Visualizing Axon Pruning
During development, neurons trim hundreds of excess axons in an intricately coordinated destructive process.
Much like tree branches, hundreds of axons extend from neurons during development. These axons serve as information highways that enable neurons to communicate with different cells across the body. Among the many axons, only one needs to reach the target. The neuron prunes the rest.
Neurons rely on the same molecular machinery used during apoptosis for this process, but how they leverage apoptotic proteins while ensuring that they do not self-destruct or prune the wrong axon is unknown. Selena Romero, a graduate student in the lab of Mohanish Deshmukh at the University of North Carolina at Chapel Hill set out to better understand this mechanism.
She cultured peripheral neurons in the central section of a three-compartment microfluidic chamber. When Romero imaged the chamber for the first time, it took her five hours. She manually captured 100 images, overlapping each by approximately 20 percent, and then stitched them together using software.
The resulting image revealed fluorescently labeled neurons in blue growing through tiny grooves to enter the wider left and right compartments, where they produced axons, also in blue, that then began to spread. “I was blown away by how striking it was because the axons were not all on the left side or all on the right side. They branched out fully,” said Romero.
This proof-of-concept image demonstrated that Romero could use the chamber to model axon pruning by depleting a key protein needed for neuronal growth from axons in one compartment without killing the neuron or the axons in the other compartment. “That’s why these compartmentalized models are important for us because we can’t study pruning in any other context,” said Romero.