The cell biology and molecular genetics of testis determination.

Abstract

The variety of sexual dimorphisms that distinguish males from females all stem from a single critical process: sex determination. In humans and other mammals, sex is determined at the time of fertilization by the inheritance of sex chromosomes. Individuals receiving two X chromosomes develop ovaries and become females, while those receiving one X and one Y chromosome develop testes and become males. These alternative sex chromosome constitutions must initiate different developmental programmes within the embryonic gonads. In mammalian embryos, testicular differentiation begins prior to ovarian differentiation. Consequently, female development has traditionally been regarded as a ‘default’ state that must be pre-empted by a male-determining signal if a testis is to form. Furthermore, Alfred Jost’s classic castration experiments on rabbit embryos, conducted over 40 years ago, showed that the testis is necessary for male-specific development of the reproductive tract and external genitalia in eutherian mammals. In the absence of the gonads, both genetic sexes follow the female pathway of differentiation (Jost 1953, 1970; reviewed in Jost et al. 1973). The masculinizing effect of the testis is due to the hormones, testosterone and Anti-Müllerian hormone (AMH), (reviewed in George and Wilson 1988). Thus, the various processes that constitute sexual differentiation depend upon the presence/absence of a testis. Testis determination is therefore a decisive developmental event.KeywordsSertoli CellTestis DeterminationGonadal DysgenesisSeminiferous CordCampomelic DysplasiaThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.