Fig. 2. Melanosomes are transported to the keratinocyte along filopodia. (a) A scanning view of a melanocyte dendrite (MD) contacting a keratinocyte (KC) is shown. The boxed area is shown in detail in sequential images taken every 8 seconds from movies made from this area (jcs.biologists.org/supplemental or www.urmc.rochester.edu/derm/scottmovies.html ). A filopodia arising from the lateral aspect of the dendrite is either attached or inserted into the keratinocyte membrane. A string of melanosomes (approximately six of them) moves in single file toward the keratinocyte (2-5). The arrowhead indicates the leading melanosome. The last image (6) shows the same melanocyte in which the melanocyte dendrite (arrowhead) is markedly attenuated. A long filopodia (arrow) is shown in which three melanosomes are present. (b) A scanning view of a melanocyte dendrite (MD) adjacent to a keratinocyte (KC) is shown. The hatched line delineates the KC membrane in the upper right hand corner. The boxed area is shown in detail in images that span 152 seconds. A string of melanosomes (approximately four of them; arrowhead) is present within a projection arising from the side of the body of the melanocyte dendrite. These projections were frequently observed in melanocytes and were shorter and thicker than filopodia. Other similar projections are present (asterisks). (c) Melanocytes and keratinocytes separately labeled with DiI (red fluorescence) and DiO (green fluorescence), respectively, were co-cultured and irradiated. Representative images taken with filters to detect both green and red fluorescence in the range of the two dyes are shown. Sham-irradiated cells showed approximately 1% of keratinocytes with yellow fluorescence (arrows; 1). 24 hours after irradiation approximately 10% of keratinocytes show yellow fluorescence (arrow) when viewed with filters to detect DiI and DiO, indicating membrane fusion (2). Bar, 50 µm.

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