Thursday, March 24, 2016

We can Edit the Human DNA – What’s Next?

We can Edit the Human DNA - What's Next 

Almost two years ago I participated at a symposium on genomics at The New York Academy of Sciences. Dr. Jennifer Doudna of UC Berkeley presented a technology called CRISPR/Cas9 that allows for precise manipulation of the DNA. 

CRISPR stands for a long sequence of words that you will most likely forget, but here it goes – Clustered Regularly Interspaced Short Palindromic Repeats. It is used by bacteria to protect themselves against invading pathogens.

When virus DNA invades bacteria, it leads to the production of two short RNAs. One of these RNAs matches the sequence of the virus. Together with Cas9 (an enzyme that can cut DNA), these RNAs form a complex that works like this:

1.The matching sequence (guiding RNA) looks for its target in the viral genome.
2.When it finds it, Cas9 cuts the target viral DNA. The virus is disabled.

Researchers found that they could engineer the system not only to cut viral DNA, but any DNA sequence they desire. To do this, they simply change the guiding RNA to match their target. This can be done in living cells too. Here’s how it works:

1.When CRISPR/Cas9 is put in the nucleus of a cell, it locks onto a sequence called PAM. 2.Cas9 unzips the DNA and matches it to the target RNA.
3.When the match occurs, Cas9 cuts both strands of the DNA.  
4.Normally, the cell tries to repair the DNA. However, the process is prone to error.

When DNA is not repaired correctly, the resulting gene could be mutated or disabled. Its altered function allows researchers to better understand how it works.

If researchers want to be more precise and replace defective (mutated) genes with healthy copies, they add a piece of DNA (the template) to the complex that carries a healthy copy. So, in this case, resuming from step 3:

For the rest of the story:

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