The family of Ras-like GTPases functions in a diversity of signal transduction routes in which they transmit signals received by cell surface receptors to downstream effector molecules. Despite the high level of homology and conservation during evolution, the function of most Ras-like GTPases other than Ras remain poorly defined. This holds also for Rap1, for which functions have been claimed as diverse as antagonzing Ras, regulation of secretion and activation of integrins (1). As a first step in elucidating the function of Rap1in C. elegans, the expression patterns of the homologues of Rap1 (C27B7.8), the related Rap2 (C25D7.7) and of two of their guanine nucleotide exchange factors (GEFs) wer studied using GFP-reproter constructs. Rap1 appears to be expressed in various neurons in the head and tail, in the hypodermis and somatic cells of the gonad. Rap2 is also expressed in various neurons and in the pharynx. Of the tow Rap1-GEFs,
pxf-1 (T14G10.2) is widely expressed, whereas the homologue of Epac (T20G5.5) is restrict to neurons in the head and ventral nerve cord. More recently we have begun to make trangenic animals overexpressing constitutively active and dominant negative versions of Rap1 and data from our first analysis of these transgenic animals will be presented. (1) Zwartkruis, F.J. and Bos, J.L. (1999) Ras and Rap1: two highly related small GTPases with distinct function. Exp Cell Res, 253, 157-165.