Cloning and characterization of leptin in a Perciform fish, the striped bass (Morone saxatilis): Control of feeding and regulation by nutritional state

In mammals, leptin is an anorexigenic peptide hormone that regulates energy homeostasis. It is produced predominantly by white adipose tissue and circulates as an endocrine indicator of energy reserves. Teleost leptin has been characterized in a few fish species, but its regulation is not well understood, particularly in response to nutritional status. In this study, we cloned a putative leptin in striped bass (Morone saxatilis) and report the first characterization of leptin in a Perciforme, the largest and most diverse order of fish. The striped bass leptin coding sequence was 65% homologous with pufferfish, 52% with Atlantic salmon, and 46% with human. PCR showed that leptin mRNA was exclusively expressed in the liver, and not adipose or other tissues. The leptin coding sequence of striped bass and the more widely cultured hybrid striped bass variety (HSB; Morone chrysops, white bass × M. saxatilis) were identical. We then evaluated whether the metabolic status of HSB might alter leptin gene expression. Juvenile HSB were subjected to 3 weeks feed deprivation followed by 3 weeks of refeeding. Quantitative PCR showed that fasting for 3 weeks reduced hepatic leptin mRNA levels relative to fed controls. Leptin mRNA levels then increased upon refeeding, albeit levels were not completely restored to those seen in control fish fed throughout the experiment. Intraperitoneal injection of human leptin suppressed appetite in HSB. In as much as hepatic HSB leptin mRNA is regulated by nutritional state and has a corresponding anorexigenic effect, our results suggest that leptin may play a role in energy homeostasis in these advanced Perciformes.

► We report the first cloning and characterization of leptin in Perciformes, the largest and most diverse order of vertebrates.
► Genomic analyses suggest Perciformes may only have one leptin gene, in contrast to that of more basal orders of teleosts.
► We show that hepatic leptin gene expression is sensitive to nutritional state and increases during anabolism in Morone.
► Exogenous leptin treatment suppresses food intake in hybrid striped bass.
► Work suggests leptin regulates energy homeostasis by suppressing appetite as energy stores increase.