Another victory for Carverian science. When you look more closely at a totally familiar object that couldn’t possibly be important, you sometimes realize it’s hugely important.
Most cells have cilia, and many cells have one primary cilium. Bacteria and other microbes use this primary cilium to get around, but it was ‘obviously’ vestigial for cells inside an organism.
However, it was unclear why other cells in our bodies, including neurons, retained this hair-like, bacterium-sized protrusion into maturity. Scientists had largely ignored these cilia because they were difficult to see with traditional imaging techniques. But recently, better imaging tools have sparked an interest in these tiny appendages.
Next, the team developed new biosensors and chemical tools to study the function of this newly discovered structure. The researchers also used an emerging imaging modality—fluorescence lifetime imaging (FLIM)—to make better measurements of biochemical events inside the cilia.
With these tools, the team was able to show step-by-step how the neurotransmitter serotonin is released from the axon onto receptors on the cilia. This triggers a signaling cascade that opens the chromatin structure and allows changes to genomic material in the cell’s nucleus.
In other words, the cilium is the input port for epigenetic settings of each neuron.
Long-term memory probably depends on this input, not on the more familiar axon-to-dendrite transfer.
Applying this fact back to the cilium of a microbe, it appears that the cilium is a sensory antenna as well as an ambulatory ‘leg’. As the cilium spins and spirals through the water, it’s picking up neurotransmitters from other cells and using them to store information about the surroundings.