Fig. 7. Model for the establishment of the MH neurogenesis pattern. The entire MH territory is competent to become a proneural cluster. Within this domain (left), the activities of Ngn1 and Coe2, their positive crossregulation of expression and their sensitivity to the lateral inhibition machinery are crucial elements controlling the commitment of progenitors towards neuronal differentiation. At the MHB, however, Her5 exerts an early inhibition on the expression of ngn1 and coe2, preventing the specification of a proneural cluster and the initiation of neurogenesis in this location, generating the IZ (right panel). As a result, neurogenesis is spatially restricted to the vcc and r2 (left panel).