Sex determination in the germ line.

Sexual identity is one of a few basic parameters that specify how development should proceed. Although sex determination has profound effects on many tissues, its most ancient and fundamental role is ensuring that some germ cells become sperm, and others become oocytes or eggs. Spermatocytes and oocytes are usually produced in male and female animals, respectively, but C. elegans is uniquely suitable for studying the control of these cell fates because both types of cells are made from a common pool of progenitors in XX hermaphrodites. Extensive genetic and molecular studies have shown that the sexual fate of germ cells in C. elegans is controlled by the same genes that regulate sexual identity in other parts of the animal. However, this regulatory pathway has additional features that are unique to the germ line. First, several genes, like the three fogs, act only in germ cells. Second, the three fem genes act in concert with targets of tra-1 to control germ cell fates, but do not act this way in the soma. Third, translational repression of tra-2 is essential for hermaphrodite spermatogenesis. Fourth, translational repression of fem-3 is needed for oogenesis. In this review, we present genetic and molecular models for how these processes work, and summarize the evidence upon which they are built.