Okay, I admit, this one’s not quite sex-related. But in some ways, the interactions between a symbiotic bacteria (like Wolbachia) and its host is kind of like sex. There needs to be two-way communication. Sometimes, both get what they want out of the relationship. And sometimes, the interaction can turn ugly.
In a recent article (here) published in the Proceedings of the National Academy of Sciences, Mazhar Hussain, Sassan Asgari and colleagues found the bacteria Wolbachia hijacks mosquito genes to express more of the genes it needs to survive. How does it do this? By using mosquito “junk” DNA.
In biology class, we learn that DNA makes RNA (the “message”) and RNA gets translated into proteins–the things that do all the real work. But the real story is a lot more complicated. Not all DNA gets used to make proteins. Some of it looks like it does nothing, hence the term “junk DNA“, but in fact a lot of that junk is actually really important. Some of it makes micro RNAs–tiny snippets of RNA that act as switches to change the way genes get used to make protein.
Our understanding of micro RNAs (or miRNAs) and other related RNAs is still not great. The discovery of RNA as a way to turn off or on genes only dates back to the ’90s, but it has turned out to be really important for biology and might have implications for medicine, too. In fact, Andrew Fire and Craig Mello won the Nobel Prize in 2006 for showing that you could turn off worm genes by injecting them with a special kind of RNA.
But I digress…back to the mosquitoes…
I recently blogged about how mosquitoes artificially infected with Wolbachia can’t reproduce unless they feed on human blood. Wolbachia infect insects and are passed on in the eggs. These bacteria can have all kinds of effects on reproduction. But no one really understands how Wolbachia is able to survive inside insect cells.
The new research shows one way that Wolbachia manipulates its host to help its own survival. When mosquitoes are infected with Wolbachia, the amount of different micro RNAs (miRNAs) they make changes. Some miRNAs go up, some go down. The researchers picked one miRNA to study further, aae-miR-2940 (catchy name, right?). Mosquitoes infected with Wolbachia make a lot of this miRNA, whereas uninfected mosquitoes make practically none.
Except for in a couple of interesting cases, miRNAs typically turn off genes, causing the loss of particular proteins. But this is one of the rare cases: aae-miR-2940 turns a gene ON. The gene it turns on makes a metallprotease. Metalloproteases are enzymes that can cut other proteins to either destroy them or activate them. The “metallo” part just means it depends on a metal for its function.
No one knows yet what this particular metalloprotease does in the mosquito, but if you get rid of it, Wolbachia have a hard time surviving. Understanding how Wolbachia “talks” to host cells is important because Wolbachia infection is actually able to reduce parasite levels in mosquitoes. These are the parasites (like malaria or Dengue) that cause disease in humans. The more we find out about how this works, the better chance we have of doing something about these mosquito-transmitted diseases.
Besides aae-miR-2940, about 34 other miRNAs were found to change in Wolbachia-infected mosquitoes. I guess we’ll have to wait to find out what they’re doing for Wolbachia.
- Human blood contains the secret ingredient for mosquito eggs (nittygrittyscience.com)
- Wolbachia bacteria reduce parasite levels and kill the mosquito that spreads malaria (medicalxpress.com)
- The Sea Change that’s Challenging Biology’s Central Dogma (discovermagazine.com)