Localization of kinesin and cytoplasmic dynein in cultured melanophores from Atlantic cod, Gadus morhua.

In this study we have analyzed pigment translocation in cultured melanophores from the cold-tempered Atlantic cod, Gadus morhua. The transport process was found to be cold-adapted, as it proceeded at low temperatures. Both the typical morphology of the melanophores with long cytoplasmic processes, and the ability to translocate pigment granules, were found to be highly dependent on microtubules. Microtubules in melanophores were relatively stable to vinblastine treatment compared to microtubules in other skin cells. Extensive posttranslational modifications of tubulin were found. Detyrosinated and polyglutamylated microtubules were frequent, while acetylated microtubules only comprised a subpopulation or domains of microtubules. Both cod kinesin and dynein were distributed in a punctate pattern throughout the melanophores in close proximity to microtubules. The motors accumulated together with pigment granules during aggregation and were dispersed during translocation of pigment granules to the periphery. Individual melanosomes were occasionally found to rapidly change direction during translocation. Our data raise the interesting possibility that both kinesin and dynein are bound to pigment granules. This is of functional significance, since pigment granules are transported back and forth in the melanophores, and may be activated differently during aggregation and dispersion to generate translocation.