CK2β is strongly expressed in MKs and platelets, and CK2β deficiency results in macrothrombocytopenia, reduced platelet life span, and an increased amount of immature reticulated platelets. (A) Representative image (bottom) and arithmetic means ± standard errors of the means (n = 6; top) of CK2β transcript levels in platelets and kidneys from ck2β^fl/fl and ck2β^−/− mice indicating a cell-specific knockout of CK2β in the MK/platelet lineage. (B) Representative immunoblots of CK2β protein levels of MKs (top) and platelets (bottom) from ck2β^fl/fl and ck2β^−/− mice (n = 4) confirming a complete knockout of CK2β in the MK/platelet lineage. (C) Count and mean platelet volume (MPV) of ck2β^fl/fl (blue diamonds) and ck2β^−/− (gray diamonds) platelets (n = 24). Each diamond represents 1 individual mouse. (D) Endogenous survival of ck2β^fl/fl (blue trace) and ck2β^−/− (gray trace) platelets measured by the determination of the percentage of fluorescently labeled platelets in vivo at indicated time points after injection of DyLight 488 α-GPIX (n = 6). (E) Flow cytometric quantification of the percentage of new, reticulated platelets as a percentage of total platelets in ck2β^fl/fl and ck2β^−/− mice. Arithmetic means ± standard errors of the means (n = 6) are shown. (F) TPO levels of ck2β^fl/fl (blue bar) and ck2β^−/− (gray bar) mice. Arithmetic means ± standard errors of the means (n = 15) are shown. (G) Platelet counts of ck2β^fl/fl and ck2β^−/− mice before and 4 days after treatment with TPO (2 µg/animal per day). Arithmetic means ± standard errors of the means (n = 8) are shown. Unpaired Student t test in panels A and D-G. *P < .05; **P < .01.