Cloning and characterization of the Caenorhabditis elegans CeCRMP/DHP-1 and -2; common ancestors of CRMP and dihydropyrimidinase?

The vertebrate CRMP (collapsin-response-mediator protein) gene family comprises at least four members. These CRMPs exhibit about 60% amino acid identity with vertebrate dihydropyrimidinase (DHP), an amidohydrolase involved in the pyrimidine degradation pathway. CRMP is also referred to as DRP (DHP-related protein), TOAD-64 (turned on after division, 64 kDa) and Ulip (Unc-33-like phosphoprotein). These vertebrate CRMPs are expressed mainly in early neuronal differentiation, which suggests that they play a role in neuronal development. In this study we isolated two cDNA clones from nematode C. elegans based on their sequence homology to vertebrate CRMPs and DHP. These two molecules, termed CeCRMP/DHP-1 and -2, turned out to be Ulip-B and -A, respectively, which were previously identified in the C. elegans genomic database by Byk et al. (1998). These newly isolated molecules were believed to represent a common ancestral state before the gene duplication between CRMPs and DHP. CeCRMP/DHP-1 and -2 protein retained all putative zinc-binding residues thought to be essential for the amidohydrolase activity of DHP and exhibited a weak amidohydrolase activity when 5-bromo-dihydrouracil was used as a substrate. Whole-mount in situ hybridization and expression analysis using GFP fusions revealed that CeCRMP/DHP-1 was transiently expressed in the hypodermis of C. elegans during the early larva stage. CeCRMP/DHP-1 was also expressed in a single nerve cell between the pharynx and ring neuropil. On the other hand, expression of CeCRMP/DHP-2 was observed in the body wall muscle throughout the lifespan of C. elegans. These results indicate that a major site of CeCRMP/DHP-1 and -2 expression is non-neuronal. Targeted gene disruption of CeCRMP/DHP-2 caused no particular difference in appearance or movement phenotype.