Effect of down-regulation of BUBR1 via RNAi. Down-regulation of BUBR1 in vitro via RNAi stimulates CFU-Mk's although BUBR1 haploinsufficiency causes an inhibition in platelet production. (A) Enriched bone marrow progenitor cells from wild-type mice were transfected with or without siRNAs targeting BUBR1 or luciferase for 2 days. Equal amounts of cell lysates were blotted for BUBR1 or α-tubulin. (B) Bone marrow progenitor cells transfected with siRNAs targeting BUBR1 or luciferase for 2 days were split for CFU-Mk assays as described in “Materials and methods.” (C) Bone marrow cells from both wild-type or BUBR1^+/– mice were used for purification of murine megakaryocytes and proplatelet assays as described in “Materials and methods.” Two typical proplatelet-producing megakaryocytes are shown. Original magnification, × 200. (D) The percentage of proplatelet-producing megakaryocytes in bone marrow cell–derived cultures. The proplatelet-producing megakaryocytes in wild-type cell cultures were arbitrarily set at 100%. The data are summarized from 3 independent experiments. Error bars represent means ± standard deviation.