Evidence for several roles of dynein in pigment transport in melanophores.

Melanophores are specialized cells that transport pigment granules to and from the cell center, giving animals the ability to change skin color. A kinesin-related plus-end motor has previously been shown to be responsible for pigment granule dispersion [V.I. Rodionov, F.K. Gyoeva, and V.I. Gelfand. Proc. Natl. Acad. Sci. USA. 1991, 88:4956-4960]. Here, we have microinjected a dynein antibody (70.1) into cultured cod (Gadus morhua) melanophores and used the dynein inhibitor vanadate on permeabilized melanophores in skin pieces, to examine the role of the microtubule minus-end motor dynein in these cells. Both pigment granule aggregation and maintenance of the spherical central pigment mass (CPM) were inhibited by the antibody and by vanadate. Vanadate or antibody treatment of cells with aggregated pigment did not induce pigment dispersion. However, when the antibody-injected cells were induced to disperse pigment, the pigment moved farther to the cell periphery, which resulted in a depletion of pigment in the cell center. Similar superdispersion of previously uniformly distributed pigment was also seen when the antibody was injected in melanophores with dispersed pigment. Our results demonstrate that both pigment aggregation and maintenance of the CPM are dynein-dependent processes. Our data further show that dynein is involved in the homogeneous distribution of dispersed pigment. These results suggest that both dynein and kinesin are active in keeping pigment granules dispersed throughout the cytoplasm, transporting pigment granules in opposite directions. The possibility that dynein is continuously active during both aggregation and dispersion, while kinesin might be the target for regulation, is discussed.