Since the CRISPR review mentioned in the last post (Hochstrasser & Doudna (2014)) was published, dealing mainly with the nitty-gritty biochemistry (including crystallography) of the three different CRISPR-Cas systems, another new review has been released. This time co-authored by the two heroes – or should I rather say heroines? – of the CRISPR craze (Doudna & Charpentier (2014)), it is relatively short, easy to read and focusses primarily on the applications of the type II CRISPR-Cas9 system.
An interesting point they make, which I hadn’t thought of before, is that CRISPR offers an excellent opportunity for studying the RNA interference (RNAi) pathway itself. Since the CRISPR system is not naturally present in eukaryotic cells and once expressed from an exogenous source is completely autonomous, it does not compete with other cellular pathways. Therefore CRISPR can be used to target/knock-out components of the RNAi pathway, such as Dicer or Argonaute proteins; this would overcome the difficulty of interpreting data obtained from knocking down expression of these proteins using short interfering RNAs (siRNAs), which themselves rely on the expression of Dicer and Argonaute.
They summarise the overarching ideas and projects involving CRISPR in this diagram (copied directly from the paper):
Most of these future applications, such as RNA targeting and gene therapy, were already discussed previously, but the review also includes some even more recent advances and forays into other areas of medicine and agriculture.
For example, it may become possible to use the CRISPR-Cas9 system in its original capacity as an anti-viral defence mechanism to remove proviruses (viruses whose genomes have integrated into the host DNA), such as HIV-1, from infected cells (Hu et al. (2014)).
Probably just as important as the therapeutic/translational applications, but somewhat neglected by me, are the applications of CRISPR in plants and fungi. Several recent papers have shown that genome-editing using CRISPR is possible not only in the plant model organism Arabidopsis thaliana, but also in crop plants such as rice and wheat (e.g. Zhang et al. (2014)). These technological advances will probably speed up a lot of research that aims to improve crop yields and increase resistances to adverse weather conditions as well as infectious diseases.
Doudna JA, Charpentier E (2014) The new frontier of genome engineering with CRISPR-Cas9. Science 346
Hochstrasser ML, Doudna JA (2014) Cutting it close: CRISPR-associated endoribonuclease structure and function. Trends in Biochemical Sciences
Hu WH, Kaminski R, Yang F, Zhang YG, Cosentino L, Li F, Luo BA, Alvarez-Carbonell D, Garcia-Mesa Y, Karn J, Mo XM, Khalili K (2014) RNA-directed gene editing specifically eradicates latent and prevents new HIV-1 infection. Proceedings of the National Academy of Sciences of the United States of America 111: 11461-11466
Zhang H, Zhang JS, Wei PL, Zhang BT, Gou F, Feng ZY, Mao YF, Yang L, Zhang H, Xu NF, Zhu JK (2014) The CRISPR/Cas9 system produces specific and homozygous targeted gene editing in rice in one generation. Plant Biotechnology Journal 12: 797-807