CD41 is expressed exclusively in a fraction of CMPs. (A) Gating strategy for BM HPCs (CMP, GMP, MEP) is shown.⁷  CD41 expression was concentrated in the CD38⁺ IL-3Rα^dimCD45RA⁻ population, which is identical to the CMP immunophenotype. (B) CD41 expression patterns in human BM HSPC fractions (top). CD41 was solely and exclusively expressed in CMPs (7.9% ± 3.2%) but not in GMPs (0.0% ± 0.2%) or MEPs (0.3% ± 0.4%). Representative FACS plots are shown. Morphological characteristics of HSPCs were examined via May-Grünwald-Giemsa staining (scale bars, 5 μm). CD41⁺ CMPs showed immature morphological features resembling those of HSCs and CD41⁻ CMPs. A fraction of CD41⁺ CMPs (1.2% ± 0.8%; n = 3) consisted of polyploid cells, indicating initiation of the endomitotic process for megakaryocyte development (middle). Side-scatter/forward-scatter (SSC/FSC) dot plots of each HSPC fraction (bottom). CD41⁺ CMPs were heterogeneous in size compared with other populations. Polyploid cells were highly enriched in FSC^high fraction (red dotted circle). (C) CD41⁺ CMPs expressed various megakaryocyte lineage markers. To avoid the effects of spectral overlaps, combinations of PE- and APC-conjugated antibodies were used. (D) Single-cell gene expression profiles of CMPs. Most CD41⁺CMPs, but not CD41⁻CMPs, expressed megakaryocyte-specific genes at high levels.