One of the most talked about biological breakthroughs in the past decade was the discovery of the genome editing tool CRISPR/Cas9, which can alter DNA and potentially remove the root causes of many hereditary diseases.
Originally found as part of the immune system of the Streptococcus pyogenes bacteria, CRISPR associated protein 9 (CAS9), in its native state, recognizes foreign DNA sequences and disables them.
In bacteria, the system is used to target foreign viral DNA from bacteriophages -- DNA that it has already recognized as an enemy through its evolutionary history and has incorporated a record of it into its own DNA.
CRISPR (Clustered regularly interspaced short palindromic repeats, pronounced "crisper") represent segments of DNA that contain short repetitions of base sequences followed by short segments of "spacer DNA" derived from previous exposures to foreign DNA. The complex consists of proteins that unravel DNA, others that cut the double helix at a specific location, and a guide RNA that can recognize enemy DNA in the cell.
Researchers studying this ancient immune system realized that, by changing the sequence of the guide RNA to match a given target, it could be used to cut not just viral DNA, but any DNA sequence at a precisely chosen location. Furthermore, new sections of DNA could be introduced to join to the newly cut sections.
The method was first conceived and developed by Jennifer Doudna (University of California, Berkeley) and Emmanuelle Charpentier (Umeå University) and has been used in cultured cells -- including STEM cells -- and in fertilized eggs to create transgenic animals with targeted mutations that help study genetic functions. CRISPR/Cas9 can affect many genes at once, allowing for the treatment of diseases that involve the interaction of many genes.
The method is improving rapidly and is expected to one day have applications in basic research, drug development, agriculture, and treating human patients with genetic diseases.
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