GENETIC IDENTIFICATION, SEQUENCE, AND ALTERNATIVE SPLICING OF THE CAENORHABDITIS-ELEGANS ALPHA-2(IV) COLLAGEN GENE

The nematode Caenorhabditis elegans has two type IV collagen genes homologous to the mammalian alpha1(IV) and alpha2(IV) collagen genes. We demonstrate by transgenic rescue of mutant animals that the genetic locus encoding the C elegans alpha2(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 alpha1(IV) collagen gene, emb-9. The sequence of the entire AC. elegans alpha2(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 alpha2(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 alpha2(IV) collagen transcripts is developmentally regulated. In embryos over 90% of the alpha2(IV) collagen mRNA contains exon 9, while larval and adult RNAs contain 80-90% exon 10. This shift in expression of alternative alpha2(IV) collagen transcripts suggests that C elegans embryos may require a different form of alpha2(IV) collagen than do larvae and adults.