Runx1^Δ/Δ cells with a Pcgf1 knockdown reveal immature characteristics. (A) Lin⁻ cells isolated from the BM of Runx1^Δ/Δ or control mice (Runx1^fl/fl) transduced with an shRNA targeting Pcgf1 (shPcgf1) or a scrambled shRNA (shCtrl) plated into methylcellulose at indicated time points are shown. Note the formation of similar colonies after 1 week (i-ii), in contrast to the dense colonies that lack mature-looking cells after 8 weeks of replating of the Runx1^Δ/Δ cells transduced with the Pcgf1 shRNA (iii). Cytospins of cells from subpanel iii stained with May-Grünwald-Giemsa revealed a blast-like appearance (iv). (B) FACS immunophenotyping of Runx1^Δ/Δ cells with Pcgf1 knockdown after 9 weeks of serial replating in methylcellulose. Cells were stained with the indicated Abs. The lower left quadrant was set according to the appropriate isotype controls. The percentage of cells measured in the gated populations is indicated.