GLP-1 is a member of the Notch family of receptors and promotes germ cell proliferation in C. elegans. Activation of the germline GLP-1 receptor is spatially regulated by the distal tip cell transmembrane ligand, LAG-2. Binding of LAG-2 to GLP-1 induces receptor cleavage generating GLP-1(INTRA), which is then presumed to translocate to the nucleus, bind LAG-1, and alter the pattern of transcription. Disruption of this pathway causes all proliferating germ cells to prematurely enter meiosis. Conversely, constitutive activation by the
glp-1(
oz112gf) mutation results in the formation of a germline tumor where proliferative cells are found throughout the gonad. Two pathways, one containing GLD-1, the other containing GLD-2, function redundantly downstream of GLP-1 to inhibit proliferation and/or promote meiotic development. GLP-1 signaling, in effect, inhibits both pathways to promote germ cell proliferation. We have taken a forward genetic approach to identify genes that function downstream of GLP-1 to promote entry into meiosis, or that function to negatively regulate GLP-1. This approach uses sensitized genetic backgrounds to screen for tumorous mutants. One screen utilized the weak
glp-1(
oz264gf) mutant and identified the allele
oz273 as a strong tumorous enhancer.
oz273 also displays a Mog (masculinization of the germline) phenotype in the
glp-1(+) background, similar to
teg-1, another mutant that enhances a weak
glp-1(gf) background (see Hansen et al, this meeting). Also similar to
teg-1, the gld-2oz273 mutant is tumorous, suggesting that
teg-1 and
oz273 could be functioning in the same pathway to regulate entry into meiosis. The gene disrupted by the
oz273 lesion is F49D11.1, which codes a 567 amino acid protein that is orthologous to yeast CDC40/PRP17 and human PRP17. These proteins are required for the second step of pre-mRNA splicing (Jones et al, 1995; Umen et al, 1995). The
oz273 mutation is an 873 bp deletion that removes the first 173 amino acids encoded by exon 2, including four of six WD-40 repeats. Also within the deleted region is a motif that is critical for splicing in yeast (Lindsey-Boltz et al, 2000), suggesting that the
oz273 deletion is a strong loss-of-function or null allele. Experiments are currently underway to further characterize the gene and determine if other splicing factors regulate entry into meiosis (also see Hanazawa et al, this meeting).