The mandarin fish cart3a gene: Structure, expression, and role in feeding regulation

The mandarin fish ( Siniperca chuatsi ) is a high-quality freshwater aquaculture species. Its lifelong habit of feeding on live prey restricts sustainable industry development, creating a critical need to switch to artificial formulated feed. The anorexigenic factor CART (cocaine- and amphetamine-regulated transcript) has a conserved function in many fish, but its role in mandarin fish remains unexplored. This study systematically investigated the structural characteristics, expression patterns, and physiological functions of the cart3a gene using molecular cloning, bioinformatics, tissue expression profiling, and prokaryotic expression. Results show the cart3a gene encodes a secreted protein with a signal peptide and a conserved CART_CTD-like domain. The N-terminal signal peptide is conserved in related species, while the C-terminal domain is absolutely conserved in all vertebrates. Phylogenetically, mandarin fish CART3a clusters with homologous sequences from perciform species. Cart3a was specifically highly expressed in the brain. Fasting markedly suppressed its brain expression, while a transient peak emerged 6 h after refeeding, indicating precise response to energy status. Intraperitoneal injection of recombinant CART3a protein (30 ng/g body weight) significantly suppressed feeding, accompanied by downregulation of NPY and upregulation of POMC. This study demonstrates for the first time that mandarin fish CART3a is a key energy-status-regulated anorexigenic neuropeptide that modulates the NPY/POMC pathway, offering crucial molecular targets and a theoretical foundation for understanding feeding regulation and developing novel feed domestication strategies.