Three forms of gonadotropin-releasing hormone characterized from brains of one species.

Abstract

Most vertebrate species have more than one form of gonadotropin-releasing hormone (GnRH) in their brains, but it is not clear whether each form has a distinct function. We report that sea bream (Sparus awrta) brains have three forms of GnRH, one of which is described herein and is called sea bream GnRH (sbGnRH). The primary structures of two forms were determined by Edman degradation and mass spectral analysis. The amino acid sequence of sbGnRH is pGlu-His-Trp-Ser-Tyr-Gly-Leu-Ser-Pro-Gly-NH2. The second peptide is identical to a form originally isolated from chicken brains (cGnRH-II): pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-ProGly-NH2. cGnRH-H is the most ancient form of GnRH identified to date in jawed fish and the most prevalent form throughout the vertebrates. The third form of GnRH has previously been identified as salmon GnRH by cDNA studies and is confirmed here by chromatographic and immunological studies. Phylogenetic distribution of GnRH peptides suggests sbGnRH arose in the perch-like fish as a gene duplication of the existing cGnRH-ll or salmon GnRH genes. All three identified GnRH peptides were synthesized and shown to release gonadotropin in vivo in the sea bream. The dominant form of GnRH stored in the pituitary was sbGnRH. Not only was the content ofsbGnRH 500-fold greater than that ofsalmon GnRH but also cGRH-II was not deeced in the pituitary. The latter evidence suggests that sbGnRH is the endogenous releaser of gonadotropin II.Gonadotropin-releasing hormone (GnRH) is both a releaser of gonadotropins and a neuromodulator (1, 2)

The GnRH system in the European sea bass (Dicentrarchus labrax)

“…To date, fourteen forms of GnRH decapeptides have been found in vertebrates, in which at least one unique form has been determined from a representative species of all vertebrate classes. Ten GnRH forms out of the fourteen were found in fish and six of them in teleosts: chicken GnRH II (cGnRH II; Miyamoto et al 1984), mammalian GnRH (mGnRH; Matsuo et al 1971, Burgus et al 1972, salmon GnRH (sGnRH; Sherwood et al 1983), catfish GnRH (cfGnRH; Ngamvongchon et al 1992), sea bream GnRH (sbGnRH; Powell et al 1994), herring GnRH (hGnRH;Carosfeld et al 2000) and Medaka GnRH (mdGnRH; Okubo et al 2000). cGnRH II is present in all vertebrate classes examined to date, and the mGnRH form is present in primitive non-teleostean bony fish, primitive teleosts (eels and others), amphibians and mammals.…”

Multiple GnRHs present in a teleost species are encoded by separate genes: analysis of the sbGnRH and cGnRH-II genes from the striped bass, Morone saxatilis

“…To date, perciform fish remain the only vertebrate order for which three forms of GnRH have been isolated and characterized at the level of the peptide (Powell et al 1994) and cDNA (Gothilf et al 1995(Gothilf et al , 1996b and for which the brain localization of all three forms has been determined (White et al 1995, Gothilf et al 1996b. For these reasons, perciform fish currently represent an excellent model system available to study the biological significance of multiple forms of GnRH within a single vertebrate species.…”

“…Teleost fish of the order Perciformes are the first group of vertebrates in which three distinct forms of GnRH, salmon (s)GnRH, seabream (sb)GnRH and cGnRH-II have been conclusively demonstrated to coexist within a single brain, as shown first in the gilthead seabream, Sparus aurata (Powell et al 1994). Subsequently the presence of three distinct forms of GnRH was confirmed in other perciform species (African cichlid (White et al 1995) and striped bass (Gothilf et al 1996a), tilapia (Weber et al 1997), red seabream (Okuzawa et al 1997) and sea bass (M M Chow, M Carillo, S Zanuy & Y Zohar, unpublished observations)).…”

Contribution of Chicken GnRH-II and Lamprey GnRH-III on Gonadotropin Secretion

“…Phylogenic evidence indicates that cGnRH-II (initially isolated from the chicken brain) is an ancient form of GnRH that has been structurally conserved for over 100 million years of evolution, suggesting that its neural functions may have an important significance (Powell et al, 1994;Rastogi et al, 1998).…”