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Updated 10:00 AM September 10, 2007




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Researchers dispute widely held ideas about stem cells

How do adult stem cells protect themselves from accumulating genetic mutations that can lead to cancer?

For more than three decades, many scientists have argued that the "immortal strand hypothesis," which states that adult stem cells segregate their DNA in a non-random manner during cell division, explains it. And several recent reports have presented evidence backing the idea.

But in a recent issue of the journal Nature, University stem cell researcher Sean Morrison, director of the Center for Stem Cell Biology at the Life Sciences Institute, and his colleagues deal a mortal blow to the immortal strand, at least as far as blood-forming stem cells are concerned.

They labeled DNA in blood-forming mouse stem cells and painstakingly tracked its movement through a series of cell divisions. In the end, they found no evidence that the cells use the immortal-strand mechanism to minimize potentially harmful genetic mutations.

It remains possible that stem cells in other tissues use this process.

Stem cells generate all of the tissues in the developing human body, and later in life provide replacement cells when adult tissues are damaged or wear out.

Adult stem cells continue to divide throughout a person's life, replenishing the supply of stem cells while generating other cells that develop into specialized tissues.

Like most cells in the body, adult stem cells divide through mitosis, the process of duplicating the chromosomes and distributing a complete set to each of two daughter cells.

DNA encodes genetic information using a four-letter alphabet. Each time a new strand is assembled alongside the template strand, there's a chance that an incorrect genetic letter will be inserted in the new strand, causing a mutation that could lead to cancer.

The lead author is Mark Kiel of the Life Sciences Institute, the internal medicine department, the Center for Stem Cell Biology, and the Howard Hughes Medical Institute.

In addition to Kiel and Morrison, U-M co-authors are Shenghui He, Rina Ashkenazi, Sara Gentry and Trachette Jackson.

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