Characterization of the C. elegans gap‐2 gene encoding a novel Ras‐GTPase activating protein and its possible role in larval development

Abstract

The Ras signalling pathway plays several important roles in the development of the nematode Caenorhabditis elegans. So far, two types of Ras-GTPase activating proteins (Ras-GAPs) have been identified in this organism. To aid the study of the regulation and function of the Ras pathway, we set out to isolate a new GAP gene from C. elegans by transcomplementation of the fission yeast gap1 mutant. We isolated a C. elegans cDNA that encoded a protein which was similar to, but not exactly homologous with mammalian p120 Ras-GAP. This gene, named gap-2, generated at least nine distinct mRNA species through transcription from different promoters and subsequent alternative splicing involving 25 exons. These isoforms were differentially expressed among tissues. A deletion of gap-2 caused no obvious phenotype by itself, but a loss of gap-2 function could suppress larval lethality in both let-23 and let-60 reduction-of-function mutants, in which the Ras activity was lowered. C. elegans gap-2 encodes a novel Ras-GAP, which is similar to vertebrate p120 but which may constitute a new GAP subfamily. gap-2 mRNA isoforms arise by an unusually extensive variation in initiation sites and associated alternative splicing, and each isoform may play a distinct role in specific tissues. GAP-2 appears to function as a negative regulator of LET-60 Ras during larval development.