PROVIDENCE, R.I. [Brown University] Even in our DNA there is no refuge from rogues that prey on the elderly. Parasitic strands of genetic material called transposable elements transposons lurk in our chromosomes, poised to wreak genomic havoc. Cells have evolved ways to defend themselves, but in a new study, Brown University researchers describe how cells lose this ability as they age, possibly resulting in a decline in their function and health.
Barbara McClintock, awarded the Nobel Prize in 1983, made the original discovery of transposons in maize. Since then scientists have found cases in which the chaos they bring can have long-term benefits by increasing genetic diversity in organisms, but in most cases the chaos degrades cell function, such as by disrupting useful genes.
"The cell really is trying to keep these things quiet and keep these things repressed in its genome," said John Sedivy, professor of medical science in the Department of Molecular Biology, Cell Biology, and Biochemistry and senior author of the new study published online in the journal Aging Cell. "We seem to be barely winning this high-stakes warfare, given that these molecular parasites make up over 40 percent of our genomes."
Cells try to clamp down on transposons by winding and packing transposon-rich regions of the genome around little balls of protein called nucleosomes. This confining arrangement is called heterochromatin, and the DNA that is trapped in such a tight heterochromatin prison cannot be transcribed and expressed.
What the research revealed, however, is that carefully maintaining a heterochromatin prison system is a younger cell's game.
"It's very clear that chromatin changes profoundly with aging," Sedivy said.
What Sedivy, lead author Marco De Cecco, and their co-authors measured in several experiments was that young and spry cells distinctly maintain open "euchromatin" formations in regions where esse
|Contact: David Orenstein|