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Cells in Reverse

Cells in Reverse

Even all the plastic surgeons in Hollywood can’t turn back the hands of time. But scientists recently found a way to rewind a seemingly irreversible biological process.


Transcript

Putting cells in reverse. I'm Bob Hirshon and this is Science Update.

For the first time, scientists have reversed the process of cell division: a trick once thought to be as impossible as un-ringing a bell. Molecular biologist Gary Gorbsky of the Oklahoma Medical Research Foundation led the effort. By tinkering with proteins that regulate the process, they turned the clock back from the end of the cell cycle to the middle.

Gorbsky:

And specifically, the end stages, where they’re actually divided in half, we’ve been able to reverse that process, and go from the stage at which you have two cells back to the stage at which you have a single cell.

This worked only when the divided cells hadn’t completely finished separating. The implications aren’t clear yet, but the technique could be useful to cancer researchers, who are always looking for ways to keep rogue cells under control. I'm Bob Hirshon, for AAAS, the science society.


Making Sense of the Research

The process that Gorbsky’s team reversed is mitosis, which you may have studied in biology class. In mitosis, a cell divides by duplicating its chromosomes (the strands of DNA containing genes), ripping them apart, and splitting the cell in two. Mitosis is divided into several stages (see “Going Further” for more information). Gorbsky’s team took cells that were in the final phase of cell division, called cytokinesis, in which the chromosomes have separated and the cell has split in two, and rewound them to metaphase, in which the duplicate chromosomes are still attached to each other, and lined up in the center of a single cell.

You can see why this is so groundbreaking. It’s one thing to glue a broken vase back together, but could you actually restore it to its original form—with no cracks, as if it were never dropped? What Gorbsky’s team did here is just as amazing. It’s almost as if they turned back the hands of time, at least for this particular cell.

But Gorbsky’s team couldn’t just make two completely separate cells find each other across a crowded petri dish and smush back into one. Rather, they had to act while the divided cells were still connected by the midbody: a small, plug-like structure that buttons the new cells together for several hours after the original cell splits in two. In other words, the reversal could happen only if the job wasn’t quite finished.

So how did they do it? Basically, by fiddling with an enzyme that plays a key role in controlling mitosis. The enzyme, in turn, is controlled by a protein called an activator. Near the end of the cell division process, this activator protein is destroyed, which turns the enzyme off and signals the cell to finish the job.

But Gorbsky’s team figured out a way to keep this activator protein around, and to turn the enzyme on and off directly, using another chemical. So, basically, they developed a way to “manually” stop the cell cycle before it was completely finished. Then they reactivated the enzyme (with the activator protein still present). That’s when something surprising happened. Instead of ditching the little midbody and splitting apart completely, the divided cells actually fused back together and rewound to the middle stage of mitosis. It’s as if they hit some kind of a biological reset button, fooling the cell into retracing its steps.

This study is a kind of basic research: work that scientists do to understand the world, rather than to invent something or solve a specific, practical problem. Prior to this study, scientists suspected that the destruction of the activator protein was partly responsible for making the cell cycle run forwards. By showing that keeping the protein around makes the cell cycle run backwards, Gorbsky’s team not only confirmed this, but also discovered something that no one knew you could do before.

Looking to the future, this knowledge may have many possible applications. As the story suggests cancer therapy is a strong possibility. Cancer, as you may know, is basically the result of rogue cells growing and dividing out of control. If scientists can not only stop these cells from dividing, but also reverse the process, it could open the door to a whole new kind of treatment.

Now try and answer these questions:

  1. What is mitosis?
  2. What exactly did this study accomplish?
  3. How did this research both confirm an existing hypothesis and discover something new?
  4. Can you think of other reasons why scientists would want to reverse the process of cell division?

For Educators

The Cell Cycle, from Cells Alive! features an animation of the cell cycle, the sequence of activities exhibited by cells. A detailed explanation of each cell phase is included on the page.

The Access Excellence activity Chromosome Shuffle is designed to clarify and reinforce student understanding of the cellular processes of mitosis and meiosis.


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