Expression pattern of the V5-Ostm1 protein in bacterial artificial chromosome transgenic mice.

Mutations in the osteopetrotic transmembrane protein 1 (Ostm1) gene are responsible for the most severe form of autosomal recessive osteopetrosis both in humans and in the gray lethal (gl/gl) mouse. This defect leads to increased bone mass with bone marrow occlusion and hematopoietic defects. To establish the expression profile of the mouse Ostm1 protein in vivo, homologous recombination in bacteria was designed to generate a V5-Ostm1 bacterial artificial chromosome (BAC) that was subsequently integrated in the mouse genome. Tissue expression of the transgene V5-Ostm1 RNA and protein in transgenic mice follow the endogenous expression profile. Immunohistochemistry analysis demonstrated expression in neuronal populations from central and peripheral nervous system and defined a unique cellular expression pattern. Importantly, together with appropriate protein post-translational modification, in vivo rescue of the osteopetrotic bone gl/gl phenotype in BAC V5-Ostm1 gl/gl mice is consistent with the expression of a fully functional and active protein. These mice represent a unique tool to unravel novel Ostm1 functions in individual tissue and neuronal cell populations and the V5-Ostm1 transgene represents an easy visual marker to monitor the expression of Ostm1 in vitro and in vivo.