The co-existence of two growth hormone receptors in teleost fish and their differential signal transduction, tissue distribution and hormonal regulation of expression in seabream

Abstract

Two genomic contigs of putative growth hormone receptors (GHRs) were identified in fugu and zebrafish genomes by in silico analysis, suggesting the presence of two GHR subtypes in a single teleost species. We have tested this hypothesis by cloning the full-length cDNA sequence of a second GHR subtype from the black seabream in which the first GHR subtype had been previously reported by us. In addition, we had also cloned the sequences of both GHR subtypes from two other fish species, namely the Southern catfish and the Nile tilapia. Phylogenetic analysis of known GHR sequences from various vertebrates revealed that fish GHRs cluster into two distinct clades, viz. GHR1 and GHR2. One clade (GHR1), containing 6 to 7 extracellular cysteine residues, is structurally more akin to the non-teleost GHRs. The other clade (GHR2), containing only 4 to 5 extracellular cysteine residues, is unique to teleosts and is structurally more divergent from the non-teleost GHRs. In addition, we had examined the biological activities of both GHR subtypes from seabream using a number of reporter transcription assays in cultured eukaryotic cells and demonstrated that both of them were able to activate the Spi 2·1 and -casein promoters upon receptor stimulation in a ligand specific manner. In contrast, only GHR1 but not GHR2 in seabream could trigger the c-fos promoter activity, indicating that the two GHR subtypes possess some differences in their signal transduction mechanisms. Also, the expression of GHR2 is significantly higher than GHR1 in many tissues of the seabream including the gonad, kidney, muscle, pituitary and spleen. In vivo hormone treatment data indicated that cortisol upregulated hepatic GHR1 expression in seabream but not GHR2, whereas testosterone decreased hepatic GHR2 expression but not GHR1. On the other hand, hepatic expression of both GHR1 and GHR2 in seabream was decreased by estradiol treatment.

Characterization of GHRs, IGFs and MSTNs, and analysis of their expression relationships in blunt snout bream, Megalobrama amblycephala

“…However, in grass carp (C. idella) (Ho et al, 1991), only one GHR gene was found. It was possible that two copies of GHR genes were the result of whole genome duplication (Jiao et al, 2006). Phylogenetic analysis of GHRs, IGFs and MSTNs revealed that the cyprinid species shared high sequence similarity.…”

“…A similar expression pattern might be caused by overlapping of the functions of GHRs (Ellens et al, 2013). But, it was found that cortisol up-regulates hepatic GHR 1 expression but not GHR 2, while testosterone decreases hepatic GHR 2 expression rather than GHR 1, and both hepatic GHR 1 and GHR 2 decreased expressions with estradiol treatment in black sea bream (A. schlegeli) (Jiao et al, 2006). Different regulation indicated that subtypes possess some differences in their signal transduction mechanisms.…”

Regulation of endocrine and paracrine sources of Igfs and Gh receptor during compensatory growth in hybrid striped bass (Morone chrysops×Morone saxatilis)

“…Based on these identities with closely related species, we consider the striped bass amplicon a partial clone of the putative Type I Ghr and hence refer to it here as Ghr1. The striped bass amplicon generated with degenerate ghr2 primers (EU595732) shared 83 and 96% nucleotide identity with gilthead sea bream (S. aurata; Saera-Vila et al , Jiao et al 2006 and European sea bass ghr2 sequences respectively. Based on these identities with closely related species, we consider the striped bass amplicon a partial clone of the putative Type II Ghr and hence refer to it here as Ghr2.…”

“…It should be noted that it is not certain whether the Ghr1 in non-salmonid fishes is a true Ghr (Jiao et al 2006, Li et al 2007 or instead the somatolactin receptor (SLR; Fukada et al 2005, Fukamachi et al 2005, Pierce et al 2007. Recent phylogentic and evolutionary analysis suggests that the SLR may in fact be a duplicated Ghr that occurred during the fish-specific genome duplication (Fukamachi & Meyer 2007).…”

Evolution of Receptors for Growth Hormone and Somatolactin in Fish and Land Vertebrates: Lessons from the Lungfish and Sturgeon Orthologues

“…Although direct evidence for the role of SL in these activities is mostly lacking, the recent identification of a SL-deficient mutant in medaka (color interfere, ci) demonstrated that SL functions in body-color regulation, lipid metabolism, or cortisol secretion in vivo (Fukamachi et al 2004(Fukamachi et al , 2005. Further analyses of the ci phenotypes might provide evidence for other potential functions since the SL receptor (SLR) is rather broadly expressed in various organs (Fukada et al 2005;Saera-Vila et al 2005;Fukamachi et al 2005;Jiao et al 2006;Ozaki et al 2006).…”