Gene Editing – What is CRISPR-Cas9?

Gene editing or genome editing is a way of making specific changes to the DNA of a cell or organism. An enzyme cuts the DNA at a specific sequence, and when this is repaired by the cell a change or ‘edit’ is made to the sequence.

Enzymes which cut DNA are known as engineered nucleases

DNA is inserted, deleted or replaced in the genome of a living organism using engineered nucleases or molecular scissors.

Currently, there are four families of engineered nucleases which are being used 1) Meganucleases, 2) Zinc finger nucleases (ZFNs), 3) Transcription activator-like effector-based nucleases (TALEN), 4) Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system.

These nucleases create site-specific double-strand breaks (DSBs) at desired locations in the genome.

The induced double-strand breaks are repaired through the end- joining or recombination, resulting in targeted mutations.

Why is Gene Editing in news?

US scientists have successfully edited the DNA of human embryos to erase a heritable heart condition that is known for causing sudden death.
Researchers from the Oregon Health and Science University in California, China and South Korea repaired a mutation in human embryos by using a gene-editing tool called CRISPR-Cas9.
Clinical trials are under way in China and in the US to use this tool for treating cancer.
In May 2017, it was shown that in mice it is possible to shut down HIV-1 replication and even eliminate the virus from infected cells.
In agriculture, a new breed of crops that are gene-edited will become commercially available in a few years.

What is CRISPR-Cas9?

CRISPR is a dynamic, versatile tool that allows us to target nearly any genomic location and potentially repair broken genes. It can remove, add or alter specific DNA sequences in the genome of higher organisms.
CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) are sections of DNA and are sections of genetic code containing short repetitions of base sequences followed by spacer DNA segments.
CAS-9 (CRISPR-associated protein 9) is an enzyme. It uses a synthetic guide RNA to introduce a double strand break at a specific location within a strand of DNA. It is a system used by bacterial cells to recognize and destroy viral DNA as a form of adaptive immunity.

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