Loss of RhoB leads to microthrombocytopenia and alters microtubule organization in circulating platelets. (A) Blots of platelet lysates from wt and RhoB^−/− mice immunoblotted for the indicated proteins. GAPDH was used as loading control (n = 3). (B) Platelet count assessed by flow cytometry. Each data point represents 1 mouse (n = 12). (C) Mean platelet volume measured with a Scilvet blood analyzer. Each data point represents 1 mouse (n = 7). (D) Platelet size assessed by forward scatter characteristics determined by flow cytometry. Each data point represents 1 mouse (n = 12). (E) Representative images of ultrastructural analysis of resting wt (left) and RhoB^−/− (right) platelets by transmission electron microscopy (TEM). Scale bar overview, 1 µm; inset, 0.5 µm. (F) Quantification of platelet diameter (relation of platelet width to length) of RhoB^−/− platelets relative to wt using TEM images described in panel E (wt n = 4; RhoB^−/− n = 5). (G) Quantification of MT coils per platelet using TEM images described in panel E. MT number was determined by manual count of at least 5 imagesper genotype. Each data point represents 1 single platelet (wt n = 4; RhoB^−/− n = 5). **P < .01; ***P < .001; Mann-Whitney U test, mean plus or minus SD. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.