Characterization of nocturnin paralogs of goldfish: gene structure, liver rhytmicity and the effect of fasting

Abstract

Nocturnin (NOC) is a protein related with the circadian system and the endocrine control of lipid metabolism. From its discovery, and based on mammalian molecular structure, it has been proposed as a putative deadenylase involved in post-transcriptional regulation of mRNAs. A recent hypothesis suggests that NOC is involved in dephosphorylation of NADPH to NADH. The aim of this study is to characterize gene structure and rhythmicity of the expressed paralogs of noc in goldfish. An in silico analysis let us to propose the existence of 4 noc paralogs as a result of a double genomic duplication 3R (teleost specific) and 4Rc (Cyprininae specific). By RT-PCR, whole coding sequences have been obtained for three paralogs that we named noc-a1, noc-a2 and noc-b1 according to the phylogenetic sequence analysis. Expected noc-b2 seems to be a pseudogene not expressed in goldfish. Besides, we confirm the existence and expression of two splicing variants for both noc-a1 and noc-a2 in goldfish which expression is modify by fasting. By RT-qPCR, we quantified the tissue relative abundance of all noc coding transcripts, showing noc-a1 and noc-a2 higher expression than noc-b1 in the nervous system, and vice-versa for the non-neural tissues, with the exception of adipose tissue where all paralogs are highly expressed. Finally, we determine the daily variation of these paralogs in liver, where noc-a2 and noc-b1 expression peaks around five hours post-feeding. In conclusion, this study presents the first description of full-length sequences and splicing variants of nocturnin in fish, proving to be an important tool for the study of relationships of this enzyme with the metabolism and circadian system.