Crossinhibitory activities of Ngn1 and Math1 allow specification of distinct dorsal interneurons

Distinct classes of neurons are generated from progenitor cells distributed in characteristic dorsoventral patterns in the developing spinal neural tu be. We define restricted neural progenitor populations by the discrete, non overlapping expression of Ngn1, Math1, and Mash1. Crossinhibition between t hese bHLH factors is demonstrated and provides a mechanism for the generati on of discrete bHLH expression domains. This precise control of bHLH factor expression is essential for proper neural development since as demonstrate d in both loss- and gain-of-function experiments, expression of Math1 or Ng n1 in dorsal progenitor cells determines whether LH2A/B- or dorsal Lim1/2-e xpressing interneurons will develop. Together, the data suggest that althou gh Math1 and Ngn1 appear to be redundant with respect to neurogenesis, they have distinct functions in specifying neuronal subtype in the dorsal neura l tube.