| Fibrillar collagens are well known for their link to genetic disease, and mutations in these genes lead to a wide variety of connective tissue disorders. Mutations in multiple collagen modifying enzymes and chaperones have also recently been identified that lead to osteogenesis imperfecta, a connective tissue disorder characterized by bone fragility. Although numerous different mutations have been identified, the etiology of many connective tissue disorders remains unknown. In the search for new human disease genes, multiple strategies are available. In these studies, the following three strategies were used: a candidate gene approach, a candidate disease condition approach, and a reverse genetics approach that employed antisense knockdown of protein synthesis. Sequencing of multiple candidate genes in individuals with osteogenesis imperfecta revealed a missense mutation in the collagen chaperone-like protein HSP47, which resulted in an unstable protein degraded via the proteasome. Type I collagen accumulated in the Golgi of patient fibroblasts and was protease-sensitive despite increased thermostability. Type XXVII collagen, a fibrillar collagen to which no known diseases are linked, was chosen as another candidate disease gene and sequenced in individuals with various chondrodysplasias, tooth enamel defects, and adolescent idiopathic scoliosis. No mutations were identified in any of the conditions analyzed. A type XXVII collagen knockdown model in zebrafish was generated concurrently with the human disease studies and revealed that type XXVII collagen is critical for zebrafish notochord morphogenesis and vertebral development. Zebrafish embryos with decreased amounts of type XXVII collagen developed scoliosis characterized by dysmorphic vertebrae. This suggested that congenital forms of scoliosis may be a candidate disease condition for mutations in type XXVII collagen. The studies described identified a new disease gene for osteogenesis imperfecta, demonstrated a functional role for type XXVII collagen in the zebrafish notochord, and set the groundwork for identification of disease conditions caused by mutations in type XXVII collagen. |
