Knock-in of nuclear localised beta-galactosidase reveals that the tyrosine phosphatase Ptprv is specifically expressed in cells of the bone collar.

Ptprv is a member of the transmembrane tyrosine phosphatase gene family reported to be expressed in osteoblasts and gonads. To better define the developmental and tissue specificity of Ptprv expression, we generated knock-in mice expressing a nuclear localised beta-galactosidase reporter under the control of resident Ptprv regulatory elements. Histochemical staining of Ptprv-nLacZ mice revealed that Ptprv expression is readily detectable in the foetal gonadal ridge of both sexes and in adult gonads where it is localised to Sertoli cells of the testis and celomic epithelial cells of the ovaries. During early limb development, Ptprv expression is prominent in the apical ectodermal ridge of the limb bud. At latter stages of development, Ptprv is predominantly expressed in the perichondrial and periosteal region of long bones, known as the bone collar. In contrast to previous indications from in vitro studies, there is little if any expression in mature osteoblasts in vivo. Analysis of Ptprv mRNA localisation by in situ hybridization in parallel with molecular markers of chondrocytes and osteoblasts confirmed the specific expression of Ptprv in immature bone collar cells. The specificity of Ptprv expression in these cells may be a useful tool to elucidate their role in the transition of skeletal elements from cartilage template to bone. Copyright 2004 Wiley-Liss, Inc.