DIFFERENTIAL EXPRESSION OF N-CAM, VIMENTIN AND MAP1B DURING INITIAL PATHFINDING OF OLFACTORY RECEPTOR NEURONS IN THE MOUSE EMBRYO

Olfactory receptor neurons extend their primary axons from the nasal e pithelium to the olfactory bulb primordium via the frontonasal mesench yme. In the present study, expression of neuronal markers (vimentin an d MAP1B) and N-CAM was immunohistochemically investigated in the devel opment of the olfactory system in mouse embryos. Expression of vimenti n and MAP1B was first observed at early day 10 of gestation (D10) in t he posterosuperior region of the medial nasal epithelium, while N-CAM was initially detected in the mesenchyme adjacent to the vimentin- and MAP1B-positive nasal epithelium. As development proceeded, the NCAM p ositive region in the nasal mesenchyme became broader and reached the olfactory bulb primordium late on day 10. In comparision with adjacent sections, the localization of neuronal marker-positive cells was most ly included in the N-CAM positive region. In addition, we adopted in s itu labelling with vital dye (DiI) to directly determine the localizat ion of the olfactory nerve and NCAM on the same sections. We demonstra ted that most extending axons were located in the N-CAM positive regio n. These results suggest that the expression of NCAM plays a crucial r ole in the initial pathfinding of the olfactory nerve.