Transposable Elements in Eukaryotes

Hi in this video we're gonna be talking about transpose herbal elements and you carry outs. So eukaryotic cells have two types of transportable elements. The first type is retro transpose eons otherwise called Class one elements. Either way. They're the exact same thing. And retro transpose eons are called that way because they use an RNA intermediate to jump. So what do I mean by that? So what happens here is you start off with D. N. A. That D. N. A. Is then transcribed and now it's R. N. A. And then that R. N. A. Is going to be turned back into D. N. A. And then jump. So the R. N. A. Intermedia is needed for that jumping. So often retro transpose seasons have their evolutionary history in RNA viruses also called retroviruses and RNA viruses. Their genomic material is just RNA. It's single stranded which is what this S s stands for single stranded RNA. And that's their genetic material. But that RNA also encodes for something called reverse transcriptase which we may have mentioned before. And reverse transcriptase is a protein that is responsible for transcribing our N. A. Into D. N. A. So it's backwards which is why it's called reverse because normally transcription and DNA to RNA reverse transcription is RNA to DNA. And so what usually how these typically evolve did you have a virus that had single stranded RNA. It infected the south that RNA was reverse transcribed to D. N. A. And then it was an integrated into the genome because it was D. N. A. And that genome was like hey there's some free DNA. Let me take that up. And so what it's called um that D. N. A. Is called something special whenever the virus you know put it in there. And so it's called a pro virus which is the D. N. A. From the virus that integrates into the genome. And so um uh this is typically how they evolved. But essentially how this works is you have you start off with our N. A. You go to D. N. A. And then it's inserted into the genome. So an example of a retro transpose on is called a long terminal repeat retro transpose sins. And this means exactly what it sounds like. It's a retro transpose on meaning that it jumps via RNA intermediate but it has these long repeats on the end. And so an L. T. R. Retro transpose on has these repeats on the end and long terminal repeat transpose on. To use that copy and paste method that we talked about before um method to transpose. Then the second class of transportable elements our D. N. A transpose owns or class two elements. And these are the ones that we're more familiar with. Their very similar to the way that the pro carry attic one jumped and they use DNA to jump. So here we have an example here is A L. T. R. Retro transpose on. So here are these long terminal repeats on either end. This is transcribed into RNA RNA is reverse transcribed into D. N. A. That D. N. A. Then integrates elsewhere in the genome. And that is how the retro the retro transpose sins actually end up jumping. So with that let's not turn the page.

Okay so now let's talk about the joseph ely A P. Element. So the joseph delia. Remember fruit flies? The P element is actually one of the first eukaryotic transpose herbal elements identified. And so the P element is a transpose on meaning that it jumps throughout the genome and it has the ability in fruit flies to severely disrupt the genome. And so scientists studying these transpose eons have actually developed um strains of them. So the strains of fly with it are called P strains. So if the fruit fly has p elements that's called peace train and there are different strains of fruit flies with different fruit flies that have them in different fruit flies that don't. So if people studying this have figured out that if you make a peace train, a mail piece train. So a male fruit fly that has these P. P elements in them with a female in strain and this is a strain that doesn't have it. So a male that has it with a female that doesn't what you get is the offspring has has phenotype called hybrid dis genesis. And this hybridization is this just means it's sort of this overarching description of all the offspring. And so this means that all the offspring are kind of screwed up. There are mutations some of them are sterile, there's chromosomal breakage but they have pretty serious defects in every single one of the offspring. Now if you do the cross of that or the inverse of that. So if you take a female piece string. So a female with those P elements and a male M. String. So a male without them then and you make them in their offspring. You get normal offspring. And so studying this, scientists were kind of perplexed and they were like why? Like what has to do with the fact that the female female has the transportable element that makes them like the transportable elements not work. And so the hypothesis and what was found to be true is that the egg, So remember coming from the female peace train has some kind of elements that can suppress the P. Element and it suppresses that jumping. And so the jumping doesn't occur and when the jumping doesn't occur you get normal spring. So right if you made a P. And a female M. What you get is hybrid is genesis where all these offspring the transpose OEMs have jumped into all these different genes. They called chromosomal breakage mutations of a variety of different things sterility. And these are very sickly flies. Whereas if you do the inverse cross, the egg contains P element suppressors. So those transpose ons do not jump. So there's no jumping and when they don't jump that means that all the genes are normal. So you get normal offspring from this cross. So this is a super important super important way that scientists have studied transportable elements. So with that let's not turn the page

