Isolation and characterization of the 5'-flanking region of the growth hormone secretagogue receptor gene from black seabream Acanthopagrus schlegeli

Ghrelin receptors in non-Mammalian vertebrates

The growth hormone secretagogue-receptor (GHS-R) was discovered in humans and pigs in 1996. The endogenous ligand, ghrelin, was discovered 3 years later, in 1999, and our understanding of the physiological significance of the ghrelin system in vertebrates has grown steadily since then. Although the ghrelin system in non-mammalian vertebrates is a subject of great interest, protein sequence data for the receptor in non-mammalian vertebrates has been limited until recently, and related biological information has not been well organized. In this review, we summarize current information related to the ghrelin receptor in non-mammalian vertebrates.

Analysis of expression and structure of the rat GH-secretagogue/ghrelin receptor (Ghsr) gene: roles of epigenetic modifications in transcriptional regulation

In the current study, to elucidate the molecular basis of cell type-specific expression of the GH-secretagogue/ghrelin receptor type 1A (GHSR1A), we characterized the structure and putative promoter region of the rat Ghsr gene. We identified an alternative 5'-untranslated first exon that contains multiple transcription start sites, and confirmed a 200-bp sequence proximal to this exon to be sufficient for basal promoter activity. A promoter-associated CpG island conserved across different species was found to be hypomethylated in Ghsr1a-expressing cell lines, while being heavily methylated in non-expressing cells. In cells with low or absent Ghsr1a expression, treatment with demethylating agents activated Ghsr1a transcription. Chromatin immunoprecipitation assays demonstrated Ghsr1a-expressing cells to display active histone modifications, whereas repressive modifications were present exclusively in other cell types. These results suggest epigenetic modifications at GHSR to play important roles in determining GHSR1A expression and abundance, and therefore the consequent sensitivity of cells to ghrelin.

Cloning of the black seabream (Acanthopagrus schlegeli) antiquitin gene and functional characterization of its promoter region

Antiquitin (ALDH7) is a member of the aldehyde dehydrogenase superfamily. In plants, ALDH7 is inducible upon dehydration and is thus believed to possess an osmoregulatory role. On the other hand, however, its exact physiological function in animals remains elusive. We herein report the isolation of the black seabream (Acanthopagrus schlegeli) antiquitin gene (sbALDH7) and the functional characterization of its promoter region. The 1.6 kb 5'-flanking region of sbALDH7 exhibits an intense promoter activity (30-170 fold of the basal) in five mammalian and fish cell lines of different origins. Progressive 5'-deletion analysis suggests that the core promoter is located within the region -297/+41 whereas a cis-acting repressor of basal transcription is present in the region -878/-297. In silico analysis of this sbALDH7 promoter region does not reveal any osmotic response element. Instead, it contains potential binding sites for cell cycle related cis-elements such as CCAAT displacement protein and cell cycle-dependent element/cell cycle genes homology region.