Guided by RNA, Researchers Flip 930,000 Bases of the Human Genome in One Piece
Bridge recombinases, which recombine DNA under RNA guidance, were engineered for human cells to achieve 20% insertion and megabase-scale inversions and deletions.
CRISPR is good at cutting DNA, but inserting large pieces at a desired site or flipping chunks of a chromosome is difficult. Researchers at the Arc Institute and UC Berkeley in the United States and the University of Tokyo reported in Science the results of engineering 'bridge recombinases,' which join DNA under RNA guidance, for the human genome.
Engineering the enzyme and the guide RNA together
The researchers identified a homologous enzyme, ISCro4, derived from a bacterial mobile element, rationally redesigned its guide RNA (the bridge RNA), and improved the enzyme itself by evaluating large numbers of variants with deep mutational scanning. As a result, the efficiency of inserting DNA into the human genome rose to as much as 20%, and the share of activity at the intended target across the whole genome (specificity) rose to as much as 82%.
They further succeeded in flipping or excising stretches of up to 930,000 base pairs (0.93 megabases) within the same chromosome, and in plasmids they also gave proof of concept for removing disease-associated regulatory regions and repeat expansion segments.
Limitations
This is basic research at the level of cultured cells and plasmids, not at the stage of use in human therapy. The 20% insertion efficiency and 82% specificity are upper values under optimal conditions, and the risk of unintended rearrangements and the problem of in vivo delivery remain.
- Bacteria-derived ISCro4 bridge recombinase redesigned for the human genome
- Insertion efficiency up to 20% and genome-wide specificity up to 82%
- Inversions and deletions of up to 0.93 megabases within the same chromosome
Limitations This is basic research at the level of cultured cells and plasmids, and the efficiency and specificity figures are upper values under optimal conditions.
Original Research
- Perry NT, Bartie LJ, Katrekar D, … Hsu PD · Arc Institute / UC Berkeley (U.S.), The University of Tokyo (Japan). Megabase-scale human genome rearrangement with programmable bridge recombinases. Science. DOI: 10.1126/science.adz0276
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