α-granule protein deficiencies in VPS16B null platelets. Immunoblots comparing platelet (PLT) whole-cell lysates or plasma from VPS16B null and normal (N) neonatal sources as indicated for each lane. Significantly reduced PF4 (A), β-TG (B), TSP1 (D), VWF (E), and fibrinogen (G) content in VPS16B null platelets (lane 2) compared with control neonatal platelets (lane 1) were observed. Platelet osteonectin (C) and P-selectin (H) were undetectable in VPS16B null platelets (lane 2) compared with normal neonatal (lanes 1). (F) In contrast, VWF was present at roughly equivalent quantities (0.5 μL plasma/lane) in VPS16B null plasma (lane 2) compared with normal neonatal plasma (lanes 1). Lysate from equivalent numbers of platelets was loaded on each gel. Equivalent protein loading is indicated by visualizing actin or GAPDH on the same immunoblot. Panels A through C were probed and developed simultaneously using primary rabbit antibodies (PF4, β-TG, osteonectin) and mouse antibodies (actin, GAPDH). (A-D) Reduced 15% SDS-PAGE. (E-F,H) Reduced 8% SDS-PAGE. (G) Nonreduced 8% SDS-PAGE.