Biology

CRISPR Cas9 in 2018. Is it still the best tool for genetics?

Cas9 can be thought of as an RNA- guided nuclease for genome editing. CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.

It is a defence mechanism that was found in Streptococcus pyogenes. This system involves a guide RNA and the cas9 protein. The guide RNA is compatible with the target sequence and the cas9 induces a cut at that specific region. The purpose of this in Streptococcus pyogenes is to cut and remove viral DNA when infected.

We have found many different variations of this technology but still the most popular is cas9. It has been altered in many ways too. Now there are CRISPR systems to replace specific sequences with others. There are enzymes that work better when working with target sequences with low G/C ratios (Cpf1). Other systems have been made to methylate or acetylate histones near specified sequences by using guide RNAs in the same way but replacing the nuclease activity of the cas9 protein with a methyl or acetyl transferase.

The difference between CRISPR and other methods are in the specificity and the convenience mostly, as it is not as expensive and it tends to perform better. ZFNs (Zinc Finger Nucleases) and TALENs (Transcription Activator-Like Effector Nucleases) also promote DSBs (double strand breaks).

What can be done with those systems is gene editing. By deleting genes (making knockout organisms) to study the functions of certain genes. By replacing genes (by inserting a reference sequence) to precisely change a specific section in a genome that may be problematic.

There aren’t many drawbacks when using CRISPR. One of the worst limitations may be the fact that this system can end up targeting multiple sites in the genome, causing unwanted edits in random areas.

There have been “clinical trials” using CRISPR. Specifically there was one in 2016 in China to treat a patient with lung cancer. The goal was to delete genes in the patients white blood cells that force the immune system to ignore the cancer cells. By doing so they thought that the organism would attempt to remove the tumour by itself. There have also been trials with HIV patients, as CRISPR may be able to remove HIV genes from infected cells. I couldn’t find the results of those trials but maybe that will come on a new post. So make sure you follow Qul Mind.

 

Sources: Chinese scientists to pioneer first human CRISPR trial , Gene-editing method tackles HIV in first clinical test , Genome engineering using the CRISPR-Cas9 system

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