Ultrastructural aspects of melanization of hamster Ab amelanotic melanoma in primary cell culture

When the hamster Ab amelanotic melanoma has been grown as subcutaneous transplants in hamsters, melanin and identifiable melanosomes have never been observed by electron microscopy. When the cells were placed in primary cell culture, melanosomes of a granular type which contained small amounts of melanin appeared during the first 24 hours of cell culture. As the cultures grew older, the number and degree of melanization of the melanosomes increased, and eventually after 3-5 days they were found in all melanoma cells.