Molecular Cloning and Transcript Analysis of Fem-3, a Sex-determination Gene in Caenorhabditis Elegans

The fem-3 gene is required for specification of the male fate in the nematode Caenorhabditis elegans: XO males need fem-3 for male differentiation in both soma and germ line; XX hermaphrodites need it for the production of sperm. We have cloned fem-3 by transposon tagging. Among eight spontaneous fem-3 mutations generated in a strain in which the transposable element Tc1 is mobile, six contain Tc1 insertions in a 2-kb region of the genome. From this region, we have identified three fem-3 transcripts. Two, 1.7 kb and 1.62 kb, are presented in embryos, and two, 1.62 kb and 1.55 kb, are present in L4s and adults. The fem-3 transcripts are not XO specific; however, in XX adult hermaphrodites, they appear to be limited to the germ line--a tissue involved in male development (both for spermatogenesis and for the maternal contribution of fem-3 to the embryo). The amount of fem-3 RNA in XO embryos is approximately sixfold greater than in XX embryos. The significance of this difference in specifying male development in XO but not in XX embryos is discussed.