IDENTIFICATION OF A NEW NONNEURONAL CELL TYPE IN RAT OLFACTORY EPITHELIUM

We have examined adult and embryonic rat olfactory epithelia by immunohistochemical techniques using the monoclonal antibody 1A-6, which was raised against embryonic rat olfactory epithelia. A heretofore unidentified cell type, reactive with the monoclonal antibody 1A-6, was observed scattered within the epithelium. The 1A-6 reactivity of these cells is most intense on the microvilli projecting from the luminal cell surfaces. For several reasons, we believe these cells are not neurons but a distinct subpopulation of supporting cells or some other sort of non-neuronal cell. (1) They have no identifiable axonal process, are not reactive with an antibody against olfactory marker protein, and are not in juxtaposition with trigeminal axons. (2) They survive ablation of the olfactory bulb. (3) Their nuclei lie within the supporting cell layer, and they resemble supporting cells morphologically and in their [H-3]thymidine birthdating and turnover characteristics. However, the 1A-6-positive cells fail to react with the general supporting cell-specific monoclonal antibody SUS-1 [see Hempstead J. L. and Morgan J. I. (1983) Brain Res. 188, 289-295] a finding which suggests that they are not typical supporting cells. Immunoreactivity to 1A-6 is developmentally regulated. Immunohistochemical preparations of almost all tissues we examined showed widespread reactivity in the embryo but a much more restricted pattern in the adult. In the olfactory epithelium of the fetus, the luminal surfaces of all cells, including supporting cells and olfactory receptor cells and cilia, are reactive, while in the adult only the non-neuronal cell subpopulation shows this reactivity. We also found that during the reconstitution of olfactory epithelium which occurs in response to olfactory bulbectomy-induced neuronal degeneration, fetal patterns of 1A-6 reactivity are not re-expressed, i.e. the only 1A-6-positive cells are the non-neuronal cells seen in unperturbed adult olfactory epithelium. Preliminary biochemical analyses of membrane fractions from E19 brain and from adult olfactory mucosa indicate that the 1A-6 reactivity is associated with two bands, having molecular weights of 42,000 and 46,000 on Western blots.