Mx-Cre–mediated deletion of the Gata1 gene in adult mice affects megakaryopoiesis. (A) Wright-Giemsa staining of peripheral blood smears prepared from the Gata1^fl/y::Mx-Cre⁺ (KO-Mx) and the control mice. The arrowheads indicate platelets. Scale bar represents 10 μm. (B) Histologic examination of spleen sections prepared from the KO-Mx and the control mice. HE indicates hematoxylin and eosin staining; AchE, acetylcholinesterase staining. Original magnification ×100. Scale bar represents 40 μm. (C) Immunohistochemical analysis of spleen using anti-Gata1 antibody (N6). The insets represent higher magnifications of the red square areas. The arrows in the right panel indicate multinuclear megakaryocytes negative for Gata1 immunostaining. Original magnification ×100. Scale bar represents 40 μm. (D) Megakaryocyte ploidy classes in the KO-Mx (■) and control (□) BM cells. (E) Rate (%) of proplatelet formation in cultured megakaryocytes in BM prepared from KO-Mx and control mice. Results are shown as mean plus or minus SD (error bars) from 3 mice (*P < .05 for KO-Mx compared with controls).