Genetic identification, sequence, and alternative splicing of the caenorhabditis elegans α2(IV) collagen gene

Abstract

The nematode Caenorhabditis elegans has two type IV collagen genes homologous to the mammalian α1(IV) and α2(IV) collagen genes. We demonstrate by transgenic rescue of mutant animals that the genetic locus encoding the C. elegans α2(IV) collagen gene is let-2 on the X chromosome. The most severe effect of mutations in let-2 is temperature-sensitive embryonic lethality. The embryonic lethal phenotype is similar to that seen in animals with mutations in the α1(IV) collagen gene, emb-9. The sequence of the entire C. elegans α2(IV) collagen gene is presented. Comparisons with mammalian type IV collagen sequences show high amino acid sequence conservation in the C-terminal NC1 domain and of crosslinking residues (Cys and Lys) in the N-terminal 7S domain. RT-PCR analysis shows that transcripts of the C. elegans α2(IV) collagen gene are alternatively spliced. Transcripts contain one of two mutually exclusive exons, exon 9 or 10. These exons encode very similar products, differing primarily in the sequence of a 9-10 amino acid Gly-X-Y interruption. The expression of these alternatively spliced α2(IV) collagen transcripts is developmentally regulated. In embryos over 90% of the α2(IV) collagen mRNA contains exon 9, while larval and adult RNAs contain 80-90% exon 10. This shift in expression of alternative α2(IV) collagen transcripts suggests that C. elegans embryos may require a different form of α2(IV) collagen than do larvae and adults.