LEE, K*; POWELL, M; REED, K; SUZUKI, K; TAKAHASHI, A; MORIYAMA, S: Progress in cloning of a cDNA encoding gonadotropin from the sea lamprey P. marinus.

Lampreys are one of two extant representatives of Agnatha (jawless fish), the oldest class of vertebrates. Two forms of gonadotropin releasing hormone (GnRH) have been identified from the hypothalamus of lampreys and act as neurohormones in controlling gametogenesis and steroidogenesis, suggesting the presence of a hypothalamic-pituitary-gonadal axis in lampreys similar to that in other vertebrates. Numerous collaborative efforts have been made to isolate the gonadotropin(s) (GTH) in lampreys, involving various protein extraction and chromatography methods. So far, no protein with identity to other known GTH molecules has been isolated, however there is strong biological and immunological evidence for a GTH-like molecule in lampreys. More recently, molecular approaches have been undertaken to identify a cDNA/gene encoding GTH. Strategies have included: 1) PCR with degenerate primers based on known GTH sequences from other vertebrates, and 2) screening genomic and cDNA libraries with oligo DNA probes and cDNA expression libraries with antibodies directed against fish and mammalian GTH. Based on immunocytochemical data that suggest lamprey GTH may be more similar to mammalian luteinizing hormone (LH) than to other vertebrate GTH?s, current attempts involve PCR with primers based on ovine LH sequence. In addition, generation of a subtracted pool of cDNA clones corresponding to mRNA upregulated in the pituitary in response to GnRH is also being attempted. The identification of GTH in agnathans will both further the study of reproduction in these fish and enhance understanding of the molecular evolution of pituitary hormones. Supported by NSF to SAS and Intl NSF-JSPS to SAS and HK.