PARATHYROID-HORMONE RELATED PROTEIN (PTHRP) GENE-EXPRESSION IN FETAL AND EXTRAEMBRYONIC TISSUES OF EARLY-PREGNANCY

Parathyroid hormone related protein (PTHrP) is an important humoral fa ctor in hypercalcaemia of malignancy. In addition there is increasing evidence that this peptide has a physiological role in fetal developme nt, especially in cellular growth and differentiation. Both in-situ hy bridization and immunohistochemistry were used together and for the fi rst time to identify sites of PTHrP gene expression and peptide in fet al and extra-embryonic tissues of first trimester human pregnancy. PTH rP mRNA and peptide were identified in the avascular amnion and the sy ncytiotrophoblast while mRNA alone was expressed in the cytotrophoblas t. Its expression in these extra-embryonic tissues is consistent with postulated roles for PTHrP in implantation, relaxation of endometrial muscle and regulation of vascular tone. Expression of both mRNA and pe ptide occurred in endo-, mese- and ectodermal structures of the fetus, consistent with local production of the peptide rather than cellular uptake from amniotic fluid and supporting a role for PTHrP in cellular growth and differentiation.