Hermaphrodites carrying dominant mutations in the gene
egl-41 (egl, egg-laying defective) lack the hermaphrodite-specific HSN neurons but have the male-specific CEM neurons and therefore are weakly masculinized (1, 2). Our analyses with a deficiency (nDf42) and a duplication (ctDp8) that span the
egl-41 locus indicate that
egl-41 is not haplo-insufficient and that the dominant mutations cause an altered function that is antagonized by wild-type activity. The existing
egl-41 alleles (
n1069,
n1074,
n1077,
e2055,
n3717) therefore most likely represent gain-of-function (gf) mutations causing altered function. It has previously been shown that
egl-41(gf) mutations enhance the masculinizing effect of weak loss-of-function (lf) mutations in
tra-2 (tra, transformer) and suppress the feminizing effect of a
tra-2(mx) (mx, mixed character) allele (1, 3). In addition, a null mutation of
fem-1 (fem, feminization) was found to be epistatic to
egl-41(gf) mutations (3). Our analyses furthermore indicate that lf mutations of
fem-2 and
fem-3 are epistatic to
egl-41(gf) mutations as well and that
egl-41(gf) mutations are epistatic to a
her-1lf) (her, hermaphroditization) mutation. We suggest the gene defined by
egl-41(gf) mutations is part of the genetic pathway that specifies sexual fate and acts between
her-1 and the fem genes. To determine the lf phenotype of
egl-41 and to facilitate the cloning of the gene by transformation rescue, we performed an F1 screen for dominant revertants of the phenotype caused by the
egl-41(gf) mutation
n1077. We screened 20,000 haploid genomes and identified one mutation,
bc189, that is closely linked to the
egl-41 locus.
bc189 completely suppresses the
egl-41(
n1077gf) phenotype but causes no obvious additional abnormalities. We therefore cloned the gene by combining fine mapping, using SNPs, and our observation that the dominant phenotype of
egl-41(
n1077gf) is antagonized by wild-type activity.
egl-41 proved to be identical to a gene previously characterized,
sel-10 (sel, suppressor/enhancer of
lin-12).
sel-10 was identified as a negative regulator of
lin-12/Notch (lin, lineage abnormal) signaling and encodes an F-box protein (4, 5). The
egl-41(gf) mutations as well as
bc189 are missense mutations in the
sel-10 ORF (G566R and D482N, respectively). We will therefore now refer to
egl-41 as
sel-10.
sel-10(
bc189 n1077) suppresses a partial lf mutation of
lin-12, enhances a gf mutation of
lin-12, and suppresses a lf mutation of
sel-12 and therefore genetically behaves like the canonical lf allele of
sel-10,
ar41. Surprisingly, using the same criteria,
sel-10(
n1077gf) also behaves like a
sel-10(lf) mutation. Furthermore, preliminary data indicate that, just like
sel-10(gf) mutations,
bc189 n1077 as well as
ar41 enhance the masculinizing effects of weak
tra-2(lf) mutations. These results suggest that
sel-10 is normally involved in the determination of sexual fate and that
sel-10(gf) mutations share certain characteristics with
sel-10(lf) mutations. Using biochemical and molecular approaches, we are currently seeking potential targets of the F-box protein SEL-10 in the sex determination pathway.