Gene interactions in gonadal development

The acquisition of a sexually dimorphic phenotype is a critical event in ma mmalian development. Although the maturation of sexual function and reprodu ction occurs after birth, essentially all of the critical developmental ste ps take place during embryogenesis. Temporally, these steps can be divided into two different phases: sex determination, the initial event that determ ines whether the gonads will develop as testes or ovaries; and sexual diffe rentiation, the subsequent events that ultimately produce either the male o r the female sexual phenotype. A basic tenet of sexual development in mamma ls is that genetic sex-determined by the presence or absence of the Y chrom osome-directs the embryonic gonads to differentiate into either testes or o varies. Thereafter, hormones produced by the testes direct the developmenta l program leading to male sexual differentiation. In the absence of testicu lar hormones, the pathway of sexual differentiation is female. This chapter reviews the anatomic and cellular changes that constitute sexual different iation and discusses SRY and other genes, including SF-I, WT1, DAX-1, and S OX9, that play key developmental roles in this process. Dose-dependent inte ractions among these genes are critical for sex determination and different iation.