Okay so now let's talk about human transportable elements. So you may be surprised that humans also contain them but humans also contain active transportable elements. These are elements that are still moving in the genome now it doesn't happen often but they still do move obviously if it happen often we would be all sorts of mutated but it doesn't happen often but we still do contain them. So the two most important ones the two most common ones at least are called signs and lines. And this stands for short interspersed nuclear elements or long interspersed nuclear elements. And that just is describing the size of them. So signs are shorter, lines are longer now both of these are retro transpose sins. Do you remember from when we talked about retro transpose sins that is going to be transcribed into RNA. A. Then back into D. N. A. Then they jump and integrate. And that is just an interesting fact about these two types of trans human transportable elements. So the most common sign in human is called A. L. U. And there's about 300,000 copies of this throughout the genome. And these are the active copies. So these can jump around. The most active line is called L. one. There's about 20,000 copies of these. And these can still jump around as well. And so the majority of all the transportable elements in the human genome actually don't move right. They've been mutated. They lost some of their transpose is they lost some of their repeats. They don't move they're just stuck there sort of filling up the genetic material. But some do. And when they do, they can actually cause disease. So there are cases of things like hemophilia is a great example. So that's a very genetic disease. But there have been at least one case of a man developing hemophilia without any genetic history of the disease. And scientists were like, oh this is very weird. What happened is that one of these transposing elements had actually jumped into the gene causing that mutation and causing hemophilia. So it's very rare but it can happen. And but however, most of the time when these transportable elements are still jumping in our genomes, they actually just moved to what's known as safe havens and these are regions of the genome that aren't going to cause any harm. So an example like if you had to guess where gene can jump or it wouldn't cause any harm, what would you say? You would say potentially entrance? Right, introns are cut out there, not coding, They're not going to hurt any genes or proteins or anything. So most transposing elements are jumping into places like entrance where they're not causing any harm to the organism. But occasionally very rarely they do jump into areas that can cause disease in humans. And so I just wanted to show you this um graph to give you an idea of how many transpose ons are actually in the human genome. So this is just a various uh this is kind of the key. Right? So if you look at protein coding genes here in this green. That's 2% right and 2% that is posed for all the proteins that make us who we are. But if you start looking at other things, these are n tron, right? And then we start looking at the transpose sins, which is this. We start this and there's even more over here. Right, This dark purple here and the green here this all right. Here are transportable elements. And that is how many of them are actually in the human genome. Now, the majority of these do not do anything right there, completely inactive. But they some of them are active, especially some of these signs and lines are active and can cause disease. So I think it's uh sort of overwhelming I think to realize how much of our genome are these transportable elements. And because there's so many in our genome, you can imagine that they have a huge impact on our evolution. And that's because transpose herbal elements jump, they move around the genome. So they're causing this sort of dynamic phenotype. Whereas they can cause mutations if they insert into a gene that is going to either, you know, that can activate it can hurt a gene, they can jump inside a gene regulatory region and sort of suppress a protein or activated protein more and that obviously is going to affect evolution of that organism and all of its offspring. They can cause chromosomal rearrangements which can cause serious defects um but also can cause, you know, some benefits occasionally very rarely, but it can and if it does, that is definitely a way that causes our promotes evolution. And they actually have the ability to relocate. So they're sitting in the genome. And if their genes really close by like right next to them, they can actually relocate those genes to new regions of the genome. And when they do, those genes are going to be activated by different promoters are going to be suppressed by different factors. And so that is going to affect evolution obviously of that individual organism and all of the offspring that come after. So transportable elements are super, super, super important. Um evolution drivers in the history of humans, but also in the history of many other organisms on the planet. Um so with that, let's not move on.

Which of the following is true regarding reverse transcriptase?

• A. It is required for transposition of DNA transposons
• B. It synthesizes DNA from RNA
• C. It is encoded within long-terminal repeats of retrotransposons
• D. The provirus uses it to insert into the genome

Which of the following elements is a transposable element in Drosophila?

• A. Ds element
• B. Alu element
• C. P element
• D. Ac element

Which of the following is an example of a safe haven for transposon movement?

• A. Intron
• B. Exon
• C. Promoter
• D. Enhancer

Which of the following would occur if an Alu element jumped into the AG splice site of a human gene?

• A. Splicing would occur, and the protein would be unaffected
• B. Translation would not occur on any part of the mRNA
• C. Splicing would not occur and the protein would be altered
• D. Chaperone proteins would correct the damage, and the protein would be unaffected