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The forkhead box O3 (foxo3) regulates the target genes expression involved in regulating cell cycle and biological metabolism. In the study, foxo3aand foxo3bof grass carp (Ctenopharyngodon idella) were cloned. The foxo3acDNA have a complete open reading frame (ORF) spanning 1431 bp, which encodes a polypeptide of 476 amino acids. The foxo3bcDNA 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 foxo3aand foxo3bgenes in grass carp are closely related to the counterparts of Danio rerioand Megalobrama amblycephala.Tissue expression analysis showed that foxo3aexpression reached the maximum in the brain while foxo3bexpression in the muscle being the highest. Circadian expression pattern showed that, foxo3aexpression presented a periodic upward trend from 3:00–9:00, 12:00–18:00 and 21:00–24:00, and the maximum level of foxo3bwas detected at 9:00. Moreover, dietary regulation of foxo3aand foxo3bexpression 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. Foxo3aexpression 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. Foxo3bexpression 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 foxo3expression in grass carp revealed that the expression of foxo3agradually increased with increasing dietary Ala-Gln dipeptide concentration and reached its highest level at a concentration of 1.5%. Conversely, foxo3bexpression 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 foxo3in fish.

•Dietary supplementation of 5% FPM significantly elevated growth and feed utilization of gibel carp.•3%-8% of FPM can successfully supplement in the diet for gibel Carp without negative effects on growth performance•Fish fed the FPM supplemented diet performed a better intestinal digestive enzymes and serum antioxidant ability.•The expression of genes involved in TOR Signaling pathway remarkably increased when fish fed The diets with 5–8% FPM.

Ghrelin can stimulate pituitary growth hormone (GH) release, and has a key role in the regulation of food intake and adiposity in vertebrates. At present, no relevant studies have reported the effects of Ghrelin on intestinal cell proliferation, protein absorption and metabolism. In this paper, firstly we established the intestinal epithelial cell lines of juvenile grass carp (Ctenopharyngodon idella) that can be passed stably and identified by the intestinal specific expression proteins E-cadherin and ZO-1. And we used this cell line as a model to investigate the effects of Ghrelin, Ala-Gln, Ala-Gln+Ghrelin on the proliferation of juvenile grass carp intestinal cells. We found that the use of Ghrelin, Ala-Gln and Ala-Gln+Ghrelin could promote the proliferation of intestinal cells of juvenile grass carp, but Ala-Gln+Ghrelin had the strongest promoting effect. Further, we investigated the effects of Ghrelin on the expression of cdx2, PepT1 and mTOR which are related to intestinal cell proliferation, protein absorption and metabolism of grass carp in vitroand in vivoexperiments. And we studied the effects of different protein sources on the expression of Ghrelin, PepT1 and mTOR in grass carp at individual level. The results suggested that Ghrelin can promote grass carp intestinal cell proliferation, and affect the expression of genes which are related to intestinal peptide absorption and metabolism in juvenile grass carp.