alpha 1(VIII)-collagen gene transcripts encode a short-chain collagen polypeptide and are expressed by various...

Type-VIII collagen is a major constituent of Descemet's membrane and contains two genetically distinct alpha chains, alpha 1(VIII) and alpha 2(VIII). We have previously cloned the human alpha 1(VIII) and alpha 2(VIII) genes and determined that they are located on chromosomes 3 and 1, respectively. Comparison of the alpha 1(VIII) and alpha 2(VIII) genes with the alpha 1(X)-collagen gene showed that the structure of the three genes and the sequence of their collagen polypeptides were strikingly similar. Therefore, we have grouped the three genes in a common subclass of collagens which we have named the short-chain collagens because of the relatively small size of their triple-helical domains. In the present study, we have isolated and characterized a mouse gene fragment encoding the entire mouse alpha 1(VIII)-collagen chain and determined the complete primary structure of the polypeptide chain. The size of mouse alpha 1(VIII)-collagen mRNA, as estimated by Northern-blot analysis, was 4.2 kb, compared with 2.8 kb previously reported for the corresponding rabbit mRNA. By cloning and sequencing of four overlapping cDNA, we demonstrate that this larger size of mouse alpha 1(VIII) mRNA is due to a larger 3' untranslated region in the mouse transcript. Using the gene fragment as a probe, we performed Northern-blot hybridization analysis of RNA prepared from newborn mice and demonstrated that alpha 1(VIII) collagen mRNA is expressed at high levels in the calvarium, eye and skin. In situ hybridization revealed that alpha 1(VIII) RNA is present in skin keratinocytes, corneal epithelial and endothelial cells, lens epithelial cells, as well as mesenchymal cells surrounding cartilage and calvarial bone and in the meninges surrounding the brain.