Genital ridge

{{short description|Developmental precursor to the gonads in an embryo}} {{Infobox embryology | Name = Genital ridge | Latin = crista gonadalis | Image = Gray1106.png | Caption = Section of the fold in the mesonephros of a chick [[embryo]] of the fourth day. (Genital ridge labeled at left.) | Image2 = | Caption2 = | System = [[Reproductive system]] | CarnegieStage = | Precursor = [[Urogenital folds]] | GivesRiseTo = [[Sex cords]] }}

In [[embryology]], the '''genital ridge''' ('''genital fold''' or '''gonadal ridge''') is the [[Developmental biology|developmental precursor]] to the [[gonads]]. The genital ridge initially consists mainly of [[mesenchyme]] and cells of underlying mesonephric origin. Once [[Oogonium|oogonia]] {{clarify|reason=what about male spermatogonia/PGCs|date=March 2023}} enter this area they attempt to associate with these somatic cells. Development proceeds and the oogonia become fully surrounded by a layer of cells (pre-[[granulosa cells]]).

The genital ridge appears at approximately five weeks, and gives rise to the [[sex cords]].

[[File:Gray1110-1.png|thumb|300px|right|A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. * 3. [[Ureter]]. * 4. Urinary bladder. * 5. [[Urachus]]. * cl. [[Cloaca]]. * cp. Elevation which becomes [[clitoris]] or [[penis]]. * i. Lower part of the [[intestine]]. * ls. Fold of integument from which the [[labia majora]] or [[scrotum]] are formed. * m, m. Right and left [[Müllerian duct]]s uniting together and running with the [[Wolffian duct]]s in gc, the [[genital cord]]. * ot. The '''genital ridge''' from which either the [[ovary]] or [[testis]] is formed (upper right). * ug. [[Sinus urogenitalis]]. * W. Left [[Wolffian body]]. * w, w. Right and left Wolffian ducts.]]

==Associated genes== Genes associated with the developing gonad can be categorized into those that form the sexually indifferent gonad, those that determine whether the indifferent gonad will differentiate as male or female, and those that promote differentiation into male or female parts. Genes that form the sexually indifferent gonad are ''[[SF1 (gene)|SF1]]'' and ''[[WT1]]''. Genes that determine sex are ''[[Testis-determining factor|SRY]]'', ''[[SOX9]]'', and ''[[DAX1]]''. Genes driving the differentiation into male or female structures are ''SF1'', ''WT1'', and ''[[WNT4]]''. The other genes have roles in development that are not exclusively sex-related.

=== ''DMRT1'' === Evidence suggests that a DM domain gene, ''[[DMRT1]]'', is involved in sexual development. This gene is located on chromosome 9. Its location suggests that it is required for the development of testis. XY humans hemizygous for the chromosome 9p, where ''DMRT1'' is located, are often feminized. This feminization can range from ambiguous genitalia to XY sex reversal. The ''DMRT1'' homolog from chicken has been localized on the Z chromosome. Birds have heterogametic females (ZW) and homogametic males (ZZ). The avian Z chromosome shows conserved synteny with chromosome 9 of humans. ZZ embryos have a higher dose of DMRT1 and therefore have the potential to have a higher expression. It has been suggested that embryos with a higher expression of Dmrt1 expression develop into males while embryos with a lower expression are led to female development.<ref name="pmid10545231">{{cite journal |vauthors=Raymond CS, Kettlewell JR, Hirsch B, Bardwell VJ, Zarkower D | title = Expression of Dmrt1 in the genital ridge of mouse and chicken embryos suggests a role in vertebrate sexual development | journal = Developmental Biology | volume = 215 | issue = 2 | pages = 208–20 | date = 1999 | pmid = 10545231 | doi = 10.1006/dbio.1999.9461 | doi-access = free }}</ref>

In the mouse gonadal primordium, the genital ridge, which forms from intermediate mesoderm, becomes morphologically distinct at E10.5. By E12, sexual differentiation of the gonad is apparent, indicating that genes involved in the formation of the bipotential gonad are expressed before E10.5 and E12. Before E10.5, Dmrt1 is expressed at similar levels in the genital ridges of XX as well as XY embryos. By E12.5 and E13.5, DMRT1 is expressed deferentially as sex specific structures start to form. By E14.5 and E15.5, DMRT1 expression is maintained in the testis while it has begun to decrease in the ovary.

=== ''SRY'' === In mice, the genital ridge houses the transcript for ''[[Testis-determining factor|SRY]]'', the Y-chromosomal gene responsible for sex determination in mammals. The urogenital ridge is made up of the gonadal [[Anlage (biology)|anlage]] and the mesonephros. The [[mesonephros]] is involved in the development of the testis, but its role is in differentiation, and not determination. This is indicated by the absence of SRY expression in the mesonephros. SRY expression is expressed exclusively in the developing gonad, lacking a presence in any other tissue in embryos or adults.<ref name="pmid7670499">{{cite journal |vauthors=Jeske YW, Bowles J, Greenfield A, Koopman P | title = Expression of a linear Sry transcript in the mouse genital ridge | journal = Nature Genetics | volume = 10 | issue = 4 | pages = 480–2 | date = 1995 | pmid = 7670499 | doi = 10.1038/ng0895-480 | s2cid = 29075577 }}</ref>

== See also == * [[Development of the gonads]]

== References == {{Reflist|33em}}

== External links== * {{EmbryologySwiss|cgametogen/keimbahn02}}

[[Category:Embryology of urogenital system]]