Live cell imaging shows misdirection of endosome-derived transport tubules in endothelial cells lacking BLOC-2. (A) GFP-CD63 expressing HUVECs were analyzed by live-cell spinning-disc confocal microscopy and demonstrate numerous endosome-derived long transport tubules (arrows) and GFP-CD63-labeled mature WPBs. Scale bar represents 5 μm. (B) Bar graphs showing total number of long transport tubules exiting endosomes per cell estimated by analyzing first frame from 8 cells each from 2 separate experiments, and number of tubules directed to the core of the cell in control and BLOC-2–depleted GFP-CD63-expressing HUVECs (**P < .01). (C) Fourfold magnified 0.3-s interval image sequences (1 to 12) are shown from the boxed region in the micrograph of a control cell on the left. A GFP-CD63–positive long transport tubule (red arrows) exits an endosome and ends on a WPB. Scale bar represents 10 μm. (D) Fourfold magnified 0.3-s interval image sequences (1 to 12) are shown from the boxed region in the micrograph of a BLOC-2–depleted cell on the left. A GFP-CD63–positive long transport tubule (red arrows) exits an endosome but is directed centrally to another endosome. Scale bar represents 10 μm.