The Role of Microtubules in Pigment Translocation in Goldfish Xanthophores.

Characterization of a novel filament system in goldfish xanthophores

“…A2 filaments are distinct from microtubules based on obvious differences in (1) subunit protein molecular weight, (2) fiber diameter, and (3) subcellular distribution (A2 filaments in xanthophores did not converge to an perinuclear focus typical of cytoplasmic microtubules in interphase cells). Furthermore, while microtubules do not change their cytoplasmic distribution during pigment aggregation or dispersion in xanthophores [Chen and Wang, 1993], A2 filaments do re-organize from a loose meshwork during pigment dispersion to a radial array during pigment aggregation. Finally, A2 filaments remained intact when treated with the microtubuledepolymerizing drug, vinblastine.…”

“…Pigment aggregation towards the cell center was shown to depend on the integrity of microtubules [Tchen et al, 1988;Chen and Wang, 1993] and dephosphorylation of a p57 protein on carotenoid pigment granules was shown to be coincident with aggregation [Lynch et al, 1986]. Intermediate filaments were identified in xanthophores and shown to be biochemically distinct from vimentin, consisting of four polypeptides of 60, 45, 56, and 51 kD [Walker et al, 1985].…”

“…In xanthophores, pigment dispersion apparently did not involve microtubules [Chen and Wang, 1993] while ATP, F-actin, and phosphorylation of a p57 protein of carotenoid droplets were proposed to be indispensable for this event [Lynch et al, 1986;Tchen et al, 1988;Yu et al, 1990]. Treatment with anti-actin antibody, phalloidin, or DNAase in digitonin-treated xanthophores completely inhibited pigment dispersion [Yu et al, 1990].…”

“…The criteria for cytoskeletal involvement in pigment translocation has relied on how this process was affected by treatments with drugs or other agents that perturb a specific component of the cytoskeleton [Chen and Wang, 1993]. The other criterion included observable changes in cytoskeletal distribution that occurred coincident with pigment movement [Leonova, 1992;Palazzo et al, 1989a].…”

Morphological studies on the mechanisms of pigmentary organelle transport in fish xanthophores and melanophores

“…High-resolution scanning electron microscopy, however, demonstrated that CD are attached to intermediate filaments in fractured xanthophores (Lim et al, 1987). This intermediate filament system showed unique reorganizing characteristics in response to pigment aggregation (Wang et al, 1997), with microtubule involvement in CD translocations (Chen and Wang, 1993). In the squirrelfish erythrophore, a fast translocator with numerous microtubules and large CD, intermediate filaments were implicated to hold CD in position and coordinate their movements during transport (Murphy and Grasser, 1984).…”