CK2β is essential for microtubule architecture and tubulin polymerization as well as EB3 binding to polymerized tubulin. (A) Representative immunofluorescence confocal microscopy images of cultured fetal liver–derived ck2β^fl/fl and ck2β^−/− MKs. α-Tubulin staining appears fragmented in Ck2β^−/− MKs undergoing proplatelet formation. Bar represents 20 μm (overview) and 5 μm (detail). (B) Representative immunoblots of 3 independent experiments of free and polymerized tubulin in ck2β^fl/fl and ck2β^−/− platelets (n = 3) in the absence and presence of paclitaxel (10 μM) in supernatant (sn) and pellet (p). (C) Representative immunoblots of EB3 bound to polymerized tubulin in ck2β^fl/fl and ck2β^−/− platelets (n = 3) after treatment with paclitaxel (10 μM) in supernatant (sn) and pellet (p).