Genital ridge

Genital ridge
Section of the fold in the mesonephros of a chickembryoof the fourth day. (Genital ridge labeled at left.)
Details
Precursor	Urogenital folds
Gives rise to	Sex cords
System	Reproductive system
Identifiers
Latin	crista gonadalis
TE	ridge_by_E5.7.1.0.0.0.5 E5.7.1.0.0.0.5
Anatomical terminology

Inembryology,thegenital ridge(orgonadal ridge) is thedevelopmental precursorto thegonads.The genital ridge initially consists mainly ofmesenchymeand cells of underlying mesonephric origin. Onceoogoniaenter 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 thesex cords.

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 becomesclitorisorpenis.
* i. Lower part of theintestine.
* ls. Fold of integument from which thelabia majoraorscrotumare formed.
* m, m. Right and leftMüllerian ductsuniting together and running with theWolffian ductsin gc, thegenital cord.
* ot. Thegenital ridgefrom which either theovaryortestisis formed (upper right).
* ug.Sinus urogenitalis.
* W. LeftWolffian 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 areSF1andWT1.Genes that determine sex areSRY,SOX9,andDAX1.Genes driving the differentiation into male or female structures areSF1,WT1,andWNT4.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, whereDMRT1is located, are often feminized. This feminization can range from ambiguous genitalia to XY sex reversal. TheDMRT1homolog from chicken has been localized on the Z chromosome. Birds have heterogametic females (ZW) and homogametic males (ZZ). The avian Z chromosome is 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.

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 is 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 forSRY,the Y-chromosomal gene responsible for sex determination in mammals. The urogenital ridge is made up of the gonadalanlageand the mesonephros. Themesonephrosis 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.

See also

• Development of the gonads

External links

• Swiss embryology(fromUL,UB,andUF)cgametogen/keimbahn02