Sequence Analysis and Expressional Regulation of Messenger RNAs Encoding   Subunits of Follicle-Stimulating Hormone and Luteinizing Hormone in the Red-Bellied Newt, Cynops pyrrhogaster

Two distinct cDNAs encoding beta subunits of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were cloned from the cDNA library constructed for the pituitary of the red-bellied newt, Cynops pyrrhogaster, and sequenced. The newt FSHbeta and LHbeta cDNAs encode polypeptides of 129 and 131 amino acids, including signal peptides of 20 and 19 amino acids, respectively. The number and position of cysteine and N-glycosylation in each of the beta subunits of FSH and LH, which are considered essential for assembly of the alpha subunit, are well conserved between the newt and other tetrapods. The high homology (41.6%) between the beta subunits of newt FSH and LH imply less specificity of FSH and LH in gonadal function. One cDNA encoding the common polypeptide chain subunit of FSH and LH was also isolated from the newt pituitary gland. The mRNAs of FSHbeta, LHbeta, and the alpha subunit were expressed only in the pituitary gland among various newt tissues. Double-staining with in situ hybridization and immunohistochemistry revealed coexpression of FSHbeta and LHbeta in the same newt pituitary cells. Ovariectomy induced a significant increase in FSHbeta mRNA levels, but there was no significant change in LHbeta or alpha subunit mRNA levels compared with those in control animals. Taken together, these data suggest that two kinds of gonadotropins, namely FSH and LH, are expressed in the same gonadotropin-producing cells in the pars distalis of the newt as well as in other tetrapods and that the expression of FSHbeta is negatively regulated by the ovaries.