Additional Cas9 variants have been developed for transcriptional regulation of
gene expression. Rather than editing DNA, these deactivated Cas9 proteins simply bind the
target site and activate or inhibit expression.
CRISPR activation (CRISPRa) systems utilize a dCas9 fused to transcriptional
activators to up regulate endogenous gene expression, whereas CRISPR interference (CRISPRi)
systems use dCas9 fused to transcriptional repressors to downregulate gene expression.
Multiple CRISPRa and CRISPRi systems have been developed using different activators or
repressors. CRISPRa gRNAs for the SAM system
are currently available in plasmid formats.
Researchers have also recently developed a Cas fusion protein, CRISPRoff, that
can epigentically modify and silence genes without editing the underlying genome. The
epigenetic memory persists through cell differentiation and is heritably passed to future
cell generations. Gene activity can be re-activated using a different fusion protein called
CRISPRon.
Technique
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Components Required
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Common Experiments
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Common Applications
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CRISPRa
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CRISPRa guide RNA +
dCas9-SAM (or other)
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Overexpression screening and hit analysis
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Drug discovery
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CRISPRi
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CRISPRi guide RNA +
dCas9-KRAB (or other)
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Transient loss-of-function, siRNA validation
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Drug discovery
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CRISPRoff/
CRISPRon
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CRISPRoff guide RNA + CRISPRoff
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Heritable gene silencing without DNA editing
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Gene therapy
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