Nucleotide (cDNA) sequence encoding the horse gonadotrophin alpha-subunit

Several cDNA clones corresponding to mRNA for the alpha-subunit of the horse (Equus caballus) pituitary and placental (chorionic) gonadotrophic hormones have been isolated and sequenced. Polyadenylated mRNA was purified from horse pituitary glands (the source of FSH and LH) and horse placental tissues (the source of chorionic gonadotrophin; CG). The mRNA preparations were characterized by in-vitro translation and Northern hybridization techniques using human and ovine gonadotrophin cDNA clones as probes. Complementary DNA libraries were created from the pituitary and placental mRNAs and a human CG alpha-subunit probe was used to isolate several horse alpha-subunit cDNA clones. The alpha-subunit nucleotide sequence from both sources of tissue was identical, thereby indicating that in the horse (as in man) the same gonadotrophin alpha-subunit gene is expressed in the pituitary and placenta. Our results are consistent with transcription of a single alpha-subunit gene for all the glycoprotein hormones in the horse, and we suggest that the reported differences between the horse CG and FSH alpha-subunit amino acid sequences determined by conventional peptide sequencing methods arose due to errors in the FSH alpha-subunit sequence. Comparison of the deduced amino acid sequence of the horse alpha-subunit with that of other alpha-subunit sequences indicated a number of significant differences which may be related to the unusual receptor-binding properties of the equine gonadotrophins.