JAK2^V617F platelets present a GPVI deficiency. (A) GPVI expression was quantified by flow cytometry (mean fluorescence intensity, MFI) on the platelets of WT (n = 11) and VavCre/JAK2^V617F (n = 24) mice 2 months after BM graft. ***P < .0003. (Bi) Representative (of 3) immunoblots of platelet extracts (10 µg) from 4 different WT mice and 4 different VavCre/JAK2^V617F (KI) mice are shown. The same membrane was stripped and reblotted with antibodies against GPVI (JAQ1), the FcRγ chain, and β-actin. (Bii) The shedding of GPVI was analyzed. One representative immunoblot is shown (n = 3). Platelets from WT mice and VavCre/JAK2 ^V617F (KI) mice were treated or not with NEM. Platelet extracts (10 µg) were immunoblotted using a polyclonal antibody to the intracellular domain of GPVI. GPVI-IC indicates the GPVI remnant cytoplasmic domain that remained associated with platelets after shedding of the extracellular domain. (Biii) Densitometric analysis of the GPVI band from 4 different mice per group. *P < .03. (C) Surface expression of GPVI was measured on SCLCreER^t /JAK2 ^V617F (TM) at different times after administration of tamoxifen (n = 7 for each group). **P < .002. (D) Platelet surface expression of GPVI in TPO^high (n = 9) and EPO-treated mice (n = 3) is shown.