LAUSR

The molecular basis for odor perception in humans remains enigmatic because of the difficulty in studying odorant receptors (ORs) outside their native environment. Efforts toward OR expression and functional profiling have been met with limited success because of the poor efficiency of their cell surface expression in vitro. Structures protruding from the surface of olfactory sensory neurons called cilia contain all of the components of the olfactory signal transduction machinery and can be placed in an ex vivo plate assay to rapidly measure odor-specific responses. Here, we describe an approach using cilia isolated from the olfactory sensory neurons of mice expressing two human ORs, OR1A1 and OR5AN1, that showed 10- to 100-fold more sensitivity to ligands as compared to previous assays. A single mouse can produce enough olfactory cilia for up to 4000 384-well assay wells, and isolated cilia can be stored frozen and thus preserved. This pipeline offers a sensitive and highly scalable ex vivo odor-screening platform that has the potential to decode human olfaction. Description Cilia isolated from the olfactory sensory neurons of transgenic mice can be used to profile human odorant receptors. Sniffing out receptors Odorant receptors (ORs), which constitute a subset of the family of G protein–coupled receptors (GPCRs), are expressed in cilia within olfactory sensory neurons (OSNs) in the nasal epithelium. Because OSNs express a single OR-encoding gene, there are too few ORs present to enable identification of the specific odor that activates a given OR in vivo. Omura et al. developed a platform through which they overexpressed a specific human OR in fluorescently tagged OSNs in transgenic mice. Cilia isolated from these OSNs were enriched for the OR and contained all of the components of the OR signaling pathway. The cilia were then screened for their responses to a range of potential ligands, both in liquid and vapor phases, enabling profiling of the receptors. This platform could be used to deorphanize human ORs ex vivo.