Helix-loop-helix (bHLH) proteins: Proneural

The nervous system is composed of morphologically and functionally diverse cell types including neurons, oligodendrocytes, and astrocytes. These cell types must be generated in the correct number from proliferating progenitors in a spatially and temporally restricted manner. Cellular diversity within the nervous system is achieved by a combination of processes that specify cell type in neural progenitors and one that determines neuronal phenotype during differentiation. The decision between neural and glial fates, and the subsequent decision to become a particular type of neuron, is termed neuronal specification. Neuronal differentiation encompasses the processes of cell cycle exit, movement laterally out of the zone of proliferation, and the expression of neural specific markers. Basic helix-loop-helix (bHLH) transcription factors that activate and repress transcription of target genes are essential molecular components of both of these processes.