Using bioluminescent proteins from a jellyfish, a team of researchers recently managed to light up the interior of a neuron - capturing video footage depicting the movement of proteins throughout the cell.
According to Professor Don Arnold of the USC Dornsife College of Letters, Arts and Sciences, the video offers a rare peek at how proteins, the brain's building blocks, are directed through neurons to renew its structure.
"Your brain is being disassembled and reassembled every day," he explained. "One week from today, your brain will be made up of completely different proteins than it is today. This video shows the process. We've known that it was happening, but now we can watch it happen."
The new imaging technique was used to illustrate how proteins are directed to one of the two types of compartments inside the neuron: the axon or the dendrites.
The axon is the region of the cell responsible for transmitting electrical signals to other cells, while the dendrites receive signals from other cells.
"It's been known for many decades that proteins are specifically targeted to one compartment or the other. However, we couldn't understand how the targeting occurs until we could actually watch the proteins traveling to one compartment or to the other," said USC Ph.D. student Sarmad Al-Bassam.
Since the mid-1990s, scientists have been able to illuminate the proteins inside of cells, including neurons, by attaching a protein isolated from jellyfish - known as GFP (green fluorescent protein) - that fluoresces bright green when exposed to blue light.
Howver, the problem with studying the flow of illuminated proteins inside of neurons is that there are several different overlapping pathways within the cell, making it difficult to study the traffic through just one.
Al-Bassam and his colleagues solved this issue by developing a new technique that involves damming up a single pathway, which creates a backlog of transport vesicles (little bubbles that travel up and down neurons carrying membrane protein cargo) impregnated with the illuminated proteins. They then used a small-molecule drug to release the backlog all at once in a bright pulse.
"Our result was very surprising... We found that rather than being targeted specifically to the dendrites, vesicles carrying proteins initially enter both compartments, but then are stopped and prevented from moving beyond the initial segment of the axon," added Arnold.