We demonstrate that discrete three-dimensional (3D) DNA components can specifically self-assemble in solution on the basis of shape-complementarity and without base pairing. Using this principle, we produced homo- and heteromultimeric objects, including micrometer-scale one- and two-stranded filaments and lattices, as well as reconfigurable devices, including an actuator, a switchable gear, an unfoldable nanobook, and a nanorobot. These multidomain assemblies were stabilized via short-ranged nucleobase stacking bonds that compete against electrostatic repulsion between the components' interfaces. Using imaging by electron microscopy, ensemble and single-molecule fluorescence resonance energy transfer spectroscopy, and electrophoretic mobility analysis, we show that the balance between attractive and repulsive interactions, and thus the conformation of the assemblies, may be finely controlled by global parameters such as cation concentration or temperature and by an allosteric mechanism based on strand-displacement reactions.

Novel applications based on the bacterial CRISPR system make genetic, genomic, transcriptional and epigenomic engineering widely accessible for the first time. A significant advantage of CRISPR over previous methods is its tremendous adaptability due to its bipartite nature. Cas9 or its engineered variants define the molecular effect, while short gRNAs determine the targeting sites. A majority of CRISPR approaches depend on the simultaneous delivery of multiple gRNAs into single cells, either as an essential precondition, to increase responsive cell populations or to enhance phenotypic outcomes. Despite these requirements, methods allowing the efficient generation and delivery of multiple gRNA expression units into single cells are still sparse. Here we present STAgR (String assembly gRNA cloning), a single step gRNA multiplexing system, that obtains its advantages by employing the N20 targeting sequences as necessary homologies for Gibson assembly. We show that STAgR allows reliable and cost-effective generation of vectors with high numbers of gRNAs enabling multiplexed CRISPR approaches. Moreover, STAgR is easily customizable, as vector backbones as well as gRNA structures, numbers and promoters can be freely chosen and combined. Finally, we demonstrate STAgR’s widespread functionality, its efficiency in multi-targeting approaches, using it for both, genome and transcriptome editing, as well as applying it in vitro and in vivo.

Highlights d Aryl hydrocarbon receptor (AhR) pathway is crucial for brain regeneration d High AhR levels promote conversion of ependymoglia to neurons during regeneration d Low AhR levels promote ependymoglial proliferation in the injured brain d AhR levels set the proper timing of restorative neurogenesis

Given the large amount of genome-wide data that has been collected during the last decades a good understanding of how and why cells change during development, homeostasis and disease might be expected. Unfortunately, the opposite is true; Triggers that cause cellular state changes remain elusive and the underlying molecular mechanisms are poorly understood. Although genes with the potential to influence cell states are known, the historic dependency on methods that manipulate gene expression outside the endogenous chromatin context has prevented us from understanding how cells organize, interpret and protect cellular programs. Fortunately, recent methodological innovations are now providing options to answer these outstanding questions, by allowing to target and manipulate individual genomic and epigenomic loci. In particular, three experimental approaches are now feasible due to DNA targeting tools: namely, activation and/or repression of master transcription factors in their endogenous chromatin context, targeting transcription factors to endogenous, alternative or inaccessible sites; and finally, functional manipulation of the chromatin context. In this article, we discuss the molecular basis of DNA targeting tools and review the potential of these new technologies before we summarize how these have already been used for the manipulation of cellular states and hypothesize about future applications.

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The bacterial CRISPR/Cas9 system has substantially increased methodological options for life scientists. Due to its utilization, genetic and genomic engineering became applicable to a large range of systems. Moreover, many transcriptional and epigenomic engineering approaches are now generally feasible for the first time. One reason for the broad applicability of CRISPR lies in its bipartite nature. Small gRNAs determine the genomic targets of the complex, variants of the protein Cas9, and the local molecular consequences. However, many CRISPR approaches depend on the simultaneous delivery of multiple gRNAs into individual cells. Here, we present a customizable protocol for string assembly gRNA cloning (STAgR), a method that allows the simple, fast and efficient generation of multiplexed gRNA expression vectors in a single cloning step. STAgR is cost-effective, since (in this protocol) the individual targeting sequences are introduced by short overhang primers while the long DNA templates of the gRNA expression cassettes can be re-used multiple times. Moreover, STAgR allows single step incorporation of a large number of gRNAs, as well as combinations of different gRNA variants, vectors and promoters.

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