GLP-1 is a Notch-type receptor that mediates an inductive signal from the somatic distal tip cells to the germ line. In the absence of GLP-1 signaling, all cells enter meiosis and differentiate. Mutations in
ego-4and ego-5were isolated as recessive enhancers of
glp-1in the germ line in a screen designed to identify components, regulators, or targets of the GLP-1-mediated signaling pathway (Qiao et al. 1995). In a
glp-1(+)background,
ego-4and ego-5mutants have a maternal effect embryonic lethal phenotype. To clone the genes, we mapped them relative to cloned marker genes and single nucleotide polymorphisms (SNPs) and used RNAi to test the predicted genes in each region to determine which has an Ego phenotype. (Many thanks to the Ahringer lab for providing feeding strains!) For each region, we found one gene with the expected set of defects: maternal effect embryonic lethality and enhancement of
glp-1(
bn18ts). The putative
ego-4gene, D2045.1, encodes a member of the Ataxin-2-like protein family. Work in yeast and humans has shown that Ataxin-2-like proteins can bind various RNA binding proteins. D2045.1(RNAi) produces an incompletely penetrant Glp-1 defect in a wildtype background and a stronger Glp-1 defect in an
ego-4mutant background. As existing
ego-4alleles are not likely to be null, this synergistic interaction is consistent with
ego-4 and D2045.1 being identical. We are sequencing
ego-4alleles to confirm this hypothesis. D2045.1(RNAi) also produces a Mog defect: the XX germ line fails to switch to oogenesis. D2045.1(RNAi) suppresses
fog-2(-), suggesting that D2045.1 acts downstream of
fog-2to promote female development. We hypothesize that D2045.1 activity may regulate the splicing and/or translation of target mRNAs important for germline mitosis and the sperm-to-oocyte switch. The putative
ego-5gene, R01H10.1, encodes the regulatory B subunit of DNA polymerase alpha-primase complex. The complex is required for initiation of DNA replication during the mitotic cell cycle; the B subunit has been implicated in complex assembly and nuclear import. We hypothesize that B subunit activity may be regulated - directly or indirectly - by GLP-1-mediated signaling to promote mitosis. Preliminary sequencing data suggest that
ego-5(
om31) contains a missense mutation in a conserved histidine residue. We examined whether other complex subunits also behave as ego genes. Preliminary data suggest that they are required for germline proliferation and viability, and do not simply enhance
glp-1(ts).