Expression of Rb in polyploid megakaryocytes.

(A) Flow cytometry. Mobilized-blood CD34⁺ cells, cultured for 8 days in the presence of SCF and PEG-rHuMGDF, were labeled with PI (panels Ai, Aii, Aiii, Aiv) and an anti-Rb mAb (panels Aii, Aiv) or an isotype control (panels Ai, Aiii). The cells were acquired in a gate (not shown) excluding aggregates and cell debris. Analysis was performed either in the total cell population (panels Ai, Aii) or in the polyploid cell population (panels Aiii, Aiv). This is a representative flow cytometric profile of an experiment performed 3 times. (B) Rb has a nuclear localization in megakaryocytes. Human megakaryocytes were labeled by indirect fluorescence by means of an anti-Rb mAb and then a secondary TRITC-labeled antibody (panel Bii), and the nucleus was counterstained with DAPI (panel Bi). A similar localization of Rb was observed on 150 megakaryocytes examined.