Depletion of BLOC-2 results in rounded, immature WPBs that are trapped in a post-TGN compartment. (A) IF analyses of BLOC-2 component HPS6-depleted and control HUVECs labeled with anti-VWF antibody and counterstained with DAPI. The insets are 4× magnifications of the boxed regions. Rod-shaped, mature WPBs distributed throughout the cell can be observed in control cells, but only round, immature WPBs, clumped perinuclearly, are evident in BLOC-2–depleted cells. Scale bars represent 10 μm. (B) Fifteen BLOC-2–depleted and control cells were randomly selected and total number of WPBs > 1.5 μM in length were determined for 2 independent studies (***P < .001). (C) Transmission EM analyses of BLOC-2–depleted and control HUVECs showing presence of mature, rod-shaped WPBs (_*) in control cells with characteristic striated appearance, whereas BLOC-2–depleted cells lacked mature WPBs altogether. Instead, only immature WPBs (block arrows) in the vicinity of the Golgi apparatus (+) were observed. Scale bars represent 500 nm (long bar) and 100 nm (short bars). (D) IF analyses of BLOC-2–depleted and control HUVECs dual-labeled with anti-VWF and Rab11 antibodies and counterstained with DAPI. The inset (magnified 4×) highlights colabeling of VWF and Rab11 in BLOC-2–depleted cells. Scale bars represent 10 μm. (E) Bar graph showing Mander’s overlap coefficient of VWF staining on Rab11 and Rab11 on VWF in Con and BLOC-2–depleted cells. Fifteen BLOC-2–depleted and control cells each from 2 experiments were analyzed (**P < .01).