Genetic and molecular characterization of genes that interact withglp-1 in Caenorhabditis elegans germline development

Signaling between cells is required for the proper specification of cell fate during the development of multicellular organisms. In Caenorhabditis elegans an inductive interaction between the somatic distal tip cells (DTCs) and the distal germline is essential in order to maintain proliferation in the developing germline. This cell signaling relies on a conserved signaling pathway with three known components: the LAG-2 ligand, GLP-1 receptor and LAG-1 effector. These proteins are homologous to members of "Notch" signaling pathways which function in multiple aspects of Drosophila development as well as the development of a number of vertebrate species. In order to identify other components of the LAG-2/GLP-1/LAG-1 mediated signaling pathway, extragenic suppressors ( sog mutations) and enhancers ( ego mutations) of a weak glp-1 loss-of-function ( lf ) phenotype in the germline have been isolated. The studies in this thesis focus on three genes that interact with glp-1 in germline development: a suppressor, sog-10 , and two enhancers, ego-2 and ego-1 . The sog-10 mutation suppresses glp-1 ( lf ) germline defects and feminizes XX germlines. Genetic studies of sog-10 have narrowed the map position of the sog-10 gene to a well defined region of chromosome III, and phenotypic analyses of the sog-10 mutant phenotype indicates involvement of sog-10 in both germline proliferation and sex determination. An analysis of the phenotype of the ego-2 mutation has identified it as a strong enhancer of both the germline defect and the maternal effect lethality of glp-1 ( lf ) mutations. Mutations in ego-1 are able to enhance the germline phenotypes of both glp-1 ( lf ) and lag-1 ( lf ) mutations (E. Maine, unpublished). In addition, ego-1 mutants exhibit various germline abnormalities in a glp-1 wildtype background which indicate defects in germline mitosis and/or meiotic prophase. The gene responsible for the ego-1 germline phenotype was first detected as a small deletion on chromosome I associated with a UV-induced allele, ego-1 ( om84 ). The ego-1 gene was sequenced and confirmed to be the one responsible for the phenotypes in ego-1 mutants by PCR amplifying and sequencing this gene region from three strains containing ego-1 mutations, om84, om97 , and om71 . The predicted EGO-1 protein contains 1632 amino acids. Northern analysis identified a transcript of ∼5.2 kb which is developmentally regulated and primarily germline specific. ego-1 mRNA is detected in later larval and adult stages which is consistent with the germline specific phenotype of the ego-1 mutants. Sequencing of the ego-1 gene region revealed a second ego-1 related gene which is immediately adjacent to ego-1 on chromosome I. In addition, sequence comparison searches for EGO-1 homologs have identified two other proteins in C. elegans ; five proteins which have been identified as RNA-directed RNA polymerases (RdRP) in tomato, wheat, tobacco, petunia and Arabidopsis; and two uncharacterized proteins, one in Arabidopsis and one in the yeast Schizosaccharomyces pombe .