Expression of glycoproteins in the vomeronasal organ reveals a novel spatiotemporal pattern of sensory neurone maturation

The main olfactory and the accessory olfactory systems are both anatomicall y and functionally distinct chemosensory systems. The primary sensory neuro nes of the accessory olfactory system are sequestered in the vomeronasal or gan (VNO), where they express pheromone receptors, which are unrelated to t he odorant receptors expressed in the principal nasal cavity. We have ident ified a 240 kDa glycoprotein (VNO240) that is selectively expressed by sens ory neurones in the VNO but not in the main olfactory neuroepithelium of mo use. VNO240 is first expressed at embryonic day 20.5 by a small subpopulati on of sensory neurones residing within the central region of the crescent-s haped VNO, Although VNO240 was detected in neuronal perikarya at this age, it was not observed in the axons in the accessory olfactory bulb until post natal day 3.5, This delayed appearance in the accessory olfactory bulb sugg ests that VNO240 is involved in the functional maturation of VNO neurones r ather than in axon growth and targeting to the bulb, During the first 2 pos tnatal weeks, the population of neurones expressing VNO240 spread periphera lly, and by adulthood all primary sensory neurones in the VNO appeared to b e expressing this molecule. Similar patterns of expression were also observ ed for NOC-1, a previously characterized glycoform of the neural cell adhes ion molecule NCAM, To date, differential expression of VNO-specific molecul es has only been reported along the rostrocaudal axis or at different apica l-basal levels in the neuroepithelium. This is the first demonstration of a centroperipheral wave of expression of molecules in the VNO, These results indicate that mechanisms controlling the molecular differentiation of VNO neurones must involve spatial cues organised, not only about orthogonal axe s, but also about a centroperipheral axis, Moreover, expression about this centroperipheral axis also involves a temporal component because the subpop ulation of neurones expressing VNO240 and NOC-1 increases during postnatal maturation. (C) 2001 John Wiley & Sons, Inc.