Ontogenetic and tissue-specific expression of preproghrelin in the Atlantic halibut, Hippoglossus hippoglossus L.

Abstract

Ghrelin is a conserved vertebrate hormone that affects both GH release and appetite. We have cloned and characterized Atlantic halibut preproghrelin cDNA and examined for the first time preproghrelin expression during fish larval development using quantitative real-time PCR. In addition, cellular sites of expression in larvae and tissue-specific expression in 3-year-old halibut were studied. A full-length cDNA for preproghrelin was isolated from halibut stomach tissue. The 899 bp cDNA encodes an open reading frame of 105 amino acids that is comprised of a signal peptide and two peptides with high similarity to ghrelin and obestatin. The deduced amino acid sequence of halibut ghrelin peptide (GSSFLSPSHKPPKGKPPRA) shows significant conservation relative to other teleostean sequences and is identical to human ghrelin for the first seven amino acids of the sequence. The putative obestatin peptide is well-conserved among fishes but shares limited similarity with its human counterpart. Expression of ghrelin was localized to two different cell types in the stomach of larval halibut by in situ hybridization. However, sensitive PCR assays on tissues collected from 3-year-old fish additionally identified ghrelin transcripts in pyloric caecae, intestine, and in immature ovary and testis. Ontogenetic studies detected ghrelin expression prior to exogenous feeding during larval development (hatching and mouth-opening stages) with increased expression occurring through metamorphosis. This increase was pronounced during climax metamorphosis and coincided with stomach differentiation. Patterns of preproghrelin expression suggest that ghrelin has important roles during and after larval development in halibut, and that ghrelin is associated with digestive and gonadal tissues in this teleost.

Molecular cloning and mRNA expression analysis of two GH secretagogue receptor transcripts in orange-spotted grouper (Epinephelus coioides)

“…Since the mRNA tissue distribution of Ghsr1b is much wider than Ghsr1a in grouper, we speculate that GHSR1b may mediate some unknown functions independent of ghrelin/GHSR1a system. During embryonic and larval development, gpGhsr1a mRNA was expressed from the neurula stage on, coinciding with the development of the nervous system and prior to the appearance of its ligand, ghrelin, which is expressed from hatching in Atlantic halibut (Manning et al 2008). The expression of gpGhsr1b mRNA can be detected as of the blastula stage, even earlier than gpGhsr1a.…”

“…The existence of ghrelin has now been demonstrated in nine teleostean species (reviewed by Unniappan & Peter 2005, Kaiya et al 2008: goldfish, Carassius auratus (Unniappan et al 2002); Japanese eel, Anguilla japonica (Kaiya et al 2003a); rainbow trout, Oncorhynchus mykiss (Kaiya et al 2003b); two tilapia species, Oreochromis mossambicus (Kaiya et al 2003c) and Oreochromis niloticus (Parhar et al 2003); channel catfish, Ictalurus punctatus ; black sea bream, Acanthopagrus schlegeli (Yeung et al 2006); sea bass, Dicentrarchus labrax (Terova et al 2008); and Atlantic halibut, Hippoglossus hippoglossus L. (Manning et al 2008). Physiological roles of ghrelin in teleosts have also been widely studied, including effects on GH secretion (Riley et al 2002, Kaiya et al 2003a,b,c, Ran et al 2004, Shepherd et al 2007, appetite stimulation (Unniappan et al 2002, Matsuda et al 2006a, Jönsson et al 2007, Miura et al 2007, Shepherd et al 2007, water intake (Kozaka & Ando 2003), reproduction (Mustonen et al 2002, Parhar et al 2003, immunity (Yada et al 2006), growth (Riley et al 2005, Fox et al 2007, intestinal motility (Olsson et al 2008), and locomotor behavior (Matsuda et al 2006a,b).…”

Ghrelin O-Acyl Transferase in Zebrafish Is an Evolutionarily Conserved Peptide Upregulated During Calorie Restriction

“…5,[12][13][14] So far, ghrelin has been identified in various fishes. [15][16][17][18][19][20][21][22] As in mammals, [23][24][25][26][27] ghrelin increases food intake and promotes body weight gain in fishes. 18,[28][29][30][31][32] Similar to mammals, 23,24 it was demonstrated that endogenous ghrelin levels and ghrelin-induced food intake depend on nutrient/feeding status.…”

Distribution of ghrelin peptide in the gastrointestinal tract of stomachless and stomach‐containing teleosts

“…Particularly, in the latter, ghrelin peptide was recently identified in two elasmobranchs, such as hammerhead shark and blacktip reef shark (Kawakoshi et al, 2007), and in some teleost species like goldfish (Unniappan et al, 2002), Nile tilapia (Parhar et al, 2003), rainbow trout , sea bass (Terova et al, 2008), zebrafish (Amole and Unniappan, 2008), and Atlantic halibut (Manning et al, 2008).…”