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Viral Fossil Brought Back To Life
hey hey hey writes "In a controversial study, researchers have resurrected a retrovirus that infected our ancestors millions of years ago and now sits frozen in the human genome. Published online by Genome Research this week, the study may shed new light on the history of these genomic intruders, as well as their role in tumors. Although this particular virus, dubbed Phoenix, is a wimpy one, some argue that resuscitating any ancient virus is inherently risky and that the study should have undergone stricter reviews."
Only 3% of the genome is genes, the rest is junk DNA which has a lot of interesting stuff like alternate versions of genes, commented out ideas, and coded critters like this one that sit in your DNA like "sunken ships". There are like 200 copies of reverse transcriptase in the human genome, different versions, all in this junk DNA. Reverse transcriptase has absolutely no legitimate purpose in a eukaryote. It can take a segment of RNA (usually viral RNA), convert it into DNA, and stich it into your genome. Only viruses need to do that. The RNA itself has code for reverse transcriptase, and we see it in our chromosomes all over the place, this gene that is useful to viruses and no one else. It's the most common gene in your body.
Viruses have a lytic cycle where they express nasty genes and build capsids inside you, and a lysogenic cycle, where they adopt a different strategy- they get into your DNA, become part of the junk DNA, and they replicate during normal cell division along with all the rest of your DNA.
Junk DNA has all sorts of nasty critters in it. One trick your body uses is to carpet especially infectious regions with methyl groups via cytosine methylation. Basically the idea is that the methyl groups jam up the machinery that comes along to express proteins, so if the proteins are viral, you can "comment them out" that way. When a cell divides, both strands of its DNA have methylated cytosines in the same regions. After the DNA replicates you have two methylated daughter strands, each coupled with a brand new complimentary strand. This complimentary strand has no methyl groups on it. So a clever enzyme comes along, DNA methyltransferase. It has a regulatory domain and a catalytic domain. The regulatory domain runs across the DNA feeling it for methyl groups. If it finds them on one strand, the catalytic domain deposits methyl groups on the other strand. That way, the stretch of DNA can be marked as "bad news" in a way that is heritable, despite the fact that no actual DNA sequence is being "inherited". As far as where the initial methylation signal came from, that can probably be put down to natural selection.
In this particular case, there were 30 copies of the virus in the genome. They worked backward to create the original virus. The resultant virus was disabled so that, after replicating once in a cell, the daughter viruses could not replicate. So there was no risk.
In the human genome, the researchers point out, are the pieces from other viruses. 8% of the human genome codes for HERV proteins or their regulatory subunits. If these pieces are activated, they can reassemble to create a new, working virus. This happens naturally.
All of these HERVs are viruses that, throughout human evolution, we and our ancestors have more or less come to terms with. At some point, many of them were probably devastating. But those that caught the virus, survived, and reproduced were able to mitigate the effects of the virus. These are viruses we've reached a "détente" with. They no longer rampage through the population. In fact, some of the proteins they produce are vital to our survival. One of these retroviral proteins permits implantation of the placenta. Without it, we'd all have placentas that don't attach to the uterine lining -- like mice, which as a result, aren't very complex when they have to be born.
Yes, HERVs are related to cancer. This occurs naturally. They act in a transposon-like manner, and they can pop into areas where they either damage mechanisms that prevent cancer or control cell replication. If we don't study these viral remains, we won't learn about them, won't learn what we can safely disable further -- and what we don't dare eliminate from our genome because we are dependent upon it.
These researchers were not Dr. Frankensteins, messing with things man was not meant to know. They were careful, they were deliberate, and theya re beginning the investigation into what could be an incredibly crucial topic in molecular biology.
Remember -- these are viruses that we learned to live with, more or less. By studying them, we can learn to mitigate the damage they still present.
This sig seemed like a good idea at the time....
My problem with evolution is that it doesn't explain the beginning.
Then you need not have a problem with evolution. Evolution and abiogenesis (life from non-life) are two separate questions and topics. Evolution tells us that descent with modification is the current best explanation for the species and forms we see today. It does not purport to tell us what the first life form(s)? were or how they came to be. That is a separate and far more speculative field of study.
Even Darwin understood this way back when. His first attempt to systemize evolution was NOT called "Origin of Life". It was called "Origin of Species". Evolution operates on extant forms of life. If it operates in the processes that lead to life starting in the first place, the mechanisms involved are likely different from the ones creationists and (reputable) biologists argue all the time. Evolution presupposes entities capable of self-reproduction. You need replicators of some sort to even talk about evolution in the first place. Once the first replicator either spontaneously arrives or is created (and no this need not be dismissed out of hand but if the only case for it is faith-based then we aren't talking science.....) then evolution can take over and eventually bring about forms vastly more varied and different from the starting point.