Differences in Division

From one to two: late stage of HeLa human cell division. Credit: Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited/Corbis

While scientists have spent the past forty years describing the intricate series of events that occur when one mammalian cell divides into two, they still haven’t agreed on how the process begins. There are two seemingly contradictory theories, which now may be reconciled by a third theory proposed by Duke’s Lingchong You, assistant professor of biomedical engineering. The theory could provide insights into cancer, which is marked by uncontrolled cell proliferation.

During proliferation, the DNA within the nucleus of a cell makes a copy of itself, and the cell then splits into two, each half taking with it an exact copy of the genetic makeup of the cell. One of the two prevailing models for explaining cell division says that the beginning of division for any specific cell is just a random event. The second model assumes that there are intrinsic differences that enable some cells to start the process earlier than others.

You’s team found that a specific gene circuit known as Rb-E2F has the ability to tell some cells to start dividing while at the same time telling other cells to lie low. You’s team began the experiments by taking an identical population of mouse cells and then starving them of nutrients—essentially putting them in a state of hibernation. The cells were then given nutrients, which caused them to start dividing. Researchers then watched to see which cells started the process first.

“The process is much like what happens after a large Thanksgiving meal,” You explains. “All the family members sit at the table and celebrate by eating a lot of food. However, after the meal, some of the family members will go outside and do something active, like playing football, while others will remain at the table or watch the game on television.”