation |last1=P A |first1=Aatsha |title=Embryology, Sexual Development |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK557601/ |work=StatPearls |access-date=2023-12-04 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32491533 |last2=Arbor |first2=Tafline C. |last3=Krishan |first3=Kewal}}

Developing internal female genitalia, from the Müllerian ducts, occurs in three phases. First, cells are directed to proliferate on the female reproductive structure development pathway. Phase two is invagination: referring to the ducts folding in on themselves, forming openings of the fallopian tubes. In phase three, Müllerian ducts proliferate and elongate, subsequently forming the uterus and upper region of the vagina. Fallopian tubes form at the end closer to the head of the body, and the uterus and upper portion of the vagina form at the opposite end.

In early prenatal development, amphibians and elasmobranchs have gonads with a dual structure; A gonadal cortex, associated with ovarian differentiation, and a gonadal medulla, associated with testicular differentiation.{{Cite journal |last1=Komatsu |first1=T. |last2=Nakamura |first2=S. |last3=Nakamura |first3=M. |date=2006 |title=A sex cord-like structure and some remarkable features in early gonadal sex differentiation in the marine teleost Siganus guttatus (Bloch) |url=https://onlinelibrary.wiley.com/doi/10.1111/j.0022-1112.2006.00897.x |journal=Journal of Fish Biology |language=en |volume=68 |issue=1 |pages=236–250 |doi=10.1111/j.0022-1112.2006.00897.x |bibcode=2006JFBio..68..236K |issn=0022-1112|url-access=subscription }}{{Cite journal |last=Costello |first=D. P. |date=1957-09-27 |title=Development of Vertebrates . Emil Witschi. Saunders, Philadelphia, Pa., 1956. xvi+ 588 pp. Illus. $8.50. |url=https://www.science.org/doi/10.1126/science.126.3274.616.b |journal=Science |language=en |volume=126 |issue=3274 |pages=616 |doi=10.1126/science.126.3274.616.b |issn=0036-8075|url-access=subscription }}{{Cite journal |last=Kempton |first=Rudolf T. |date=1968 |title=Sharks, Skates, and Rays. Perry W. Gilbert , Robert F. Mathewson , David P. Rall |url=http://dx.doi.org/10.1086/physzool.41.1.30158491 |journal=Physiological Zoology |volume=41 |issue=1 |pages=125–126 |doi=10.1086/physzool.41.1.30158491 |issn=0031-935X|url-access=subscription }} In contrast, amniotes have single-structure gonads. Sex-specific development is dependent on the fate of the primary sex cord. There are also species-specific anomalies in sex cord development. Freemartin cattle are one notable phenomenon of abnormal gonad development.{{Citation |last1=JOST |first1=ALFRED |title=Studies on Sex Differentiation in Mammals |date=1973 |url=http://dx.doi.org/10.1016/b978-0-12-571129-6.50004-x |work=Proceedings of the 1972 Laurentian Hormone Conference |pages=1–41 |access-date=2023-12-04 |publisher=Elsevier |last2=VIGIER |first2=BERNARD |last3=PRÉPIN |first3=JACQUES |last4=PERCHELLET |first4=JEAN PIERRE|volume=29 |doi=10.1016/b978-0-12-571129-6.50004-x |pmid=4584366 |isbn=9780125711296 |url-access=subscription }}{{Cite journal |last=Lillie |first=Frank R. |date=1916-04-28 |title=The Theory of the Free-Martin |url=https://www.science.org/doi/10.1126/science.43.1113.611 |journal=Science |language=en |volume=43 |issue=1113 |pages=611–613 |doi=10.1126/science.43.1113.611 |pmid=17756274 |bibcode=1916Sci....43..611L |issn=0036-8075|url-access=subscription }} These are genetically female cattle that develop testicle-like structures in replacement of ovaries due to exchange of blood during development in parabiosis with male twin(s).

• Development of the gonads
• Sex cord–gonadal stromal tumour

{{Reflist}}

• {{EmbryologyUNSW|Medicine/BGDlabXYXX_5}}

{{Development of urinary and reproductive systems}}

{{Authority control}}

Category:Embryology of urogenital system