Germ-line regulation of the Caenorhabditis elegans sex-determining gene tra-2

The Caenorhabditis elegans sex-determining gene tra-2 promotes female devel opment of the XX hermaphrodite soma and germ line. We previously showed tha t a 4.7-kb tra-2 mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of the tra-2 locus. This paper focuses on t he germ-line activity and regulation of tra-2. First, we characterize a 1.8 -kb tra-2 mRNA, which is hermaphrodite-specific and germ-line-dependent. Th is mRNA encodes TRA-2B, a protein identical to a predicted intracellular do main of TRA-2A. We show that the 1.8-kb mRNA is oocyte-specific, suggesting that it is involved in germ-line or embryonic sex determination. Second, w e identify a tra-2 maternal effect on breed size that may be associated wit h the 1.8-kb mRNA. Third, we investigate seven dominant tra-2(mx) (for mixe d character) mutations that sexually transform hermaphrodites to females by eliminating hermaphrodite spermatogenesis. Each of the tra-2(mx) mutants p ossesses a nonconserved missense change in a 22-amino-acid region common to bath TRA-2A and TRA-2B, called the MX region. We propose that the MX regio n mediates a posttranslational regulation of tra-2 essential for the onset of hermaphrodite spermatogenesis, Finally, we discuss aspects of tra-2 func tion and regulation that are specific to the unusual control of cell fate i n the hermaphrodite germ line. (C) 1998 Academic Press.