BIDIRECTIONAL PIGMENT GRANULE MIGRATION IN ISOLATED RETINAL-PIGMENT EPITHELIAL-CELLS REQUIRES ACTIN BUT NOT MICROTUBULES

In the teleost retinal pigment epithelium (RPE), melanin pigment granu les disperse into long apical projections in the Light and reaggregate into the cell body in the dark. To investigate the cytoskeletal mecha nisms responsible for these movements, we have examined the effects of cytoskeletal inhibitors on pigment granule transport in cultured, dis sociated RPE cells using time-lapse video microscopy. The kinetics of pigment granule transport during normal aggregation and dispersion are quite distinct: during aggregation, all pigment granules undergo simu ltaneous, nonsaltatory centripetal movement (mean velocity 3.6 mu m/mi n); during dispersion, individual granules undergo independent, bidire ctional saltatations (mean velocities 3.7 mu m/min centrifugal; 1.1 mu m/min centripetal). Nocodazole disruption of microtubules within the RPE apical projections had little effect on the kinetics of pigment gr anule movement, and essentially no effect on extent of pigment granule aggregation or dispersion, or on maintenance of the fully aggregated or fully dispersed states. In contrast, cytochalasin D (CD) treatment blocked net aggregation and dispersion of pigment granules, and compro mised maintenance of the fully aggregated and dispersed states. These observations suggest that the actin cytoskeleton plays an important ro le in both centripetal and centrifugal transport of pigment granules i n teleost RPE cells. (C) 1997 Wiley-Liss, Inc.