Characterization and steroidal regulation of gonadotropin beta subunits in the male leopard frog, Rana pipiens

Abstract

In ranid frogs, the secretion of gonadotropins (GtHs), luteinizing hormone (LH), and follicle-stimulating hormone (FSH), is potently regulated by gonadal steroids. To better understand the gonadal regulation of GtHs at the molecular level, we elucidated the full-length cDNA sequences of LH and FSH β subunits from the leopard frog, Rana pipiens. The cDNAs for LHβ and FSHβ were 1084 and 667 bp in size excluding the poly (A) tail, and encoded proteins of 138 and 127 amino acids, respectively. Using reverse-transcription polymerase chain reaction (RT-PCR), the messages for LHβ and FSHβ were found in the pituitary, but not in the brain, heart, kidney, or the liver. Semi-quantitative RT-PCR revealed a significant elevation of FSHβ, but not LHβ, in mature male R. pipiens 21 days after gonadectomy (GDX). 17β-estradiol implant for 21 days in GDX male frogs significantly suppressed the levels of both LHβ and FSHβ transcripts, whereas 5α-dihydrotestosterone implant suppressed only the latter. Together, these results laid the groundwork for investigating gonadal regulation of GtHβ subunits in a ranid frog. Importantly, these data also revealed differential feedback effects of an androgen and an estrogen upon GtHβ expression.