The sense of smell allows chemicals to be perceived as diverse scents. We used single neuron RNA-Sequencing (RNA-Seq) to explore developmental mechanisms that shape this ability as nasal olfactory neurons mature in mice. Most mature neurons expressed only one of the roughly 1000 odorant receptor genes (Olfrs) available, and that at high levels. However, many immature neurons expressed low levels of multiple Olfrs. Coexpressed Olfrs localized to overlapping zones of the nasal epithelium, suggesting regional biases, but not to single genomic loci. A single immature neuron could express Olfrs from up to seven different chromosomes. The mature state in which expression of Olfr genes is restricted to one per neuron emerges over a developmental progression that appears independent of neuronal activity requiring sensory transduction molecules.

The identification of receptors that detect environmental stimuli lays a foundation for exploring the mechanisms and neural circuits underlying sensation. The mouse vomeronasal organ (VNO), which detects pheromones and other semiochemicals, has 2 known families of chemoreceptors, V1Rs and V2Rs. Here, we report a third family of mouse VNO receptors comprising 5 of 7 members of the formyl peptide receptor (FPR) family. Unlike other FPRs, which function in the immune system, these FPRs are selectively expressed in VNO neurons in patterns strikingly similar to those of V1Rs and V2Rs. Each FPR is expressed in a different small subset of neurons that are highly dispersed in the neuroepithelium, consistently coexpress either Gα i2 or Gα o , and lack other chemoreceptors examined. Given the presence of formylated peptides in bacteria and mitochondria, possible roles for VNO FPRs include the assessment of conspecifics or other species based on variations in normal bacterial flora or mitochondrial proteins.