Distinct megakaryocytic and erythroid progenitors can be isolated on the basis of <i>Runx1 P2-hCD4</i> expression.

<p>(A) Contour plots of adult BM LK Mk/Ery progenitors. The PreMegE, MkP, PreCFUe and CFUe populations can by distinguished on the basis of cKit, CD41, SLAMF1 (CD150), CD16/32 and Endoglin cell surface expression. (B) Representative FACS plots of P1-GFP/P2-hCD4 expression in PreMegE, MkP, PreCFUe and CFUe subsets. (n = 8). (C) P1-GFP/P2-hCD4 expression in BM MkP-derived cultured CD41⁺ megakaryocytes. (n = 4). (D–H) CFU-C activity of <i>WT</i>, <i>P1</i>^<i>+</i><i>P2</i>^<i>-</i> and <i>P1</i>^<i>+</i><i>P2</i>^<i>+</i> PreMegEs. Cells were cultured either in pro-myeloid semi-solid methylcellulose-based medium (D) or in pro-megakaryocytic collagen-based MegaCultTM medium (F). Photographs of representative PreMegE-derived methylcellulose (E) and MegaCultTM (G) colonies. (n = 5) (H) Numbers of megakaryocytes per MegaCultTM CFU-Mk colony from 3 independent experiments (mean ± SD, Mann-Whitney <i>U</i> test). (I) Contour plots of OP9 co-cultured PreMegE cells isolated on day 7 and stained with CD41 and Ter119 antibodies. (J) Quantification of CD41⁺ megakaryocytes and Ter119⁺ erythrocytes in the PreMegE/OP9 co-culture assays. (n = 5). (K) Representative FACS plots of PreMegE cells following short-term (12 hours) culture in pro-myeloid liquid medium. Top: CD150/CD41 expression of LK CD16/32^- progenitor cells. Middle: Endoglin/CD150 expression of LK CD41 negative CD16/32 negative progenitors. Bottom: <i>P1-GFP</i>/<i>P2-hCD4</i> expression of immunophenotypic PreMegE (LK CD41- CD16/32- Endoglin- CD150⁺) cells (n = 3).