Mammalian sex determination and gonad development.

From a developmental biology perspective, gonadogenesis is of particular interest because it provides a unique example of how distinct organs, the testis and ovary, can arise from a common bipotential primordium. Gonadogenesis is also highly relevant from a clinical perspective, as congenital disorders of sex development (DSDs) are not uncommon, occurring in approximately 1 in 4500 live births. In recent years, there has been significant progress in our understanding of the genes and pathways that control important aspects of gonadogenesis including the initial decision to develop as a testis or ovary (sex determination), elaboration and cross-repression of the testis and ovary developmental pathways, and maintenance of the gonadal phenotype after birth. In this chapter, we provide an overview of gonadal morphogenesis and cell lineage specification, focusing primarily on these processes in mice and humans. We also provide an update on the genetic mechanisms that control murine gonadogenesis and maintenance and, where possible, discuss new insights into the pathological mechanisms of DSDs associated with mutation of orthologous genes in mice and humans.