Viruses are pretty interesting things in biology. We still cannot come to an agreement whether they are alive or whether they are just a bunch of chemicals sometimes replicating themselves. They are everywhere. They can kill but they can also serve as a powerful tool for evolution. What if I told you, that there is one virus that had infected your ancestor and you couldn’t be born without this event? Today I’d like to tell you something about one special kind of viruses – retroviruses.
As you might know, stretched DNA from one human cell is approximatelly 2m long. That is quite long, and you might suggest that it has to contain tremendeus amount of information. And yes, partially it is true. But it looks like only 10% of our DNA is used for something useful. The rest of it? We don’t know, seems to be junk. Copies of genes that lost function, meaningless repeats of letters and believed it or not – inactivated ancient viruses. How did they get there?
One of the reasons why it is so hard to get rid of HIV from your body is that once it infects you, it inserts in to your DNA. So no matter how much you fight against the viruses in your body, you are never truly cured if the information stays in your DNA. HIV is just one example and there is a lot of them out there. And not all of them can be as deadly. Around 8% of our genomes are ancient viruses (or what remains from them during evolution) that are inactivated and do nothing. But there is one really cool example that evolution can transform something as hostile as a virus into something useful.
Placenta is an organ that is absolutelly essential for every human being to be born. Exchanging of nutrition, getting rid of waste, exchanging of gases etc. Placenta is capable of all of this. But in order to do this, placenta has to be properly formed. During formation of the placenta, the cells has to fuse together to create an important physiological system.
When the scientists analyzed the protein, called syncytin-1, responsible for the fusing, they found out that it has very a similar sequence to retroviral surface gene (look above). When retrovirus infects the cell, it has to fuse with it. The very same gene responsible for fusing virus particle with the cell was shaped by evolution to function as a tool for creating placenta. How cool is that? Our ancestor got infected by a retrovirus and millions of years later, part of this virus is activated so you can be born.
Isn't it absolutely amazing?
