Ultrastructural observations on melanosome aggregation in genetically defective melanocytes of the mouse.

Cultivated mouse melanocytes with the genotype of D/- and d/d obtained from dorsal skin of infants, and the variant melanoma cells (subline agm) in which melanosomes were aggregated around the nucleus were characterized by means of electron microscopy. In D/- melanocytes, dendrites contained a number of microtubules and 10-nm filaments, mitochondria, endoplasmic reticulum, and peripherally distributed melanosomes. On the other hand, in d/d melanocytes and agm cells, melanosomes were aggregated in the perinuclear region of the cell body. Their fibrous dendrites contained numerous microtubules and 10-nm filaments, mitochondria, and endoplasmic reticulum. It is suggested that the interactive process of melanosomes with cytoskeletal elements is defective in d/d melanocytes, and that a similar defect is present in agm cells.