Expression of the growth hormone variant gene in human placenta

Besides the hGH-N gene, which codes for the pituitary 22 and 20K GH variants, the human genome contains a second GH gene, namely the GH-V, which has been thought to be silent. We recently discovered a placental variant of human growth hormone (hPGH), which appears in maternal serum at mid-pregnancy and which rises in concentration thereafter to term. As hPGH and GH-V proteins display very similar characteristics, including a high affinity for hepatic GH receptors, they could be identical. To verify this hypothesis, we sought hGH-V mRNA in placenta. Hybridization experiments were performed between dot-blotted mRNA originating either from placenta or from one pituitary hGH secreting adenoma and synthetic polynucleotide probes corresponding to specific portions of the hGH-V or hGH-N gene sequences. The results indicate that the V gene is indeed expressed in the placenta and, at a very low level, in the pituitary adenoma. Therefore hPGH is most likely the expression product of the hGH-V gene.