Retroviruses Are WAY Older Than We Previously Thought
Thats Nice... but.. uh... What The Hell Is A Retrovirus?
Unlike the image above would have you believe, retroviruses are not named because of their Afros and moves on the dance floor.
Ahem! A retrovirus is an RNA virus, meaning its genome is composed only of single stranded RNA (unlike our genomes which are double stranded DNA). These viruses infect their hosts and inject their RNA, which is then converted into DNA by an enzyme called a reverse transcriptase. After a complementary DNA (cDNA) copy of the viral genome has been constructed the virus utilizes another enzyme called an Integrase which inserts the viral genome into the genome of the cell it has infected. At this point the virus is a part of the cell and is referred to as a provirus. After integration the virus can go dormant for years, or the RNA (its real genome) can be expressed by the host cell's RNA producing machinery. This leads to expression of the virus' proteins and re-construction of lots of new baby viruses which then are free to burst out of the cell and infect new cells (repeating the cycle described above!)
Boy That Sounds Awful...Are There Human Retroviruses?
There sure are, one very prominent disease causing virus you are most assuredly familiar with is a retrovirus: Human Immunodeficiency Virus (HIV). However HIV is far from the only retrovirus infecting humans, its not even the only disease causing retrovirus, there are also a pair of T-cell infecting viruses called human T-lymphotropic virus type 1 (HTLV-I) and human T-lymphotropic virus type 2 (HTLV-II). HTLV was actually the first human retrovirus discovered (before HIV), and is known to be a cause of T Cell Lymphoma (a cancer of the white blood cells, not something you want to be diagnosed with).
There are actually a whole host of other retroviruses that infect humans, but you will be at least a little bit relieved to know that the majority of these viruses are not known to cause any diseases (well at least none that we know of YET!) (source). What is interesting is that our genome is actually littered with the tattered remains of proviruses (remember these are retroviruses that have integrated themselves into a hosts genome). Many of these proviruses have been a part of the human genome for a long time and only bits and pieces remain (these are termed endogenous retroviruses, and are relics of past infections). Some of them even encode for functional virus proteins (and these proteins have been implicated in auto immune disorders like lupis).
What may be even more surprising to you is that many people actually have a fully functional whole virus in their genome right now (source). In the article I just cited, the authors discovered that in a screen of 2500 genomes, 50 of those had the fully functional virus. This means that their might be a 2% chance that YOU have this virus in your genome (if we can generalize their findings to the human population as a whole, which we may or may not be able to do), those odds are better then being struck by lightning at some point in your life (0.008%).
Okay... Okay, I Might Be Harboring a Fugitive Virus... Enough of That... Get To The Topic At Hand!
Scientists have gained knowledge about a good many things. However the origins of retroviruses has not been one of those things. Until recently we just haven't had the technology to really analyze enough genomes of any type to get a clear enough picture of what is there. Earlier I mentioned endogenous retroviruses (the left over pieces of past infections, that are still a part of the human genome), well the oldest of these was thought to be around 100 million years old (based on limited exploration of the human genome).
However in the article titled "Marine origin of retroviruses in the early Palaeozoic Era" the authors were taking advantage of our latest and greatest genome sequencing technologies (which I discussed for you HERE (<--- Click it... check it out... you know you want to know more!!) and explored the lineages of the endogenous retroviruses from frogs and fish. What they found is that the estimate that retroviruses being only 100 million years old is way way off! Instead they determined that the retroviral elements present in these genomes were up to 450 million years old, which is as old as their hosts are themselves!
How Do They Determine These Ages?
Analysis of evolution and of course math (ewww math)...
The researchers looked at the evolution of the viruses through studying the accumulation of mutations. When initially doing this the authors found that the formula they were using to calculate these mutation rates made it seem like viral mutation rates were slowing down if longer time frames were examined. However mutations occur at a regular rate for a retrovirus over any time period (they are a function of the relative poor copying abilities of the viral reverse transcriptase... it just makes a bunch of mutations). So upon correcting for the apparent slow down in mutations rates the authors were able to extrapolate the age of these viruses back to a similar time to when their animal hosts came into existence.
TL;DR
Retroviruses are RNA viruses that incorporate their genomes into their hosts. They are generally not disease causing agents in humans with the notable exception of HIV (causes AIDS) and HTLV (causes leukemia). Researchers had thought for quite some time that these viruses evolved into existence long after their hosts (animals.. vertabrates... humans etc.) however recent work indicates that they may have co-evolved along with these hosts! Neat.
For more information check out the following article on nature.com:
http://www.nature.com/news/ancient-retroviruses-emerged-half-a-billion-years-ago-1.21274
Or if you are brave, dive right into the primary article:
http://www.nature.com/articles/ncomms13954
Additional References
1 https://en.wikipedia.org/wiki/Retrovirus
2 http://www.health.state.mn.us/divs/idepc/diseases/retrovirus/
3 https://www.ncbi.nlm.nih.gov/books/NBK7934/
4 https://steemit.com/science/@justtryme90/science-lesson-dna-part8-dna-sequencing-how-do-we-determine-a-genome-s-sequence
5 http://www.lightningsafety.noaa.gov/odds.shtml
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I think all of us know what HIV is but only a few knew how it exactly works! (I didn't know at all). Thank you for sharing and I LOVE the way you write; seriously, how can you make it so fun? jajaja I have to learn that skill
I appreciate your kind words, a lot! It means a lot to me that great posters such as yourself enjoy my writing! Thanks for reading, I'm looking forward to your next post, I liked your last one on extraction of essential oils :)
It's me who is honored! Thanks to you :)
The more I learn about viruses, the more amazing they are. We still know so little about them.
Indeed, we still know so little about many biological topics. With biology you have to wait for things to grow...Slows down progress :D
Fun post. I didn't realize you were a cofounder of SteemSTEM. Great idea for an account. I've followed you as well now.
Thank you. You've written some fun posts yourself. The steemSTEM project, it's been slow to grow (I honestly thought more people would have liked it then so far have, only 100ish followers). Ideally we would like it to be able to really give a boost to upandcoming STEM writers, but for now it's more getting known by the community and using what funds we accumulate from its own posts to give back directly. We are always looking for more help, so if you've interest come chat with us on steemit.chat.
Do you minds helping me understand the link between the retroviruses and the afro people? Thanks in advance!
Except for this, I have learned a lot! Thanks for sharing!
The term retro also means old or throwback in a culture style context. So Afro's were a common hair style in the 1970's but are gone largely from modern culture, so they are a retro style. Same goes for the disco references.
My jokes don't always come across clearly :D
Aaaah got it :D I am too tired :)
Very informative post and at the same time written with humor, a pleasure to read. thank you!
Thank you for reading
Very interesting. Nice work sir. I think the autoimmune theory is very interesting. I have Type I diabetes...now the "theory" is that some virus causes molecular mimicry. I would imagine most are not retroviruses. However, for some it may be an unknown retrovirus. Thanks for the part about dating retroviruses. I had not thought/know about this.
Edits In Rapid Fire: Kept saving when I hit enter. Corrected two links for formatting and added a source that was neglected.
Reworded a sentence about the age of the viruses. It comes across more clearly now.