Association of ecto-5'-nucleotidase with specific cell types in the adult and developing rat olfactory organ.

A unique feature of the olfactory epithelium is its ability to give rise to new sensory neurons throughout life and also following injury. Cells at the basal side of the epithelium serve as neurogenic progenitor cells. The enzyme ecto-5'-nucleotidase is expressed at the surface of developing nerve cells and is regarded as a marker of neural development. To study the expression pattern of the enzyme, we analyzed its distribution in the adult and developing rat olfactory organ. Labeling is restricted to specific cell types and varies between the epithelia investigated. At the basal side of the olfactory epithelium, activity of 5'-nucleotidase is associated specifically with the dark/horizontal basal cells. Neither the light/globose basal cells, which are the immediate precursors of the sensory receptor cells, nor subsets of potentially immature olfactory receptor cells are labeled. On the other hand, microvillar cells dispersed at the lumenal side of the epithelium contain 5'-nucleotidase activity. The enzyme is also present at the inner lining of the ducts of Bowman's glands as they traverse the epithelium. Within the respiratory epithelium, activity of 5'-nucleotidase is associated with basal cells as well as with the epithelial surface. During development, 5'-nucleotidase is initially limited to the respiratory epithelium, including its basal cells. Dark/horizontal basal cells of the olfactory epithelium, which are positive for 5'-nucleotidase, first appear at the border of the respiratory epithelium, suggesting that they might originate from immigrating basal cells of the respiratory epithelium. Within the vomeronasal organ, labeling is largely restricted to the receptor-free epithelium. Although the functional role of 5'-nucleotidase in the olfactory system needs to be further defined, the distribution of the enzyme can be used successfully as a marker for defined cell types.