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An evolutionary perspective on GnRH in fish
Fradinger, E.A.; von Schalburg, K.; Sherwood, N.M. (2000). An evolutionary perspective on GnRH in fish, in: Norberg, B. et al. (Ed.) Proceedings of the 6th International Symposium on the Reproductive Physiology of Fish, Bergen, Norway, July 4-9, 1999. pp. 35-38
In: Norberg, B. et al. (Ed.) (2000). Proceedings of the 6th International Symposium on the Reproductive Physiology of Fish, Bergen, Norway, July 4-9, 1999. Department of Fisheries and Marine Biology, University of Bergen: Bergen. ISBN 82-7461-048-2. 499 pp., more
In: International Symposium on the Reproductive Physiology of Fish. Museo Nacional de Ciencias Naturales, more

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  • Fradinger, E.A., correspondent
  • von Schalburg, K., correspondent
  • Sherwood, N.M., correspondent

Abstract
    There are fourteen distinct forms of gonadotropin-releasing hormone (GnRH) at present; two are identified in jawless fish, two in cartilaginous fish and seven in bony fish. All forms are decapeptides with positions 1, 4, 9 and 10 conserved. For fish studied to date, each brain has two or more forms of GnRH. In cartilaginous and bony fish, one form is chicken (c) GnRH-II. The second form in cartilaginous fish is dogfish GnRH; and in bony fish is mammalian GnRH, salmon (s) GnRH or catfish GnRH. In teleosts that have three forms of GnRH, herring, sea bream or pejerrey GnRH have been identified and appear to displace the second form in the preoptic-hypothalamic region. Forms of GnRH identical to those in the brain have been identified in the ovary and testis. We isolated two cDNAs encoding sGnRH and one cDNA encoding cGnRH-II from rainbow trout gonad. One of the sGnRH mRNAs was found to use an upstream promoter and alternative splice site in gonads as compared to brain. In the trout embryo three transcripts were expressed as early as embryonic day 14. One transcript was identical to that found in the brain, whereas the other two transcripts used an alternate promoter and/or retained intron 1. In the first two years of life, GnRH mRNA was expressed in the gonads intermittently, but continuously in the last few months before spawning. Our results show that the tetraploid trout has duplicate genes encoding identical peptides (sGnRH) that are differentially controlled.

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