Several model systems have been developed to investigate intracellular organelle motility. A relatively novel system that is simple but useful for studying mechanisms of organelle motility is the fish retinal pigment epithelial (RPE) cell. Primary cultures of dissociated RPE cells are easily prepared and amenable to organelle motility studies. In vivo, melanin-containing pigment granules (melanosomes) within the RPE migrate long distances in response to light flux. When cultured in vitro, RPE cells attach to the substrate with the apical projections extending radially from the central cell body. Melanosomes can be chemically triggered to aggregate or disperse throughout the projections, and can be easily observed using phase contrast microscopy. Melanosome migration in RPE apical projections is dependent on actin filaments, and thus renders this model system useful for investigations of actin-dependent organelle motility.
