The helix-loop-helix (HLH) structures are known motifs commonly found in membrane-active and DNA-binding proteins. The helix-loop-helix proteins HEN1 and HEN2 are DNA-binding proteins that may be involved in cell-type determination in the early nervous system. Studies of expression in normal tissues have demonstrated expression of NHLH1/NSCL-1 and NHLH2/NSCL-2, the genes encoding HEN1 and HEN2, in the developing central and peripheral nervous system, specifically in developing neurons.