A BANDED TOPOGRAPHY IN THE DEVELOPING RATS OLFACTORY EPITHELIAL SURFACE

In situ hybridization studies from various laboratories have shown tha t the rat's olfactory epithelium has four distinct regions in which mo st putative odor receptors are located. To determine whether morpholog ical features accompany this biochemical patterning, olfactory epithel ial surfaces of rat nasal endoturbinates and septa were examined with scanning electron microscopy, placing particular emphasis on endoturbi nate IIb. There was some morphological patterning at embryonic day 15 (E15), but distinct regions were not yet discernible. Regionalization became distinct at E16 and E18. Posterior regions (Regions 1 and 2) ha d much higher receptor cell knob densities than more anterior regions closer to the respiratory epithelium (Regions 3 and 4). Supporting cel l microvilli were longer in Region 1 than in Region 2. Apices of cells surrounding the receptor cells were flatter in Regions 1 and 2 than i n Regions 3 and, especially Region 4. In Regions 1-3, these surroundin g cells were made up mainly of supporting cells; in Region 3 they incl uded respiratory cells. Regions 3 and 4 also had glandular openings an d scattered microvillous cells that resemble hair cells of the ear. Ol der fetuses and adults showed similar evidence of patterning, but deta iled examination was precluded by the increased length and entanglemen t of receptor cell cilia and supporting cell microvilli. In conclusion , a distinct topographic pattern, involving both receptor and surround ing cells, emerges during development of the rat olfactory epithelial surface. Location of the bands roughly matches the zones seen by in si tu hybridization. (C) 1997 Wiley-Liss, Inc.