"Jumping genes," or retrotransposons, are sequences of DNA that are easily and naturally copied from one location in the genome and inserted elsewhere, particularly in developing eggs and sperm. There are more than 500,000 copies in the human genome of the retrotransposon the scientists studied, accumulated over the millions of years of human evolution.
But the sheer quantity of these elements isn't as striking as what else they might be doing as they jump around, says Jef Boeke, Ph.D., professor of molecular biology and genetics in the Institute for Basic Biomedical Sciences at the Johns Hopkins School of Medicine.
"Textbooks always show these elements inserting themselves cleanly into new places in the DNA," says Boeke, who headed the research team from Hopkins, "but we saw that about 10 percent of the time, in addition to inserting, it's taking out a big chunk of the chromosome. The interesting thing isn't where these elements are going, but what happens when they get there."
Jumping genes are tightly regulated, and the jumping process probably doesn't happen as often in living organisms as in laboratory dishes, notes Boeke. However, in cells that develop into egg and sperm, even in adults, jumping genes are active. If retrotransposons cause as much chaos in sperm as they do in the lab, they might allow new genetic changes to begin in the next generation, Boeke speculates.
"Assuming that what we see in the laboratory is also happening in real life, it suggests that these elements have been remodeling host genomes more than previously realized, with deletions, insertions and
Contact: Joanna Downer
Johns Hopkins Medical Institutions