EXPRESSION OF PARATHYROID HORMONE-RELATED PEPTIDE AND ITS RECEPTOR MESSENGER RIBONUCLEIC-ACIDS DURING FETAL DEVELOPMENT OF RATS

PTH-related peptide (PTHrP) is a causative agent of hypercalcemia asso ciated with malignancy. PTHrP binds to and activates the same receptor as does PTH. Because PTHrP has been suggested to regulate the growth and differentiation of cells as a paracrine/autocrine factor, we exami ned the expression of bath PTHrP and its receptor genes during fetal d evelopment of rats (15-20 days gestation) by in situ hybridization wit h riboprobes. Both PTHrP and its receptor messenger RNAs (mRNAs) were expressed not only in the skeleton, but also in many fetal extraskelet al tissues, such as choroid plexus, ears, lungs, tooth buds, heart, an d skin. In these extraskeletal tissues, PTHrP mRNA was expressed mainl y in surface-lining cells, whereas its receptor mRNA was expressed mai nly in adjacent mesenchymal cells. In endochondral bones, these two ge nes were expressed in largely discrete, but mostly neighboring, areas, although the localizations of these two mRNAs changed over developmen tal stages. The expression patterns of PTHrP and its receptor mRNAs du ring fetal development suggest PTHrP's roles as a paracrine factor and its involvement in epithelial-mesenchymal(-like) interactions.