Cloning of Phoenixin-20 gene in Lateolabrax maculatus and the effects of starvation and re-feeding on its expression

【Objective】To determine whether the Phoenixin-20 gene(LmPNX-20) was involved in the regulation of the feeding mechanism of Lateolabrax maculatus, and to reveal the role of PNX-20 in the regulation mechanism of fish feeding, and to provide a theoretical basis for enriching and improving the endocrine regulatory network of L. maculatus.【Method】The LmPNX-20 gene sequence was cloned by PCR and RACE, and bioinformatics analysis was performed by online softwares ExPASy, SignalP 5.0, ProtScale, NetPhos 3.1 and ClustalX. The expression characteristics of LmPNX-20 gene in various tissues were analyzed by real-time fluorescence quantitative PCR detection and effects of different starvation and re-feeding strategies on the expression of LmPNX-20 gene were detectednormal feeding(F), starvation for 3 d(H3), starvation for and 3 d re-feeding for 1 d(R3-1), starvation for 3 d and re-feeding for 2 d(R3-2), starvation for and 3 d re-feeding for 3 d(R3-3), starvation for 7 d(H7), starvation for 7 d and re-feeding for 1 d(R7-1), starvation for 7 d and re-feeding for 2 d(R7-2), starvation for 7 d and re-feeding for 3 d(R7-3). 【Result】LmPNX-20 gene had open reading frame(ORF) of 210 bp, encoding 69 amino acids residues. The encoded molecular weight of LmPNX-20 protein was 7.87 kD, with theoretical isoelectric point(pI) of 9.85. LmPNX-20 amino acid sequence contained 5 phosphorylation sites, but there was no signal peptide. Homology analysis of the amino acid sequence revealed that LmPNX-20 shared a high similarity of 69.70% to 89.86% with PNX-20 sequences from other bony fish species. LmPNX-20 gene was widely distributed in the brain tissue, with higher expression levels observed in the hypothalamus and pituitary. After starvation fasting and re-feeding treatments, the expression of LmPNX-20 gene in the whole brain tissue of juvenile L. maculatus showed obvious changes. After 3 and 7 d of starvation and re-feeding for 1 d, there was significant up-regulation of LmPNX-20 gene expression(P<0.05). After starvation for 7 d and re-feeding, the expression level of LmPNX-20 was upregulated compared to that after 3 d of starvation and re-feeding. 【Conclusion】LmPNX-20 gene is relatively conserved along fish evolution. Moreover, the expression level is high in the growth axis(hypothalamus, pituitary and liver) and reproductive axis(hypothalamus, pituitary and gonad), which may be involved in the physiological process of growth and reproduction of L. maculatus. Different starvation and re-feeding treatments affect the expression of LmPNX-20 gene in the whole brain tissue of juvenile L. maculatus, and the expression of this gene is greatly increased after re-feeding, that is, LmPNX-20 gene has a certain promotion effect on the feeding regulation of juvenile L. maculatus.