Despite the identical genetic makeup of the neurons associated with smell in the fruit fly, scientists are one step closer to understanding how certain neurons perceive specific smells, according to an article released on May 27, 2008 in the open access journal PLoS Genetics.
Embryonic development begins with a single cell, containing the genetic information to create all parts of the organism that is developing. As this cell divides, it provides this full compliment of genes to each subsequent daughter cell, which in turn has the potential to become any of the cells found in the organism in a property known as totipotency. Much has yet to be learned about how and why these cells differentiate, on both a large scale and a small scale, and understanding these regulatory processes is the genetic foundation of developmental biology.
In the fruit fly, of the genus Drosophila, two organs are related to the sense of smell: the antennae extending from the head and the maxillary palps in the mouth. In the palps, there are six different types of neurons present to transmit information from the sensory area to the brain itself. Based on these patterns, different receptors will discriminate different odors. Each type has a specific and predictable pattern of olfactory receptors, but until now it has not been clear how the neurons were instructed to develop in these different but highly predictable ways.
To investigate this question, Anandasankar Ray and colleagues at Yale University compared the recently published genetic sequences of all 12 typically studied species of Drosophila. In doing this, they identified regions of the DNA upstream from and near the genes for the receptors themselves that are nearly identical across the species. Hypothesizing that these were control regions, which will influence when and how the genes will develop, the team genetically altered certain control regions experimentally, showing that these genes were indeed necessary for the control of this part of development. Some regions regulate the receptor expression positively, so that if they are not present, the necessary proteins do not appear. Others regulate it negatively, so when they are missing the receptors will appear, even in the wrong neurons.
Notably, these regulatory sequences may have other roles in the nervous system — they may also potentially act in the process of connecting neurons to other neurons in the antennae, called axon guidance. This suggests that these genes are not just necessary for the sense of smell, but may also be integral to Drosophila’s nervous system.
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A regulatory code for neuron-specific odor receptor expression.
Ray A, van der Goes van Naters W, Carlson JR
PLoS Biol 6(5): e125.
doi:10.1371/journal.pbio.0060125
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Written by Anna Sophia McKenney