Discovery of growth hormone-releasing hormones and receptors in nonmammalian vertebrates

Abstract

In mammals, growth hormone-releasing hormone (GHRH) is the most important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary. In nonmammalian vertebrates, however, the previously named GHRH-like peptides were unable to demonstrate robust GH-releasing activities. In this article, we provide evidence that these GHRH-like peptides are homologues of mammalian PACAP-related peptides (PRP). Instead, GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and African clawed frog were identified. Moreover, receptors specific for these GHRHs were characterized from goldfish and zebrafish. These GHRHs and GHRH receptors (GHRHRs) are phylogenetically and structurally more similar to their mammalian counterparts than the previously named GHRH-like peptides and GHRH-like receptors. Information regarding their chromosomal locations and organization of neighboring genes confirmed that they share the same origins as the mammalian genes. Functionally, the goldfish GHRH dose-dependently activates cAMP production in receptor-transfected CHO cells as well as GH release from goldfish pituitary cells. Tissue distribution studies showed that the goldfish GHRH is expressed almost exclusively in the brain, whereas the goldfish GHRH-R is actively expressed in brain and pituitary. Taken together, these results provide evidence for a previously uncharacterized GHRH-GHRH-R axis in nonmammalian vertebrates. Based on these data, a comprehensive evolutionary scheme for GHRH, PRP-PACAP, and PHI-VIP genes in relation to three rounds of genome duplication early on in vertebrate evolution is proposed. These GHRHs, also found in flounder, Fugu, medaka, stickleback, Tetraodon, and rainbow trout, provide research directions regarding the neuroendocrine control of growth in vertebrates. molecular evolution ͉ genome duplication ͉ pituitary adenylate cyclase-activating polypeptide

Genomic structure, polymorphism and expression analysis of growth hormone-releasing hormone and pituitary adenylate cyclase activating polypeptide genes in the half-smooth tongue sole (Cynoglossus semilaevis)

“…Consistent results have also been reported in fish, such as catfish (Ictalurus punctatus) (McRory et al, 1995), zebrafish (Danio rerio) (Fradinger and Sherwood, 2000) and salmon (Parker et al, 1997). Recent research has indicated that GHRH-like peptides were homologues of mammalian PACAP-related peptides, whereas, genes encoding only GHRH peptides were identified in goldfish (Carassius auratus), zebrafish (D. rerio), and African clawed frog (Xenopus tropicalis) (Lee et al, 2007). Moreover, the cDNAs encoding PRP/PACAP and GHRH in half-smooth tongue sole were also cloned, respectively (Ji et al, 2011).…”

Neuroendocrine regulation of somatic growth in fishes

“…These fish ghrhs are expressed at high levels in the hypothalamus, telencephalon, spinal cord, and at a relative low level in the ovary. Similarly, their specific receptors, ghrh-rs, are abundant in the hypothalamus, telencephalon, spinal cord, diencephalon, and pituitary, but only present at low levels in the ovary [44,47]. Based on our recent pituitary transcriptome studies, the levels of both ghrh and ghrh-r expression were less than 1 RPKM in the zebrafish pituitary at both 45 and 90 d post-fertilization (dpf) [48].…”

“…The 27-aa fish GHRH mature peptides exhibit 81.5% homology with human GHRH [44]. Until recently, the GHRH/ GHRH-R system has only been documented in a few teleostean species, including zebrafish, goldfish, olive flounder, Fugu, medaka, rainbow trout, half-smooth tongue sole, and orange-spotted grouper [44][45][46][47]. These fish ghrhs are expressed at high levels in the hypothalamus, telencephalon, spinal cord, and at a relative low level in the ovary.…”

High-Level Expression, Purification, and Characterization of the Recombinant Grass Carp Pituitary Adenylate Cyclase-Activating Polypeptide

“…12) Recently, non-mammal GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and frog were identified. 13) In the goldfish, a 4-h incubation of pituitary cells with increasing doses (0.1 nM-1 mM) of goldfish GHRH resulted in a dose-dependent increase in GH release, the minimum effective dose being 10 nM. 13) Like GHRH, PACAP 38 (0.1 nM-1 mM) was also effective in inducing GH release from both goldfish and grass carp perifused pituitary cells in a dose-dependent manner.…”

“…13) In the goldfish, a 4-h incubation of pituitary cells with increasing doses (0.1 nM-1 mM) of goldfish GHRH resulted in a dose-dependent increase in GH release, the minimum effective dose being 10 nM. 13) Like GHRH, PACAP 38 (0.1 nM-1 mM) was also effective in inducing GH release from both goldfish and grass carp perifused pituitary cells in a dose-dependent manner. 6,7) These findings indicate that both PACAP and GHRH are y To whom correspondence should be addressed.…”