Odorant receptor genes expression patterns

Flanagan JG (2006) Neural map specification by gradients.Curr Opin Neurobiol 16(l) 59-66 Fuss SH, Omura M, Mombaerts P (2007) Local and cis effects of the H element on expression of odorant receptor genes in mouse.Cell 130(2) 373-384 Goodman CS, Shatz CJ (1993) Developmental mechanisms that generate precise patterns of neuronal connectivity.Cell 72(Suppl) 77-98... 

In insects, odorant molecules are captured by Olfactory Receptor Neurons (ORNs) (-90,000 in the locust) distributed on their antennae. A large number of ORNs that express the same odorant receptor genes converge onto many fewer glomeruli (-900 in the locust), presumably for improved sensitivity. The odorant identity is then robustly represented in the glomerulus layer as a spatially distributed pattern. In the following we will... 

Figure 32.16 Differing gene expression and connection patterns in olfactory and bitter taste receptors., In olfaction, each neuron expresses a single OR gene, and the neurons expressing the same OR converge to specific sites in the brain, enabling specific perception of different odorants. In gustation, each neuron expresses many bitter receptor genes, and so the identity of the tastant is lost in transmission.

How is the information about which receptors have been activated transmitted to the brain Recall that each neuron expresses only one OR and that the pattern of expression appears to be largely random. A substantial clue to the connections between receptors and the brain has been provided by the creation of mice that express a gene for an easily detectable colored marker in conjunction with a specific OR gene. Olfactory neurons that express the OR—marker protein combination were traced to their destination in the brain, a structure called the olfactory bulb (Figure 32.8). The processes from neurons that express the same OR gene were found to connect to the same location in the olfactory bulb. Moreover, this pattern of neuronal connection was found to be identical in all mice examined. Thus, neurons that express specific ORs are linked with specific sites in the brain. This property creates a spatial map of odorant-responsive neuronal activity within the olfactory bulb. 

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