Evidence that the mutation responsible for osteopetrosis in the op rat is not contained within the coding region of the Slc9a3r2 gene.

Abstract

The spontaneously occurring mutation in op rats produces an animal with severe osteopetrosis. Production of affected F2 animals with recombinant events has localized this mutation to a 0.51 cM portion of rat chromosome 10. Lying within the genetic critical region for the op gene is the Slc9a3r2 gene. Slc9a3r2 is a sodium/hydrogen exchanger. Considering the critical role of proton pumping into the resorption lacunae during bone resorption, this gene would be considered a functional candidate for op. In this study, we tested if this gene could be responsible for the osteopetrosis seen in the op rat. M-13 tailed primer sets were designed from rat genomic sequence to cover the 8 exons of the rat Slc9a3r2 gene. These primer sets were amplified by PCR against genomic DNA from affected mutant animals and the two parental strains, BN and LEW. Mutational analysis of the Slc9a3r2 sequences from the three strains failed to reveal significant differences between the affected mutant animals and the two parental strains although single nucleotide polymorphisms (SNPs) between BN and the other two strains were identified. These data indicate that the osteopetrosis seen in the op rat is not the result of a mutation within the coding region of the Slc9a3r2 gene. Analysis of additional functional and positional candidate genes will be required to identify the causative mutation in this animal model of failed bone homeostasis. Elucidation of the op mutation will improve our understanding of the genetic control of osteoclast function and may indicate novel therapeutic paradigms in osteopetrosis, osteoporosis, rheumatoid arthritis and Paget’s disease of bone where failed bone homeostasis is an instigating or exacerbating component of the disease process.