The C587R mutation sensitizes platelet to apoptosis without compromising megakaryopoiesis. (A) Absolute numbers of reticulated platelets were determined by thiazole orange staining. (B) Average megakaryocyte number per field of view (average of 6 fields per individual mice; n = 5 mice per group). (C) Average platelet count in response to APS-induced thrombocytopenia in C587R/+ mutant and littermate controls; n = 5 mice per group. (D) Average megakaryocyte number per field of view (average of 5 fields per individual mice; n = 3 mice per group) upon APS-induced thrombocytopenia. (E) C587R/+ platelets have a survival defect. Platelet survival curve in C587R/+ mutant and control mice. Platelets were labeled via IV injection of DyLight 488–conjugated anti-GPIbβ antibody. Data represent mean ± SD; n = 6 mice per group. (F) Survival defect is cell-intrinsic. Platelets purified from C587R/+ mice and littermate controls were injected IV into GFP-transgenic recipients to assess their survival; n = 5 mice per group. (G) Loss of proapoptotic gene Bak1 restores survival defect. Platelet survival curve in Bak1^−/−Nxf1^C587R/+ and Bak1^−/− control mice. (H) Platelet counts in response to APS-induced thrombocytopenia in Bak1^−/−Nxf1^C587R/+ and Bak1^−/− littermate controls; n = 3-4 mice per group. (I) Platelets count in splenectomized Bak1^−/−Nxf1^C587R/+ and Bak1^−/− control mice. (J) Absolute numbers of TO⁺ reticulated platelets in Bak1^−/−Nxf1^C587R/+ and Bak1^−/− control mice. (K) Platelet counts in splenectomized Bak1^−/−Nxf1^C587R/+ and Bak1^−/− control mice. (A-B,I-K) Circles and triangles represent cell counts for an individual mouse. Data show mean with SD. *P < .05; **P < .01; ***P < .001; and ****P < .0001. FOV, field of view; GFP, green fluorescent protein; Tg, transgenic; TO, thiazole orange.