1 00:00:15,150 --> 00:00:19,710 Since the discovery of DNA's fundamental role in building and sustaining life, 2 00:00:20,109 --> 00:00:25,530 scientists have dreamed of having the ability to easily edit DNA in very precise ways. 3 00:00:25,890 --> 00:00:27,410 But why would they want to do this? 4 00:00:27,969 --> 00:00:33,649 Well, making specific changes to DNA sequences can help scientists better understand the function of certain genes, 5 00:00:34,210 --> 00:00:39,530 produce specific disease models, or even repair defective genes that cause diseases in humans. 6 00:00:40,070 --> 00:00:45,229 This is an exciting prospect, but methods to try and do this weren't practical or rightly applicable. 7 00:00:45,689 --> 00:00:51,229 However, a few years ago, a gift from biology came from the basic research of the bacteria immune system, 8 00:00:51,229 --> 00:00:56,829 which gave scientists the ability to easily, customizably, and precisely edit genomes. 9 00:00:57,289 --> 00:01:01,969 Bacteria evolved ingenious ways of protecting themselves against pathogens such as viruses 10 00:01:01,969 --> 00:01:04,670 by using a system called CRISPR-Cas. 11 00:01:05,170 --> 00:01:08,689 CRISPRs are stretches of DNA sequence found in the bacterial genome, 12 00:01:08,689 --> 00:01:15,269 In close proximity to CRISPR are the Cas genes, which encode proteins necessary for the CRISPR system. 13 00:01:16,469 --> 00:01:22,670 Up until a few years ago, what was known about the CRISPR-Cas system is that bacteria infected by a virus 14 00:01:22,670 --> 00:01:27,030 incorporate elements of the virus's DNA into the CRISPR sequence. 15 00:01:27,489 --> 00:01:30,510 This protected the bacteria from future infection by this virus. 16 00:01:31,469 --> 00:01:35,030 Scientists observed that when a virus invades a bacterium, 17 00:01:35,030 --> 00:01:42,790 the CRISPR DNA produces one or two small RNAs called CRRNA and tracer RNA. 18 00:01:43,569 --> 00:01:50,370 These RNAs bound to Cas proteins and formed complexes that cut the DNA of the invading virus, 19 00:01:50,810 --> 00:01:52,750 thus protecting the bacteria from infection. 20 00:01:53,969 --> 00:01:56,150 But many questions still remained. 21 00:01:56,569 --> 00:02:01,849 How did the small RNAs and Cas work together to detect and destroy viral DNA? 22 00:02:01,849 --> 00:02:20,129 In 2012, a group of scientists made a major breakthrough and discovered not only how the CRISPR RNAs and Cas cut DNA, but also how to create a new technique to specifically change the DNA sequence of any organism with great ease. 23 00:02:20,750 --> 00:02:29,449 This discovery came from a group of scientists led by Jennifer Dunna at UC Berkeley and Emmanuel Charpentier at Umeå University in Sweden. 24 00:02:29,449 --> 00:02:33,229 They published their results in Science in an article titled 25 00:02:33,229 --> 00:02:39,229 A Programmable Dual RNA-Guided DNA Endonuclease in Adaptive Bacterial Immunity. 26 00:02:40,129 --> 00:02:45,569 So what exactly did these scientists find, and why is it so important for future biomedical research? 27 00:02:46,169 --> 00:02:51,210 First, the scientists dissected how Cas9 and the two RNAs can cut DNA. 28 00:02:51,849 --> 00:02:58,009 They found that the two RNAs, CRRNA here in red and tracer RNA here in green, pair up, 29 00:02:58,009 --> 00:03:04,349 recruit Cas9 protein, and direct it to bind the target DNA via the complementary base pairing 30 00:03:04,349 --> 00:03:07,569 between the red CRISPR RNA and the target DNA. 31 00:03:08,030 --> 00:03:12,270 Once at the proper DNA site, Cas9 cleaves both DNA strands. 32 00:03:12,849 --> 00:03:16,389 This cleavage occurs at a very specific and conserved position 33 00:03:16,389 --> 00:03:20,349 that is dictated by the sequence in the red CRISPR RNA molecule. 34 00:03:21,550 --> 00:03:27,009 This process is similar to finding your plane by matching the gate number to the one on your boarding pass. 35 00:03:29,319 --> 00:03:33,120 The scientists then wondered if they could engineer one RNA molecule 36 00:03:33,120 --> 00:03:38,340 that mimicked the structure of the CRISPR RNA and tracer RNAs bound together 37 00:03:38,340 --> 00:03:42,520 that would guide Cas9 to cut DNA at a specific location. 38 00:03:43,759 --> 00:03:49,199 The scientists designed one RNA molecule that consisted of the red and green RNA molecules 39 00:03:49,199 --> 00:03:51,879 connected together by a hairpin structure. 40 00:03:52,680 --> 00:03:57,479 In this case, they engineered the RNAs to target specific sequences of the gene 41 00:03:57,479 --> 00:04:04,759 encoding the green fluorescent protein, GFP. They added the engineered RNA molecules to the GFP DNA 42 00:04:04,759 --> 00:04:11,539 sequence along with the Cas9 protein and asked whether Cas9 would cut GFP DNA at specific 43 00:04:11,539 --> 00:04:20,089 sequences. And it did. When the RNA molecules were designed to bind to different regions of the GFP 44 00:04:20,089 --> 00:04:30,329 sequence, the GFP DNA sequence was cleaved at that specific location. On a gel that separates DNA 45 00:04:30,329 --> 00:04:35,790 according to size, you can see distinctly sized fragments of the GFP DNA molecule, 46 00:04:36,290 --> 00:04:41,949 resulting from having been cut in a specific location. This was huge as it meant that 47 00:04:41,949 --> 00:04:48,709 scientists could engineer one RNA sequence, introduce Cas9, and cut DNA at a specific 48 00:04:48,709 --> 00:04:54,709 location of their choice. By having this simple and easily programmable system, 49 00:04:54,709 --> 00:04:58,709 scientists can now induce breaks in the DNA at precise locations. 50 00:04:58,709 --> 00:05:03,709 When the cell tries to repair the broken DNA strands by ligating them back together, 51 00:05:03,709 --> 00:05:09,709 it often causes a small insertion or deletion that changes the DNA sequence. 52 00:05:09,709 --> 00:05:17,709 Scientists can take advantage of this process to add or remove specific DNA sequences at the site of the break. 53 00:05:17,709 --> 00:05:23,709 We now have a DNA word processor that can be used to change genome sequences, 54 00:05:23,709 --> 00:05:30,850 including our own. CRISPR has a bright future ahead to advance our understanding of human disease 55 00:05:30,850 --> 00:05:37,089 by creating a tool from basic research that is now widely used in the fields of molecular biology 56 00:05:37,089 --> 00:05:43,910 and genetics to change the genomes of any organism. But much work needs to be done to make the system 57 00:05:43,910 --> 00:05:50,569 more reliable. Use of the CRISPR system to edit human embryos is also a controversial issue and 58 00:05:50,569 --> 00:05:55,569 And researchers have already started the conversation about using this technology ethically and 59 00:05:55,569 --> 00:06:01,370 safely to advance human knowledge. 60 00:06:01,370 --> 00:06:05,810 This video has been provided to you by Eureka Science and iBiology, bringing the world's 61 00:06:05,810 --> 00:06:07,029 best biology to you.