新的细胞分裂形式被发现

Researchers at the University of Wisconsin Carbone Cancer Center have discovered a new form of cell division in human cells. They believe it serves as a natural back-up mechanism during faulty cell division, preventing some cells from going down a path that can lead to cancer.

"If we could promote this new form of cell division, which we call klerokinesis, we may be able to prevent some cancers from developing," says lead researcher Dr. Mark Burkard, an assistant professor of hematology-oncology in the Department of Medicine at the UW School of Medicine and Public Health.

Burkard presented the finding on Dec. 17 at the annual meeting of the American Society for Cell Biology in San Francisco.

A physician-investigator who sees breast cancer patients, Burkard studies cancers in which cells contain too many chromosomes, a condition called polyploidy（多倍体）.

About 14 percent of breast cancers and 35 percent of pancreatic cancers have three or more sets of chromosomes, instead of the usual two sets. Many other cancers have cells containing defective chromosomes rather than too many or too few.

"Our goal in the laboratory has been to find ways to develop new treatment strategies for breast cancers with too many chromosome sets," he says. The original goal of the current study was to make human cells that have extra chromosomes sets. But after following the accepted recipe, they unexpectedly observed the new form of cell division.

Until now, Burkard and most cell biologists today accepted a century-old hypothesis developed by German biologist Theodor Boveri, who studied sea urchin eggs. Boveri surmised that faulty cell division led to cells with abnormal chromosome sets, and then to the unchecked cell growth that defines cancer. With accumulated evidence over the years, most scientists have come to accept the hypothesis.

Normal cell division is at the heart of an organism's ability to grow from a single fertilized egg into a fully developed individual. More than a million-million rounds of division must take place for this to occur. In each division, one mother cell becomes two daughter cells. Even in a fully grown adult, many kinds of cells are routinely remade（重造，再做） through cell division.

The fundamental process of cells copying themselves begins with a synthesis phase, when a duplicate copy is made of cell components, including the DNA-containing chromosomes in the nucleus. Then during mitosis, the two sets are physically separated in opposite directions, while still being contained in one cell. Finally, during cytokinesis（胞质分裂）, the one cell is cut into two daughter cells, right at the end of mitosis（有丝分裂）.

Burkard and his team were making cells with too many chromosomes--to mimic cancer. The scientists blocked cytokinesis with a chemical and waited to see what happened.

"We expected to recover a number of cells with abnormal sets of chromosomes," Burkard explains.