Rab3B is detectable on WPBs before Rab27A and colocalizes with Slp4-a. (A) HUVECs immunolabeled for endogenous Rab3B (mouse Ab, green), Slp4-a (rabbit Ab, red), and VWF (sheep Ab, blue). Here and in other figures, grayscale images are from regions indicated by white boxes. (B) HUVECs expressing Proregion-EGFP (Pro-EGFP, green, 24 hours after nucleofection) immunolabeled for endogenous Rab3B (mouse Ab, red). Grayscale images represent regions with perinuclear immature (right) or peripheral mature WPBs (bottom). (C) HUVECs immunolabeled for Rab3B (mouse Ab, red), Rab27A (rabbit Ab, green), and VWF (sheep Ab, blue). Insets: right, arrowheads point to Rab3B-positive, Rab27A-negative perinuclear immature WPBs; bottom, Rab3B- and Rab27A-positive mature WPBs. (D) HUVECs immunolabeled for Rab3B (goat Ab; red), Rab27A (mouse Ab, green), and Slp4-a (rabbit Ab, blue). Inset: right, Rab3B-positive, Rab27A-negative, Slp4-a-positve perinuclear immature WPBs; bottom, mature WPBs positive for all markers. Scale bars represent 10 μm.