Differential effect of cytochalasin B on the aggregation of melanosomes in cultured mouse melanoma cells.

Mouse B16 melanoma cells in cultures were treated with 2 microgram/ml cytochalasin B. Melanosomes, localized in dendrites as well as those in the peripheral cell body, formed aggregates which then showed centripetal migration. After 24 hr of treatment, melanosomes were found as large aggregates near the nucleus. However, cytochalasim B showed no effect on the distribution of mitochondria and endoplasmic reticulum. When cells were released from the 24 hr-treatment with cytochalasin B, each melanosome began centrifugal migration. In this process, melanosomes were situated in the periphery, and were in close association with microtubules. Side arm-like structures were observed between microtubules and melanosomes, or mitochondria. These results seem to indicate the presence of mechanism(s) specific to melanosome migration, and possible participation of microtubules in this melanosome migration.