Experimental pigment donation in vivo

Abstract

The uptake of mouse melanosomes by guinea pig keratinocytes was induced experimentally in vivo without the action of melanocytes. The uptake mechanisms were discriminatory as small melanosomes, isolated from B16 mouse melanomas, were taken up in groups, maintaining membrane-bound aggregates within the cytoplasm of the recipient epidermal cells. By contrast, large melanosomes, prepared from the hair bulbs of C57 BI mice, were incorporated as singles into keratinocytes and were dispersed singly within their cytoplasm. The intracytoplasmic distribution patterns of melanosomes obtained were identical with the distribution patterns which occur normally in keratinocytes of different species and races; the appearance of the single melanosomes and their envelopes as well as that of the aggregated melanosomes and their surrounding membranes did not differ from the single and aggregated melanosomes occurring under normal, physiologic conditions. Since these results were obtained in a system which bypasses the melanocyte, they suggest that the distribution patterns of melanosomes within keratinocytes, i.e., aggregation or dispersion, are independent of the actions of the pigment cell and do not represent different stages of a single, uniform process. They appear to be determined by the mechanisms by which melanosomes are taken up into keratinocytes, and these in turn are influenced by the sizes of the individual melanosomes.