The progenitors of pDCs are within stem cell–containing fraction and early lymphoid progenitors, and are negatively regulated by Notch receptor ligation. (A) Lin^-ckit^HiSca1⁺GFP^- (stem cell enriched), Lin^-ckit⁺Sca1^- GFP^-CD34⁺FcγR^Lo (myeloid progenitors), Lin^-ckit^Hi Sca-1⁺GFP⁺ (early lymphoid progenitors), Lin^-ckit^Lo Sca-1^LoGFP⁺ (prolymphocytes), and B220⁺CD19^- CD11c^LoLy6C^- (Ly6C^- cohort) were isolated from RAG1/GFP knock-in mice. Cells (10 000) of each kind were cultured for 8 days on OP9 stromal cells with Flt3-L. Cells were harvested and stained with CD45R/B220 and CD19. The B220⁺CD19^- population was sorted and restained with CD11c and Ly-6C (i). The yield of CD11c^LoLy-6C⁺ pDCs recovered per input precursor is shown in the bar graph (ii). CMP indicates common myeloid progenitors. (B) GFP expression was analyzed in B220⁺CD19^-CD11c^LoLy6C⁺ pDCs recovered from HSCs, ELPs, and Pro-L cultures. (C) Lin^-ckit^Hi Sca-1⁺CD27⁺ ELPs (10 000) from C57BL/6 BM were cultured for 8 days on OP9-GFP or OP9-DL1 stromal cells. The yield of pDCs per input precursor is shown in the bar graph.