Transcript

CRISPR: Editing our genetic instructions | Rachel Haurwitz | TEDxSanFrancisco

[Music] All organisms share DNA as the fundamental coding unit of life. It's just four letters, A, T, C, and G. And yet these molecular blueprints instruct all cells which proteins to make and when. There's tremendous variation in the many, many ways that these four letters can be strung together to give different instructions, giving us the tremendous diversity of life that we see on our planet today. Everything from bacteria to elephants to us. Subtle differences help explain, for example, why my brother has blue eyes while I have brown ones, or perhaps why two very closely related plants that only have a small number of DNA sequence differences between them might respond to certain weather conditions completely differently. One might thrive in low water conditions while the other one dies very quickly in a drought. Mutations or mistakes in human DNA can cause devastating diseases like cystic fibrosis, muscular distrophe or cickle cell anemia. What if we could access this code? What if we could actually get into cells and precisely change these DNA sequences? Thanks to an incredibly exciting new technology called crisper cast 9, this is possible and researchers are able to access the DNA and unprecedented ease and speed and specificity make changes to the code inside of living cells. This is typically referred to as gene editing or genome engineering. And crisper is joining a growing toolbox of ways that scientists can do this. It's basically a biological word processor. And I'll try to give you a little bit of a flavor for how it works. Let's pretend this is a little snippet of DNA inside of our cell. But this cell has a problem. It has an extra word in its genome. It has the word not. And so it means that this cell does not make the correct protein. Using the crisper cast 9 technology, researchers can directly target that word not cut it out and leave the cell now with the correct sequence and allow the cell to make the correct protein. So how does this work? At the heart of gene editing is the ability to make a cut in the DNA at the exact spot where you want to insert or delete DNA sequences. In the crisper technology, a specialized protein called cast 9 is the pair of molecular scissors that's able to make this cut. Now, it turns out cells really hate having their DNA being broken, and all kinds of alarm bells go off when that happens. And if they can't fix it, they'll die. Most cells have at least two ways to fix these breaks. And depending on which ones they use, different editing outcomes are possible. One method is called non-homologous endjoining or NHJ for short and it's really the molecular equivalent of putting a bandage or maybe stitches onto the broken site. The cell successfully glues those broken bits back together, staving off death, but in the process inserts or deletes a few nucleotides, a few pieces of DNA, ultimately changing the sequence of the DNA at that site and almost always disrupting the ability for the gene that used to be coded there to be expressed. And so this is how we delete genes from the genome or knock them out. The other common method is called homology directed repair or HDR for short and it's more like a molecular cut and paste mechanism. In this process, cells take cues from extra strands of DNA that scientists provide as part of the experiment. And these strands of DNA have information. They're basically a template for what sequences should be put into that broken site to help repair it. Through this process, we're actually able to insert new genetic material at those particular sites. It could be as simple as one new nucleotide of DNA, or it could be an entire new gene that we land at that spot. The average human cell has more than six billion base pairs of DNA. And I told you we need to make the cut at the site that we want to edit. So how on earth are we able to find one site in that very very long coding sequence? At the heart of this technology is that special protein that I mentioned cast 9. And it does the hard work of actually cutting the DNA. But it turns out that on its own it's pretty useless. It actually can't cut DNA. It needs an RNA partner to work with it and guide it to a particular site in the genome so that it can then turn on and cut the DNA. RNA is basically the molecular cousin of DNA and it can base pair or form bonds with DNA in the same way that two strands of DNA can base pair with each other as well. This particular RNA that cast 9 relies on is called a guide RNA. And it has a special sequence in it that's about 20 nucleotides long. And that sequence actually spells out the exact sequence of the DNA site to be cut. And so scientists can reprogram this guide RNA by spelling out a new sequence in the genome, pairing it with cast 9. And the guide RNA then drags cast 9 to that site and makes a cut. So I'd like to show you a little video that explains a little bit about how cast 9 and the guide RNA are actually able to access the DNA and make a cut. We'll start way zoomed in on a 3D rendering of the cast 9 protein holding on to a guide RNA. We'll zoom back out, look at the complex, and then see how it's able to interact with doublestranded DNA and it actually melts the DNA open at the site that matches the RNA. The RNA base pairs with the DNA and then cast 9 can cut. So here we are inside that complex zooming out. In gold is the protein and in red and blue is the guide RNA. You can see that cast 9's holding pretty tight onto that guide RNA. And we're going to see that 20 nucleotide sequence displayed that spells out the target site that this RNA is looking for. It's then able to find that matching site in doublestranded DNA, melt that open, base pair with it, and that locks cast 9 in place. And now cast 9 can make that cut. Cast 9 comes to us from a rather obscure corner of nature, from a bacterial immune system called crisper. In this immune system, bacteria are actually able to steal