EXPRESSION OF OLFACTORY RECEPTORS, G-PROTEINS AND AXCAMS DURING THE DEVELOPMENT AND MATURATION OF OLFACTORY SENSORY NEURONS IN THE MOUSE

Three mouse olfactory receptors have been cloned and sequenced and wer e found to be expressed in different zones of the olfactory epithelium . In situ hybridisation (ISH) results showed that each olfactory recep tor was expressed at an early stage in development (E12), was not depe ndent on the maturation of the receptor neurons, and was present long before the onset of odour detection. Cells positive for these same olf actory receptors and the G-protein (G beta) were also found in non-neu ral regions of the nasal epithelium in the earlier stages of developme nt (E12-16). Ncam, and Big-2 expression were, however, restricted to t he region of developing olfactory neurons. Ncam expression appeared in advance of the olfactory receptor expression, while Big-2 appeared af ter olfactory receptor expression and neither were expressed in cells outside the olfactory epithelium. Both showed the highest number of po sitive cells in the early post-partum period when olfactory detection is functional. Ncam is known to be involved in guidance of the develop ing olfactory axons and was expressed earlier than any of the olfactor y receptors, while Big-2 appears somewhat later (E14) at a time when d eveloping axons reach the olfactory bulb. Moreover the highest periods of expression occur at post-natal day 7 when a proliferation of bulba r glomeruli are observed, suggesting the role of Big-2 to be primarily concerned with synaptogenesis. (C) 1998 Elsevier Science B.V. All rig hts reserved.