Two divergent leptin paralogues in zebrafish (Danio rerio) that originate early in teleostean evolution

Abstract

We describe duplicate leptin genes in zebrafish (Danio rerio) that share merely 24% amino acid identity with each other and only 18% with human leptin. We were also able to retrieve a second leptin gene in medaka (Oryzias latipes). The presence of duplicate leptin genes in these two distantly related teleosts suggests that duplicate leptin genes are a common feature of teleostean fishes. Despite low primary sequence conservation, we are confident in assigning orthology between mammalian and zebrafish leptins for several reasons. First, both zebrafish leptins share their characteristic gene structure and display key features of conserved synteny with mammalian leptin genes. Secondly, the cysteine residues that make up leptin's single disulphide bridge are equally spaced in mammalian and zebrafish leptins and are unique among all members of the class-I helical cytokine family. Thirdly, the zebrafish leptins cluster with other fish leptins and mammalian leptins in phylogenetic analysis, supported by high bootstrap values. Within the leptin cluster, leptin-b forms a separate clade with the leptin-b orthologue from medaka. Finally, our prediction of the tertiary structures shows that both leptins conform to the typical four a-helix bundle structure of the class-I a-helical cytokines. The zebrafish leptins are differentially expressed; the liver shows high leptin-a expression (in concordance with what we observed for carp leptins), while leptin-b is expressed at much lower levels, which are downregulated further upon fasting. The finding of duplicate leptin genes in teleosts adds to our understanding of the evolution of leptin physiology in the early vertebrate lineage.

Immunolocalisation of leptin in the digestive system of juvenile European sea bass (Dicentrarchus labrax)

“…Leptin amino acid sequence is conserved in mammalian and fish classes even though it seems to show higher diversity within teleosts (Kurokawa et al 2005). Thus recent reports identify additional leptin in several teleosts (leptin-a and leptin-b), such as carp (Cyprinus carpio), zebrafish (Danio rerio) and medaka (Oryzias latipes) (Huising et al 2006;Gorissen et al 2009;Kurokawa & Murashita 2009). Leptin-a shares high primary sequence conservation within zebrafish and carp (61%), whereas leptin-b shares only 25% amino acid identity.…”

“…Among teleosts, the presence of leptin orthologues has been recently reported in pufferfish, medaka, carp and zebrafish, suggesting the possibility of a redundant leptin network in teleosts (Gorissen et al 2009). Leptin is a potent stimulator of pituitary prolactin release in tilapia (Tipsmark et al 2008), it regulates the reproductive system in sea bass (Peyon et al 2001), it is responsible for food intake in rainbow trout ) and in goldfish (Volkoff et al 2003), and body weight regulation in goldfish (De Pedro et al 2006).…”

“…Leptin was immunodetected in the blood, brain, heart and liver of several bony fish species (Johnson et al 2000), in the enteric epithelium and nervous system of trout (Muruzàbal et al 2002) and in salmon adipocytes (Vegusdal et al 2003). Furthermore, leptin expression has been found in liver, adipose tissue, ovary and pituitary gland (Kurokawa et al 2005;Huising et al 2006;Gorissen et al 2009). No studies are available about the juvenile stages of the species used in aquaculture, including the sea bass.…”

Molecular cloning, characterization and evolutionary analysis of leptin gene in Chinese giant salamander, Andrias davidianus

“…Leptins also were identified in non-mammalians, including birds [3][4][5], reptiles [2], amphibians [6][7][8], and teleosts, the later generally possess duplicated leptins [8][9][10][11][12][13][14][15]. Leptin has been found to be responsible for the regulation of body weight and energy homeostasis [16,17], and it also is involved in regulating appetite, reproduction [18], the immune system [19], bone formation [20], angiogenesis [21], and stress response [22,23].…”

“…Although, positive selections of leptins are revealed in several mammal lineages, for example, pikas (Ochotona curzoniae), Cetacea and Pinnipedia, and heterothermic bats [24][25][26], the conserved gene structure (three exons separated by two introns) and secondary and tertiary structures of leptins were found from teleosts to mammals [2,3,6,11,27,28]. Phylogeny reconstruction of vertebrate leptins showed that most vertebrates form distinct clades with topology consistent with the generally accepted vertebrate topology except that the relationships among teleosts remain inconsistent [2,11,29].…”