Determinants of odorant receptor transcription and gene choice

The mammalian olfactory system enables the detection of a wide variety of chemical compounds via the expression of a repertoire of olfactory receptors comprising the largest gene family in the mammalian genome. Olfactory sensory neurons each express only one odorant receptor (OR) gene. In mice, this requires activation of one OR gene and repression of over 1400 other OR genes. In this review, we describe the mechanisms that support the transcription of OR genes and how these mechanisms impact which OR is expressed in each neuron. First, we discuss what is currently known about the role of transcription in OR choice. We then describe the role of specific features of OR genes and enhancers in the regulation of OR transcription. Finally, we discuss characteristics of olfactory sensory neurons which specify transcription of some OR genes while restricting the transcription of others.