GLP-3 IS REQUIRED FOR MITOSIS AND MEIOSIS IN THE CAENORHABDITIS-ELEGANS GERM-LINE

The germ line is the only tissue in Caenorhabditis elegans in which a stem cell population continues to divide mitotically throughout life; hence the cell cycles of the germ line and the soma are regulated diff erently. Here we report the genetic and phenotypic characterization of the glp-3 gene. In animals homozygous for each of five recessive loss -of-function alles, germ cells in both hermaphrodites and males fail t o progress through mitosis and meiosis, but somatic cells appear to di vide normally. Germ cells in animals grown at 15 degrees appear by DAP I staining to be uniformly arrested at the G2/M transition with <20 ge rm cells per gonad on average, suggesting a checkpoint-mediated arrest . In contrast, germ cells in mutant animals grown at 25 degrees freque ntly proliferate slowly during adulthood, eventually forming small ger m lines with several hundred germ cells. Nevertheless, cells in these small germ lines never undergo meiosis. Double mutant analysis with mu tations in other genes affecting germ cell proliferation supports the idea that glp-3 may encode a gene product that is required for the mit otic and meiotic cell cycles in the C. elegans germ line.