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CRISPR 101: Multiplex Expression of gRNAs

Posted by Mary Gearing on Sep 10, 2020 7:45:00 AM

Originally published Jan 28, 2016 and last updated Sep 10, 2020 by Jennifer Tsang.

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 on one plasmid. 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: CRISPR, CRISPR 101, CRISPR gRNAs

CRISPR 101: RNA Editing with Cas13

Posted by Mary Gearing on Jul 31, 2020 8:30:00 AM

Originally published Nov 30, 2017 and updated Jul 31, 2020.

Cas13 enzymes are quickly becoming major players in the CRISPR field. Just a year after Feng Zhang’s lab identified Cas13a (C2c2) (Abudayyeh et al., 2016) as a RNA-targeting CRISPR enzyme, they adapted Cas13b for precise RNA editing (Cox et al., 2017). This new system, termed REPAIR (RNA editing for programmable A to I (G) replacement) is the first CRISPR tool for RNA editing. Two years after that, the lab published a paper on an RNA editor that allows C to U edits (RESCUE). We’ll walk through how these tools were developed and potential ways you can use it in your research.

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Topics: CRISPR, CRISPR 101, Cas Proteins

CRISPR 101: Anti-CRISPR Proteins Switch Off CRISPR-Cas Systems

Posted by Beth Kenkel on Jul 23, 2020 9:20:27 AM

Originally published May 23, 2017 and last updated Jul 23, 2020 by Jennifer Tsang.

CRISPR-Cas technology is constantly evolving. Variants of Cas proteins can be used for genome editing, activating gene expression, repressing gene expression, and much more. But there’s one thing that was missing: a way to shut off Cas’s activity. The concern is that the longer Cas remains active in a cell, the greater chances there are for off-target edits to occur. Although methods to switch on Cas activity using light or drugs have been developed, the field lacked an “off-switch” for Cas proteins.

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Topics: CRISPR, CRISPR 101

CRISPR 101: Epigenetics and Editing the Epigenome

Posted by Mary Gearing on Jun 24, 2020 1:45:00 PM

Originally published Feb 14, 2017 and updated Jun 24, 2020.

Epigenetic modifications are an additional layer of control over gene expression that go beyond genomic sequence. Dysregulation of the epigenome (the sum of epigenetic modifications across the genome) has been implicated in disease states, and targeting the epigenome may make certain processes, like cellular reprogramming of iPSCs, more efficient. In general, epigenetic chromatin modifications are correlated with alterations in gene expression, but causality and mechanisms remain unclear. Today, targeted epigenetic modification at specific genomic loci is possible using CRISPR, and Addgene has a number of tools for this purpose.

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Topics: CRISPR, CRISPR 101

CRISPR 101: Ribonucleoprotein (RNP) delivery

Posted by Andrew Hempstead on Sep 6, 2018 8:02:59 AM

CRISPR has greatly enhanced the ability of scientists to make genomic alterations, bringing about a revolution in genome engineering, with new techniques rapidly being developed. Performing a CRISPR experiment requires delivery of, at minimum, two components: the Cas9 protein and a guide RNA (gRNA) targeting your genomic site of interest. This is commonly performed by transfecting cells with a plasmid, such as PX459, which encodes Cas9 and contains a site for inserting a custom gRNA.  While this methodology has proven to be incredibly valuable to scientists, there are some potential complications that must be considered when using this method:

  1.     Cells must be amenable to transfection or viral transduction
  2.     Appropriate promoters must be chosen for both Cas9 and gRNA expression  
  3.     Plasmid DNA may be incorporated into the genome
  4.     Off-target effects can occur due to prolonged Cas9 expression
  5.     The requirement for Cas9 transcription and translation delays editing
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Topics: CRISPR, CRISPR 101, CRISPR Expression Systems and Delivery Methods

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