Figure 8.

Two-phase model of neuronal fate specification in the neocortex. A schematic model of cellular and genetic cascades underlying early and late stages of neuronal phenotype specification in the neocortex. The early phase (<E14.5) is dependent on Ngn1/2, which induces expression of cortical, glutamatergic and lower-layer specification programs, while simultaneously repressing the differentiation of GABAergic neurons. The late phase of neuronal fate specification (>E14.5) occurs in the absence of Ngn1/2 activity, and is dependent on synergistic interactions between Tlx and Pax6, which specify a cortical and glutamatergic identity while repressing a GABAergic phenotype.