Molecular characterization and dietary regulation of the forkhead box O3 (foxo3a and foxo3b) in grass carp (Ctenopharyngodon idella)

Abstract

The forkhead box O3 (foxo3) regulates the target genes expression involved in regulating cell cycle and biological metabolism. In the study, foxo3a and foxo3b of grass carp (Ctenopharyngodon idella) were cloned. The foxo3a cDNA have a complete open reading frame (ORF) spanning 1431 bp, which encodes a polypeptide of 476 amino acids. The foxo3b cDNA contains a complete ORF encompassing 1959 bp, encoding a protein consisting of 652 amino acid residues. The analysis of genetic codon preference and phylogenetic relationships revealed that the foxo3a and foxo3b genes in grass carp are closely related to the counterparts of Danio rerio and Megalobrama amblycephala. Tissue expression analysis showed that foxo3a expression reached the maximum in the brain while foxo3b expression in the muscle being the highest. Circadian expression pattern showed that, foxo3a expression presented a periodic upward trend from 3:00–9:00, 12:00–18:00 and 21:00–24:00, and the maximum level of foxo3b was detected at 9:00. Moreover, dietary regulation of foxo3a and foxo3b expression were performed in our research. In the feeding trial with different protein sources, the groups of fishmeal, rapeseed meal and soybean meal are in contrast to each other. Foxo3a expression was significantly higher in fish fed with rapeseed meal compared to those fed with soybean meal and fishmeal at 14th and 21st days of the experiment. Foxo3b expression was highest in the fishmeal group, followed by rapeseed meal, while it was lowest in soybean meal at 14th and 28th days. Analysis of the effect of dietary alanine-glutamine dipeptide on foxo3 expression in grass carp revealed that the expression of foxo3a gradually increased with increasing dietary Ala-Gln dipeptide concentration and reached its highest level at a concentration of 1.5%. Conversely, foxo3b expression significantly decreased when the dipeptide concentration reached 2%. The findings of this study may provide new insights into the molecular properties, spatiotemporal dynamics, and nutritional regulation of foxo3 in fish.