Cell
Volume 117, Issue 6, 11 June 2004, Pages 833-846
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Article
Axon Guidance of Mouse Olfactory Sensory Neurons by Odorant Receptors and the β2 Adrenergic Receptor

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Abstract

Odorant receptors (ORs) provide the core determinant of identity for axons of olfactory sensory neurons (OSNs) to coalesce into glomeruli in the olfactory bulb. Here, using gene targeting in mice, we examine how the OR protein determines axonal identity. An OR::GFP fusion protein is present in axons, consistent with a direct function of ORs in axon guidance. When the OR coding region is deleted, we observe OSNs that coexpress other ORs that function in odorant reception and axonal identity. It remains unclear if such coexpression is normally prevented by negative feedback on OR gene choice. A drastic reduction in OR protein level produces axonal coalescence into novel, remote glomeruli. By contrast, chimeric ORs and ORs with minor mutations perturb axon outgrowth. Strikingly, the β2 adrenergic receptor can substitute for an OR in glomerular formation when expressed from an OR locus. Thus, ORs have not evolved a unique function in axon guidance.

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Present address: Department of Zoology and Animal Biology and NCCR Frontiers in Genetics, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland.