Decreased number and abnormal DGs in Rab32/Rab38 DKO mouse platelets. (A) TEM images showing the ultrastructure of WT and DKO platelets. Right, the close-up views illustrate the various abnormal DG morphologies in DKO mice. Images are representative of at least 3 independent platelet preparations. Scale bar, 1 µm. (B) Evaluation of mepacrine uptake by WT and DKO platelets. Bar graph represents the percentage of mepacrine-positive resting or degranulated platelets (prestimulation with 1 U/mL thrombin) following incubation with 10 µM mepacrine for 30 minutes (n = 3 independent experiments). ***P < .001 using 1-way ANOVA. (C) FIB/scanning electron microscopy images and 3D reconstructions of whole platelets. (Right panel) Dark spots represent DGs reconstructed by drawing the granule membranes on each slice. Note the heterogeneity of the size of the DGs in both genotypes. (Left panel) Quantification of the number of DGs per platelet using 3D FIB/scanning electron microscopy reconstructions (n = 25). (D) TEM images showing the presence of normal MVBs in DKO mouse MKs differentiated in culture from Lin⁻ cells compared with WT. Images are representative of at least 20 MKs. Scale bars, 500 nm.