The effects of single nucleotide polymorphisms in Neuropeptide Y and prepro-orexin on growth in Nile tilapia (Oreochromis niloticus)

In teleosts, starvation induces an increase in appetite-related gene expression and peptide secretion in the hypothalamus. This reduces autonomic nervous activity and promotes food intake and body weight gain. We have previously demonstrated that single nucleotide polymorphisms (SNPs) in the 5 ' flanking region of ghrelin affect gene regulation and are associated with superior growth traits in Nile tilapia (Oreochromis niloticus). Recent findings have also suggested that Ghrelin, Neuropeptide Y (NPY), and Prepro-orexin combine in the hypothalamus to regulate appetite in organisms, thus we hypothesized that SNPs in NPY and prepro-orexin may also indirectly regulate the growth of Nile tilapia. Accordingly, we examined the effects of SNPs in NPY and preproorexin in two populations of Nile tilapia-the GIFT (GF) and Egyptian (EG) populations-by cloning the 5 ' flanking and coding regions of each gene and screening the SNPs in these regions to identify associations with superior growth traits. After preliminary screening and secondary prediction of function, 6 SNP loci (1 from NPY and 5 from prepro-orexin) were identified in the GF population, from which 9 diplotypes were constructed. Of these, four loci from prepro-orexin (g. -1108C > G, g. -1107C > G, g. -1063C > T, and g. -883C > T) and one diplotype were associated with superior growth traits. In the EG population, 4 SNP loci (1 from NPY and 3 from prepro-orexin) were identified and 6 diplotypes were constructed; however, none of these were associated with superior growth traits. Considering these findings, we discuss the necessity for functional prediction of SNP loci, and consider the differential conservativeness of the 5 ' flanking and coding regions of appetite-related genes.