small pieces of viral DNA when they're infected, store it in their own genomes, and use it as a sort of molecular memory card of past infections. This immune system then helps them fight off future infections. And the way it works is that they make little RNAs, guide RNAs, holding on to these viral sequences. Cast 9 grabs those guide RNAs and is constantly surveilling the cell looking to see if there's new matching virus DNA that has come in. If they find it, cast 9 is able to engage just as we saw and cut and destroy the virus, saving the cell from infection a few years ago. Now scientists were able to co-opt this system out of its native bacterial context, reprogram these RNAs so that they could target not only viral DNA but the human genome, plant genomes and many other genomes and use this as a sightspecific way to do genome engineering. So why is this important? Why is this valuable? And why are scientists so excited about this? First off, genome engineering has the potential to absolutely transform basic research. We're seeing thousands of labs around the world start to use this technology as one of their go-to molecular biology tools. One of the things that many groups are able to do is build much better cellular models of disease. They can take mutations that have been identified in patients, recapitulate those in cells in a dish, and really understand the biology of the disease, the biology of development, and potentially start developing new drugs to better target these diseases. Likewise, they can use the same technology to make better animal models of disease, directly modifying the genomes of animals, whether it's mice or rats, rabbits, or pigs, to better recapitulate human disease, understand what causes it, and hopefully learn new ways to treat it. But on top of all of that, I'm incredibly excited about the opportunity to directly use this technology to treat and potentially even cure genetic diseases. Here's an example. Cickle cell anemia is a blood disorder that's caused by a a particular mutation in the hemoglobin gene. Patients with this disease have red blood cells that form a sickle shape, sort of look like crescent moons, and they don't do a very good job at carrying oxygen. And today, there's no cure for that disease. In theory, doctors could extract a patient's own blood stem cells, put them on the bench, use the crisper cast 9 technology to correct that mutation, and then transplant those corrected stem cells back into the patient, allowing them to repopulate the blood system and providing uh red blood cells that are better at carrying oxygen. There's a tremendous amount of work still to be done to fully transform this from an exciting technology into real therapies and there are many many many groups around the world working on this right now. The first handful of trials that will test using this technology in humans are starting this year, next year, and the year after that. And they'll be studying ways to potentially treat or even cure everything from cancer to genetic diseases. But it's not just humans who will benefit from this technology. We have the potential to really address some major unmet needs with respect to animal health and animal well-being. Our company had the opportunity recently to join a collaboration with a number of other researchers who are attempting to help pigs fight off a particular virus called porcelain uh reproductive and respiratory syndrome virus or pers. It's one of the worst viruses that farmers have to face in their pig populations and there's no cure for it today. Our collaborators have already shown that by using gene editing, they can remove just a single protein from the pig's genome, making it completely resistant to the virus. The virus needs that protein to actually gain access to the pig's cells. And so without it, the virus cannot infect. Again, there's still a lot of work to be done in terms of developing this as a product, but it's an exciting potential opportunity to save a number of pigs lives, to increase food security, and to also reduce the amount of losses that farmers suffer every year when their pigs get ill. Additionally, there's a tremendous opportunity to use crisper cast 9 in agriculture to ensure that our food system is able to produce an adequate and nutritious number of crops to feed an ever growing and hungry world population. There was a really great example recently of work done by an academic group here in the United States using the crisper cast 9 gene editing system to develop a mushroom that doesn't brown as quickly. That and products like it are a great way we can reduce food going into the waste stream as they spoil before we're ever able to cook them. There are many groups around the world who are using this technology in a large variety of crops right now to better understand plant genetics and ultimately to use this to make crops that are droughtresistant, disease resistant, and possibly even allergenfree. With the tremendous potential of a technology like crispercast 9 gene editing comes the responsibility to use it wisely. There are many conversations ongoing nationally and internationally right now between scientists, doctors, regulators, and the public about when and where are the ethical and appropriate places to use this technology, who should be funding research into it, and how products made with it should be regulated. I fundamentally believe that any practitioner of this technology has to be a steward of it. For example, our company believes it's inappropriate to use this technology to modify human embryos. We won't do it ourselves and we don't allow our partners or our lences to do so either. There is such a positive potential for the broad use of crisper cast 9 gene editing in both health care and food. And I call on all of you to be part of the ongoing discussions in our communities today about the potential intended and unintended consequences of this technology and where it should and should not be used. Thank you. [Music]