Three Forms of Gonadotropin-Releasing Hormone, Including a Novel Form, in a Basal Salmonid, Coregonus clupeaformis1

Abstract

Multiple forms of GnRH within individual brains may have different functions. However, some vertebrates such as salmonids continue to reproduce even though they have lost or do not express 1 of the 3 forms of GnRH found in most other teleosts. We examined a basal salmonid, lake whitefish, to determine the mechanism by which a reduction in the number of GnRH forms occurs. We identified for the first time 3 distinct GnRHs in a salmonid. One form is novel and is designated whitefish GnRH. The primary structure is pGlu-His-Trp-Ser-Tyr-Gly-Met-Asn-Pro-Gly-NH(2). HPLC and RIA were used for purification followed by Edman degradation for sequence determination. Mass spectroscopy was used to confirm the sequence and amidation of the peptide. The other 2 forms, salmon GnRH and chicken GnRH-II, are identical to the 2 forms found in salmon, which evolved later than whitefish. Synthetic whitefish GnRH is biologically active, as it increased mRNA expression of growth hormone and the alpha-subunit for LH and thyroid-stimulating hormone in dispersed fish pituitary cells. Our data support the hypothesis that the ancestral salmonid had a third GnRH form when the genome doubled (tetraploidization), but the third form was lost later in some salmonids due to chromosomal rearrangements. We suggest that the salmon GnRH form compensated for the loss of the third form.

GnRH systems of Cichlasoma dimerus (Perciformes, Cichlidae) revisited: a localization study with antibodies and riboprobes to GnRH-associated peptides

“…To date, 14 structurally distinct forms of GnRH have been identified in vertebrates (Adams et al 2002), and many species express more than one form. In particular, several species of perciform teleosts express three different forms of GnRH in their brains: sea bream GnRH (sbGnRH or Gn RH I), chicken II GnRH (cGnRH II or GnRH II), and salmon This work was supported by grants UBACYT X-217, Conicet PIP 0539/R188; NIH-HD-29186 and Fogarty International Fellowship TW00086.…”

PKC and ERK are differentially involved in gonadotropin-releasing hormone-induced growth hormone gene expression in the goldfish pituitary

“…To date, a total of 16 forms of GnRH have been identified in various vertebrate and protochordate species, largely through the isolation and sequencing of peptides (1,49). Recently, in silico analysis identified seven novel decapeptide GnRHs in tunicates (2).…”

Role of PKC in the regulation of gonadotropin subunit mRNA levels: interaction with two native forms of gonadotropin-releasing hormone

“…FSH and LH are secreted from the pituitary as heterodimers composed of a common ␣ subunit noncovalently linked to a specific ␤ subunit (42). To date, a total of 24 molecular variants of GnRH have been characterized in various vertebrate and invertebrate species (1,2,24). At least two forms of GnRH, including the ubiquitous chicken (c)GnRH-II, are detected in all vertebrate species.…”