Effect of megakaryocyte depletion on osteoblast thickening. (A) Flow cytometric analysis of peripheral blood at days 0, 3, and 6 of DT injections showing depletion of peripheral platelets (top) and flow cytometric analysis of BM from PF4/iDTR mouse after 5-day treatment with DT and 48 hours after irradiation showing depletion of CD41⁺ cells (below). (B) Mean platelet counts decreased by 85% compared with DT-treated controls. (C) IF-stained sections (20× top; 40× middle) of BM metaphysis showing significant CD41 (red) depletion and thickening of GFP (green)-labeled osteoblasts in PF4/iDTR × Col2.3GFP triple transgenic mice and PF4Cre^– controls treated with DT and 48 hours after irradiation. H&E-stained sections (40× bottom) of PF4/iDTR and PF4Cre^– control mice demonstrating similar osteoblast thickening. (D) Analysis of osteoblast thickness in PF4Cre DT depletion compared with PF4Cre^– controls shows increased osteoblast thickness compared with irradiated controls (cell thickness, 7.51 ± 0.62 μm vs 7.16 ± 0.43 μm; P = ns). RBC, red blood cell.