Cocaine- and amphetamine-regulated transcript in perciforms I. Phylogenetic, structural and spatial conservation

Cocaine- and amphetamine-regulated transcript (Cart) is a pleiotropic neuropeptide involved in the regulation of stress and anxiety, depression, reproduction and circadian functions, yet it is mainly known for its metabolic regulation of body weight and appetite. While mammals possess a single cart gene, the genomes of birds may contain up to two carts and fish may possess up to ten cart genes. Furthermore, in some fish species the number of cart paralogues exceeds the number expected according to whole-genome duplication events in actinopterygians, suggesting a species-specific diversification of the cart system. In the current study, we identified multiple cart genes in two fish species with global importance -Nile tilapia and gilthead seabream. Bioinformatics analysis revealed seven cart genes in the tilapia genome and six cart genes in the seabream genome, all of which show high homology with carts of other vertebrates. Additionally, the predicted mature cart peptide sequences contain all the cysteines known to stabilize the tertiary peptide structure in other vertebrates. Nevertheless, protein structure modeling suggested that some carts lost part or all of the cysteine-based disulfide bridges. Quantitative-PCR analyses of all cart genes cloned in this research demonstrated that while all carts are mainly expressed in the brain, some cart genes show wider tissue distribution with significant expression in peripheral tissues including the kidney and gonads. Taken together, these findings emphasize the complexity of the piscine cart system.