Abstract
In mammals, leptin has been demonstrated to perform important roles in many physiological activities and to influence development, growth, metabolism and reproduction. However, in fish, its function is still unclear. Duplicate leptin genes, leptin-a and leptin-b, have been identified in the orange-spotted grouper. In the present study, the polymorphisms in the leptin-b gene of the orange-spotted grouper were detected, and the relation between these polymorphisms and 12 growth traits were analyzed. Six polymorphisms (including 3 single nucleotide polymorphisms (c.14G>A, c.93A>G, c.149G>A) in exon 1, 2 SNPs (c.181A>G, c.193G>A) in intron 1, and 1 SNP (c.360C>T) in exon 2) were identified and genotyped from 200 different individuals. The results revealed that the SNP c.149G>A was significantly associated with growth traits, that the heterozygous mutation genotype GA having negative effects on growth traits. However, the other five SNPs (c.14G>A, c.93A>G, c.181A>G, c.193G>A, c.360C>T) did not show significant associations with all the growth traits. Compared with our findings in leptin-a gene, the results suggested that the leptin-a hormone has more important physiological effects in fish bodies than the leptin-b type. Moreover, leptin genes were supposed to be one class of major candidate genes of regulating growth traits in the orange-spotted grouper.
Highlights
Leptin, the protein product of the obese gene, was a hormone synthesized by adipocytes that signals available energy reserves to the brain and acts on target tissues via receptor mediating mechanism [1,2]
Our results revealed that two missense mutations altering arginine to glutamine, c.14G>A and c.149G>A, existed in the leptin-b gene open reading frame of the orange-spotted grouper, with the SNP c.14G>A showing no significant associations and the SNP c.149G>A showing significant associations with growth traits in the orange-spotted grouper
We inferred that the amino acid altering by the SNP c.149G>A existed in an important function domain of leptin-b, and the amino acid variation interfered with the normal physiological effects of leptin-b in fish bodies, so that the SNP c.149G>A was associated with growth traits and the mutation genotype
Summary
The protein product of the obese (ob or Lep) gene, was a hormone synthesized by adipocytes that signals available energy reserves to the brain and acts on target tissues via receptor mediating mechanism [1,2]. Orthologs of mammalian Lep genes were isolated from several fish, such as pufferfish (Takifugu rubripes) [6], common carp (Cyprinus carpio) [7], zebrafish (Danio rerio) [8], Japanese medaka (Oryzias latipes) [9], grass carp (Ctenopharyngodon idella) [10], rainbow trout (Oncorhynchus mykiss) [11], Atlantic salmon (Salmo salar) [12], striped bass (Morone saxatilis) [13], goldfish (Carassius auratus) [14] and orange-spotted grouper [15]. The duplicate leptin genes have been detected, for instance zebrafish [8], Japanese medaka [9], and orange-spotted grouper [15]. The polymorphisms in leptin related genes have been demonstrated to be associated with the growth traits, swine [16,17,18] and cattle [19,20,21,22,23,24]. The cDNAs of leptin-a and leptin-b gene were 671 bp and 684 bp in length, each containing
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