The Role of Microtubules in Pigment Translocation in Goldfish Xanthophores.

In xanthophores, microtubules were observed to radiate out from the microtubule organization center which was also the center of a central pigment mass. A similar pattern of microtubules was identified in both cells with dispersed or aggregated pigments. Brief vinblastine incubation, which depolymerized the microtubules of pigment-aggregated cells, failed to disrupt the central pigment mass. Subsequent removal of the vinblastine and the addition of ACTH dispersed pigment granules before the reassembly of microtubules. These results suggest that a radiating microtubular system is not essential to the maintenance or the dispersion of the aggregated pigment mass. Prolonged incubation with vinblastine eventually dispersed the aggregated pigment mass even in an ACTH-free medium, suggesting that certain components responsible for pigment association were finally destroyed by vinblastine. Moreover, these dispersed pigments could be induced to reaggregate into small clusters in the absence of microtubules, and finally into a large, tight aggregate when the microtubule system was fully reconstituted. We thus conclude that microtubules may serve to guide the centripedal movement of small pigment clusters toward the cell center, and they may not be essential to pigment dispersion and the maintenance of the central pigment mass.