CRISPR also called CRISPR/ Cas9 that is Clustered Regularly Interspaced Short Palindromic Repeats/ CRISPR associated protein9. CRISPR technology was adapted from the natural defence mechanisms of bacteria that detect and destroy DNA of foreign invader (virus) attacking it. Due to bacterial anti-viral system, the DNA of foreign invader is chopped and destroyed by bacteria using its CRISPR-derived RNA and various Cas proteins, including Cas9. This forms the basis of a technology known as CRISPR/ Cas9 that precisely snips DNA, transfers and manipulates genes within the desired organism.

CRISPR-Cas9 as a genome-editing tool

To put it in simple words, the CRISPR part is the DNA sequence in bacteria that tells the virus destroying scissors (Cas9) which part of the DNA, the organism in which gene editing has to be done, to cut.  This is done by first transcribing (making complementary RNA sequence) CRISPR and processing it into CRISPR RNA, or crRNA. This crRNA helps Cas (CRISPR-associated) protein to act as a guide and recognize the DNA that has to be cut. The other RNA-guided Cas proteins cuts both strands of the DNA double helix of the organism in which gene editing is being done. Once the Cas9 scissors cut the DNA just where we intend, the cell will try to repair the break using any available DNA it can find. So, we also inject the new gene we want to insert. The random diffusion (called Brownian motion) now delivers the new gene to the place where it fits. As a built-in safety mechanism to ensures that Cas9 doesn’t just cut DNA just anywhere or everywhere. PAMs (“protospacer adjacent motifs”) short DNA are made to act as tags and sit adjacent to the target DNA sequence. If the Cas9 complex doesn’t see a PAM next to its target DNA sequence, it won’t cut. This is one possible reason that Cas9 doesn’t ever attack its own CRISPR region in bacteria. The Cas9 could be directed to cut any region of DNA. By simply changing the nucleotide sequence of crRNA Cas9 could be made to cut any particular region of DNA. Thus making gene editing simple, effective and highly precise.

Applications:

In recent time CRISPR has found place in following applications:

  1. In modifying stem cells that may then be re-injected into patients to replace damaged organs and cross-species organ transplants.
  2. In blocking replication of HIV in living cells. CRISPR  was used to damage thereby deleting genetic diseases from the cells of experimental human culture cells.
  3. For resurrecting the long-extinct species (like woolly mammoth).
  4. In treating diseases like cystic fibrosis, cataracts, cancer, huntington’s disease, Duchenne muscular dystrophy, chronic pains, lyme disease, malaria and Fanconi anemia.
  5. CRISPR technology has also been applied in the food and agricultural industries to vaccinate industrial cultures  against viruses and treating plant disease like citrus greening.
  6. It is also being used in crops to improve yield, drought tolerance and nutritional properties.
  7. In germline editing i.e making genetic modifications to human embryos and reproductive cells such as sperm and eggs. However this has raised many ethical concerns. Safety of such a procedure is yet to be introspected.

Nevertheless businesses should be interested in this technology and must invest capital so as to create application processes. One who invests today will be the winner tomorrow.

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