Evidence for only one beta-luteinizing hormone and no beta-chorionic gonadotropin gene in the rat

We have examined the rat genome and placenta for the presence of a mRNA or gene which codes for a protein identical or similar to the beta-subunit of LH. A cDNA clone was isolated that encodes for amino acids 44 through 121 of the mature beta-subunit of rat LH (rLH). This r beta LH cDNA was used as a hybridization probe to study the structure of the gene(s) which encode for the beta-subunit of either LH or a LH-like protein in the rat genome. Restriction enzyme digestion analysis of rat genomic DNA using Southern blots revealed only one fragment that hybridized to 32P-labeled r beta LH cDNA. In contrast, restriction enzyme analysis of human and rhesus monkey genomic DNA (known to have both LH and CG) gave multiple fragments which hybridized to a 32P-labeled human beta LH DNA. We have also examined the possibility of a mRNA which can encode the beta-subunit of either LH or CG in the rat placenta. Northern blot analysis of total RNA isolated from rat placenta and rat anterior pituitary revealed that only the anterior pituitary contains a mRNA which is complementary to rLH cDNA. These results suggest that: there is only one gene which encodes the beta-subunit of LH in the rat haploid genome; there is no gene which encodes for a beta-subunit of a CG molecule in the rat; there is no mRNA in the rat placenta which encodes for the beta-subunit of LH or an LH-like molecule.