Fig. 8. Model of Numb function during cortical development. Numb asymmetry generates differences between sister cells at different stages of development. At E10, asymmetric Numb distribution generates different Nestin⁺ progenitor cells. At E13, besides asymmetric progenitor divisions (not shown) Numb generates asymmetric P/N and N/N divisions. Numb may function by inhibiting Notch activity in some or all of these divisions. For example, during E13 P/N divisions Numb may inhibit Notch activity in one daughter of a radial glial cell to make it differentiate into a neuron. At N/N divisions, Numb may inhibit Notch in one daughter to generate a different neuron type.