A Novel Mutation of COL1A1 Confers a Defect of Osteogenesis

Using ENU (N-ethyl-N-nitrosourea), we have produced a novel recessive mutation in mouse (C57BL/6J background), associated with an inducible defect of hind limb movement. The mutation was named seal because homozygotes appeared to “waddle” like seals on land. The phenotype is induced by the examination of grasping, which turned out causing the spinal bone fracture. Objectives: The purpose of this study was identifying the causative gene and characterizing the seal phenotype. Methods: The transmissibility was analyzed in C57BL/6J and C3H/HeN background. Gross visual evaluation, necropsy and histological analysis were performed in C57BL/6J background. Positional cloning was conducted using polymorphisms of microsatellite markers between C57/B6J and C3H/HeN. Results: Homozygous animals demonstrated hind limb paralysis after being picked up by grasping the loose skin over the nape of the neck. About 50% of seal homozygotes also have swollen heels and foot pads. The seal phenotype was fully penetrant on the C57BL/6 and C3H/HeN x C57BL/6 hybrid backgrounds. All of the examined seal show the spinal fracture after induction of paralysis. An irregular arrangement of trabeculae and thinner cortical bones were observed in seal tibia by histological analysis. The mutation was mapped to chromosome 11. After the confinement to a 1.4 Mbp critical region on 2050 meioses, the mutation was found on the Col1a1 gene in the splicing donor site right after exon 36 with substitution of A for T (#10914, GI: 149288871). Conclusion: The Col1a1 was identified as the responsible gene for the seal phenotype. The phenotype of seal is quite similar to the symptom of human Osteogenesis imperfecta caused by the defect on the Col1a1 gene. Seal is a quite valuable phenodiviant as a disease model and might contribute to the mineralized tissue research. Currently, the mechanism of causing the phenotype by the mutation is being analyzed. Supported by NIH grant AI054523