In another experiment they found that the TAAR axons leading to glomeruli at the top of the bulb express a cell adhesion molecule that is associated with olfactory receptor axons leading only to glomeruli at the bottom part of the olfactory bulb.
What convinced Barnea and his colleagues that TAAR neurons constitute an olfactory subsystem were differences in how these neurons choose the receptor gene that they express. They used mice in which one TAAR gene is swapped with a marker that turns the cell blue. When the same strategy was used in olfactory receptor-expressing neurons, the blue marker was switched off and another olfactory receptor gene was selected. By contrast, TAAR-expressing neurons did not turn off the blue marker. They selected another TAAR gene, but continued to be stained blue.
This observation led Barnea and longtime collaborator Stavros Lomvardas of the University of CaliforniaSan Francisco to identify several other differences between TAAR neurons and olfactory receptor neurons in how the neurons carry out gene expression.
"The logic of gene choice in TAAR neurons is different," Barnea said. "Their patterns of projection [to the bulb] are different, and the mechanisms that control their projections are different. Altogether these observations suggest that it's a different subsystem."
The smell of fear?
TAARs were discovered in the nose in 2006 by Stephen Liberles of Harvard Medical School, one of Barnea's collaborators and co-authors of this pape
|Contact: David Orenstein|