This project deals with heritable matrix protein defects that cause chondrodysplasia syndromes. We seek to define the protein consequences of mutations in genes that encode structural components of cartilage matrix. In prior work we focused on mutations in COL2A1, the gene for type II collagen, that cause dominant negative effects on matrix biology within the spondyloepiphyseal dysplasia (SED)/spondyloepimetaphyseal dysplasia (SEMD)/Kniest dysplasia spectrum of disease. We now address a class of collagen-associated proteins, the matrilins. Protein screening analyses have identified the metatropic dysplasias, spondylometaphyseal dysplasias (SMD) and related clinical phenotypes as candidates for matriline 1 or matriline 3 (MATNi or MATN3 gene) mutations. Mutations are being sought in candidate cases by direct sequencing of POR amplified exons from genomic DNA and RTPOR amplified cDNAs from chondrocyte RNA. Since metatropic dysplasia and Kniest dysplasia have overlapping phenotypes and matriline 1 is known to bind to collagen II fibrils in cartilage matrix, we hypothesize that the phenotypic similarity will be explained by an effect on a common pathway of matrix interaction. The project includes plans to create mice by knock-in methods that express 1) a COL2A1 mutation that mimics a defect causing human Kniest dysplasia, 2) MATNi or MATN3 mutations designed to have dominant negative effects on molecular assembly and cellular export. In addition, methods of protein screening continue to be applied to new unclassified cases of chondrodysplasia seeking as the molecular basis abnormalities in candidate matrix proteins including collagens II, IX and Xl and the matrilins.
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