Isoform-specific functional roles of PIP5KI in megakaryocytes and platelets. (A) PIP5KI-α/β double knockout platelets have impaired generation of the second messenger Ins(1,4,5)P3 following activation with the platelet agonist, thrombin. (B) In contrast, PIP5KI-γ knockout platelets produce normal amounts of Ins(1,4,5)P3 after thrombin stimulation. (C) However, megakaryocytes differentiated from progenitor cells of PIP5KI-γ knockout mice display defective anchoring of their cellular membrane to their underlying cytoskeleton. This is shown in the confocal images of megakaryocytes bound to immobilized fibrinogen and stained with green fluorescence protein (GFP) fused to the PLC-δ pleckstrin homology domain. (D) Schematic cartoon illustrating defective plasma membrane attachment to the cytoskeleton in the PIP5KI-γ knockout megakaryocytes compared with the wild-type megakaryocytes when analyzed by an optical trap (laser tweezers).
