Appetite control systems in fish: Identification of fish leptin and agouti-family genes
2008
Kurokawa, T.(National Research Inst. of Aquaculture, Mie (Japan))
To understand the regulation systems of appetite in fish, we identified cDNA coding for leptin and agouti family proteins in pufferfish (Takifugu rubripes). The Takifugu leptin was found using genomic synteny around the human leptin gene as a first non-mammalian leptin gene. The Takifugu leptin mRNA was expressed in the liver that contained abundant lipids. In addition, the homologues to Takifugu leptin for some fish and amphibians were found in the databanks. The phylogenetic analysis shows rapid rates of molecular divergence among leptins from different vertebrate classes. Takifugu has four types of agouti-family genes (AGRP1, AGRP2, ASIP1 and ASIP2). The Takifugu ASIP1 expression level was about five times higher in the white ventral skin than in the black dorsal skin. This indicates that the Takifugu ASIP1 functions to retain the dorsal-ventral pigmentation pattern like to mammalian ASIP. On the other hand, ASIP2, AGRP1 and AGRP2 mRNA expression were detected in various organs in Takifugu. Therefore, the physiological functions of melanocortins and agouti-family proteins seem to be more complex in fish than in mammals.
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