The
fog-1 gene controls whether germ cells differentiate as sperm or as oocytes. Sequence analysis revealed that FOG-1 is a Cytoplasmic Polyadenylation Element Binding (CPEB) protein. These proteins are known to bind the 3'-UTR of messenger RNAs and regulate their translation. The
fog-1 message contains a consensus binding site for CPEB proteins. We used northern analysis and co-immunoprecipitation assays to show that FOG-1 can bind its own 3'-UTR in vitro , and that this binding depends on wild-type FOG-1 activity. By contrast, FOG-1 does not bind control transcripts, like that of
unc-37 . These data suggest that FOG-1 regulates germ cell fates translationally, and that one of its targets might be
fog-1 , itself. In Xenopus , CPEB proteins are known to interact with maskin and CPSF to regulate translation of target messages. To isolate genes that regulate or interact with FOG-1, we performed a screen looking for mutations that suppress the temperature-sensitive allele,
fog-1(
q253). We identified 17 recessive and two semi-dominant suppressors from approximately 40,000 haploid genomes. Eight recessive mutations form a single complementation group on chromosome III, and four compose a second group on chromosome II. We call these loci
sof-1 and
sof-2 , respectively ( sof = s uppressor o f f og-1) . Three criteria suggest that the suppressor alleles of these genes cause a loss-of-function. First, these mutations are common. Those in
sof-1 arose at a frequency of 1/5000 haploid genomes, while those in
sof-2 occurred at a frequency of 1/10,000. Second, these
sof-1 and
sof-2 alleles are recessive. Third, we isolated additional alleles from non-complementation screens, and these new alleles also suppress
fog-1(
q253 ts ) . Seven of these new
sof-1 alleles were identified (at a frequency of approximately 1/700 haploid genomes), and one new
sof-2 allele was identified (at a frequency of 1/1500). The penetrance of
sof-1 mutations ranges from 50-90%, while that of
sof-2 mutations ranges from 40-60%. Furthermore, mutations in
sof-1 and
sof-2 are allele specific suppressors, since they do not suppress null alleles of
fog-1 . Finally,
sof-1 and
sof-2 mutations have no detectable phenotype in a wild-type genetic background. However,
sof-2(
v3);
sof-1(
v20) double mutants show a significantly increased hermaphrodite broodsize. This result suggests that they might be functionally redundant genes that normally promote germ cells to differentiate as oocytes rather than as sperm. To learn their biochemical functions, we are cloning
sof-1 and
sof-2 . So far,
sof-1 has been mapped to a region spanning approximately 83 kb, at position -0.76 on chromosome III. We are using transformation rescue and RNAi to finish cloning
sof-1 , and are employing a similar strategy to clone
sof-2 . Molecular analyses of these two genes might elucidate how CPEB proteins interact with other molecules to regulate the polyadenylation and translation of specific targets, and how translational control can specify cell fates.