Regulation of neuroD2 expression in mouse brain.

The basic helix-loop-helix (bHLH) transcription factor, neuroD2, induces neuronal differentiation and promotes neuronal survival. Reduced levels of neuroD2 were previously shown to cause motor deficits, ataxia, and seizure propensity. Because neuroD2 levels may be critical for brain function, we studied the regulation of neuroD2 gene in cell culture and transgenic mouse models. In transgenic mice, a 10-kb fragment of the neuroD2 promoter fully recapitulated the endogenous neuroD2 staining pattern. A 1-kb fragment of the neuroD2 promoter drove reporter gene expression in most, but not all neuroD2-positive neuronal populations. Mutation of two critical E-boxes, E4 and E5 (E4 and E5 situated 149 and 305 bp upstream of the transcriptional start site) eliminated gene expression. NeuroD2 expression was diminished in mice lacking neurogenin1 demonstrating that neurogenin1 regulates neuroD2 during murine brain development. These studies demonstrate that neuroD2 expression is highly dependent on bHLH-responsive E-boxes in the proximal promoter region, that additional distal regulatory elements are important for neuroD2 expression in a subset of cortical neurons, and that neurogenin1 regulates neuroD2 expression during mouse brain development.