Translational control via 3'UTRs is critical in the germline of many species. In Xenopus , an RNA-binding protein, CPEB (Cytoplasmic Polyadenylation Element Binding Protein), binds to 3' UTRs of specific maternal mRNAs and is thought to regulate their translation. The C. elegans genome contains 4 putative CPEB homologs. The similarity is greatest in the region that contains 2 RNA Recognition Motifs (RRMs) and a novel C/H-containing Zn-binding domain, both of which are needed for Xenopus CPEB to bind RNA. Using RNAi, we find that one CPEB homolog,
cpb-1 , is required for spermatogenesis in both hermaphrodites and males;
cpb-1(RNAi) animals have arrested primary spermatocytes and lack secondary spermatocytes or mature sperm. Wild-type males produce viable cross-progeny when mated to the
cpb-1(RNAi) hermaphrodites; thus
cpb-1 is not required for oogenesis.
cpb-1 mRNA is germline-specific. CPB-1 protein is detected in the meiotic region of the L4 germline, but not in adults. Using CPB-1 as bait in the two-hybrid system, we recovered FBF, a repressor of
fem-3 required for the sperm/oocyte switch; the interaction's significance is being investigated. A second homolog encodes
fog-1 , a gene required to specify sperm fate. The homolog maps to the
fog-1 locus, and RNAi directed against the gene results in a feminized (Fog) germ line. We sequenced this gene from a
fog-1(
q253) mutant and found an amino acid substitution in a residue highly conserved among CPEBs, confirming that it is the
fog-1 gene (also see Jin et al abstract). Using FOG-1 as bait in a two-hybrid screen, we've found one specific partner to date; analysis of this partner will be presented. In every species examined, CPEBs are implicated in oogenesis. However, in C. elegans , animals subjected to RNAi against all CPEB homologs simultaneously are Fog. Moreover, oocytes of these animals support embryogenesis and produce viable cross-progeny. Thus CPEBs are dispensable for oogenesis in C. elegans . This is the first report of CPEBs having a role in spermatogenesis, and contrasts with the roles of Xenopus CPEB and Drosophila orb . Worm CPEBs are required for two steps in spermatogenesis:
fog-1 specifies the sperm fate, and
cpb-1 implements that decision. We suggest that CPB-1 and FOG-1 bind to and regulate specific mRNAs to execute these functions.