Studies of mutant mice with light-colored coats have uncovered a pathway in which microtubules and microfilaments cooperate to transport melanosomes. The pigment in mammalian hair is produced in cells called melanocytes, cells that are very similar to the fish and frog melanophores discussed earlier (see Figure 18-29). Melanocytes are found in the hair follicle at the base of the hair shaft and contain pigment-laden granules called melanosomes. Melanosomes are transported to the dendritic extensions of melanocytes for subsequent exocytosis to the surrounding epithelial cells. Transport to the cell periphery is mediated, just as in frog melanophores, by a kinesin family member. At the periphery, they are then handed off to myosin V and delivered for exocytosis. If the myosin V system is defective, the melanosomes are not captured and stay in the melanocyte cell body. Thus microtubules are responsible for the long-range transport of melanosomes, whereas microfilament-based myosin V is responsible for their capture and delivery at the cell cortex. This type of division of labor—long-range transport by microtubules and short-range transport by microfilaments—has been found in many different systems, from transport in filamentous fungi to transport along axons.