Glycoprotein (GP) Ibα is expressed on the surface of platelets and megakaryocytes and is anchored to the membrane skeleton by Filamin A (FlnA). Whilst GPIb and FlnA have fundamental roles in platelet biogenesis, the nature of this interaction in megakaryocyte biology remains ill-defined. We generated a mouse model expressing either human wild-type (WT) GPIbα (hGPIbaWT) or a FlnA-binding mutant (hGPIbaFW) and lacking endogenous mouse GPIbα. Mice expressing the mutant GPIbα transgene …