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To visualize cellular signals within a neuron, the researchers distributed the reporters in (green) clusters throughout the cell. They then identified the signal represented by each cluster (multiple colors) Credit: C. Linghu, S. Johnson et al./Cell 2020
New imaging technology allows scientists to spy on the barrage of messages passed inside cells as they do so. . . potentially everything.
Until now, most scientists could only visualize one or two of these intracellular signals at a time, says Ed Boyden, a researcher at the Howard Hughes Institute of Medicine, Massachusetts Institute of Technology. His team’s new approach could make it possible to see as many signals as you want – in real time, at the same time, says Boyden – giving researchers more detailed insight into the cell’s internal discussions than ever.
In tests with neurons, the researchers looked at five signals involved in processes such as learning and memory, Boyden and his colleagues report today (November 23, 2020) in the journal Cell. “We could apply this technology to all kinds of biological mysteries,” he says. “Every cell works thanks to all the signals inside it.” Since signaling contributes to all biological processes, a better means of studying it could illuminate a number of diseases, from Alzheimer’s to diabetes and cancer.
The team’s new approach is a breakthrough, says Clifford Woolf, a neurobiologist at Harvard Medical School who was not involved in the work. He plans to use it to examine how pain-sensitive neurons become more sensitive to injury or disease. With the new imaging technology, he says “we can disassemble what’s happening in cells in a way that wasn’t possible before.”
You feed information to a computer or the human brain and it will burst with electrical impulses as it prepares for a response. Within cells, these impulses cause bursts of multiple molecular signals. Boyden describes this process as a group conversation. “The signals inside a cell are like a collection of people trying to decide what to do for the evening: they consider many possibilities and then decide what to do collectively,” he says.
These cellular discussions are what prompts, for example, a neuron to encode a memory or a cell to become cancerous. Despite their importance, scientists still don’t have a strong understanding of how these signals work together to guide a cell’s behavior.
To see cell signaling in action, scientists typically introduce genes that encode sensors linked to fluorescent proteins. These molecular reporters perceive a signal and then emit a specific color under the microscope. Researchers can use a different colored reporter for each signal to distinguish the signals. But finding groups of reporters with colors that a microscope can differentiate is difficult. And a typical cellular conversation can involve dozens of signals, or more.
Changyang Linghu and Shannon Johnson, scientists at Boyden’s lab, bypassed this limitation by staring journalists at small, self-assembling proteins that act like LEGO bricks. These small proteins “clung together,” forming clusters that were randomly scattered across the cell as small islands. Each cluster, which appears under the microscope as a luminescent point, reports only one type of cellular signal. “It’s like having some islands with thermometers to report temperature and other islands with barometers to measure pressure,” says Johnson.
In experiments with neurons, the team created clusters that each glowed upon detection of one of five different signals, including calcium ions and other important signaling molecules. After capturing the living cells, the researchers applied molecular labels to the bright spots to identify the reporters there. Using computer analysis, the team transformed the dots into magenta, yellow and other colors, depending on whether they represented football or another signal. This allowed them to see which signals were turning on and off inside a cell.
By monitoring so many signals at the same time, the team was able to figure out how each signal related to each other. “Separating these relationships could help scientists understand complex processes, such as learning,” says Linghu.
Compare a cell to an orchestra and its signals to a symphony. “It is difficult to fully appreciate a symphony by listening to just one instrument,” he says. Because the new technique allows scientists to observe multiple signals simultaneously, “we can understand the symphony of cellular activities.”
Boyden’s team estimates that it may be possible to detect up to 16 signals with their technology, but improvements in genetic engineering techniques could increase that number significantly. “Potentially, you could be looking at dozens, hundreds or even more signals,” he says. “The next challenge,” says Boyden, “is to put sensors for all those signals into a cell.”
Reference: “Spatial Multiplexing of Fluorescent Reporters for Dynamic Imaging of Signal Transduction Networks” by Changyang Linghu, Shannon L. Johnson et al., November 23, 2020, Cell.
DOI :: 10.1016 / j.cell.2020.10.035
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