DNA Takeover

A long time ago in a galaxy far far away R2d2 set out to take over the genome …..

Selfish elements are genes or sections of DNA that cause themselves to be inherited preferentially even at the cost of the rest of the genome. One such selfish element of the mouse genome is known as R2d2. R2d2 is found on chromosome 2 and starts ‘acting’ selfishly when seven or more copies accumulate.

This week in Molecular Biology and Evolution John Didion and colleagues described how R2d2 can spread through mouse in a devious fashion. They found R2d2 mimics advantageous mutations in order to spread through the population.

In the investigation the group looked into DNA samples from wild mice from Europe and North America to determine the abundance of R2d2. Additionally, in the lab they bred mice in order to see how fast R2d2 is capable of spreading.

The results were rather impressive. For example, in one lab population R2d2 more than tripled from 18% to 62% within 13 generations. In another population in the lab R2d2 reached fixation (meaning all of the mice in the population were carriers of the element) within 15 generations.

R2d2 doesn’t follow usual Mendelian inheritance patterns of the genome. Instead of there being a 50% chance of transmission it is preferentially incorporated into female eggs. The only slight nag in the cunning plan of R2d2 is that the female mice possessing it have small litter sizes than mice without it.

This is an important finding as it suggests that genes which are not beneficial to an organism may be able to cheat their way into the genome.  Also it is important in studying adaptation as what appears to be an advantageous mutation may actually be a selfish element.

It’s not all bad news, though. This finding could prove useful in control of arthropod vector spread diseases such as malaria with the use of gene-drives.  Also in the wild mice populations R2d2 levels were low ,suggesting they may have developed a suppression mechanism.

Photo: Public Domain