The Caenorhabditis elegans small GTP-binding protein RhoA is enriched in the nerve ring and sensory neurons during larval development.

p21 Ras has been implicated in vulval differentiation in Caenorhabditis elegans. We now describe the characteristics during nematode development of the related p21 RhoA which has been ascribed a morphological role in mammals. The CeRhoA cDNA isolated in this study encodes a sequence of 192 amino acids residues with 87.6% identity to human RhoA. Genomic Southern analysis indicates the presence of a single Rho gene in C. elegans. Its 2-kilobase mRNA is expressed at the highest levels during embryogenesis and decreases gradually thereafter. However, the level of the 24-kDa protein detected by the anti-CeRhoA antibody is high at 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 which is predominantly cytosolic, most of CeRhoA is associated with the membrane and the cytoskeleton throughout development. Indirect immunofluorescence analysis indicates an ubiquitous expression of CeRhoA throughout development with a particular enrichment at larval stages in the pharyngeal nerve ring and at the tip of the head containing chemosensory and mechanosensory neurons. This suggests a stage-specific role for p21 RhoA in mediating the signaling pathway underlying the sensory circuitry in C. elegans post-embryonic development.