Two distinct species of human growth hormone-variant mRNA in the human placenta predict the expression of novel growth hormone proteins.
Cooke N.E., Ray J., Emery J.G., Liebhaber S.A.
We have sought direct evidence for the in vivo expression of the human growth hormone-variant (hGH-V) gene by screening a placental cDNA library with a hGH-V-specific oligonucleotide. Nine independent hGH-V cDNA clones were isolated and analyzed, and three distinct species were detected. Five of these hGH-V cDNAs represent mRNAs spliced and processed in a pattern analogous to that of the highly homologous human growth hormone and human chorionic somatomammotropin gene transcripts. Each of the remaining four hGH-V cDNAs contains an additional segment of 253 nucleotides corresponding in position and sequence to the fourth intron of the hGH-V gene. In addition, one of the mRNAs in this second group uses an alternative downstream polyadenylation site. The alternatively spliced hGH-V mRNA, which we refer to as hGH-V2 mRNA, constitutes approximately 30% of the hGH-V transcripts both in the human term placenta and in a stable mouse fibroblast line expressing the transfected hGH-V gene. The placental expression of the hGH-V gene is specific to villous tissue. The hGH-V2 mRNA is predicted to encode a protein which substitutes the 65 carboxyl-terminal amino acids of hGH-V with a new 104-residue carboxyl terminus resulting in significant divergence in their relative physical properties. The alternative splicing of the hGH-V transcripts to hGH-V and hGH-V2 mRNAs expands the potential complexity of the hGH-V gene's role in normal placental function.
J. Biol. Chem. 263:9001-9006(1988) [PubMed] [Europe PMC]