Cascades of CRISPR I-E and I-B demonstrated in human cells
We are just beginning to grasp the variety and usability of natural CRISPR systems found in bacteria and archaea. In addition to popular type II CRISPR (which includes CRISPR-Cas9), scientists are working on mastering the other four types. A team from Duke University recruited a new player to the genome engineering game: CRISPR type I.
Despite being a technological novelty, CRISPR type I is well-known in basic biology. In fact, it is the first CRISPR system discovered in the iconic E. coli, and then described in A. fulgidus a few decades ago.
The main feature of CRISPR type I is both promising and challenging. Unlike simple CRISPR-Cas9, type I consists of multiple proteins joined into complex Cascade. Its size (up to eight genes) poses an obvious technical obstacle. However, at the same time, more proteins guarantee more possibilities in terms of targeting various sequences in the genome. For instance, CRISPR I-E recognizes a wide range of PAM sequences (5′-AAG, AGG, ATG, GAG, TAG-3′).
Two of the type I systems, namely I-E (EcoCascade) and I-B (LmoCascade), were successfully introduced as plasmids into human embryonic kidney cells. Immunological assays confirmed the proper association of complexes. Further experiments proved that CRISPR type I is capable of modifying gene regulation – activating as well as repressing genes.
The study paves the way for more robust genome engineering methods. In addition to the inherent advantages of CRISPR type I, the system can be used to alter whole gene regulatory networks. Follow-up work will certainly explore interesting possibilities provided by CRISPR I-E and I-B.
Publication: Pickar-Oliver, A., Black, J. B., Lewis, M. M., Mutchnick, K. J., Klann, T. S., Gilcrest, K. A., … & Reddy, T. E. (2019). Targeted transcriptional modulation with type I CRISPR–Cas systems in human cells. Nature biotechnology, 1-9. Doi:10.1038/s41587-019-0235-7.