PIP4Kα resides in or near MK internal membranes. (A) Immunoblot of cultured primary mouse MKs with a specific PIP4Kα antibody detects expression of full-length and truncated (Δ59N) splice variants (asterisks). (B) Indirect immunofluorescence with PIP4Kα antiserum. A representative z-section is shown after deconvolution microscopy. (C) EGFP-fused Δ59N-PIP4Kα was forcibly expressed in primary MKs, and serial z-sections from fluorescence deconvolution microscopy revealed internal (not peripheral or nuclear) localization, in a membrane-associated distribution that resembles the DMS. (D-E) Cultured MKs stained with antibodies against type I PIP kinases reveal that the cellular distribution of these enzymes differs from that of PIP4Kα. Single z-sections are shown after deconvolution. Scale bars: 15 μm.