The RTL6 proteins, shown in green, guard the mouse brain capillaries (the branch-like structures in black) against ‘infection’ by clustering around the magenta-colored bacterial mimic. Credit: Tomoko Kaneko-Ishino
Key Points:
- Infections that occurred millions of years ago have shaped human evolution, with viral genes being incorporated into DNA and passed down generations.
- Researchers have discovered two ancient genes left behind by a viral infection that have evolved to help defend the brain against new infections.
- The study results are the first example of viral-derived genes that have been re-purposed to protect mammalian brains.
Scientists in Japan have discovered that two mouse genes—left behind by a viral infection at least 120 million years ago—have evolved to help defend the human brain against new infections. The genes, known as retrotransposon Gag-like 5 and 6 (Rtl5/Rtl6), are carried by almost all mammals, and are similar to genes found in retroviruses, such as HIV.
Researchers first discovered that Rtl5 and Rtl6 are switched on in the brain in cells called microglia, which act as the “first responders” to infection. Seeking more information, the team set up fake infections in mice brains to test how the microglia producing RTL5 or RTL6 would respond to either bacteria or viruses.
In their study published in Development, the researchers found that microglia-containing RTL6 protein responded to the bacteria-like mimic, whereas the microglia with RTL5 reacted to the simulated viral infection. In addition, when the researchers removed the Rtl6 gene, they found that the mice could not eliminate the fake bacterial infections, while the mice without Rtl5 could not clear the viral mimics—meaning that together Rtl5 and Rtl6 protect the brain against two of the most common types of infection.
According to the researchers, these results provide the first example of viral-derived genes that have been re-purposed to protect mammalian brains.
“Virus-acquired genes are essential parts of our genome, playing various—but essential—roles in mammalian and human development,” said study author Fumitoshi Ishino, professor of molecular biology at Tokyo Medical and Dental University. “We think it is possible to extend this idea to primate- and human-specific acquired genes from retroviruses to help us understand human evolution.”
Information provided by The Company of Biologists.