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Department of Biochemistry and Molecular Biology, University of New Hampshire, Room 310, 46 College Road, Durham, New Hampshire 03824, USA
¹ Laboratory of Molecular Endocrinology, School of Fisheries Sciences, Kitasato University, Sanriku, Iwate 022-0101, Japan
² Sado Marine Station, Niigata University, Sado, Niigata 952-2135, Japan

(Requests for offprints should be addressed to S A Sower; Email: sasower{at}cisunix.unh.edu)

A full-length transcript encoding a functional lamprey glycoprotein hormone receptor I (lGpH-R I, GenBank AY750688 [GenBank] ) was cloned from the testes of the sea lamprey, Petromyzon marinus, using the GpH-R protein fingerprint GLYCHORMONER from the PRINTS database. The present study is the first to identify a GpH-R transcript in an agnathan, which is one of the only two representatives of the oldest lineage of vertebrates. The 719-amino acid full-length cDNA encoding lGpH-R I is highly similar and is likely a homolog of the vertebrate GpH-Rs (including LH, FSH, and TSH receptors). The key motifs, sequence comparisons, and characteristics of the identified GpH-R reveal a mosaic of features common to all other classes of GpH-Rs in vertebrates. The lGpH-R I was shown to activate the cAMP signaling system using human chorionic gonadotropin in transiently transfected COS-7 cells. The highest expression of the receptor transcript was demonstrated in the testes using reverse transcriptase-PCR. Lower levels of the receptor transcript were also detected in brain, heart, intestine, kidney, liver, muscle, and thyroid. The high expression of lGpH-R I in the testis and the high similarity with gnathostome gonadotropin hormone receptors suggest that lGpH-R I functions as a receptor for lamprey gonadotropin hormones. We hypothesize from these data that there is lower specificity of gonadotropin and its receptor in agnathans and that during co-evolution of the ligand and its receptor in gnathostomes, there were increased specificities of interactions between each GpH (TSH, LH, and FSH) and its receptor.