Molecular aspects of gonadal differentiation in a teleost fish, the Nile tilapia.

In contrast to many developmental processes, sex-determining mechanisms show no clear evolutionary conservation among phyla. However, recent studies indicate that some downstream products of sex determination genes are functionally similar in diverse species. To date, numerous conserved genes involving gonadal sex differentiation have been examined in the teleost fish Nile tilapia (Oreochromis niloticus). Morphogenesis during gonadal differentiation is also conserved, as is evident in the differentiation and development of parenchyma/medullary cells (testis cord) and follicles. Therefore, it is important to understand the mechanisms of gonadal sex differentiation from the perspective of the relationship between conserved gene expression cascades and morphogenesis during gonadal sex differentiation. This article reviews the expression profiles of male- and female-related genes involved in histogenesis during sex differentiation in tilapia and discusses gene function in gonadal sex differentiation, especially the role of endogenous estrogens for ovarian differentiation. 2009 S. Karger AG, Basel.