Dataset Information

Programmable Genome Editing Tools and their Regulation for Efficient Genome Engineering.

ABSTRACT: Targeted genome editing has become a powerful genetic tool for studying gene function or for modifying genomes by correcting defective genes or introducing genes. A variety of reagents have been developed in recent years that can generate targeted double-stranded DNA cuts which can be repaired by the error-prone, non-homologous end joining repair system or via the homologous recombination-based double-strand break repair pathway provided a suitable template is available. These genome editing reagents require components for recognizing a specific DNA target site and for DNA-cleavage that generates the double-stranded break. In order to reduce potential toxic effects of genome editing reagents, it might be desirable to control the in vitro or in vivo activity of these reagents by incorporating regulatory switches that can reduce off-target activities and/or allow for these reagents to be turned on or off. This review will outline the various genome editing tools that are currently available and describe the strategies that have so far been employed for regulating these editing reagents. In addition, this review will examine potential regulatory switches/strategies that can be employed in the future in order to provide temporal control for these reagents.

SUBMITTER: Guha TK

PROVIDER: S-EPMC5279741 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Programmable Genome Editing Tools and their Regulation for Efficient Genome Engineering.

Guha Tuhin Kumar TK Wai Alvan A Hausner Georg G

Computational and structural biotechnology journal 20170112

Targeted genome editing has become a powerful genetic tool for studying gene function or for modifying genomes by correcting defective genes or introducing genes. A variety of reagents have been developed in recent years that can generate targeted double-stranded DNA cuts which can be repaired by the error-prone, non-homologous end joining repair system or via the homologous recombination-based double-strand break repair pathway provided a suitable template is available. These genome editing rea ...[more]

PMID: 28179977

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Project description:BACKGROUND:Rhodobacter sphaeroides is a metabolically versatile bacterium that serves as a model for analysis of photosynthesis, hydrogen production and terpene biosynthesis. The elimination of by-products formation, such as poly-β-hydroxybutyrate (PHB), has been an important metabolic engineering target for R. sphaeroides. However, the lack of efficient markerless genome editing tools for R. sphaeroides is a bottleneck for fundamental studies and biotechnological exploitation. The Cas9 RNA-guided DNA-endonuclease from the type II CRISPR-Cas system of Streptococcus pyogenes (SpCas9) has been extensively employed for the development of genome engineering tools for prokaryotes and eukaryotes, but not for R. sphaeroides. RESULTS:Here we describe the development of a highly efficient SpCas9-based genomic DNA targeting system for R. sphaeroides, which we combine with plasmid-borne homologous recombination (HR) templates developing a Cas9-based markerless and time-effective genome editing tool. We further employ the tool for knocking-out the uracil phosphoribosyltransferase (upp) gene from the genome of R. sphaeroides, as well as knocking it back in while altering its start codon. These proof-of-principle processes resulted in editing efficiencies of up to 100% for the knock-out yet less than 15% for the knock-in. We subsequently employed the developed genome editing tool for the consecutive deletion of the two predicted acetoacetyl-CoA reductase genes phaB and phbB in the genome of R. sphaeroides. The culturing of the constructed knock-out strains under PHB producing conditions showed that PHB biosynthesis is supported only by PhaB, while the growth of the R. sphaeroides ΔphbB strains under the same conditions is only slightly affected. CONCLUSIONS:In this study, we combine the SpCas9 targeting activity with the native homologous recombination (HR) mechanism of R. sphaeroides for the development of a genome editing tool. We further employ the developed tool for the elucidation of the PHB production pathway of R. sphaeroides. We anticipate that the presented work will accelerate molecular research with R. sphaeroides.

Project description:Genome engineering with programmable nucleases depends on cellular responses to a targeted double-strand break (DSB). The first truly targetable reagents were the zinc finger nucleases (ZFNs) showing that arbitrary DNA sequences could be addressed for cleavage by protein engineering, ushering in the breakthrough in genome manipulation. ZFNs resulted from basic research on zinc finger proteins and the FokI restriction enzyme (which revealed a bipartite structure with a separable DNA-binding domain and a non-specific cleavage domain). Studies on the mechanism of cleavage by 3-finger ZFNs established that the preferred substrates were paired binding sites, which doubled the size of the target sequence recognition from 9 to 18bp, long enough to specify a unique genomic locus in plant and mammalian cells. Soon afterwards, a ZFN-induced DSB was shown to stimulate homologous recombination in cells. Transcription activator-like effector nucleases (TALENs) that are based on bacterial TALEs fused to the FokI cleavage domain expanded this capability. The fact that ZFNs and TALENs have been used for genome modification of more than 40 different organisms and cell types attests to the success of protein engineering. The most recent technology platform for delivering a targeted DSB to cellular genomes is that of the RNA-guided nucleases, which are based on the naturally occurring Type II prokaryotic CRISPR-Cas9 system. Unlike ZFNs and TALENs that use protein motifs for DNA sequence recognition, CRISPR-Cas9 depends on RNA-DNA recognition. The advantages of the CRISPR-Cas9 system-the ease of RNA design for new targets and the dependence on a single, constant Cas9 protein-have led to its wide adoption by research laboratories around the world. These technology platforms have equipped scientists with an unprecedented ability to modify cells and organisms almost at will, with wide-ranging implications across biology and medicine. However, these nucleases have also been shown to cut at off-target sites with mutagenic consequences. Therefore, issues such as efficacy, specificity and delivery are likely to drive selection of reagents for particular purposes. Human therapeutic applications of these technologies will ultimately depend on risk versus benefit analysis and informed consent.

Dataset Information

Programmable Genome Editing Tools and their Regulation for Efficient Genome Engineering.

Publications

Programmable Genome Editing Tools and their Regulation for Efficient Genome Engineering.

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