Figure 8.
Models of the responses of individual hematolymphoid precursors to Notch/Delta signaling. Effect of culture on OP9-DL1 or OP9-control for precursors with ability to delay T/B-lineage commitment. (Left) Fast-responding cells behave as bipotent precursors described by the standard instructive model for Notch/Delta signaling: deterministic model of Notch actions in T-cell development. In this model, the activation of the T-cell alternative automatically excludes the B-cell alternative. (Right) This model does not explain the persistence under polarizing conditions of cells with the capacity for both, as seen in the slow responding cells. In this model, different precursors can respond asynchronously to Notch/Delta signaling or its absence. Cells remaining “multipotent” in this model, as T- or B-cell development is first being induced in other cells, are capable of making the transit to T- or B-cell differentiation at a later time, as permitted by culture conditions, as shown in Figure 5B and D.