A Sensitized Genetic Screen to Identify Regulators of Caenorhabditis Elegans Germline Stem Cells

GLP-1/Notch signaling and a downstream RNA regulatory network maintain germline stem cells in Caenorhabditis elegans. In mutants lacking the GLP-1 receptor, all germline stem cells enter the meiotic cell cycle precociously and differentiate into sperm. This dramatic germline stem cell defect is called the "Glp" phenotype. The lst-1 and sygl-1 genes are direct targets of Notch transcriptional activation and functionally redundant. Whereas single lst-1 and sygl-1 mutants are fertile, lst-1 sygl-1 double mutants are sterile with a Glp phenotype. We set out to identify genes that function redundantly with either lst-1 or sygl-1 to maintain germline stem cells. To this end, we conducted forward genetic screens for mutants with a Glp phenotype in genetic backgrounds lacking functional copies of either lst-1 or sygl-1. The screens generated 9 glp-1 alleles, 2 lst-1 alleles, and 1 allele of pole-1, which encodes the catalytic subunit of DNA polymerase ε. Three glp-1 alleles reside in Ankyrin repeats not previously mutated. pole-1 single mutants have a low penetrance Glp phenotype that is enhanced by loss of sygl-1. Thus, the screen uncovered 1 locus that interacts genetically with sygl-1 and generated useful mutations for further studies of germline stem cell regulation.