While smell is essential for human social interactions, it is crucial for ants. Researchers from NYU and the University of Florida found that the protein Orco, essential for olfactory cell function, is also vital for their survival in ants.
Their study showed that mutating the orco gene in Harpegnathos saltator ants significantly reduced the number of olfactory neurons, indicating Orco’s role in these cells‘ development and life. Understanding how the nervous system develops is a critical challenge in modern neuroscience.
Ants, with their approximately 400 smell receptors, are not so different from humans in this regard. However, what sets them apart is their use of pheromone communication, a unique trait that makes them perfect for studying sensory-based social behavior. Their many odorant receptor genes are the key to their communication in large societies, a fascinating aspect of their social structure.
Loss of odorant receptor neurons impairs smell and is linked to social isolation and disorders like schizophrenia and autism. To study ants’ sense of smell and social interactions, NYU researchers used CRISPR to edit the orco gene in ants. These “mutant” ants, lacking the Orco protein, showed changes in their smell organs and struggled to interact.
In their new study published in Science Advances, the researchers employed advanced techniques such as single-nucleus gene expression profiling and fluorescence microscopy to study ant antennae. These methods allowed them to observe the effects of the Orco protein mutation in detail. They found that mutant ants lacking Orco lose most of their olfactory neurons before reaching adulthood, a significant finding in the field of ant biology.
At first, the cells usually develop, grow, and switch on genes like odorant receptors. However, once the receptors activate, the cells start dying rapidly. This cell death might be due to stress. Without Orco, the receptors can’t reach the cell membrane, causing them to clog organelles and leading to cell stress and death.
This neuronal death may be unique to social insects. These processes haven’t been found in solitary insects and might show how neural development evolved with more odorant receptor genes.
Some odorant receptors survived without Orco. The cells with these receptors also had other types, suggesting their activity is crucial for development. Some neurons need to ‘fire’ periodically to develop. Without Orco, smell cells couldn’t ‘fire’ and complete their development, leading to death.
The researchers discovered some odorant receptors in non-smell cells, like motion-detecting neurons and glia, which support neuron function. This might be due to imperfect gene regulation, causing odorant receptors to be activated by nearby genes. Alternatively, these receptors might have new functions similar to those in the glia of C. elegans worms or human sperm.
Hua Yan, assistant professor of biology at the University of Florida and the study’s senior author, said, “Turning on odorant receptor genes in the cells that are not smell-sensing could be useless for the organism—but then again, evolution tends to make use of such mistakes to give existing genes new function, so perhaps there is some exciting new role of odorant receptors in non-smell cells that we will discover in the future. Our findings enhance our understanding of social insects’ sensory systems, including olfactory neural development that establishes a framework for social communication.”
Journal reference:
- BOGDAN SIERIEBRIENNIKOV, KAYLI R. SIEBER et al., Orco-dependent survival of odorant receptor neurons in ants. Science Advances. DOI:10.1126/sciadv.adk9000.
