Fig. 1

Location of OECs in the primary olfactory nervous system. a Schematic of the olfactory nervous system. Olfactory axons extend from cell bodies of olfactory sensory neurons in the olfactory epithelium of the nasal cavity to the olfactory bulb. OECs are present in close contact with these axons in all the way from the periphery to the olfactory bulb in the CNS. In the lamina propria, OECs contribute to axon fasciculation. In the olfactory nerve, fascicles extend towards the bulb, OECs surround axon fascicles. In the outer nerve fibre layer (NFL), OECs contribute to axon defasciculation. In the inner NFL, OECs are involved in axon sorting, refasciculation and targetting to glomeruli based on odorant receptor expression. b Shown is an image of a cryostat section from the olfactory epithelium (OE) and lamina propria (LP) of a transgenic mouse (S100βDsRed-OMPZsGreen) in which primary olfactory neurons and OECs express a green and red fluorescent protein, respectively. Primary olfactory neurons (green) within the olfactory epithelium send their axons into the lamina propria where axon fascicles are ensheathed by OECs (red). Scale bar: 35 µm. Blue: nuclei (4′,6-Diamidine-2′-phenylindole dihydrochloride; DAPI). c Schematic of an olfactory axon fascicle ensheathed by several OECs surrounding numerous axons. d, e Arrangement of Schwann cells and axons in peripheral nerves for comparison. d A large-diameter axon myelinated by Schwann cells. e A Remak bundle in which non-myelinating Schwann cells support small-diameter unmyelinated axons