Ontogeny of the expression of leptin and its receptor in themurine fetus and placenta

Leptin is a 167-amino acid protein that is secreted from adipose cells and expressed in placental tissues. It is important nutritionally in the regula tion of energy balance, but also has other functions such as a role in repr oduction. To investigate the function of the leptin system in fetal develop ment we examined, primarily by in-situ hybridization and immunohistochemist ry, the expression (both mRNA and protein) of leptin and its receptor (incl uding the signalling splice variant) in tissues from 11.5, 13.5, 16.5 and 1 8.5 d postcoitus murine fetuses and associated placentas. We detected lepti n mRNA (at low levels) and protein predominantly in the cytotrophoblasts of the labyrinth part of the placenta, an area of nutrient exchange between t he developing fetus and the placenta, and in the trophoblast giant cells si tuated in the junctional zone at the maternal interface. In addition, lepti n was strongly expressed in the fetal cartilage-bone and at a lower level i n the hair follicles, heart, and liver of the murine fetus at differing sta ges of development. The leptin receptor, including the signalling splice va riant, was also identified in specific fetal tissues. The physiological imp ortance of expression of both leptin and the leptin receptor (OB-R and OB-R b) in the placenta remains to be determined. In addition, the high levels o f expression of leptin and its receptor in discrete areas of the murine fet us suggest that leptin has a critical role in fetal development.