THE CAENORHABDITIS-ELEGANS SMALL GTP-BINDING PROTEIN RHOA IS ENRICHEDIN THE NERVE RING AND SENSORY NEURONS DURING LARVAL DEVELOPMENT

p21 Res has been implicated in vulval differentiation in Caenorhabditi s elegans. We now describe the characteristics during nematode develop ment of the related p21 RhoA which has been ascribed a morphological r ole in mammals. The CeRhoA cDNA isolated in this study encodes a seque nce of 192 amino acids residues with 87.6% identity to human RhoA Geno mic Southern analysis indicates the presence of a single Rho gene in C . elegans. Its 2-kilobase mRNA is expressed at the highest levels duri ng embryogenesis and decreases gradually thereafter. However, the leve l of the 24-kDa protein detected by the anti-CeRhoA antibody is high a t the larval stages but low in embryos. The glutathione S-transferase/ CeRhoA fusion protein expressed in Escherichia coli displays conserved biochemical activities. Unlike its counterpart in mammalian cells whi ch is predominantly cytosolic, most of CeRhoA is associated with the m embrane and the cytoskeleton throughout development. Indirect immunofl uorescence analysis indicates an ubiquitous expression of CeRhoA throu ghout development with a particular enrichment at larval stages in the pharyngeal nerve ring and at the tip of the head containing chemosens ory and mechanosensory neurons. This suggests a stage specific role fo r p21 RhoA in mediating the signaling pathway underlying the sensory c ircuitry in C. elegans post-embryonic development.