Virus-like genes that jump from spot to spot in the genome may help shape the nerves in our brains, possibly helping explain why brains differ so much, even in identical twins.
The finding, reported in the current issue of the journal Nature, investigated a genetic element called an L1 retrotransposon -- a piece of DNA that has the ability to make copies of itself and insert them in new spots in the genome.
About 20% of the human genome is made up of L1 retrotransposons, although most are damaged and cannot move around. Scientists had considered them to be largely junk.
Previously, these elements had been known to jump only in testes and ovary tissue.
A team led by Fred Gage, neuroscientist at the Salk Institute in La Jolla, found they jumped around in the brain.
The team observed the activity of an L1 retrotransposon that had been engineered so that every time it jumped within the genome the cell would glow green.
The modified L1 was put into mice. "We saw these green neurons all over the brain and nervous system," Gage said. "It was pretty amazing."
The jumping appeared to occur inside neural stem cells that gave rise to brain and nervous system cells. The scientists saw signs that the jumps could alter the development of the cells.
It is possible, Gage said, that this creates diversity in the structure of brains by altering ratios of different types of brain cells or changing the way they link up. It could affect the electrical properties of the cells.
Gage said, "The fundamental question is: OK, here's a novel mechanism for generating diversity, but does it really matter? Is there any real consequence of this?"
His team plans to probe this question by, for instance, creating mice in which the elements cannot jump and seeing how they differ from mice in which elements can.