Screening for Genes downstream of GLP-1/Notch Signaling Pathway that Promote Meiotic Development in C. elegans

Alejandro Akrouh¹, Momoyo Matsuyama², Tim Schedl², Biology Department, Washington University, St. Louis, MO¹, Department of Genetics, Washington University School of Medicine²

C. elegans, the nematode worm, is an excellent model organism for germ line developmental research due to its rapid life cycle and transparent body. Some of this work is concentrated on the LAG-2/GLP-1 signaling pathway homologous to the Delta/Notch pathway in Drosophila. GLP-1 is a transmembrane protein that is involved in maintaining a pool of proliferating germ cells in the distal end of the gonad arm. The somatic distal tip cells express a ligand known as LAG-2 that binds to the extracellular portion of GLP-1. This binding, in turn, causes cleavage of the GLP-1 receptor releasing the intracellular domain. The GLP-1 intracellular domain then moves into the nucleus and promotes mitotic proliferation. LAG-2 only affects the cells within a 20-cell diameter length from the distal end of the gonad arm. Germ cells beyond 20-cell diameter undergo meiotic development.

Downstream of the GLP-1 pathway lies GLD-1, a KH domain containing RNA binding protein and GLD-2, a Poly-A RNA polymerase. GLD-1 is thought to act as a translational repressor in mitotic development and GLD-2 is thought to act as a translational activator in meiotic development. When either the gld-1 or gld-2 gene is knocked out, meiotic entry still occurs. However, if both genes are knocked out, no entry into meiosis is observed and a tumor is formed. This indicates that gld-1 and gld-1 function redundantly to promote entry into meiosis.

My project involves the identification of novel genes that lie downstream of GLP-1 and function in the mitosis/meiosis decision. A gld-1(op236) strain of C. elegans with a sensitized gld-1 background was mutagenized with EMS (Ethyl methanesulfonate) and successive generations were screened for tumorous mutations. With this strain, if a mutation did occur in genes that belong to either the gld-1 or gld-2 pathway, a more severe phenotype would be observed in half of the progeny worms. Only worms with weakly penetrant phenotypes were found.