Evolution of neuroendocrine peptide systems: Gonadotropin-releasing hormone and somatostatin

Nine vertebrate and two protochordate gonadotropin-releasing hormone (GnRH) decapeptides have been identified and sequenced. Multiple molecular forms of GnRH peptide were present in the brain of most species examined, and cGnRH-II generally coexists with one or more GnRH forms in all the major vertebrate groups. The presence of multiple GnRH forms has been further confirmed by the deduced GnRH peptide structure from cDNA and/or gene sequences in several teleost species and tree shrew. High conservation of the primary structure of GnRH decapeptides and the overall structure of GnRH genes and precursors suggests that they are derived from a common ancestor. Somatostatin (SRIF) is a phylogenetically ancient, multigene family of peptides. A tetradecapeptide, SRIF (SRIF(14)) has been conserved, with the same amino acid sequence, in representative species of all classes of vertebrate. Four molecular variants of SRIF,, have been identified. SRIF(14) is processed from preprosomatostatin-I, which contains SRIF(14) at its C-terminus; preprosomatostatin-I is also processed to SRIF(28) in mammals and SRIF(26) in bowfin. Teleost fish possess a second somatostatin precursor, preprosomatostatin-II, containing [Tyr(7), Gly(10)]-SRIF(14) at the C-terminus, that is mainly processed into large forms of SRIF. (C) 1998 Elsevier Science Inc. All rights reserved.