Endosomal tubules dynamically contact melanosomes. (A) Spinning-disc confocal microscopy was used to capture concomitant movements of Tf-positive endosomes (green) and melanosomes (red). (a) View of an entire cell at 30 min after Tf uptake and a magnified view of the boxed area (b) are shown. Fluorescently labeled endosomes are distributed throughout the cell and are frequently observed in close contact with melanosomes as shown in the inset (b, arrows). Note that in regions of the cell with fewer melanosomes (e.g., at the periphery of the cell), Tf-positive endosomes also appear to contact melanosomes (a, arrowheads). (B) Consecutive time-lapse images and corresponding binary-rendered images of the boxed region illustrated in A during 50 s are presented as a gallery. Note that melanosomes are found in close contact with endosomes (arrows). (C) The intensity of the Tf-A488 signal within 5 pixels (645 nm) of melanosomes was measured during the length of the time-lapse acquisition. Graphs represent the frequency of distribution of binned Tf-A488 intensities in the vicinity of all tracked melanosomes in the cell (black graph) and all melanosomes within the boxed region in A (red graph). Note the coincidence between both melanosome and endosome densities. (D) The intensity of the Tf-A488 signal was measured as in C, and the averaged time (mean frame number) of contact between individual, tracked melanosomes with individual Tf-A488–binned objects (red graph) was evaluated. Note that the time of contact between melanosomes and endosomes is stable regardless of the density of melanosomes (Video 1). Bars: (A) 10 µm; (B) 2 µm.