Effect Of Fasting-refeeding On Neuropeptide Y And Leptins In Silver Carp(Hypophthalmichthys Molitrix)

In animals, the regulation of food intake and energy balance is vital for growth, as inadequate food intake and an energy imbalance will inhibit growth, delay puberty and may result in lower resistance to parasites and diseases. Due to various factors, the fish often face to suffer the shortage of food resources in its life cycle in the natural environment. Leptin(LEP) and neuropeptide Y(NPY) are two key factors of the appetite regulation system, and they act together to regulate animal’s food intake and energy metabolism.Silver carp(Hypophthalmichthys molitrix) is a typical filter-feeding freshwater fish that is distributed throughout the major rivers and lakes in China. It is a vital animal protein source for the Chinese people because of its low price and high yield, which has a significant economic value. In the present study, we cloned the leptin, leptin receptor, Leptin receptor overlapping transcript and neuropeptide Y genes, detected the tissue expression of these four genes and designed a fasting-refeeding experiment to characterize the m RNA expression of these four genes as an initial step toward understanding the biological roles of LEP, LEPR, LEPROT and NPY in silver carp. Our major results are as follows:1. Cloning and expression of NPY in silver carp(Hypophthalmichthys molitrix) during fasting and refeedingThe full length cDNA sequence of sc NPY is 782 bp, including a 291 bp open reading frame with a coding potential for a 96-amino acid protein, a 68 bp 5’-untranslated region and a 423 bp 3’- untranslated region; The similarity of NPY amino acid sequence and phylogenetic analysis showed that NPY gene was relatively conservative in molecular evolution; sc NPY m RNA was expressed ubiquitously in the tissues examined and abundantly expressed in pituitary; In brain, the expression of NPY m RNA was increased significantly during fasting, and then decreased to basal level at 6h after refeeding, which indicates that NPY plays a positive role in food intake in silver carp; In liver, the expression of NPY m RNA was increased significantly until 5d after fasting, but decreasedsharply at 7d, finally returned to basal level at 4h after refeeding; The tissue-specific expression of NPY lies between brain and liver; Additionally, the function of NPY in liver needs further study.2. Cloning and expression of leptin, leptin receptor and leptin receptor overlapping transcript genes in silver carp(Hypophthalmichthys molitrix) during fasting and refeedingThe full-length c DNA sequences of sc LEPR and sc LEPROT were 3662 bp and 718 bp and encoded 1079 and 130 amino acid residues, respectively; The deduced amino acid sequence of sc LEP and sc LEPR were not conserved, sharing only 20.2% and 25.9% identity with human LEP and LEPR, respectively, However, the sc LEPROT amino acid sequence was relatively conserved; Phylogenetic analysis indicated that teleost LEP, LEPR and LEPROT genes were all separated from the tetrapod genes; Tissue expression analysis showed that the sc LEP m RNA was highly expressed in liver, while sc LEPR and sc LEPROT m RNAs were abundant in the pituitary gland; The expression of sc LEP, sc LEPR and sc LEPROT m RNAs was highly increased in brain after fasting was induced and subsequently rapidly reversed after refeeding; In liver, although the m RNA expression varied, the overall tendency was for decreased expression from fasting to refeeding.In this study, the m RNA expression of sc LEP, sc LEPR and sc LERPOT responding to fasting and refeeding was distinct for mammals and certain other teleosts. Additionally, available data showed that the models regulating food intake and energy metabolism in teleosts were various and most of them were distinct for mammals. We speculate the diversity of LEP regulative model in teleosts might be associated with the feeding habits of different fish. These results provide useful information for studying the roles of NPY and LEP in silver carp and lay the foundation for the silver carp breeding on hunger resistance.