A feedback mechanism regulates monoallelic odorant receptor expression.

In olfactory neurons, expression of a single odorant receptor (OR) from a repertoire of >1000 genes is required for odor coding and axonal targeting. Here, we demonstrate a role for OR protein as an essential regulator in the establishment of monoallelic OR expression. An OR-promoter-driven reporter expresses in a receptor-like pattern but, unlike a native OR, is coexpressed with an additional OR allele. Expression of a functional OR from the identical promoter eliminates expression of other OR alleles. The presence of an untranslatable OR coding sequence in the mRNA is insufficient to exclude expression of a second OR. Together, these data identify the OR protein as a critical element in a feedback pathway that regulates OR selection.