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sexual differentiation

Wednesday 26 May 2004

Sexual differentiation can be defined as the series of events whereby the sexually indifferent fetus progressively acquires male or female characteristics in the gonads, genital tract and external genitalia.

Normal sex development consists of several sequential stages. Genetic sex, as determined by the chromosome constitution, drives the primitive gonad to differentiate into a testis or an ovary.

Subsequently, internal and external genitalia will follow the male pathway in the presence of specific testicular hormones, or the female pathway in their absence.

Since the presence of the fetal testis plays a determining role in the differentiation of the reproductive tract, the term " sex determination " has been coined to designate the differentiation of the gonad during early fetal 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.

Pathology (Anomalies of sex differentiation)

- disorders of sexual differentiation (DSDs) or intersex disorders (intersexuality or intersex)

  • XY intersex
  • XX intersex

See also

- primitive gonad

  • gonadal ridge
  • primitive germ cells

- male sex determination

  • testicular differentiation

- female sex determination

  • ovarian differentiation

- sexual dimorphism

Online textbooks

- endotext.org

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#

- Genetic and molecular insights into the development and evolution of sexual dimorphism. Williams TM, Carroll SB. Nat Rev Genet. 2009 Nov;10(11):797-804. PMID: 19834484

- Federman DD. The biology of human sex differences. N Engl J Med. 2006 Apr 6;354(14):1507-14. PMID: 16598047

- Rinn JL, Snyder M. Sexual dimorphism in mammalian gene expression. Trends Genet. 2005 May;21(5):298-305. PMID: 15851067

- 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

- MacLaughlin DT, Donahoe PK. Sex determination and differentiation. N Engl J Med. 2004 Jan 22;350(4):367-78. PMID: 14736929

- MacLaughlin DT, Donahoe PK. Sex determination and differentiation. N Engl J Med. 2004 Jan 22;350(4):367-78. PMID: 14736929

- Arnold AP. Sex chromosomes and brain gender. Nat Rev Neurosci. 2004 Sep;5(9):701-8. PMID: 15322528

- Cotinot C, Pailhoux E, Jaubert F, Fellous M. Molecular genetics of sex determination. Semin Reprod Med. 2002 Aug;20(3):157-68. PMID: 12428196

- Vaiman D, Pailhoux E. Mammalian sex reversal and intersexuality : deciphering the sex-determination cascade. Trends Genet. 2000 Nov ;16(11):488-94. PMID : 11074290