As organisms grow, their cells have to move into the right places. Cells also move as they divide, build, and maintain all kinds of organisms. Single-celled microbes need to be able to navigate around their environment as well. The physics underlying these dynamics are still not well understood. Researchers have now recreated the process of cell division, outside of a cell, to learn more about it. The findings, which include the short video below, have been reported in the Proceedings of the National Academy of Sciences (PNAS) and can help scientists create better synthetic materials and artificial cells.
“The mechanisms that allow organisms to move and change shape are inherent to life, and they are all underlaid by physics,” noted the senior author of the report Margaret Gardel, a professor of physics at the University of Chicago. “But despite how central they are for our understanding of biology, a great deal of these remain poorly understood.”
While cells have to migrate to different physical locations, cell division involves very complex movements of structures within the cell; different proteins have to get into place, the cytoskeleton has to make the right shapes, and chromosomes have to be copied and properly sorted, for example.
“How cells divide is one of the most basic aspects of trying to create life, and it's something we've been trying to understand for hundreds of years,” said Gardel.
The first author of the report, postdoctoral fellow Kim Weirich, began to use cellular components - actin, a part of the cell’s cytoskeleton, and myosin, motor proteins that are critical to muscle function - to engineer things outside of the cellular environment.
The researchers were shocked to see that when actin proteins were separate, almond-shaped droplets would form. When myosin proteins were added, they moved to the center of the droplet, and the droplet pinched in two. “There's no precedent for this,” said Gardel. “It looks exactly like the spindles that drive cell division."
Modeling the chemistry and physics showed that actin molecules, shaped like rods, align into an ovoid shape, and myosin, trying to stay parallel to the actin, moves to the center. As more myosins accumulate, they cluster, tilting instead of remaining parallel, and pinching the structure in two. Now researchers have taken a detailed look at the process, which is very different from cell division, but probably has similar principles, the researchers suggested.
“This is the kind of thing you need to know to imagine building things like artificial tissue for a wound,” Gardel said.
“Ultimately, a great deal of problems in biology are about how ensembles of molecules work together, and because these are often materials with chemical reactions going on inside, they're very hard to model,” she added. “These kinds of studies allow us the opportunity to explore the basic principles of the forces at play.”
In the video above, Margaret Gardel is featured discussing the physical properties of cells.