Leptin is a recently identified protein product of the mouse obese gene. Mice with mutations in the obese gene that block the synthesis of leptin have been found to be obese and diabetic and to have reduced activity, metabolism and body temperature. cDNA clones encoding leptin have been isolated from human, simian, mouse and rat cells. Human leptin shares approximately 84% sequence identity with the mouse protein. Human Leptin cDNA encodes a 167 amino acide residue protein with a 21 amino acid residue signal sequence that is cleaved to yield the 146 amino acid residue mature protein. The expression of leptin mRNA has been shown to be restricted to adipose tissue. Leptin plays an important role in reproduction, immunological response and neuroendocrine signaling.