The present invention relates to nucleic acids that encode novel basic helix-loop-helix polypeptides. The present invention also relates to novel basic helix-loop-helix polypeptides, in particular, rat Relax and human ngn3 polypeptides. The invention also relates to methods for the detection of nucleic acids and polypeptides according to the invention. The invention also relates to methods for the detection of activators or inhibitors of the polypeptides of the invention. Finally, the present invention relates to methods of prevention and/or treatment of pathologies, dysfunctions, disorders or conditions affecting the nervous system.