ENHANCERS OF GLP-1, A GENE REQUIRED FOR CELL-SIGNALING IN CAENORHABDITIS-ELEGANS, DEFINE A SET OF GENES REQUIRED FOR GERMLINE DEVELOPMENT

The distal tip cell (DTC) regulates the proliferation or differentiati on choice in the Caenorhabditis elegans germline by an inductive mecha nism. Cell signaling requires a putative receptor in the germline, enc oded by the glp-1 gene, and a putative signal from the DTC, encoded by the lag-2 gene. Both glp-1 and lag-2 belong to multigene gene familie s whose members are essential for cell signaling during development of various tissues in insects and vertebrates as well as C. elegans. Rel atively little is known about how these pathways regulate cell fate ch oice. To identify additional genes involved in the glp-1 signaling pat hway, we carried out screens for genetic enhancers of glp-1. We recove red mutations in five new genes, named ego (enhancer of glp-1), and tw o previously identified genes, lag-1 and glp-4, that strongly enhance a weak glp-1 loss-of-function phenotype in the germline. Ego mutations cause multiple phenotypes consistent with the idea that gene activity is required for more than one aspect of germline and, in some cases, somatic development. Based on genetic experiments, glp-1 appears to ac t upstream of ego-1 and ego-3. We discuss the possible functional rela tionships among these genes in light of their phenotypes and interacti ons with glp-1.