Structure and expression of the collagen genes of C. elegans

Nematode collagen genes

The collagen genes of nematodes encode proteins that have a diverse range of functions. Among their most abundant products are the cuticular collagens, which include about 80% of the proteins present in the nematode cuticle. The structures of these collagens have been found to be strikingly similar in the free-living and parasitic nematode species studied so far, and the genes that encode them appear to constitute a large multigene family whose expression is subject to developmental regulation. Collagen genes that may have a role in cell-cell interactions and collagen genes that correspond to the vertebrate type IV collagen genes have also been identified and studied in nematodes.

Sequence comparisons of developmentally regulated collagen genes of Caenorhabditis elegans

Collagen genes col-6, col-7 (partial), col-8, col-14 and col-19 from the nematode Caenorhabditis elegans were sequenced, and compared to the previously sequenced genes col-1 and col-2. The genes are between 1.0 and 1.2 kb in length, and each includes one or two short introns. The presumptive promoter regions contain sequences similar to the eukaryotic TATA promoter element. Two distinct, conserved sequences were found in the presumptive promoter regions of, respectively, the dauer larva-specific genes col-2 and col-6, and the primarily adult-specific genes col-7 and col-19. The domain structures of the collagen polypeptides are similar: each polypeptide contains two triple-helix forming (Gly-X-Y)n domains, one of 30-33 amino acids (aa), and the other of 127-132 aa. The latter domain is interrupted by one to three short (2-8 aa) non-(Gly-X-Y)n segments that occur at relatively conserved locations in each polypeptide. Sets of cysteine residues flank the (Gly-X-Y)n domains in all of the polypeptides. The genes can be placed into three families based upon amino acid sequence similarities. Genes within a family do not always exhibit similar developmental expression programs, suggesting that structural and regulatory regions of the genes have evolved separately. The codon usage in the genes is highly asymmetrical, with adenine appearing in the third position of 85% of the glycine codons, and 93% of the proline codons.

Domain organization and intron positions in Caenorhabditis elegans collagen genes: the 54-bp module hypothesis revisited

The amino acid (aa) sequences of the polypeptides encoded by five collagen genes of the nematode Caenorhabditis elegans, col-6, col-7 (partial), col-8, col-14, and col-19, were determined. These collagen polypeptides, as well as those encoded by the previously sequenced C. elegans collagen genes col-1 and col-2, share a common organization into five domains: an amino-terminal leader, a short (30-33 aa) (Gly-X-Y)n domain, a non(Gly-X-Y) spacer, a long (127-132 aa) (Gly-X-Y)n domain, and a short carboxyl-terminal domain. The domain organizations and intron positions of these polypeptides were compared with those of the polypeptides encoded by Drosophila and Strongylocentrotus type IV, and vertebrate types I, II, III, IV, and IX collagen genes; the C. elegans collagen polypeptides are most similar to the vertebrate type IX collagens. It is suggested that the collagen gene family comprises two divergent subfamilies, one of which includes the vertebrate interstitial collagen genes, and the other of which includes the invertebrate collagen genes and the vertebrate type IV and type IX collagen genes. Only the vertebrate interstitial collagen genes display clear evidence of evolution via the tandem duplication of a 54-bp exon.

The sqt-1 gene of C. elegans encodes a collagen critical for organismal morphogenesis

Different mutations in the sqt-1 gene of C. elegans can lengthen, shorten, or helically twist the entire animal. We have cloned the sqt-1 gene and have shown that it encodes a collagen. sqt-1 was localized to a 35 kb region of DNA by physical mapping of chromosomal deficiencies. A transposon (Tc1)-induced mutation of sqt-1 was generated and utilized to identify the sqt-1 gene within this 35 kb region. Sequence analysis of the sqt-1 gene shows that it encodes a 32 kd collagen polypeptide that is similar in size and structure to other members of the C. elegans collagen family. The Tc1 insertion mutant has no detectable sqt-1 transcripts, yet it is morphologically normal, indicating that the null phenotype of sqt-1 is wild type. These results demonstrate that collagen mutations can have dramatic effects on organismal morphology.