Enabling large-scale genome editing at repetitive elements by reducing DNA nicking.

To extend the frontier of genome editing and enable editing of repetitive elements of mammalian genomes, we made use of a set of dead-Cas9 base editor (dBE) variants that allow editing at tens of thousands of loci per cell by overcoming the cell death associated with DNA double-strand breaks and single-strand breaks. We used a set of gRNAs targeting repetitive elements-ranging in target copy number from about 32 to 161 000 per cell. dBEs enabled survival after large-scale base editing, allowing targeted mutations at up to ∼13 200 and ∼12 200 loci in 293T and human induced pluripotent stem cells (hiPSCs), respectively, three orders of magnitude greater than previously recorded. These dBEs can overcome current on-target mutation and toxicity barriers that prevent cell survival after large-scale genome engineering.

A Survey of Transcription Factors in Cell Fate Control.

Transcription factors (TFs) play a cardinal role in the development and maintenance of human physiology by acting as mediators of gene expression and cell state control. Recent advancements have broadened our knowledge on the potency of TFs in governing cell physiology and have deepened our understanding of the mechanisms through which they exert this control. The ability of TFs to program cell fates has gathered significant interest in recent decades, and high-throughput technologies now allow for the systematic discovery of forward programming factors to convert pluripotent stem cells into numerous differentiated cell types. The next generation of these technologies has the potential to improve our understanding and control of cell fates and states and provide advanced therapeutic modalities to address many medical conditions.

The Future of Multiplexed Eukaryotic Genome Engineering.

Multiplex genome editing is the simultaneous introduction of multiple distinct modifications to a given genome. Though in its infancy, maturation of this field will facilitate powerful new biomedical research approaches and will enable a host of far-reaching biological engineering applications, including new therapeutic modalities and industrial applications, as well as "genome writing" and de-extinction efforts. In this Perspective, we focus on multiplex editing of large eukaryotic genomes. We describe the current state of multiplexed genome editing, the current limits of our ability to multiplex edits, and provide perspective on the many applications that fully realized multiplex editing technologies would enable in higher eukaryotic genomes. We offer a broad look at future directions, covering emergent CRISPR-based technologies, advances in intracellular delivery, and new DNA assembly approaches that may enable future genome editing on a massively multiplexed scale.