Isolation and Characterization of a GnRH-like Peptide from Octopus vulgaris

Tello

General and Comparative Endocrinology

et al. 2008

105

Successful reproduction in vertebrates depends upon the actions of gonadotropin-releasing hormone (GnRH). Despite the wide presence of GnRH in Phylum Chordata, GnRH has not been isolated in protostomes other than the common octopus. To provide information on the evolution of this critical hormone, we isolated the full-length cDNA of a GnRH-like molecule from the central nervous system of a gastropod mollusk, the sea hare Aplysia californica. The open reading frame of this cDNA encodes a protein of 147 amino acids. The molecular architecture of the deduced protein is highly homologous to that reported for the prepro-octopus GnRH (oct-GnRH) and consists of a putative signal peptide, a GnRH dodecapeptide, a downstream processing site, and a GnRH-associated peptide (GAP). The deduced amino acid sequence of the Aplysia GnRH (ap-GnRH) is QNYHFSNGWYAG and differs from oct-GnRH by only two amino acids. The transcript for ap-GnRH is widely expressed in the central nervous system (CNS), the ovotestis, and the atrial gland, an exocrine gland. Immunocytochemistry (ICC) using an antiserum against oct-GnRH detected immunoreactive neurons in all CNS ganglia examined, and the staining was abolished by the preadsorption of the antiserum with synthetic ap-GnRH. In sum, ap-GnRH sequence is the first gastropod GnRH-like molecule to be elucidated. Further, it represents one of the only two GnRH-like molecules found outside Phylum Chordata. These data refute the possibility that oct-GnRH arose singly in cephalopods by convergent evolution and provide valuable support for an ancient origin of GnRH during metazoan evolution.

Section: Discussionmentioning

confidence: 99%

“…1). Further, the oct-GnRH prohormone contains the highly conserved dibasic cleavage site (Lys 14 -Arg 15 ) downstream of Gly 12 (Iwakoshi et al, 2002), another universal feature of chordate GnRH prohormones.…”

Section: Introductionmentioning

confidence: 99%

Molecular cloning, expression pattern, and immunocytochemical localization of a gonadotropin-releasing hormone-like molecule in the gastropod mollusk, Aplysia californica

Tello

General and Comparative Endocrinology

et al. 2008

105

Journal of Biological Chemistry

“…All calculations were performed using the ff99 AMBER force field (22), employing the Amber7 suite of programs to refine the energy of the peptide models. Residues for the N-terminal pyrolyzed glutamic acid and the amidated glycine present at the C terminus generated using the RESP procedure (23) 2ϩ ions probably arise due to protonation of the amide Gly 10 ; however, since we cannot determine the biological significance of this chemical form and due to some ambiguity in assigning this site of charge, the doubly protonated peptides were not investigated further in this study. For each of these 8 chemically distinct peptides, 300 candidate gas-phase minimized structures were generated using a simulated annealing approach.…”

Section: Methodsmentioning

confidence: 99%

“…To date 13 structural variants of the GnRH decapeptide have been identified in vertebrates (8), 9 from protochordates, which are vertebrate progenitors (8,9), and a 12-amino acid homolog from an octopus species (10) (Fig. 1).…”

mentioning

confidence: 99%

Evolution of Constrained Gonadotropin-releasing Hormone Ligand Conformation and Receptor Selectivity

