Impaired myelopoiesis by

Cbfb^Cbfb-MYH11/+ ES cells. (A) Hematopoietic colony formation by ES cells heterozygous for a “knocked-in” Cbfb-MYH11 allele, from which the 71-kd CBFβ-SMMHC fusion protein is expressed.41 The average values (± SD) from 5 independent experiments are presented. (B) Colony types formed from Cbfb^+/+ andCbfb^Cbfb-MYH11/+ ES cells. Data represent the mean percentage of colonies of specific lineages per total colonies, followed by SD in parentheses, from 5 independent experiments. The differences between the number of myeloid and EryP colonies formed by the Cbfb^+/+ andCbfb^Cbfb-MYH11/+ ES cells are significant atP < .005 by Student t test. There is no significant difference between the number of EryD or mixed lineage colonies. (C) Cytocentrifuge preparations of hematopoietic cells derived from secondary cultures of Cbfb^+/+ andCbfb^Cbfb-MYH11/+ ES cells. All cells from one plate were collected, washed, counted, and used for cytocentrifugation. The percentage of each cell type (average of 4 experiments ± SD) is indicated below. The differences in erythroid and immature cells between Cbfb^+/+ andCbfb^Cbfb-MYH11/+ ES cells is significant atP < .01 by Student t test. The difference in myeloid cells in the 2 populations is significant atP < .0001.