Biology

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)
This new revolutionary genome editing tool will enable the elimination of many genetic diseases. It could also be used to modify crops, screen for cancer genes, eradicate virus’ and for genome engineering. This has sparked debate on whether ethically, this could lead to a slippery slope on what grounds can a genome be edited?

Crispr potential

CRISPR’s ability range to edit DNA organisms. Illustrated by: Davide Bonazzi

How exactly does this technique work? 

CRISPR editing is a process whereby scientists can rewrite the genetic code of an organism by cutting out and replacing the individual components of DNA. This can prevent many genetic diseases such as Huntington’s Disease or Cystic Fibrosis.

If we look at the way bacteria work, we can use CRISPR using the Cas-9 bacterial enzyme to our advantage. The stages explained are:

  1. When bacteria encounter an invading source of DNA, such as from a virus, they can copy and incorporate segments of the foreign DNA into their genome as “spacers” between the short DNA repeats in CRISPR.
  2. These spacers enhance the bacteria’s immune response by providing a template for RNA molecules to quickly identify and target the same DNA sequence in the event of future viral infections.
  3. If the RNA molecules recognize an incoming sequence of foreign DNA, they guide the CRISPR complex to that sequence. There, the bacteria’s Cas proteins, which are specialized for cutting DNA, cut out and disable the invading gene.

Crispr in action

The CRISPR/Cas system. (From E. Pennisi, Science, 341:833-6, 2013. Credit: K. Sutliff/Science)

Professor Jennifer Doudna, is credited with developing the gene-editing technology using the bacterial enzyme Cas-9. She explains CRISPR by comparing it to a film editor. “Think about a film strip, you see a particular segment of the film that you want to replace. And if you had a film splicer, you would go in and literally cut it out and piece it back together, maybe with a new clip. Imagine being able to do that in the genetic code, the code of life,” Doudna added. “You could go in and snip out a piece and replace it with something that corrects a mutation that would cause disease.”

It is believed that with more research and development CRISPR could also be a cure for HIV. It would be used to cut the DNA of the inactive phase of the virus out of an infected cell. However more research is required because of the difficulty scientists have to target the specific area of the genome that the virus lives in, especially because HIV can remain dormant in the body for many years. Scientists need to understand where the virus lives and what it needs to survive before they carry out the technique. If they cut in the wrong area of the genome then this can produce more damaging effects.

Doudna states “We can expect to see clinical applications of CRISPR within the next few years.” But with CRISPR’s potential comes some fears of what embryo-editing leads to. Doudna goes on to say “We’re talking about something that would affect human evolution.”

Genome editing

http://blogs.discovermagazine.com/crux/files/2015/11/DNA_edits.jpg

http://www.umassmed.edu/news/news-archives/2015/04/editing-hiv-out-of-our-genome-with-crispr/

http://www.cbsnews.com/news/crispr-jennifer-doudna-gene-editing-technology-diseases-dangers-ethics/

http://motherboard.vice.com/read/what-is-crisprcas9-and-why-is-it-suddenly-everywhere

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