Germ-Line Regulation of theCaenorhabditis elegansSex-Determining Genetra-2

Abstract

TheCaenorhabditis eleganssex-determining genetra-2promotes female development of the XX hermaphrodite soma and germ line. We previously showed that a 4.7-kbtra-2mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of thetra-2locus. This paper focuses on the germ-line activity and regulation oftra-2.First, we characterize a 1.8-kbtra-2mRNA, which is hermaphrodite-specific and germ-line-dependent. This mRNA encodes TRA-2B, a protein identical to a predicted intracellular domain 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, we identify atra-2maternal effect on brood size that may be associated with the 1.8-kb mRNA. Third, we investigate seven dominanttra-2(mx) (for mixed character) mutations that sexually transform hermaphrodites to females by eliminating hermaphrodite spermatogenesis. Each of thetra-2(mx) mutants possesses a nonconserved missense change in a 22-amino-acid region common to both TRA-2A and TRA-2B, called the MX region. We propose that the MX region mediates a posttranslational regulation oftra-2essential for the onset of hermaphrodite spermatogenesis. Finally, we discuss aspects oftra-2function and regulation that are specific to the unusual control of cell fate in the hermaphrodite germ line.