Expression of NeuroD and TrkB in developing and aged mouse olfactory epithelium.

To better understand the roles of NeuroD, a member of the basic helix-loop-helix transcription factor family, during the differentiation of olfactory receptor neurons, we studied the expression of NeuroD in developing and aging mouse olfactory epithelium (OE). During embryonic period, NeuroD expression is confined in the basal compartment of OE. During neonatal period, NeuroD expression is detected in the middle compartment and in the basal compartment of OE. In the adult, the number of NeuroD expressing cells in the basal compartment significantly decreased, while the NeuroD-positive cells in the middle compartment was maintained throughout lifetime. This dual phase expression pattern of NeuroD suggests multiple roles of NeuroD in the neurogenesis of ORNs.