Spexin-Mediated Dietary Adaptation in Siniperca chuatsi: Molecular Characterisation and Functional Insights into FABP2 Interaction.

Neuropeptide Q (spexin, spx) is a pleiotropic signalling molecule that regulates appetite and metabolism primarily via activation of galanin and melanocortin receptors. Here, we cloned the open reading frame (ORF) of spx from Siniperca chuatsi (Scspx), characterised its spatiotemporal expression, elucidated spx regulatory features during starvation and feed adaptation, and identified SPX-interacting proteins using glutathione S-transferase pull-down and mass spectrometry. The Scspx ORF was 312 bp, encoding 103 amino acids. The predominant expression of spx was found in the liver of feed-trained S. chuatsi, where it was 17.36-fold greater than in muscle. During fasting (0, 3, 5, and 7 d), spx expression in the muscle, liver, and intestine initially increased and then declined, whereas brain and stomach tissues exhibited the opposite tendency. Compared to the smallest individuals, hepatic and brain spx expression was substantially lower in the largest individuals, whereas stomach expression was higher (p < 0.05). Fatty acid binding protein 2 was identified as a novel SPX-interacting partner, implicating SPX in feed adaptation through lipid metabolic regulation via the peroxisome proliferator-activated receptor signalling pathway. Our results provide the first evidence of a direct SPX-FABP2 interaction in fish, pointing to a coordinated role in downstream gene regulation. This work hereby uncovers a novel regulatory axis within the piscine energy metabolism network. These findings provide new insight into the regulatory role of SPX in feed adaptation in S. chuatsi, offering a foundation for genetic analysis.