Characterization of Leptin and Leptin Receptor Gene in the Siberian Sturgeon (): Molecular Cloning, Tissue Distribution, and Its Involvement in Feeding Regulation.

Leptin is an adipokine known as a regulator of feeding and metabolism in mammals. Previous studies on fish have revealed its role in food intake regulation in limited teleosts. However, its specific function in Siberian sturgeon, an ancient Chondrostei fish, remains poorly understood. This study represents the first successful cloning of sequences for and in Siberian sturgeon, achieved using RT-PCR. The predicted leptin sequence in this species consists of 168 amino acids that exhibit low identity with other fish species, except within the Acipenseriformes order. Tissue distribution analysis revealed a high expression of Siberian sturgeon mRNA in the liver and mRNA in the hypothalamus. Fasting differentially affected the expression of and mRNA, with decreased levels in the hypothalamus and increased levels in the liver (: 3-15 days; : 6-15 days). Recombinant Siberian sturgeon leptin (Ssleptin) was produced via expression, and intraperitoneal injection (100 ng/g BW) significantly inhibited food intake. The anorectic effect was correlated with changes in hypothalamic gene expression, including downregulation of orexigenic factors (, , , and ) and upregulation of anorexigenic factors (, , and ). Meanwhile, the peripheral administration of Ssleptin promoted the expression of in the liver and concurrently increased and mRNA levels in the valvular intestine. Furthermore, Ssleptin injection stimulated the expression of hypothalamic , , , and mRNA. These findings suggest that leptin plays a significant role in the feeding control of Siberian sturgeon and provide new insights into the evolutionary function of leptin in fish.