This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have long wondered how cells organized into sheets begin to move together to form organs, especially when the sheets form closed, sphere-like surfaces and tissues with no edges to direct motion. Researchers at the University of Chicago and UC San Diego used a combination of live imaging, genetic experiments and mathematical modeling to understand how cells in the fruit fly egg chamber synchronize their movement.
They found that cells can spontaneously organize and rotate together through a self-reinforcing mechanism in which a specific protein helps individual cells align their movement. Once the cells start moving, that motion polarizes the protein to the back of the cell, which promotes further movement by the cells behind it in the same direction. Mechanical connections between adjacent support cells and the global egg chamber geometry mediate the coordination of cell movements.
"Epithelial cells that form surfaces in the body undergo collective migrations while tissues are developing, during the closing of wounds, the spread of cancers or the constant turnover of things like your intestinal lining," said Sally Horne-Badovinac, Ph.D., professor of molecular genetics and cell biology at UChicago and senior author of the study. "But when there are closed surfaces, there are no external cues that tell the cells which way to go. So, this is a self-organized process." One challenge of studying this phenomenon in egg chambers is that it happens quickly.
Scientists typically can keep them stable under a microscope for a short time and may miss crucial events. Graduate student Sierra Schwabach used a mixture of chemicals that forms something like a blood clot, creating a cushion to hold the egg chamber in place longer. This allowed her to capture images of the cells for up to 12 hours and observe the initiation of rotation.
"Before, we would see cells that were already rotating or that hadn't yet initiated rotation. So, it was a numbers game," Schwabach said. "Being able to watch tissues for hours allowed us to catch the switch-like process of initiation, so that was key." The study, published in PNAS, also explains why the egg chamber always rotates around its long axis.
Initially, this is caused by the physical forces through which the egg chamber interacts with nearby support tissues. As the egg chamber grows and becomes more oval-shaped, its own geometry helps stabilize the rotation axis. This work holds potential implications for understanding both normal development and diseases in which collective cell movement goes awry.
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