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Abstract
The sensory neurons in the olfactory epithelium (OSNs) are equipped with a large repertoire of olfactory receptors and the associated signal transduction machinery. In addition to the canonical OSNs, which express odorant receptors (ORs), the epithelium contains specialized subpopulations of sensory neurons that can detect specific information from environmental cues and relay it to relevant neuronal circuitries. Here we describe a subpopulation of mature OSNs in the main olfactory epithelium (MOE) which expresses CD36, a multifunctional receptor involved in a series of biological processes, including sensory perception of lipid ligands. The Cd36 expressing neurons coexpress markers of mature OSNs and are dispersed throughout the MOE. Unlike several ORs analyzed in our study, we found frequent coexpression of the OR Olfr287 in these neurons, suggesting that only a specific set of ORs may be coexpressed with CD36 in OSNs. We also show that CD36 is expressed in the cilia of OSNs, indicating a possible role in odorant detection. CD36-deficient mice display no signs of gross changes in the organization of the olfactory epithelium, but show impaired preference for a lipid mixture odor. Our results show that CD36-expressing neurons represent a distinct population of OSNs, which may have specific functions in olfaction.
Highlights
CD36 is known to play several roles in sensory perception
High levels of Cd36 expression were observed in tissues known to strongly express the gene, such as the heart and adipose tissue (17- fold the expression levels in olfactory epithelium (OE); Fig. 1a), in agreement with the transcript levels originally described for rat tissues[14]
Previous studies have shown that CD36 and its homologue play a role in chemosensory responses to lipid ligands in insects and mammals[16,19]
Summary
CD36 is known to play several roles in sensory perception. The sensory neuron membrane protein (SNMP), a D. melanonogaster CD36 homologue, mediates proper responses to the lipid pheromone cis-vaccenyl acetate (cVA) in a population of sensory olfactory neurons[16,17]. It was shown that CD36 mediates fatty acid detection in taste cells and preference for lipid ingestion in rodents[18,19], suggesting a conserved role for this receptor in lipid sensory recognition. We show that CD36 is expressed in the cilia of a subpopulation of OSNs in the MOE. These neurons coexpress typical markers for mature olfactory sensory neurons, including proteins involved in the canonical OR signal transduction cascade. No coexpression was observed when other types of ORs were analyzed, indicating that the CD36 expressing neurons may express only a particular subgroup of all possible existing ORs. In addition, we show that innate preference for lipid odor is impaired in CD36-deficient mice. Our results suggest that CD36 may play important roles in olfaction
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