Ck2β^−/−mice display BM MK hyperplasia and an upregulation of extramedullary thrombopoiesis. (A) Representative images of GPIb immunostaining of BM sections from 2-month-old ck2β^fl/fl and ck2β^−/− mice (left). Quantification of ck2β^fl/fl and ck2β^−/− BM MKs per visual field. Arithmetic means ± standard errors of the means (n = 6; right) are shown. (B) Representative images of GPIb immunostaining of spleen sections from 6-month-old ck2β^fl/fl and ck2β^−/− mice (left). Quantification of ck2β^fl/fl and ck2β^−/− spleen MKs per visual field. Arithmetic means ± standard errors of the means (n = 6; right) are shown. (C) Representative H&E staining of spleen sections from 6-month-old ck2β^fl/fl and ck2β^−/− mice (left). Arithmetic means ± standard errors of the means (n = 8; right) of relative spleen weight in ck2β^fl/fl and ck2β^−/− mice. (D) Ploidy histogram of ck2β^fl/fl and ck2β^−/− MKs (left) and arithmetic means ± standard errors of the means (n = 6; right) are shown. Unpaired Student t test. *P < .05; **P < .01.