Barran

Roeske

Pawson

et al. 2005

Gonadotropin-releasing hormone (GnRH) is the central regulator of reproduction in vertebrates. GnRHs have recently been identified in protochordates and retain the conserved N-and C-terminal domains involved in receptor binding and activation. GnRHs of the jawed vertebrates have a central achiral amino acid (glycine) that favors a type II ␤-turn such that the N-and C-terminal domains are closely apposed in binding the GnRH receptor. However, protochordate GnRHs have a chiral amino acid in this position, suggesting that they bind their receptors in a more extended form. We demonstrate here that a protochordate GnRH receptor does not distinguish GnRHs with achiral or chiral amino acids, whereas GnRH receptors of jawed vertebrates are highly selective for GnRHs with the central achiral glycine. The poor activity of the protochordate GnRH was increased >10-fold at vertebrate receptors by replacement of the chiral amino acid with glycine or a D-amino acid, which favor the type II ␤-turn. Structural analysis of the GnRHs using ion mobility-mass spectrometry and molecular modeling showed a greater propensity for a type II ␤-turn in GnRHs with glycine or a D-amino acid, which correlates with binding affinity at vertebrate receptors. These findings indicate that the substitution of glycine for a chiral amino acid in GnRH during evolution allows a more constrained conformation for receptor binding and that this subtle single amino acid substitution in a site remote from the ligand functional domains has marked effects on its structure and activity.In vertebrates, gonadotropin-releasing hormone (GnRH) 2 is synthesized in hypothalamic neurones and conducted a few millimeters in the hypophysial portal system to the anterior pituitary, where it binds to high affinity receptors in gonadotrophs to stimulate the release of gonadotropins (1). The gonadotropins in turn stimulate hormone and gamete production by the testes and ovaries. GnRHs have also been isolated from protochordate species (2, 3) and are thought to be secreted from neurones to directly regulate the gonads (2-4) in these representatives of vertebrate progenitors. GnRHs and GnRH receptors have also been found to directly affect vertebrate gonadal function (5), possibly reflecting the earliest role of GnRH as exemplified in protochordates (6, 7). It appears, therefore, that GnRHs have an ancient evolutionary role as regulators of reproduction, first through direct neural delivery to the gonads and later as hypothalamic neuroendocrine regulators of the gonads indirectly through gonadal stimulation by gonadotropins.To date 13 structural variants of the GnRH decapeptide have been identified in vertebrates (8), 9 from protochordates, which are vertebrate progenitors (8, 9), and a 12-amino acid homolog from an octopus species (10) (Fig. 1). All of the GnRHs are characterized by the conservation of the N-terminal residues (pGlu-His-Trp-Ser) and the C-terminal residues (Pro-Gly-NH 2 ) with the exception of two conservative substitutions (Fig. 1). In cartilaginous and bon...

Proc. Natl. Acad. Sci. U.S.A.

“…The high conservation of GnRH signaling within the chordate phylum (deuterostomians) raises the important question as to whether the appearance of this system might date back prior to the divergence of protostomian and deuterostomian lineages, between 670 MYA and 1 billion years ago. As a first step toward demonstrating the early emergence of GnRH, GnRH-related peptides have been established in 2 protostomian phyla: mollusks and annelids (5)(6)(7)(8)(9). This leads to several important questions regarding the evolution of the GnRH family.…”

mentioning

confidence: 99%

Adipokinetic hormone signaling through the gonadotropin-releasing hormone receptor modulates egg-laying in Caenorhabditis elegans

Lindemans

Liu

Janssen

et al. 2009

140

136

In mammals, hypothalamic gonadotropin-releasing hormone (GnRH) is a neuropeptide that stimulates the release of gonadotropins from the anterior pituitary. The existence of a putative functional equivalent of this reproduction axis in protostomian invertebrates has been a matter of debate. In this study, the ligand for the GnRH receptor in the nematode Caenorhabditis elegans (Ce-GnRHR) was found using a bioinformatics approach. The peptide and its precursor are reminiscent of both insect adipokinetic hormones and GnRH-preprohormone precursors from tunicates and higher vertebrates. We cloned the AKH-GnRH-like preprohormone and the Ce-GnRHR and expressed the GPCR in HEK293T cells. The GnRHR was activated by the C. elegans AKH-GnRH-like peptide (EC50 ‫؍‬ 150 nM) and by Drosophila AKH and other nematode AKH-GnRHs that we found in EST databases. Analogous to both insect AKH receptor and vertebrate GnRH receptor signaling, Ce-AKH-GnRH activated its receptor through a G␣q protein with Ca 2؉ as a second messenger. Gene silencing of Ce-GnRHR, Ce-AKHGnRH, or both resulted in a delay in the egg-laying process, comparable to a delay in puberty in mammals lacking a normal dose of GnRH peptide or with a mutated GnRH precursor or receptor gene. The present data support the view that the AKH-GnRH signaling system probably arose very early in metazoan evolution and that its role in reproduction might have been developed before the divergence of protostomians and deuterostomians.C. elegans ͉ G protein-coupled receptor ͉ molecular evolution ͉ neuropeptide ͉ neuroendocrinology