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Back to Bacteria: CRISPR gRNA Multiplexing Using tRNAs

Posted by Mary Gearing on Jun 2, 2015 2:06:00 PM

In the short time since its development, CRISPR/Cas9 genome editing has been used to study the effect of gene knockout in vivo and in vitro, as well as to insert targeted mutations through homologous recombination. To further increase the utility of CRISPR/Cas9, it will be necessary to improve its multiplexing capacity. Multiplexing is key due to the natural redundancy of biological pathways;  to observe a phenotype, the modification of multiple genes is often necessary.

Guide RNAs (gRNAs) are commonly packaged in 400-500 bp cassettes containing the RNA pol III promoter, gRNA and pol III terminator. These relatively large cassettes (considering the gRNA itself is ~100 bases) limit the number of gRNAs that can be packaged together in a single vector. In addition, the pol III promoter is relatively weak, and low expression of gRNAs from these constructs could lower genome editing efficiency.

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Topics: Plasmid Technology, Genome Engineering, CRISPR

Transgenic Organisms, Cas9 Gene Drives, and Appropriate Safeguards

Posted by Guest Blogger on May 22, 2015 12:58:12 PM

This post was contributed by Kevin Esvelt, a Wyss Technology Development Fellow at the Wyss Institute and Harvard Medical School.

Scientists making transgenic organisms with Cas9 should be aware of the potential hazards of creating “gene drives” capable of spreading through wild populations. Whereas most genomic changes impose a fitness cost and are eliminated by natural selection, gene drives distort inheritance in their favor and consequently can spread even when costly.

If even a single organism carrying a synthetic gene drive were to escape the laboratory, the drive could eventually spread through the entire wild population with unpredictable ecological effects. Because the consequences of such a mistake would necessarily extend far beyond the laboratory and seriously damage public trust in scientists, experiments involving potential gene drives should be conducted with extreme caution.

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Topics: Plasmid Technology, Lab Tips, CRISPR, CRISPR 101

CRISPR Meets Synthetic Biology: A Conversation with MIT’s Christopher Voigt

Posted by Kendall Morgan on Apr 22, 2015 10:06:00 AM

As Christopher Voigt explains it, his lab at the Massachusetts Institute of Technology has been “working on new experimental and theoretical methods to push the scale of genetic engineering, with the ultimate objective of genome design.” It’s genetic engineering on a genomic scale, with the expectation for major advances in agriculture, materials, chemicals, and medicine.

As they’ve gone along, Voigt’s group has also been assembling the toolbox needed for anyone to begin considering genetic engineering projects in a very big way. In one of his latest papers, published in Molecular Systems Biology in November, Voigt and Alex Nielsen describe what’s possible when multi-input CRISPR/Cas genetic circuits are linked to the regulatory networks within E. coli host cells.

We talked with Voigt about this collision that’s taking place between CRISPR technology and synthetic biology, the tools he’s making available through Addgene, and where all of it is likely to lead us in the future. 

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Topics: Genome Engineering, Investigator Feature, Synthetic Biology, CRISPR

CRISPR 101: Non-Homologous End Joining

Posted by Guest Blogger on Apr 16, 2015 11:45:08 AM

This post was contributed by David Wyatt and Dale Ramsden, UNC at Chapel Hill.

One advantage to using the CRISPR/Cas system for genome engineering is the fact that Cas9 can be easily programmed to make a DNA double strand break (DSB) in the genome wherever the user chooses. After the initial cut, the next steps in the process involve repairing chromosomal DSBs. It is important to know that cells possess two major repair pathways  Non-Homologous End Joining (NHEJ) and Homology Directed Repair (HDR) – and how these pathways work, as this could be relevant when planning your experiment. This blog has previously considered the HDR pathway; below we’ll discuss NHEJ, and how it impacts what happens to Cas9-mediated DSBs in the genome.

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Topics: Genome Engineering, CRISPR, CRISPR 101

Rewiring Metabolic Circuitry with CRISPR RNA Scaffolds [Video]

Posted by Guest Blogger on Apr 7, 2015 12:21:00 PM

This post was contributed by Adam Chin-Fatt, a Ph.D. student at the University of Western Ontario. Adam summarizes Zalatan JG, et al.'s recent paper, "Engineering Complex Synthetic Transcriptional Programs with CRISPR RNA Scaffolds." Adam has also created a video to help scientists visualize the concepts discussed in the paper.

The transcriptional control of multiple loci is deftly coordinated by the eukaryotic cell for the execution of many complex cellular behaviors, such as differentiation or metabolism. Our attempts to manipulate these cellular behaviors often fall short with the generation of various flux imbalances. The conventional approach has typically been to either systematically delete/overexpress endogenous genes or to introduce heterologous genes, but the trend of research has shifted in recent years toward tinkering with regulatory networks and multiplex gene control. However, these approaches are often met with the challenges of regulatory bottlenecks and their scope is limited by the lack of well characterized inducible promoters. Far removed from the bio-industry’s vision of ‘biofactories’, most successes in metabolic engineering have been limited to the overexpression of various metabolites in Escherichia coli or Saccharomyces cerevisiae with few techniques that are easily transferrable across host species or metabolic pathways. A new study takes us one step closer to the vision of metabolic biofactories by demonstrating the use of CRISPR-based RNA scaffolds to mimic natural transcriptional programs on multiple genes.

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Topics: Plasmid Technology, Genome Engineering, Synthetic Biology, CRISPR

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