The CRISPR-Cas9 system exploits a defense system naturally found in many bacteria and archaebacteria. To protect against foreign genetic elements such as those present in invading viruses and plasmids, bacteria incorporate short pieces of foreign DNA into segments of their own genomes that are called CRISPR (clustered regularly interspaced short palindromic repeats). These CRISPR regions thus provide a ‘memory’ of invading elements that can be used by a bacterial population to defend more effectively when subsequently challenged by a similar invader. In the so-called type II CRISPR system, a repeat invasion causes the CRISPR segments to be expressed as CRISPR RNAs (crRNAs) that match the foreign DNA, bind to it, and hence help it recruit a specific enzyme (Cas9) that can then specifically dismantle the invading DNA.
Key steps of this intriguingly simple molecular defense mechanism were elucidated at the University of Vienna in the Max F. Perutz Laboratories at the Vienna BioCenter by Emmanuelle Charpentier and her group. In a first landmark publication with the master’s student Elitza Deltcheva as lead author (Deltcheva et al., Nature 2011), the team serendipitously discovered the nature of the so-called tracrRNA that takes part in the process that cleaves long pre-crRNAs into individual sequences able to guide Cas9 to its targets. In 2012, the team subsequently published (in conjunction with their collaborators from Jennifer Doudna’s group at Berkeley) a breakthrough study (Jinek, Chylinski et al., Science 2012) that revealed the exact molecular mechanism of the type II CRISPR system. Crucially, this study also demonstrated that the mechanism could be engineered into a simple, two-component system (a single guide RNA plus the Cas9 enzyme) that can be easily “programmed” by scientists to bind and cleave any DNA sequence of interest. This two-component system (commonly referred to as CRISPR-Cas9) has quickly become enormously popular, and triggered an avalanche of applications, most notably in the site-specific editing of genomes. Due to its simplicity, the system has meanwhile been used for genome editing in numerous species, greatly expanding the biomedical toolbox.
The pivotal role of former MFPL group leader Emmanuelle Charpentier and her team has been recognized globally. Charpentier has been awarded a series of scientific awards, including the 2015 Breakthrough Prize, which recognizes transformative advances towards understanding living systems and extending human life, and the 2018 Kavli Prize, recognizing scientists for their seminal advances in astrophysics, nanoscience, or neuroscience. Krzysztof Chylinski, the Vienna BioCenter PhD student who was second author on the 2011 study, and shared first author on the 2012 publication, continues his work on CRISPR-Cas9 at the Vienna BioCenter Core Facilities (VBCF). He has received the Vienna BioCenter PhD award, the Bank Austria Research Award, and the Award of Excellence from the Austrian Federal government for his critical contributions. The CRISPR-Cas9 system and its manifold variations hold enormous promise for the understanding and treatment of conditions ranging from cancer and ageing to inherited genetic disorders, as well as having a huge range of potential applications in agriculture. It may even be used to eliminate the mosquito that transmits malaria.
The discovery of the tracrRNA and the development of the CRISPR/Cas9 system at MFPL wonderfully illustrate the role of serendipity in basic research and support the adage of physicist Joseph John Thomson that “research in pure science leads to revolutions”.
Original Publications in Nature and Science:
Deltcheva E, Chylinski K, Sharma CM, Gonzales K, Chao Y, Pirzada ZA, Eckert MR, Vogel J, Charpentier E. CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III.
Jinek M, Chylinski K, Fonfara I, Hauer M, Doudna JA, Charpentier E. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity.