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UMass Team Finds Surprising Final Step in Cell Division
By Elizabeth Cooney
Worcester Telegram & Gazette
10 October 2005
WORCESTER - UMass Medical School scientists studying cell division have discovered remarkable activity in an overlooked cellular structure that may unlock secrets to aging, cancer and stem cells.
In the current issue of the scientific journal Cell, Dr. Stephen J. Doxsey and his colleagues describe what goes on in the final stage of human cell division, when two daughter cells snap apart. One of the most surprising things they found was that when a cell divides into two, the two daughters cells are not exactly alike.
The researchers made their discovery when they were exploring the little-studied "residual body," which is the ever-narrowing bridge that forms between two daughter cells when the cell is breaking into two. They were interested in this thin structure because they had seen the protein centriolin there, which was unexpected.
Centriolin is involved earlier in the process of cell division, when chromosomes are separated so that the two daughter cells get faithful copies of their genetic material. In a paper published in 2003, Dr. Doxsey reported that the protein was also necessary for the final stage of cell division. The current paper demonstrates how.
The team found that centriolin anchors a mid-body ring of protein complexes needed for breaking apart the daughter cells. Just before the daughter cells split apart, one daughter sends small sacs of fluid down this bridge to the daughter on the other side of the mid- body ring. These vesicles fuse and then burst, splitting the two daughter cells apart.
One daughter cell keeps the protein-dense mid-body ring while the other doesn't. In fact, Dr. Doxsey's lab has found cells carrying as many as six mid-body rings. If cells accumulate mid-body rings every time they divide, the rings could be markers for older cells or possibly contribute to aging itself.
Such differences between cells may yield clues about how cells age and die. That raises questions about cancer, in which tumor cells continue to grow, and also in stem cells, which continue to give rise to new cells that go on to have different functions.
"We believe this opens up a new area of research on aging and potentially on how stem cells divide and maintain their ability to keep dividing without differentiating," Dr. Doxsey said last week. "There also may well be implications for cancer research, because a hallmark of tumor cells is their ability to divide indefinitely."
PHOTO; In this image from the Doxsey lab, two human cells are about to divide. The area in green shows the emerging daughter cells; the blue is their nuclei. The black line marked by the arrow is the mid- body ring discovered by Doxsey's team.
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