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Optimizing Donor DNA for Enhanced CRISPR Genome Editing

Posted by Guest Blogger on Mar 24, 2016 10:30:00 AM

This post was contributed by guest blogger Chris Richardson, a Postdoctoral Researcher in Jacob Corn’s lab.

CRISPR-Cas9 (Cas9) is an RNA-guided nuclease that targets and cuts genomic DNA. The interplay between Cas9 (which causes the breaks) and host cell DNA repair factors (which repair those breaks) makes Cas9 extremely effective as a genome editing reagent. This interplay falls into two broad categories and thus, causes two types of editing outcomes: Cas9 breaks repaired by the non-homologous end-joining (NHEJ) pathway disrupt target gene sequences (thus inactivating genes), while breaks repaired by homology directed repair (HDR) pathways can modify the sequence of a gene (thus altering its function). HDR is crucial for certain applications, for example, correcting the allele that causes sickle cell anemia. However, HDR occurs much less frequently than NHEJ and the efficiency of these editing reactions is low. Understanding the biological cause of this repair bias is a fascinating (and yet unanswered) question. Our recent paper (Richardson et al 2016) revealed some of the biophysical parameters that can influence the HDR/NHEJ decision.

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Topics: Genome Engineering, CRISPR

CRISPR Methods for Bacterial Genome Engineering

Posted by Mary Gearing on Mar 3, 2016 10:30:00 AM

This post was updated on Dec 5, 2017.

Although CRISPR systems were first discovered in bacteria, most CRISPR-based genome engineering has taken place in other organisms. In many bacteria, unlike other organisms, CRISPR-induced double stranded breaks are lethal because the non-homologous end-joining (NHEJ) repair pathway is not very robust. In many cases, homology-directed repair does not function effectively either, but scientists have devised means of co-opting phage genetic systems to facilitate homologous recombination in bacteria. These quirks change the way CRISPR-mediated genome engineering functions in bacteria, but have no fear - plasmids from Addgene depositors are making it easier than ever to do CRISPR editing in E. coli and other commonly-used bacterial species. Read on to learn about the tools available for bacteria and some of the applications for which they’ve been used.

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Topics: Genome Engineering, CRISPR

PITChing MMEJ as an Alternative Route for Gene Editing

Posted by Mary Gearing on Feb 23, 2016 10:30:00 AM

If you follow CRISPR research, you know all about using non-homologous end-joining (NHEJ) to make deletions or homology-directed repair (HDR) to create precise genome edits. But have you heard of another double-stranded break repair mechanism: MMEJ (microhomology-mediated end-joining)? MMEJ, a form of alternative end-joining, requires only very small homology regions (5-25 bp) for repair, making it easier to construct targeting vectors. Addgene depositor Takashi Yamamoto’s lab has harnessed MMEJ to create a new method for CRISPR gene knock-in, termed PITCh (Precise Integration into Target Chromosomes). Using their PITCh plasmids, GFP knock-in cell lines can be created in about a month and a half, without the need for complicated cloning of homology arms.

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Topics: Plasmid Technology, Genome Engineering, CRISPR, Techniques

CRISPR 101: Multiplex expression of gRNAs

Posted by Mary Gearing on Jan 28, 2016 10:50:00 AM

This post was updated on Dec 5, 2017.

CRISPR makes it easy to target multiple loci - a concept called multiplexing. Since CRISPR is such a robust system, editing or labeling efficiency doesn’t usually change when you add multiple gRNAs. Sound good? Addgene has many tools to help you multiplex - we’ll use mammalian plasmids to introduce you to some of your potential options and cloning methods, but please scroll down for plasmids suitable for other model systems, including E. coli, plants, Drosophila, and zebrafish!

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Topics: Genome Engineering, CRISPR, CRISPR 101, Plasmid Kits

Enhancing CRISPR Targeting Specificity with eSpCas9, SpCas9-HF1, & HypaCas9

Posted by Tyler Ford on Dec 16, 2015 10:30:00 AM

As evidenced by all the CRISPR publications, press, and plasmids out there, it’s obvious that CRISPR is a ground-breaking technology that’s already had a huge impact on research and will be affecting our everyday lives very soon. Not only is CRISPR having effects on various biological disciplines, the base technology itself is constantly improving. Cas9 variants have been modified for genome editing, activating gene expression, visualizing genomic loci, and much more. Now, researchers from the Zhang, Joung, and Doudna labs have improved the on-target specificity of the Cas9 nuclease with engineered variants: eSpCas9SpCas9-HF1, & HypaCas9.

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Topics: Genome Engineering, CRISPR

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