A single gonadotropin α-subunit gene in normal tissue and tumor derived cell lines

The structure of gene sequences coding for the mRNA of human chorionic gonadotropin (hCG) α-subunit was investigated by Southern blot analysis of genomic DNAs using a cloned, full length cDNA probe. While four hormones, lutropin, follitropin, thyrotropin, and choriogonadotropin, have homologous α-subunits, only one gene that bears hCG-α sequences could be detected per haploid complement. The structure of this single gonadotropin α-subunit gene, which contains intervening sequences, is the same in DNA from frist trimester and term placentae. However, polymorphism was observed for the presence of a HindIII site and of an EcoRI site in the gene's 3' flanking sequences. The organization of hCG-α sequences in several trophoblastic and nontrophoblastic tumor cell lines, which produce hCG subunits, was also examined. In each, the same gene copy number and structure were seen as in normal tissue. Thus, the characteristics of ectopic α-subunit expression in these cells seem not to be determined by DNA rearrangements.