Abstract
A mature olfactory sensory neuron (OSN) of the main olfactory epithelium (MOE) typically expresses one allele of one odorant receptor (OR) gene. It is widely thought that the great majority of the 1,141 intact mouse OR genes are expressed in one of four MOE zones (or bands or stripes), which are largely non-overlapping. Here, we develop a multiplex method to map, in 3D and MOE-wide, the expression areas of multiple OR genes in individual, non-genetically modified mice by three-color fluorescence in situ hybridization, semi-automated image segmentation, and 3D reconstruction. We classify the expression areas of 68 OR genes into 9 zones. These zones are highly overlapping and strikingly complex when viewed in 3D reconstructions. There could well be more zones. We propose that zones reflect distinct OSN types that are each restricted in their choice to a subset of the OR gene repertoire.
Highlights
In mammals, most odorants are detected by odorant receptors (ORs), G-protein-coupled seven-transmembrane domain proteins that are expressed in olfactory sensory neurons (OSNs) of the main olfactory epithelium (MOE) (Buck and Axel, 1991)
We propose that the zonal organization of OR gene expression in the mouse MOE reflects a small number of molecularly distinct OSN types, each of which is restricted in its choice to a subset of the OR gene repertoire
The difficulty of describing the zonal organization of OR gene expression in the MOE lies in the sheer size of the OR gene repertoire and in the emergent nature of the zones; they are defined solely by the areas within which OSNs expressing a given OR gene reside
Summary
Most odorants are detected by odorant receptors (ORs), G-protein-coupled seven-transmembrane domain proteins that are expressed in olfactory sensory neurons (OSNs) of the main olfactory epithelium (MOE) (Buck and Axel, 1991). There is a fifth, small zone called the patch (Strotmann et al, 1992; Strotmann et al, 1994b), in which 19–22 OR genes (1.9% of the repertoire) are expressed (Hoppe et al, 2006; Tan and Xie, 2018). This historical view has been challenged in rat (Iwema et al, 2004) and mouse (Miyamichi et al, 2005). Continuous and overlapping expression domains have been proposed (Miyamichi et al, 2005), such that expression areas are specific to each OR gene
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