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Plasmids 101: Knockout/Knock-In Plasmids

Posted by Benoit Giquel on Dec 1, 2016 10:30:00 AM

One of the most powerful strategies to investigate a gene's function is to inactivate, or "knockout", the gene by replacing it or disrupting it with an piece of DNA designed in the lab. Specially constructed plasmids can be used to replace genes in yeast, mice, or Drosophila through homologous recombination. The concept is simple: deliver a template with a modified version of the targeted sequence to the cell which will recombine the template with the endogenous gene. Here, we'll describe the techniques and the plasmids used to inactivate specific genes in mammalian cells. Despite the popularity of CRISPR-based knockout/knock-in systems, these systems remain valuable, especially in cases where CRISPR cannot be used (e.g. there are no suitable PAM sequences nearby or your gene of interest is difficult to target specifically with a gRNA). Be sure to keep these techniques in mind when choosing a knockout strategy!

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Topics: Plasmid How To, Genome Engineering, Plasmids 101

Single Base Editing with CRISPR

Posted by Mary Gearing on Aug 16, 2016 10:30:00 AM

This post was updated on Nov 27, 2017.

When we talk about CRISPR applications, one negative always comes up: the low editing efficiency of homology-directed repair (HDR). Compared to non-homologous end joining, HDR occurs at a relatively low frequency, and in nondividing cells, this pathway is further downregulated. Rather than try to improve HDR, Addgene depositor David Liu’s lab created new Cas9 fusion proteins that act as base editorsThese fusions contain dCas9 or Cas9 nickase and a cytidine deaminase, and they can convert cytosine to uracil without cutting DNA. Uracil is then subsequently converted to thymine through DNA replication or repair. Later work has improved base editor targeting flexibility and specificity. New adenine base editors also allow you to change adenine to inosine, which is then converted to guanine.

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Topics: Genome Engineering, CRISPR

Google Forums Round Up: First Impressions of NgAgo

Posted by Guest Blogger on Aug 4, 2016 10:30:00 AM

Update (November 18, 2016): Researchers from a variety of institutions recently reported their inability to recapitulate the results of Gao et al 2016 in a letter to Protein & Cell.

Update (August 3rd, 2017) THE ORIGINAL NgAgo ARTICLE DISCUSSED IN THIS POST HAS BEEN RETRACTED AND FOLLOW UP STUDIES HAVE FAILED TO DEMONSTRATE GENOME EDITING BY THIS TOOL

This post was contributed by guest blogger Pooran Dewari. Any views in this post are those of the guest blogger and do not necessarily represent the views of Addgene. Addgene performs Sanger sequencing on select regions of all distributed plasmids as part of quality control, but does not perform functional tests.

The newest genome engineer sharing the stage with much-lauded CRISPR-Cas9 is DNA-guided endonuclease NgAgo! We'll discuss how NgAgo is faring with users in a minute, but, to start, let's review why NgAgo is in the spotlight and take a moment to remember that NgAgo has only been available for genome editing for a few months. More time is required for its optimization and development before it can truly be pitted against CRISPR head-to-head. 

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Topics: Genome Engineering, CRISPR

Recombinase-based State Machines Enable Order-dependent Logic in vivo

Posted by Guest Blogger on Jul 28, 2016 10:30:00 AM

This post was contributed by guest blogger Nathaniel Roquet, a PhD student in the Harvard Biophysics program and researcher in the Lu Lab at MIT.

Note: The following blog post reduces the content of our paper, “Synthetic recombinase-based state machines in living cells” (1), into a more straight-forward, concise explanation of how to adapt our engineered devices, recombinase-based state machines for your own experimental needs. For more context, exposition, and detail, please refer to the paper.

Why Might One Be Interested in State Machine Technology?

Biological research has produced a massive amount of information regarding which regulatory proteins, signaling molecules, mutations, and environmental conditions drive certain cellular behaviors, but little is known about the order or timing of these factors. Recombinase-based state machines (RSMs), which take on a particular DNA-sequence configuration (state) based on the identity and order of a particular set of inputs, may be used to better understand and engineer cellular processes that are influenced by temporally ordered biochemical events.

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Topics: Genome Engineering, Synthetic Biology

Cpf1 Update: Comparison to Cas9 and NgAgo

Posted by Mary Gearing on Jul 14, 2016 10:30:00 AM

In 2015, Feng Zhang’s lab characterized two Cpf1 nucleases, distant cousins of well-known Cas9. Cpf1 cleaves DNA in a staggered pattern and requires only one RNA rather than the two (tracrRNA and crRNA) needed by Cas9 for cleavage. Now, two new studies show that Cpf1 displays lower off-target editing than Cas9, confirming that this protein is well suited for genome editing. 

Find Cpf1 Plasmids at Addgene

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Topics: Genome Engineering, CRISPR

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