Ants interacting in a lab environment. Red circles show examples of an ant using its antennae to smell and interact with others. Video credit: Ching-Han Lee, George Liu, Bogdan Sieriebriennikov
Neuron survival depends on Orco
In their new study in Science Advances, the researchers used single-nucleus gene expression profiling of ant antennae and fluorescence microscopy to analyze olfactory cell development. It emerged that mutant insects lacking Orco lose most of their olfactory neurons before adulthood.
“The cells appear to be made normally, and they start developing—growing, changing shape, and switching on certain genes they will need later, such as odorant receptors,” noted Sieriebriennikov. “Once the developing cells turn on the odorant receptors, very soon they start dying in massive amounts.”
This neuronal death may be because of stress. As the odorant receptors in the mutant ants cannot form a complex with Orco to travel to the cell membrane, the newly made receptors clog the organelles, leading to stress and death.
Such neuronal death may also show patterns particular to social insects. “So far, these unique processes have not been found in solitary insects and may provide important evidence of evolution of neural development to adapt to the expansion of odorant receptor genes,” said Kayli Sieber, a doctoral candidate at the University of Florida and the co-first author of the study.
Interestingly, some odorant receptors survived even without Orco. The cells in which they were present also expressed other types of receptors, suggesting that the activity they facilitate is essential for neuronal development.
“Some neurons must periodically ‘fire’ to develop properly. Without Orco, smell cells did not ‘fire’ and complete their development, leading to their death," said Sieriebriennikov.
