RESEARCH OF THE MUTATED GENE RESPONSIBLE FOR RAT OSTEOCHONDRODYSPLASIA AND INVESTIGATION OF THE EMBRYONIC PATHOGENESIS.

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The gene, ocd, responsible for rat osteochondrodysplasia is located on rat chromosome 11. In this study, we made a fine map around the ocd locus to identify the candidates. We also revealed the pathogenesis of the mutant rat during late embryonic stage. Linkage analysis was performed using backcross progeny obtained from the mating between HGN (hgn/hgn) females and F1 (BNxHGN:+/hgn) males. RH map around the ocd locus was obtained by typing Rat/Hamster radiation hybrid clones with closely related markers to the ocd locus. In another linkage analysis, we genotyped the affected rats of the OCD strain with microsatellite (MS) makers showing polymorphism in the strain. The ocd locus was finally localized into 100kb-region on rat Chr.11. At present, two candidate genes for ocd are located in the region. RT-PCR analysis revealed the expressions of these genes in the fetal tissue of the affected rats. In the experiments of embryonic pathogenesis, at first, we confirmed the pleiotropic effects … More of the ocd on the backcross newborns (derived from HGN x F1) under altered genetic background, indicating that ocd affects on the fetal development of multiple organs. At second, we revealed the fetal pathogenesis of the affected rats of JCD strain. The fetal rats were obtained from pregnant mothers by cesarean section at embryonic day (ED) 16.5-21.5. They were genotyped by the PCR of the MS flanking the ocd locus. The body weight was significantly smaller in the affected than normal fetuses at ED 16.5. The reductions of the length of the limbs became severe with increase of embryonic ages. The double-staining with alcian blue and alizarin red S revealed that systemic cartilage formation of the affected fetus was already hypoplasitc at ED 16.5 and that the ossification was accelerated in the affected rat after ED 18.5. Histological examination revealed that, although the ossification center was formed, the accumulation of cartilage matrices was poor in the affected rats after ED 16.5. These results suggnst that normal allele for ocd might be expressed before ED 16.5 and that the normal expression of the gene is critical for, normal development. Less