Pro- and antiangiogenic regulatory proteins are segregated into separate, distinct α-granules in megakaryocyte proplatelets. Double immunofluorescence microscopy of proplatelets using antibodies against VEGF (A) and endostatin (B) and an overlay (C). Double immunofluorescence microscopy of proplatelets using antibodies against bFGF (D) and TSP-1 (E) and an overlay (F). Double immunofluorescence microscopy of proplatelets using antibodies against fibrinogen (G) and von Willebrand factor (H) and an overlay (I). Double immunofluorescence microscopy of proplatelets against VEGF (J) and fibrinogen (K) and an overlay (L).