As your skeleton helps your body move, the thin skeleton-like fibers inside your cells also help cellular structures move. Now, Salk researchers have developed a new imaging method that allows them to monitor a small subset of these filaments, called actin.
“Actin is the most abundant protein in the cell, so when you imagine it, it̵7;s all over the cell,” says Uri Manor, director of the Soph’s Biophotonics Core facility and co-author of the paper. “So far, it has been really difficult to show where the actin interest molecules are because it is difficult to separate the corresponding signal from all backgrounds.”
With the new imaging technique, the Salk team has been able to use the way actin mediates an important function: by helping cellular “power stations” known as mitochondria split in two. The work, which appeared in the diary Methods of nature on August 10, 2020, may provide a better understanding of mitochondrial dysfunction, which has been linked to cancer, aging, and neurodegenerative diseases.
Mitochondrial fission is the process by which these energy-producing structures, or organelles, divide and multiply as part of normal cell maintenance; organelles divide not only when a cell itself is dividing, but also when cells are under large amounts of stress or mitochondria are damaged. However, the exact way in which one mitochondrion sinks into two mitochondria is poorly understood, especially how the initial constriction occurs. Studies have found that removing actin from a cell as a whole, among many other effects, leads to less mitochondrial division, suggesting a role for actin in the process. But the destruction of all actin causes so many cellular defects that it is difficult to study the exact role of protein in any process, the researchers say.
So, Manor and his colleagues created a new way to imitate the act. Instead of labeling all the actin in the cell with fluorescence, they created a target actin probe on the outer membrane of the mitochondria. Only when the actin is within 10 nanometers of the mitochondria does it attach to the sensor, causing the fluorescence signal to increase.
Instead of looking at the actin strangely distributed around all the mitochondrial membranes, as they might not have separate interactions between actin and organelles, the Manor team looked at bright actin spots. And when looked closely, the hotspots were located in the same locations where another organelle called the endoplasmic reticulum passes into the mitochondria, previously discovered to be fracture sites. Indeed, as the team watched the actin hotspots light up and disappear over time, they found that 97 percent of the mitochondrial separation sites had actin fluorescence around them. (They speculate that there was also the act in the other 3 percent of the division seats, but it was not noticeable).
“This is the clearest evidence I have ever seen that actin is accumulating at the sites of grinding,” says Cara Schiavon, co-author of the paper and a joint postdoctoral fellow in the laboratories of Uri Manor and Professor Salk Gerald Shadel. “Much is much easier to see than when using any other actin marker.”
By modifying the actin probe so that it attaches to the endoplasmic reticulum membrane rather than to the mitochondria, the researchers were able to create together the order in which different components come together in the process of mitochondrial fracture. The team results suggest that actin joins the mitochondria before reaching the endoplasmic reticulum. This provides an important insight into how the endoplasmic reticulum and mitochondria work together to coordinate mitochondrial division.
In additional experiments described in a pre-printed printed manuscript available in bioRxiv, the Manor team also reports that the same accumulation of reticulum-associated endoplasmic actin has been seen in places where other cellular organelles – including endosomes, lysosomes and peroxisomes – are separated. . This suggests a broad new role for an actin subordination in organelle dynamics and homeostasis (physiological equilibrium).
In the future, the team hopes to look at how genetic mutations known to alter mitochondrial dynamics may also affect actin interactions with mitochondria. They also plan to adapt actin probes to visualize actin that is close to other cell membranes.
“This is a universal tool that can now be used for many different applications,” says Tong Zhang, a light microscopy specialist at Salk and the first author of the paper. “By turning off the target sequence or nanobode, you can address other fundamental questions in cell biology.”
“We are in a golden age of microscopy, where new instruments with ever higher resolution have always been invented; but despite this there are still great limitations to what you can see,” says Manor. “I think the combination of these powerful microscopes with new methods that choose exactly what you want to see is the next generation of the image.”
Actin filters control the shape of the cell structure that divides plant cells
The actin chromobody image reveals the dynamics of sub-organelle actin, Methods of nature (2020). DOI: 10.1038 / s41592-020-0926-5, www.nature.com/articles/s41592-020-0926-5
Provided by Salk Institute
citation: The imaging method highlights the new role for the cellular protein ‘skeleton’ (2020, August 10) taken August 11, 2020 from https://phys.org/news/2020-08-imaging-method-highlights-role- cellular.html
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