First evidence of nocturnin in fish: two isoforms in goldfish differentially regulated by feeding

Abstract

Nocturnin (NOC) is a unique deadenylase with robust rhythmic expression involved in the regulation of metabolic processes in mammals. Currently, the possible presence of NOC in fish is unknown. This report aimed to identify NOC in a fish model, the goldfish ( Carassius auratus), and to study the possible regulation of its expression by feeding. Two partial-length cDNAs of 293 and 223 bp, named nocturnin-a ( noc-a) and nocturnin-b ( noc-b), were identified and found to be highly conserved among vertebrates. Both mRNAs show a similar widespread distribution in central and peripheral tissues, with higher levels detected for noc-a compared with noc-b. The periprandial expression profile revealed that noc-a mRNAs rise sharply after a meal in hypothalamus, intestinal bulb, and liver, whereas almost no changes were observed for noc-b. Food deprivation was found to exert opposite effects on the expression of both NOCs (generally inhibitory for noc-a, and stimulatory for noc-b) in the three mentioned tissues. A single meal after a 48-h food deprivation period reversed (totally or partially) the fasting-induced decreases in noc-a transcripts in all studied tissues and the increases in noc-b expression in the intestinal bulb. Together, this study offers the first report of NOC in fish and shows a high dependence of its expression on feeding and nutritional status. The differential responses to feeding of the two NOCs raise the possibility that they might be underlying different physiological mechanisms (e.g., food intake, lipid mobilization, energy homeostasis) in fish.

Differential processing and localization of human Nocturnin controls metabolism of mRNA and nicotinamide dinucleotide metabolites

“…To further corroborate the processing of NOCT protein, we appended a 3xFLAG (3F) tag to the C-terminus of NOCT and examined the proteins produced in HEK293 cells from plasmids that express wild type NOCT or the deletion of MTS (NOCT ∆ (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)) or N-terminus (NOCT ∆(2-67)). Full length NOCT (1-431)-3F was processed to form a ~44 kDa product, whereas deletion of the MTS in NOCT ∆(2-15)-3F prevented processing, resulting in expression of a ~58 kDa product (Figure 1d).…”

“…Nocturnin (NOCT) is a eukaryotic protein that belongs to the Exonuclease-Endonuclease-Phosphatase (EEP) superfamily of enzymes and is conserved from insects to vertebrates (1)(2)(3)(4)(5)(6). While members of the EEP superfamily can act on diverse substrates, ranging from nucleic acids to phospholipids, NOCT is most similar to the CCR4 subclass of EEP enzymes, which is indicative of a role in RNA metabolism (1,2).…”

“…The role of the two potential initiation sites was tested by mutating M1 AUG codon to GGG (M1X) or M67 AUG codon to a glycine codon, GGG (M67G). The role of the N-terminal predicted MTS in processing of NOCT protein was tested; deletion of the MTS in NOCT ∆(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) or NOCT ∆(2-15)+M67G abolishes processing, consistent with mitochondrial localization and processing. "Mock" indicates untransfected cells.…”

Regulatory roles of vertebrate Nocturnin: insights and remaining mysteries

“…NOCT mRNA levels are constant in white adipose tissue from ad lib fed mice but become rhythmic in response to daytime feeding, and dietary fat induces NOCT mRNA expression in the proximal small intestine [19,55]. The connection between feeding and NOCT mRNA expression in certain contexts appears to be evolutionarily conserved, as several tissues in the goldfish Carassius auratus exhibit increased noc-a mRNA expression following a meal [16]. …”

“…Starvation has also been connected with increased curled mRNA abundance in Drosophila [14], as well as time- and tissue-dependent induction of noc-b and repression of noc-a mRNA expression in C. auratus [16]. The links between NOCT expression and nutrient availability suggest a role for NOCT in modulating metabolic activity, perhaps regulating the expression of genes involved in energy uptake, storage, and utilization [9,15,16,19,55]. Whether nutrient availability and feeding regulate NOCT expression in humans remains to be explored.…”