Polymorphisms Of Leptin Genes Ssociatied With Growth Traits In Orange-Spotted Grouper(Epinephelus Coioides)

The orange-spotted grouper (Epinephelus coioides) is a highly valued cultured marine species and is farmed in many countries. Leptin, a product of the obese (ob) gene, acts on target tissues via receptor mediating mechanism. In mammals, leptin has been demonstrated to perform important roles in body weight regulation, energy expenditure, fat metabolism, food intake, appetite regulation, bone remodeling, hematopoiesis, immune function and reproduction. However, its function in teleosts is still unclear, but several studies have been conducted on the teleost leptin genes. In this study, the polymorphic analyses of two leptin genes in the orange-spotted grouper(Epinephelus coioides) were performed in an experimental population with200individuals. Six polymorphism sites were identified in opening reading frames of each leptin genes (leptin-a, leptin-b). By association analysis between polymorphism variations and12growth traits of the orange-spotted grouper, four molecular makers associated with growth traits were detected in leptin-a and leptin-b genes, which could be used for marker-assisted selection (MAS) in orange-spotted grouper populations. The results demonstrate that developing molecular makers in leptin genes is with high research and practical value. In teleost, this is the first study to provide further evidence for the association of leptin gene polymorphisms with growth traits, and these findings could lead to a greater understanding of the functions and regulation of leptin gene expression related to fish growth. The main results are as follows:1.We obtained the gene sequence, performed polymorphic analysis, and identified6SNPs in the leptin-a gene open reading frame (ORF) of orange-spotted grouper. Two SNPs in intron1(c.182T>G, c.183>GT) were in complete linkage. Based on the association analysis results, the polymorphism c.182+183TG>GT in intron1was significantly associated with body weight, body width, caudal peduncle width and snout length, with the mutation genotype AB (TG/GT) showing positive effects on such growth traits. Additionally, the SNP c.447G>A in exon2was significantly associated with body weight, body width, overall length, body length, trunk width, head length, caudal peduncle width and interorbital distance, with the genotype GA positively affecting these growth traits. Finally, the SNP C.531C>T in exon2was significantly associated with eyeball diameter, and fish with the genotype TT showed poorer growth performance.2. We obtained the gene sequence, performed polymorphic analysis, and identified6SNPs in the leptin-b gene ORF of orange-spotted grouper. Based on the association analysis results, the missense mutation c.149G>A in exon1was significantly associated with body width and head length, with the genotype GA negatively affecting these growth traits.