In vivo–enforced expression of miR-146a in hematopoietic stem/progenitor cells does not alter circulating platelet or white blood cell counts. (A) Experimental approach. Lineage-depleted bone marrow cells were transduced with MDH-GFP retroviruses expressing miR-146a or an irrelevant microRNA (miR-195) as control and transplanted into lethally irradiated recipients. Hematopoietic reconstitution was analyzed 4-16 weeks after transplantation. (B) Q-PCR analysis of miR-146a expression in circulating mononuclear cells at 9 weeks after BMT; n = 5 mice from each group. Error bars represent SD of the mean. The control group was arbitrarily assigned the value 1. P = .0005. (C) Analysis of circulating platelets 9 weeks after bone marrow transplantation. Platelets were stained with anti-CD42 antibody and analyzed for GFP expression. GFP⁺ platelets were derived from retrovirus-infected donor hematopoietic cells. The GFP^– portion of total platelets were derived from noninfected donor cells or residual host cells. Note that miR-146a-overexpressing mice and controls do not differ with respect to total platelet count (P = .43) or the proportion of GFP+ platelets (P = .40). There were n = 5 mice analyzed for each group. Similar results were obtained from the same mice at 4 and 12 weeks after transplantation. (D) Total and GFP⁺ white blood cells 9 weeks after transplantation, analyzed as described for panel C. White blood cells were identified by forward- and side-scatter analysis of whole blood. Similar results were obtained from the same mice at 4 and 12 weeks after transplantation.