Expression of LH-alpha and -beta subunit mRNAs in the rat placenta

Gonadotropic activity is present in the placenta of various mammals including humans. Human and equine chorionic gonadotropin (CG) are well characterized and known to be glycoprotein hormones, as are pituitary LH, TSH and FSH. In the rat, however, the placental gonadotropin molecule has not been identified, and in fact the existence of CG in the rodent is still controversial. In the present study, the placental expression of mRNA for CG-like molecules was investigated by PCR with mixed primers designed for the CG-beta subunit based on the amino acid sequences common to the rat LH-beta, human LH-beta, equine LH-beta and human CG-beta subunits and for the alpha subunit designed from the rat LH-alpha subunit. PCR with mRNA extracted from the placenta (day 10 of pregnancy) amplified several bands including cDNA identical to part of rat LH-alpha and -beta. Furthermore, expression of these genes was confirmed in the placenta on days 10, 12, 14, 16, 18 and 20 of pregnancy by PCR with another set of primers specific to rat LH-alpha and -beta and by Southern hybridization with 32P-labeled cDNAs for LH-alpha and -beta. The specific bands for these subunit mRNAs were amplified in the placenta, as well as in the positive control i.e. the anterior pituitary gland, but were not detected in other tissues including decidual tissue, liver, spleen, intestine, brain and kidney. Expression of the mRNAs was observed in both the junctional and labyrinth zones of the placental tissue. The rat choriocarcinoma cell line Rcho-1 also expressed LH-alpha but not LH-beta regardless of the stage of differentiation in vitro. Here we show the expression of LH-alpha and -beta mRNAs in the rat placenta.