The human nose has millions of olfactory（嗅觉的） neurons grouped into hundreds of different neuron types. Each of these neuron types expresses only one odorant receptor, and all neurons expressing the same odorant receptor plug into one region in the brain, an organization that allows for specific odors to be sensed. For example, when you smell a rose, only those neurons that express a specific odor receptor that detects a chemical the rose emits get activated, which in turn activates a specific region in the brain. Rotten eggs, on the other hand, activate a different class of neurons that express a different (rotten egg) receptor and activate a different part of the brain. How the one-receptor-per-neuron pattern -- critical for odor discrimination -- is achieved in olfactory neurons is a mystery that has frustrated scientists for long.

Now a team of scientists, led by neurobiologists at the University of California, Riverside, has an explanation. Focusing on the olfactory receptor for detecting carbon dioxide in Drosophila (fruit fly), the researchers identified a large multi-protein complex in olfactory neurons, called MMB/dREAM, that plays a major role in selecting the carbon dioxide receptors to be expressed in appropriate neurons.

Study results appear in the Nov. 15 issue of Genes & Development. The research is featured on the cover of the issue.