Yellow Catfish Leptin:Gene Cloning, Tissue Expression And Its Relationship With Lipid Metabolism

Leptin, a16-kDa hormonal product of the obese (ob) gene, is a member of the class-I alpha helical cytokines secreted primarily by adipose tissue, it functions in regulating feed intake, energy balance, reproduction, hematopoiesis, immune response, and bone formation in mammals, but information regarding its role in teleosts is still limited. In the present study, full-length mRNA sequences of leptin, leptin receptor and leptin receptor overlapping transcript in yellow catfish were identified. Besides, the lipid metabolism during the ovarian development of yellow catfish was evaluated.1. The validated cDNA of yellow catfish leptin (ycLEP), leptin receptor (ycLEPR) and LEPROT were1119bp,4195bp and827bp in length, encoding the peptide of172,1086and130amino acid residues, respectively.The tissue expression patterns of ycLEP, ycLEPR and ycLEPROT mRNA was analyzed with real-time quantitative PCR (Q-PCR) with β-actin as a reference gene. The ycLEP mRNA expression levels were observed to be highest in liver. The ycLEPR and ycLEPROT mRNA levels were the highest in pituitary.2. The lipid metabolism during the ovarian development were evaluated by determining morphological parameters and lipid content, and by studying the activity and/or expression of various genes involved in lipid metabolism. All of these changes indicate a common strategy of lipid metabolism in fish, consisting of two distinct phases. The first phase is characterized by lipid accumulation in storage sites and results from the promotion of the specific transfer of liver lipid to those stores, dietary absorbed fat or lipogenesis while the second phase is characterized by lipid depletion from storage sites and results from the stimulation of lipolys is and specific transfer of lipid to ovary and the inhibition of dietary absorbed fat and lipogenesis.Leptin mRNA level peaked in liver, brain and ovary at stage Ⅲ, perhaps indicating leptin signals the amount of fat stores to the brain to indicate energy stores are adequate for the normal ovarian development. Whereas the low mRNA levels of leptin and leptin receptor at stage V-spawning in brain may signal the successful completion of maximum accumulation of various lipids and the beginning of spawning.