THE INTERACTION OF AGOUTI SIGNAL PROTEIN AND MELANOCYTE-STIMULATING HORMONE TO REGULATE MELANIN FORMATION IN MAMMALS

Important regulatory controls of melanogenesis that operate at the sub cellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are revi ewed. Melanocyte stimulating hormone and agouti signal protein have an tagonistic roles and possibly opposing mechanisms of action in the mel anocyte. In the mouse, melanocyte stimulating hormone promotes melanog enic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin productio n and elicits the synthesis of pheomelanin rather than eumelanin. We a re now beginning to understand the complex controls involved in regula ting this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physio logical consequences for melanocyte function and undoubtedly play impo rtant roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection.