EXPRESSION ANALYSES OF NPY AND POMC GENES IN EXTREME GROWTH AND STARVATION-REFEEDING BIGHEAD CARP (HYPOPHTHALMICHTHYS NOBILIS)

Fish growth is one of the most complex traits that may be influenced by many physiological processes. Among them, feeding is a necessary prerequisite to ensure the growth, development and survival of fish. In order to study the effects of feeding promoting and feeding inhibiting genes on genetic regulation of growth and starvation-refeeding, cDNA sequences of neuropeptide Y (HynNPY) and pro-opiomelanocortin (HynPOMC) genes were cloned in bighead carp (Hypophthalmichthys nobilis) in this study. By using qRT-PCR, expression levels of NPY and POMC genes were studied in hypothalamus and intestine of extreme growth and starvation-refeeding of bighead carp by setting control (feeding), starvation, and starvation-refeeding group, respectively. The full-length cDNA of NPY and POMC genes were 839 and 799 bp, encoding 96 and 218 amino acids, respectively. Phylogenetic analysis showed that NPY and POCM are highly conserved in teleosts. The expression of NPY in hypothalamus was the highest, followed by intestine and brain. The expression of POMC in intestine was the highest, followed by hypothalamus and liver. In the hypothalamus and intestine of extreme large (mean 42.4 g) and extreme small (mean 18.8 g) individuals cultured in the same pond, the expression of NPY in extremely large group was higher than that of extremely small group, while the expression of POMC in extreme small group was significantly higher than that of extreme small group. Starvation increased the expression ofNPY in hypothalamus and intestine. After starvation, the expression of NPY increased in the hypothalamus and increased significantly in the intestine. After refeeding, the expression of NPY decreased in the hypothalamus and intestine. The expression of POMC in hypothalamus and intestine of starvation group increased significantly, and decreased to the level of control group after refeeding. Histological observations showed that structure of intestine in extremely large group is better than that of extremely small group, meanwhile, broken intestinal villi and leukocyte infiltration in starvation group tend to recover gradually after refeeding. In short, NPY promotes the intake of more food and POMC supresses appetite, and both of them are involved in feeding mediation of central and peripheral nerve systems of bighead carp. NPY and POMC may directly or indirectly affect the growth of bighead carp by controlling feeding behavior, intake of feed nutrition and GH secretion. These results would provide insights into further understanding of molecular mechanisms for differential growth in bighead carp and gene resources for genetic improvement.