Reporter gene expression allows for the identification of functionally distinct populations. (A-C) Cloning frequency of seeded single cells (left), and FACS plots from representative clones generated from single Rag1^low or λ5Tg⁺ CLPs (right). Single cells were sorted directly into the cultures based on the expression of surface markers and reporter genes. LMPPs were sorted as LIN^−/lowSCA1^highKIT^highFLT3^high, whereas CLP (Rag1^low, Rag1^high, and λ5Tg⁺) and FrA (Rag1^high and λ5Tg⁺) subpopulations were sorted as shown in Figure 1A. (A) Data from cocultures of single-sorted cells on OP9 stroma cells under B cell–promoting conditions. Bars represent total frequency of clones and frequency of clones containing CD19⁺ B cells (B). (B) Data from cocultures of single-sorted cells on OP9 stroma cells under conditions promoting NK-cell development. Bars represent the total frequency of clones as well as the frequency of clones containing only CD19⁺ B-lineage cells (B), NK1.1⁺ and CD19⁺ cells (B/NK), or only NK1.1⁺ cells (NK). (C) Data from cocultures of single-sorted cells on OP9DL1 stroma cells to stimulate the development of THY1.2⁺ T-lineage cells. Bars represent total cloning frequency, the frequency of clones with only CD19⁺ cells (B), THY1.2 and CD19⁺ cells (B/T), or only THY1.2⁺ (T). Data in graphs represent average (range) from 2 independent experiments analyzing approximately 96 seeded cells.