In the C.elegans germ line, the GLP-1/Notch signaling pathway regulates the switch from proliferation to meiosis. GLP-1 is activated in the distal germ line by a signal from the somatic distal tip cell, and distal germ cells are thereby induced to proliferate. In the absence of GLP-1 signaling, germ cells exit mitosis, enter meiosis, and differentiate. The ego (enhancement of
glp-1) screen was designed to identify components, regulators, and targets of the GLP-1-mediated signaling pathway in the germ line (Qiao et al., 1995). An
ego-2 mutation,
om33, was recovered as an enhancer of a weak
glp-1 loss-of-function mutation in the germ line (Qiao et al., 1995). To clone
ego-2, we localized its map position to a 137 kb region, and then tested individual genes within the region for enhancement of
glp-1 by RNAi. RNAi of one gene in the region, Y53H1C.2, enhances a weak
glp-1(lf) mutation in the germ line. Therefore, Y53H1C.2 is an ego gene. We obtained the full-length Y53H1C.2 cDNA by RT-PCR and determined the sequence. By blasting with the Y53H1C.2 protein sequence, we found that only the C.briggsae protein is conserved throughout, but the amino terminal half of the Y53H1C.2 protein is conserved with yeast BRO1 protein, non-receptor protein tyrosine phosphatase (type 23), and Rhophilin. The amino terminal half contains two more highly conserved domains, which the NCBI database calls the BRO1 and DUF164 domains. We sequenced the Y53H1C.2 gene from our
ego-2(
om33) strain, and found a mutation that changes a conserved amino acid in the BRO1 domain. We conclude that Y53H1C.2 is
ego-2. In a
glp-1(+) background,
ego-2(
om33) has a temperature-sensitive spermatogenesis defective phenotype. Preliminary data suggest that
ego-2(
om33) does not suppress the
glp-1(gf) phenotype in the germ line, suggesting that
ego-2 may act upstream of or in parallel with
glp-1. We are now testing whether depletion of the EGO-2 protein by RNAi can suppress
glp-1(
oz112). Consistent with this finding, neither
ego-2(
om33) nor Y53H1C.2 RNAi suppresses the
gld-2 gld-1 meiotic entry defect. Interestingly, both
ego-2(
om33) and Y53H1C.2 RNAi enhance a weak
glp-1(lf) in the embryo, suggesting that EGO-2 may be a general regulator of GLP-1 signaling. Preliminary data suggest that expression of
ego-2 in both germ line and soma may be important for germline proliferation. Experiments are in progress to better define the site(s) of EGO-2 function. Qiao et al. (1995) Genetics 141, 551-569