CRISPR genome editing allows scientists to modify DNA, which encodes an organism’s hereditary information. This powerful new technology is transforming science and has profound implications. But it also raises ethical concerns.
The system is based on a natural process used by bacteria to fight invading viruses. They snip out pieces of the virus’s DNA and use them to recognise and fight the invader next time.
CRISPR-Cas9 is a revolutionary gene-editing technology that promises to transform biological research. It is currently the simplest, most versatile, and precise method for editing DNA in cells and organisms. But it raises many ethical concerns.
Like ZFNs and TALENs, CRISPR-Cas9 promotes genome editing by stimulating the insertion or deletion of DNA sequences29. Once cleaved by Cas9, target DNA typically undergoes error-prone NHEJ or high-fidelity HDR repair29. NHEJ is prone to producing indels, which can be exploited for targeted genetic modification.
Researchers adapted the system from bacterial type II CRISPR systems that provide adaptive immunity to viruses and plasmids. The technique uses an RNA duplex (tracrRNA:crRNA) to guide a Cas9 endonuclease to a specific sequence of DNA in a cell. Once Cas9 binds to the DNA, it cuts the strand of DNA at the target location, mirroring how bacteria break down foreign DNA. The guide RNA then replaces the broken DNA sequence with new DNA that encodes functional proteins.
CRISPR-RNA is a gene editing tool that allows scientists to insert new genetic sequences into a cell or organism. It is often used to modify genes that cause disease. It works by cutting DNA at a targeted sequence. Then, a DNA repair mechanism tries to fix the damaged DNA.
Scientists can program the Cas9 protein to find and cut any target DNA sequence by pairing it with a guide RNA. The gRNA must be carefully designed to minimize off-targeting. For example, the length of the gRNA affects its off-targeting probability.
Francisco Mojica and other scientists first discovered CRISPRs in bacteria. They found that these DNA sequences had repeating segments separated by unique spacers that came from invading viruses, Quanta Magazine reported. They also found that the Cas enzyme could snip out a segment of DNA from these bacterial genomes and use it to help fight off invading viruses. This is how the CRISPR system evolved into the gene-editing tool it is today.
The CRISPR system is one of the immune systems that bacteria and archaea use to respond to viral pathogens. Scientists can now take advantage of this system to introduce changes to genes in mammalian cells. The CRISPR genome editing system has two components: a guide RNA and the Cas9 enzyme. The guide RNA (gRNA) is designed to target a specific genomic sequence in the cell. The Cas9 enzyme cleaves the DNA at this location and creates a mutation.
The gRNA and Cas9 can be delivered by a plasmid or viral vector for transfection into eukaryotic cells. The guide RNA can also be fused to fluorescent proteins for tracking in living cells. This system has been used for forward genetic screens to identify genes that influence a desired phenotype.
Pooled lentiviral CRISPR libraries have been designed to knock out, activate or repress human and mouse genes in a large number of cells at once. The libraries can then be screened under specific conditions for relevant phenotypes.
CRISPR enables gene editing and other scientific applications such as dynamic tracking of repetitive or non-repetitive genomic sequences in living cells. For genome editing, a guide RNA with a target sequence is delivered into a cell. The guide RNA binds to DNA, and a protein called Cas9, which acts like molecular scissors, cuts the targeted sequence.
The CRISPR system is based on the natural defenses of bacteria and archaea, single-celled microorganisms. They use specialized sequences of DNA and proteins to foil attacks by viruses. When a virus infects a bacterium, the microbe’s immune system snips pieces of the invader’s DNA and stores them as memory.
Scientists have adapted this system to engineer genes in complex organisms such as mice and humans. The technology can be used to rapidly create cell and animal models for research into diseases. This accelerates the search for treatments. Moreover, the method can be applied to study human diseases such as cancer and mental illness.