In situ localization of PTH/PTHrP receptor mRNA in the bone of fetal and young rats.

We characterized cells that express parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) receptor mRNA in bones of fetal and postnatal rats by in situ hybridization. During endochondral development of fetal bones, PTH/PTHrP receptor transcripts were highly expressed both in maturing chondrocytes and in osteoblasts in the periosteum and ossification center, but not in fully hypertrophic chondrocytes. Similar to the localization in the fetal bones, PTH/PTHrP receptor mRNA expression was highly localized to maturing chondrocytes in the articular cartilage and growth plate, and to osteoblasts in the femur of young rats. In both young and fetal rats, transcripts for Type X collagen were localized to hypertrophic chondrocytes, mostly between chondrocytes and bone cells both of which express PTH/PTHrP receptor mRNA. Transcripts for PTH/PTHrP receptors and alkaline phosphatase co-localized in the bone of young rats, but they did not co-localize in fetal bones at the early stages of endochondral ossification. These results show that PTH/PTHrP receptor mRNA is expressed in a cell-type and stage-specific manner during skeletal development.