Cloning and Developmental Regulation of a Novel Member of the Insulin-like Gene Family inCaenorhabditis elegans

Abstract

Aging, metabolism and fat accumulation inCaenorhabditis elegans(C. elegans) are influenced by mutations in DAF-2, a putative insulin-like receptor. Ten putative insulin-like genes have been recently identified from theC. elegansgenome database. However, it is unclear if these genes are orthologues of human insulin since they lack the C-peptide dibasic amino acid proteolysis sites. We have identified and measured mRNA expression during development of two novel members of theC. elegansinsulin-like gene family. We also report the sequence characterization and gene structure for one of these, the insulin-like protein-1 (ILP1). We focused onILP1characterization because it has structural features consistent with its being a candidate insulin ligand for the DAF-2 insulin-like receptor. For example, ILP1 has a putative C-peptide flanked by dibasic amino acids, exhibits conserved cysteine residues that could provide disulfide bonds between the A and B chains, and has two introns. Northern blot analysis revealed thatILP1mRNA is expressed at very high levels in embryos and is downregulated very early during postnatal development, suggesting that it may influence embryonic development, but not Dauer formation. We also identified a novel insulin-like growth factor-1-like protein (T28B8/IGF-I) that exhibits a very different developmental expression profile than ILP1. Our results are consistent with the hypothesis that members of the unusually large and complexC. elegansinsulin-like protein family exhibit complex and perhaps redundant roles.