Just as human relationships are a two-way street, fusion between cells requires two active partners: one to send protrusions into its neighbor, and one to hold its ground and help complete the process. Researchers have now found that one way the receiving cell plays its role is by having a key structural protein come running in response to pressure on the cell membrane, rather than waiting for chemical signals to tell it that it's needed. The study, which helps open the curtain on a process relevant to muscle formation and regeneration, fertilization, and immune response, was published online on February 12, 2016 in journal Developmental Cell. "We knew that in cell fusion, one cell attacks its fusion partner, but we didn't know what the other cell was doing," says Elizabeth Chen, Ph.D., an Associate Professor of Molecular Biology and Genetics at the Johns Hopkins University School of Medicine. "Now we know that the other cell is putting up some resistance." The merging of two cells, which is crucial to conception, development, and physiology of complex organisms, was long thought to be a symmetrical process, where two cells contribute equally. But two years ago, Dr. Chen's research group showed that, in fact, one of the fusion partners initiates the process by extending fingerlike protrusions into the other partner. For the current study, Dr. Chen's group and collaborators focused on the receiving partner. Using fruit fly embryos and lab-grown fly cells that were induced to fuse, they saw that in the areas where the attacking cells drilled in, the receiving cells quickly fortified their cellular skeletons, effectively pushing back. "We think that by stiffening its skeleton in this way, the receiving cell avoids moving away from the attacking cell, in which case fusion couldn't occur," Dr. Chen says.
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