Purifying selection on leptin genes in teleosts may be due to poikilothermy.

Abstract

Leptin is a key harmone in regulating food intake, immune function and energy metabolism in vertebrates. Since it was first cloned in mouse (Zhang et al. 1994) , the leptin gene has received much attention and people started to research its function in energy homoeostasis and reproductive regulation (Campfiled et al. 1995). A large number of researchers have discovered that leptin is present in several fishes and it plays a similar role in regulation of food intake and energy metabolism in fishes as in mammals (Copeland et al. 2011). Although evidence of positive selection on the leptin gene has been documented in primates, seals and chiropterans (Yu et al. 2011), studies on evolution of leptin gene in fishes are fewer. Leptin, the product of the ob gene, was discovered in 1950 (Coleman 2010). The discovery was followed by intense research into the properties and physiological action of leptin. In initial studies, people considered that the primary functions of leptin were its influence on metabolic rate and mobilization of fat stores (Minokoshi and Kahn 2003). With further research, we now know that leptin is pleiotropic, exerting effects on reproduction, immune function, capillary growth and bone remodelling (Friedman 2009). In mammals, leptin acts on the hypothalamus which sends further signals to the brain, leading the brain to regulate food intake and metabolism (Pelleymounter et al. 1995). To our knowledge, mutations in the leptin genes were associated with a large number of hormonal and metabolic alterations (Kennedy 1953). Deficiency of leptin can cause obesity and diabetes in humans and mice (Strobel et al. 1998). Leptin genes of some fishes have been cloned and people have started to study their structure and biological functions of the protein (Murashita et al. 2008; Aguilar et al. 2010). Although leptin genes of several several species of teleosts have been cloned (Kurokawa et al. 2005; Huising et al. 2006; Ronnestad et al. 2010), physiological function of the