Basic helix-loop-helix (bHLH) proteins are involved in many kinds of tissue-specific transcription. The bHLH proteins basically contain domains for DNA-binding, transcription regulation, and dimerization. They bind to E-box or N-box as a homodimer or heterodimer, and dimerization partners can modulate the regulatory potential. A subset of bHLH proteins participate in mammalian neurogenesis through a cascade of regulatory factors, which is analogous to the Drosophila Wingless signal transduction pathway. Expression of a NeuroD-Related Factor persists in brain subdomains of mammals from relatively late period to the embryogenesis to adulthood. NeuroD-Related Factor is thought to be involved in development and maintenance of neurons.