INSITU LOCALIZATION OF PTH PTHRP RECEPTOR MESSENGER-RNA IN THE BONE OF FETAL AND YOUNG-RATS/

We characterized cells that express parathyroid hormone/ parathyroid h ormone related peptide (PTH/PTHrP) receptor mRNA in bones of fetal and postnatal rats by in situ hybridization. During endochondral developm ent of fetal bones, PTH/PTHrP receptor transcripts were highly express ed both in maturing chondrocytes and in osteoblasts in the periosteum and ossification center, but not in fully hypertrophic chondrocytes. S imilar to the localization in the fetal bones, PTH/PTHrP receptor mRNA expression was highly localized to maturing chondrocytes in the artic ular cartilage and growth plate, and to osteoblasts in the femur of yo ung rats. In both young and fetal rats, transcripts for Type X collage n were localized to hypertrophic chondrocytes, mostly between chondroc ytes and bone cells both of which express PTH/PTHrP receptor mRNA. Tra nscripts for PTH/PTHrP receptors and alkaline phosphatase co-localized in the bone of young rats, but they did not co-localize in fetal bone s at the early stages of endochondral ossification. These results show that PTH/PTHrP receptor mRNA is expressed in a cell-type and stage-sp ecific manner during skeletal development.