EXPRESSION OF THE GROWTH-HORMONE GENE IN OVINE PLACENTA - DETECTION AND CELLULAR-LOCALIZATION OF THE PROTEIN

In several species, placenta has been found to express GH-related prot eins. In the ovine placenta, such a protein, ovine chorionic somatomma motropin, has been described, but its involvement in the fetal/placent al growth process is not clearly established. The aim of this study wa s to investigate the occurrence of another GH-related peptide in the o vine placenta. Placental extracts (days 30-140 of pregnancy) showed GH immunoreactivity between days 35-70. SDS-PAGE analysis of these extra cts indicated that this immunoreactivity corresponded to 22- and 28-kD a proteins. GH-like immunoreactivity was localized on cotyledonary fro zen sections in the syncytium and the trophectoderm. Northern blot ana lysis of placental RNA showed the expression of GH-hybridizing transcr ipts migrating to the same position as that of GH pituitary messenger RNA (mRNA). Those transcripts were highly expressed between days 40 an d 50. Their sequence analysis showed the existence of three GH mRNA (G HP1, GHP2, and GHP3). GHP1 is identical to pituitary GH mRNA and proba bly codes for the 22-kDa protein. GHP2 and GHP3 encode the same protei n, which differs from GHP1 by four amino acids. This study establishes the expression of GH gene and GH-immunoreactive proteins in the ovine placenta.