1E-08 A new Gdf5 allele with fusion of knee joint

M100451 obtained from ENU mutagenesis program in RIKEN lacks bones of digit. It was suggested that development of interphalangeal joint was affected in this mutant. Linkage analysis performed that this mutation was tightly linked to Gdf5 gene that functions in joint formation or distal portion of limb. Sequence analysis revealed that M00451 have an amino acid substitution. This residue located between Cys that function in dimerization of Gdf5 ligand. And it was highly conserved in Gdf5 gene of vetetebrate and mouse BMP family. We found sever shortening of upper and lower limbs, and fusion of nee joint in its homozygotes. This phenotype was not reported in known loss-of-function type mutant of Gdf5. Reporter gene assay using cultured cell performed that M10451 type Gdf5 strongly inhibited down-stream promoter activity even with the expressio of wild type. This suggests W409R is a dominant negative type mutation of Gdf5.