CRISPR is the newest, most efficient and most accurate method to edit a cell's genome. It opens up a myriad of wonderful opportunities as well as frightening ethical challenges in healthcare. We have to understand it and prepare for the medical revolution it brings upon us, so here I summarized everything to know about this genome editing method from DNA-scissors to currently unimaginable possibilities, such as having an army of gene-edited soldiers. Since there is so much to know about it, I broke down the story into three parts. First, let me introduce you the history and discovery of CRISPR. I know what you are thinking. “Holy Jesus, what am I going into? I would never get something like that. I was the closest to CRISPR when I wanted to look up the calories in crisps on Google and I accidentally misspelled it”. Don’t worry, I’m going to walk you through it. By CRISPR (pronounced crisper), the medical community means the CRISPR/Cas9 system. It is a bacterial-derived RNA-directed endonuclease that generates blunt ends. Yes, go through it again. I know you still have doubts about the topic. Your thoughts wander to issues whether you watered the plants and when the next episode of The Walking Dead comes out. Just keep on reading. DNA Scissors and the Never-ending War – A One-minute Biology Lesson Basically. Life and evolution have invented a method to remove DNA segments from an organism’s DNA. The system actually invents and uses DNA scissors that only cut DNA where you need them to. In a more complicated manner. CRISPR stands for “Clustered regularly interspaced short palindromic repeats” and is a series of short repetitions in bacterial DNA. Why in bacteria? It is due to the oldest war on Earth – bacteria versus viruses. And believe me, it would be a lot bloodier than Game of Thrones if it were going on with their human-sized versions. CRISPR is actually a prokaryotic immune system that helps bacteria fight foreign genetic elements of invader viruses. When a bacterium survives a virus attack, some genetic elements of the virus still remain inside the bacterium, and it stores them for possible future attacks as an antidote – these are basically the CRISPR sequences, in the form of a CRISPR RNA molecule, so a kind of molecular messenger that converts genes into proteins. You can imagine them as a “molecular most-wanted gallery”, representing the enemies the microbe has encountered through its short life. Next time a virus attacks, the CRISPR-Cas9 system will have the appropriate response. The small RNA molecule directs the Cas9 enzymes (the word Cas stems from CRISPR Associated) to the specific DNA sequence as a state-of-the-art GPS, and the Cas9 enzyme chops the viral DNA in two, preventing the virus from replicating. It is somehow similar to the adaptive immune system of humans – as for example in the case of measles, the system learns to recognize the measles virus in couple of days, and it produces antigens wiping it out of your body. Once the infection is over, we can hold onto these immunological memories. A few immune cells tailored to measles stay with us for our lifetime, ready to attack again. Something similar happens with CRISPR and bacteria. And why is CRISPR important? The overall aim of most microbiological researches is to understand how things work. And it is usually fascinating enough to keep up the good work. But in the case of CRISPR, the discovery can turn into something bigger, something, which can be put to practice, namely a genome editing tool. Scientists discovered lately that by delivering the Cas enzymes and so-called guide RNAs into a cell, they can cut the cell’s genome at a desired location. This way, they can remove existing genes and/or add new ones. Almost without limits. Do you Already See How Significant the Discovery is? So How did it Happen? The Voyage Into the Innermost Secrets of our Bodies Humans have been experimenting with nature and life for thousands of years. Think about all the domesticated plants and animals. Through selective breeding humans enabled the life of certain species with certain traits beneficial for them, while let others with less advantageous characteristics die out. It is the basis of genetic engineering. Although the structure of the DNA was discovered officially in 1953 by James Watson and Francis Crick, a Swiss chemist extracted it from white blood cells as early as the 1800s. Scientists in the 1960s started to use radiation on plants to cause random mutations in the genetic code. They haven’t had the tools for targeted alterations, thus they reclined upon random chance. Either they could manipulate a plant into something else useful – or not. Later, researchers started to experiment with DNA-injections in bacteria, plants and animals alike. The earliest genetically modified animal was born as early as 1974. Right, over 40 years ago! In the 1980s, various engineered bacteria such as oil-eating bacteria was patented. The first genetically modified food was introduced in 1994 with the Flavr Savr Tomato – which then disappeared soon after from the shelves of supermarkets. And there is still a huge debate about GMOs – which shows the tremendous technological, biological, moral and legal issues around the interference with genes. Editing the genome has been a uniquely challenging task. It involved a lot of time-consuming methods in the past, required advanced laboratory equipment with the associated skills and success rates still varied. Genome editing has been a sexy topic in genetics since the completion of the Human Genome Project in April 2003, so the mapping of the complete genetic blueprint of a human being, but it hasn’t really materialized in practice. But we cannot really say that from the completion of the Human Genome Project, it was just one step to the discovery of CRISPR. It was rather a half-marathon. What Has DNA with Yogurt in Common? In 1987, Yoshizumi Ishino and colleagues at Osaka University in Japan published the sequence of a genecalled “iap” belonging to the gut microbe E. coli. To better understand how the gene worked, the scientists also sequenced some of the DNA surrounding it. There, what they found was a peculiar genetic sandwich. Scientists were puzzled over it throughout years, and only in 2002, Ruud Jansen of Utrecht University in the Netherlands and colleagues dubbed these peculiar sequences CRISPR and the accompanying collection of genes Cas genes. Later, after studying CRISPR and Cas genes for years, Eugene Koonin came up with the idea that perhaps microbes use it as weapons against viruses. The theory was bold enough to catch the attention of a microbiologist called Rodolphe Barangou. He decided to test it for his employer, the yogurt-maker Danisco. The company depended on bacteria to convert milk into yogurt, and sometimes entire cultures would be lost to outbreaks of bacteria-killing viruses. To test Koonin’s hypothesis, Barrangou and his colleagues infected a milk-fermenting microbe with two strains of viruses. They killed many of the bacteria, but some survived. When those resistant bacteria multiplied, their descendants turned out to be resistant too. Some genetic change had occurred. CRISPR and its secrets caught also the imagination of Jennifer Doudna, a biochemist at the University of California, Berkeley. She started to analyse it, and later Emmanuelle Charpentier of the Helmholtz Centre for Infection Research in Germany joined her research lab in 2007. Their team presented the first demonstration of CRISPR’s potential only in 2012. They crafted molecules that could enter a microbe and precisely snip its DNA at a location of the researchers’ choosing. In January 2013, they went one step further. They cut out a particular piece of DNA in human cells and replaced it with another one. But CRISPR has a lot more to offer than “only” editing genes. Researchers are discovering only now that gene-editing is just the tip of the iceberg. They have to analyse CRISPR more thoroughly to come to terms with its huge potential. ٍSource
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