The prevailing model of olfaction is that individual neurons express only one odorant receptor (OR). Goldman et al.challenge this view by finding that one olfactory receptor neuron (ORN) in the Drosophila sensilla in the maxillary palp (a fly olfaction organ) expresses two highly divergent Or genes. Seven Or genes were expressed in the six types of neurons found in maxillary palp sensilla. In a receptor-to-neuron map of the ORNs in the maxillary palp, three Or genes were expressed in the pb2 class of sensilla. Each class of sensilla consists of an A- and a -B type neuron. To determine if the genes were expressed in the A or B neuron, the Or-specific promoters were used to express the proapoptic protein Reaper, causing selective cell death in only one of the two neurons. When Or33c or Or85e promoters were used, the surviving neuron was pb2B. Thus, both Or33c and Or85e appear to be expressed in the pb2A neuron. Or85e and Or33c transcripts were present in the same ORN in three different species of fly. The combined receptors may be specific for unidentified odorants, potentially increasing further the complexity and specificity of odorant perception. — NG
Neuron 45, 661 (2005).