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 hom ologous to the mammalian alpha1(IV) and alpha2(IV) collagen genes. We demonstrate by transgenic rescue of mutant animals that the genetic lo cus 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 temperatur e-sensitive embryonic lethality. The embryonic lethal phenotype is sim ilar to that seen in animals with mutations in the alpha1(IV) collagen gene, emb-9. The sequence of the entire AC. elegans alpha2(IV) collag en gene is presented. Comparisons with mammalian type IV collagen sequ ences show high amino acid sequence conservation in the C-terminal NC1 domain and of crosslinking residues (Cys and Lys) in the N-terminal 7 S domain. RT-PCR analysis shows that transcripts of the C elegans alph a2(IV) collagen gene are alternatively spliced. Transcripts contain on e of two mutually exclusive exons, exon 9 or 10. These exons encode ve ry similar products, differing primarily in the sequence of a 9-10 ami no acid Gly-X-Y interruption. The expression of these alternatively sp liced alpha2(IV) collagen transcripts is developmentally regulated. In embryos over 90% of the alpha2(IV) collagen mRNA contains exon 9, whi le larval and adult RNAs contain 80-90% exon 10. This shift in express ion of alternative alpha2(IV) collagen transcripts suggests that C ele gans embryos may require a different form of alpha2(IV) collagen than do larvae and adults.