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A CRISPR on-off Switch for Genes Controls Expression

Scientists have discovered a new gene-silencing tool to switch Genes on and off without altering genetic sequences. The description of the tool was published in Cell. This tool is used as a modified CRISPR-Cas9 system to introduce reversible epigenetic changes that control gene expression.

The classic CRISPR-Cas9 system was developed a decade ago and led to an explosion in Genes editing studies. CRISPR-Cas9 uses RNA to chaperone the Cas9 nuclease to a particular site in the DNA and create a double-strand break. The scientists tried adding a short sequence of DNA, then can introduce permanent genetic changes to the cell. This oligonucleotide is used as a template by the cell when repairing the double-strand break, incorporating the sequence into the cell’s genome. This approach can cause unintended genetic changes.

Jonathan Weissman, PhD, professor of biology at the Massachusetts Institute of Technology made a statement that as beautiful as CRISPR-Cas9 is, it hands off the repair to natural cellular processes, which are complex and multifaceted. They also added that it is very hard to control the outcomes.Weissman and his colleagues attempted to find a way to control gene expression without altering the genetic sequence. Gene expression is controlled naturally in the cell through epigenetic changes, such as adding methyl groups to the DNA strands. These chemical tags make DNA sequences inaccessible for transcription by RNA polymerase, thus silencing the Genes.

Weissman and colleagues saw that they could use this natural process to create a system that would enable them to switch Genes on and off. A result is a tool called CRISPRoff, which uses an inactive Cas9 protein fused to domains from transcriptional repressor proteins. Guide RNAs can target CRISPRoff to methylate Genes of interest and silence them. Another tool called CRISPRon, a fusion protein including transcriptional activator domains, can reverse the process and switch the Genes back on.

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