Rat placental mRNA directs the synthesis of a polypeptide immunologically related to alpha-subunit of glycoprotein hormones.
In order to investigate the existence of a chorionic gonadotropin (CG) in the rat, placental mRNA was prepared from either the foetal disc or the maternal site of implantation in pregnant rats and translated in a wheat-germ cell-free translation system in the presence of 35S-labeled methionine and cysteine. Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the radioactive material immunoprecipitated using antiserum specific to native rat alpha-subunit allowed us to isolate in translation products from both sources (foetal disc and maternal site of implantation) a single polypeptide of 17 kDa having the electrophoretic properties of the rat pituitary alpha-precursor. This polypeptide was absent in media derived from translation of mRNA extracted from uterine horn of non-pregnant female rats, and was approximately 10 times more abundant when RNA was derived from the maternal part (about 0.25% of cpm in total proteins) rather than the foetal part (0.026%) of the placenta. Immunoprecipitation was prevented in the presence of an excess of rat (but not ovine) alpha-subunit. Antisera directed against denatured bovine alpha-subunit, which cross-react with the rat pituitary alpha-precursor, did not bind the placental peptide. These results suggest that this rat placental polypeptide and the rat alpha-subunit of pituitary glycoprotein hormones have important differences in their primary structure, but share discrete structurally and/or conformationally related regions in their polypeptide chains. The possibility that these partial homologies account for gonadotropin-like activity of a presumed rat CG remains to be ascertained.
D000818:Animals; D011232:Chemical Precipitation; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit; D008970:Molecular Weight; D010908:Pituitary Hormones, Anterior / Q000302:isolation & purification*; D010920:Placenta / Q000032:analysis*; D011247:Pregnancy; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis* / Q000235:genetics; D051381:Rats; D011919:Rats, Inbred Strains
D015292:Glycoprotein Hormones, alpha Subunit; D010908:Pituitary Hormones, Anterior; D012333:RNA, Messenger