Scl^–/Δ mice show defective platelet production and megakaryocyte hyperploidy. (A) Thrombocytopenia seen in Scl^–/Δ mice. Mice of the indicated Scl genotypes were bled more than 1 month following PI-PC treatment, and platelet counts were determined using a blood analyzer. Results are the mean + standard deviation of 5 mice in each group. (B) Measurement of platelet lifespan. Mice were treated with N-hydroxy-succinomidyl biotin on day 0 and the percentage of biotinylated platelets determined daily using flow cytometry (top panel). Relating this value to the determined platelet count yielded the number of nonbiotinylated platelets (bottom panel). Data are mean ± standard deviation of quadruplicate determinations. (C) Megakaryocyte frequency in the bone marrow of Scl^+/Δ and Scl^–/Δ mice. Sternal bone marrow sections were prepared and analyzed using light microscopy. The number of megakaryocytes per 400 × microscopic HPF is indicated for each genotype. Results are the mean + standard deviation of 15 adjacent fields analyzed for 4 separate mice. (D) Hyperploidy of Scl^–/Δ megakaryocytes. The DNA content of bone marrow megakaryocytes was determined using propidium iodide staining and flow cytometry. The level of staining corresponding to the numbers of haploid genomes (N) contained in each cell is indicated. Data are representative of 3 separate mice of each genotype analyzed.