testicular development
Testicular development is guided by testis determining factor (TDF), which is encoded by the SRY (sex-determining region on the Y chromosome) gene located on the short arm of the Y chromosome.
Under the influence of testis determining substance TDF, germ cells in the genital ridge differentiate (sexual cords) into Sertoli cells, which secrete müllerian inhibiting substance (MIS) (or müllerian inhibiting factor or MIF), and Leydig cells, which produce testosterone. MIF causes complete regression of the müllerian ducts, whereas testosterone promotes maturation of spermatogonia and regulates development of the male phenotype by means of paracrine and endocrine actions. By means of paracrine action, the wolffian duct develops into the epididymis, vas deferens, ejaculatory duct, and seminal vesicles.
In the absence of the Y chromosome, gonads differentiate into ovaries at around 11–13 weeks gestation. Ovarian hormones are thought to play no role in female phenotype differentiation. Absence of MIF leads to persistence of müllerian structures, which develop into the fallopian tubes, uterus, cervix, and upper vagina. Because of the absence of testosterone, the wolffian ducts involute.
References
Brennan J, Capel B. One tissue, two fates: molecular genetic events that underlie testis versus ovary development. Nat Rev Genet. 2004 Jul;5(7):509-21. #PMID: 15211353#