Gene Editing : CRISPR-Cas9 System


Gene editing hand is inserting a sequence of DNA.


CRISPR-Cas9 is a genome-editing tool.  It is faster, cheaper and more accurate than previous techniques of editing DNA and has a wide range of potential applications. CRISPR-Cas9 is a unique technology that enables geneticists and medical researchers to edit parts of the genome by removing, adding or altering sections of the DNA  sequence. The CRISPR-Cas9 system consists of two key molecules that introduce a mutation into the DNA. These are an enzyme and a piece of RNA.  The enzyme is Cas9, which acts as a pair of ‘molecular scissors’ that can cut the two strands of DNA at a specific location in the genome so that bits of DNA can then be added or removed.  The piece of RNA is called guide RNA (gRNA). The pre-designed RNA sequence is located within a longer RNA scaffold. The scaffold part will then bind to DNA and the pre-designed sequence will then ‘guide’ Cas9 to the right part of the genome. This makes sure that the Cas9 enzyme cuts at the right point in the genome. The Cas9 follows the guide RNA to the same location in the DNA sequence of the other strand and makes a cut across both. The cell will then recognize that the DNA is damaged and try to repair it. For a long time, geneticists used chemicals or radiation to cause mutations. However, this method was ineffective because there was no control as to where in the genome the mutation would occur. Gene targeting was another method, introduce changes in specific places in the genome, by removing or adding either whole genes or single bases. Traditional gene targeting has been very valuable for studying genes and genetics, but it takes a long time to create a mutation and is fairly expensive.


CRISPR and Vertex were preparing to test the ability of a new gene-editing technology, CRISPR/Cas9, in cutting out and replacing disease-causing snippets of DNA when the FDA placed it on hold but now has uplifted the hold. The trial is now scheduled to start by the end of 2018. This tool could be used in fighting cancer, extracting HIV, eliminating malaria, protecting plants, and creating biofuel.


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