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Protein Tagging with CRISPR/Cas9: A Conversation with Mendenhall and Myers

Posted by Kendall Morgan on Jul 28, 2015 10:30:00 AM

As Eric Mendenhall of the University of Alabama in Huntsville explains it, a major goal in his laboratory is to understand the function of the non-coding portion of the genome. Mendenhall and Richard Myers of HudsonAlpha (where Mendenhall is also an adjunct faculty member) have together been working toward this goal for years as members of the ENCyclopedia of DNA Elements Project (ENCODE), an NIH-funded effort to define all of the functional elements in the human genome.

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Topics: Interview, CRISPR

A Match Made in Heaven: CRISPR and AAV

Posted by Mary Gearing on Jul 14, 2015 10:30:00 AM

This post was updated on Dec 4, 2017.

CRISPR genome editing has quickly become the most popular system for in vitro and germline genome editing, but in vivo gene editing approaches have been limited by problems with Cas9 delivery. Adeno-associated viral vectors (AAV) are commonly used for in vivo gene delivery due to their low immunogenicity and range of serotypes allowing preferential infection of certain tissues. However, packaging Streptococcus pyogenes (SpCas9) and a chimeric sgRNA together (~4.2 kb) into an AAV vector is challenging due to the low packaging capacity of AAV (~4.5 kb.) While this approach has been proven feasible, it leaves little room for additional regulatory elements. Feng Zhang's group previously packaged Cas9 and multiple gRNAs into separate AAV vectors, increasing overall packaging capacity but necessitating purification and co-infection of two AAVs.

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Topics: CRISPR, Viral Vectors

Another Pathway into Cells: iTOP

Posted by Mary Gearing on Jun 23, 2015 4:37:00 PM

Primary cells recapitulate the natural biology of a cell type of interest better than immortalized lines derived from the same cell type; however, their usage has been limited by technical problems. For instance, it’s much more difficult to introduce a gene of interest into primary cells, so most primary cell lines require viral infection. A new paper from Niels Geijsen’s lab suggests that primary cells may be better transduced using only protein. Read on for a description of the lab’s iTOP protein-only transduction method and its potential applications to CRISPR/Cas9 genome editing.

 

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Topics: CRISPR, Techniques

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

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