Like all stem cells, the fruit fly's sperm-making stem cells can renew themselves or can develop into more specialized cells -- eventually sperm in this case. While a few types of fairly specialized cells can naturally revert to their stem cell origins at times -- think regrowth of salamanders' lost limbs -- the researchers' experiments document what is thought to be one the first clear examples of an artificially triggered reversal of cell fate in an adult creature.

"With a few exceptions, it is thought that once cells start down the path toward specialization, they can't go back," says Erika Matunis, Ph.D., assistant professor of cell biology in Hopkins' Institute for Basic Biomedical Sciences. "But we've clearly shown in fruit flies that lost sperm-making stem cells can be replaced, not by replication of remaining stem cells, but by reversal of more specialized cells."

The Hopkins team studied fruit flies whose "don't-specialize" signal for stem cells can be turned on or off by changing the temperature around them. In experiments to examine what happens when the signal is turned off and then turned back on, second-year graduate student Crista Brawley discovered that cells that are two steps -- but not more -- away from their stem cell origins can revert to the more primitive state.

Understanding how and until what point specialized cells can reverse course might help scientists figure out how to use stem cells to regenerate lost or injured tissue, or how to trigger remaining tissue to better heal itself. There is no immediate application for people, however, because little is known about the corresponding process in humans.

"In fruit flies, we literally can count each stem cell i
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Contact: Joanna Downer
jdowner1@jhmi.edu
410-614-5105
Johns Hopkins Medical Institutions
18-May-2004