Cloning and sequence analysis of the extracellular region of the polar bear (Ursus maritimus) luteinizing hormone receptor (LHr), follicle stimulating hormone receptor (FSHr), and prolactin receptor (PRLr) genes and their expression in the testis of the black bear (Ursus americanus)

Male black bears undergo seasonal changes in testicular activity. The teste s are fully functional from May through July, regress from July through Dec ember, and recrudesce from January until May. The mechanisms responsible fo r the initiation of testicular recrudescence in the bear are unknown. The o bjectives of this study were to: (1) clone and sequence a substantial fragm ent of the extracellular portion of the luteinizing hormone receptor (LHr: 646 bp) and follicle stimulating hormone receptor (FSHr: 852 bp), and the e xtracellular/transmembrane portion of the prolactin receptor (PRLr: 680 bp) in the bear using reverse transcription-polymerase chain reaction (RT-PCR) ; and (2) determine whether the expression of LH-, FSH-, and PRL-receptor m RNA transcripts differs between the beginning and terminal stages of testic ular recrudescence. Comparisons of the partial cDNA and predicted amino aci d sequences of ursine receptors with the corresponding sequences from the p ig, cow, human, and rat suggest that the LHr and FSHr are highly conserved (LHr: 87.1-93.7%; FSHr: 86.0-92.7%) whereas the PRLr is less well conserved (81-87%). Testicular LHr mRNA was more abundant during the breeding season in May than during the non-breeding season (early stage of recrudescence) in January. In contrast, testicular FSHr mRNA abundance was greater in Janu ary than in May. Testicular PRLr mRNA appeared equally abundant in January and May; however, two additional transcripts were present during the breedi ng season in May. This study provides molecular tools for future investigat ions of the control of testicular recrudescence in the black bear and demon strates that the expression of testicular gonadotropin and PRL receptor mRN A is seasonally regulated. (C) 2000 Wiley-Liss, Inc.