Mutations of the gene
tra-3 result in partial masculinization of XX animals of C. elegans, which are normally hermaphrodites (males are XO). A total of 43
tra-3 revertants (one intragenic, 42 extragenic) have been isolated and analyzed, in the hope of identifying new sex- determination loci. Most (38) of the extra-genic suppressors cause partial or complete feminization of XX and XO animals; the remaining four are weak suppressors. The feminizing suppressors are mostly alleles of known sex-determining genes:
tra-1 (11 dominant alleles),
tra-2 (one dominant allele),
fem-1 (four alleles) and
fem-2 (four alleles), but 18 are alleles of a new gene,
fem-3. Additional alleles have been isolated for the
fem-2 and
fem-3 genes, as well as
fem-3 deficiencies. Mutations in
fem-3 resemble alleles of
fem-1 (previously characterized): putative null alleles result in complete feminization of XX and XO animals, transforming them into fertile females. Severe alleles of
fem-2 also cause complete feminization of XX animals at all temperatures, but feminization of
fem-2 XO animals is temperature-sensitive: complete at 25 degrees, incomplete at 20 degrees. As with
fem-1, severe mutations of
fem-2 and
fem-3 are wholly epistatic to masculinizing alleles of
tra-2 and
tra-3, and epistatic to
tra-1 masculinizing alleles in the germline, but not in the soma. All three fem genes are essential for male development and appear to have a dual role in promoting spermatogenesis and repressing
tra-1 activity. All three fem genes exhibit strong maternal effects; the maternal contribution of fem gene products may be inactivated in XX animals by a posttranscriptional mechanism. Maternal contributions of wild-type
fem-3 product are necessary for normal XO male development and XX hermaphrodite (as opposed