Retinoid signaling distinguishes a subpopulation of olfactory receptor neurons in the developing and adult mouse.

We asked whether retinoic acid (RA) influences olfactory receptor neurons (ORNs) in the developing and mature mouse olfactory epithelium (oe). The distribution of retinoid receptors and binding proteins in the oe changes between embryonic days 11.5 and 13.5, the period when ORNs first differentiate and send axons into the nascent olfactory nerve. Coincident with this change, RA, which is produced in the frontonasal mesenchyme at these ages, begins to activate gene expression in a bilaterally symmetric subset of ORNs in the dorsolateral oe, as judged by the expression of an RA-responsive transgene. Axons from these RA-activated ORNs are segregated in the olfactory nerve as it extends through the frontonasal mesenchyme toward the forebrain. In vitro, RA potentiates ORN neurite growth on laminin, which, in the embryo, is found in a stripe of frontonasal mesenchyme directly associated with the olfactory nerve. RA does not modify growth on fibronectin, type IV collagen, or L1, which olfactory axons encounter in different regions of the territory between the olfactory epithelium and the brain. The pattern of RA-mediated transcriptional activation and axon segregation persists in early postnatal mice, and RA signaling can be recognized in a subset of adult ORNs in the dorsolateral oe. Thus, RA-mediated gene expression distinguishes a subpopulation of ORNs in a distinct region of the oe during the early development of the olfactory pathway, and may influence differentiation and axonal projections of ORNs in this region throughout life.