Leptin, the protein product of the ob gene , is produced mainly in adipose tissue and plays an important role in the regulation of energy expenditure , appetite , body weight . Leptin receptor OB- R receptor is a class I cytokine family , and is produced in several isoforms produced by alternative splicing of the transcript. It is believed that only long-chain functional isoform of the receptor is a receptor for the protein. Leptin receptor OB- R activates the Janus kinase (JAK ) and STAT transcription factors .