CRISPR Based System for Targeted Reduction of Gene Expression
posted on 05/07/2013
A CRISPR based gene silencing system using sequence specific RNA to repress expression of endogenous transcripts.
- Provides a platform to target specific mRNA transcripts in both prokaryotic and eukaryotic cells.
- Potential therapeutic strategy against pathogenic bacteria and viruses.
Since the discovery of silencing genes through RNA interference (RNAi), researchers have spent over $10 billion in obtaining small RNAs. RNAi is an indispensable tool to study gene function and is extensively utilized in basic research as well as drug discovery. Due to the ability to specifically target a disease causing protein, RNAi offers the capability to develop personalized treatment. Use of RNAi requires overcoming the hurdle of delivering RNAi systemically and limiting potential side effects. There are no current RNAi drugs on the market, but 22 clinical trials are progressing for ocular and retinal disorders, cancer, kidney disease, and antivirals. Concerns over off target effects, stimulation of immune response, and perturbation to endogenous RNAi machinery have halted previous clinical trials. A method to silence RNA through an alternative pathway may eliminate these pitfalls. In addition, reducing gene expression in prokaryotic organisms has not been explored and leaves an opportunity to develop strategies to suppress infectious pathogens.
Regulation of gene expression is a critical component of adaptive immunity where the host cell recognizes and destroys aberrant nucleic acid. Eukaryotes employ the RNA interference (RNAi) pathway to target mRNA transcripts specifically for destruction, thwarting protein expression. Bacteria do not have a homologous RNAi system, but contain the newly characterized bacterial clustered regularly interspaced short palindromic repeat (CRISPR) pathway to modulate gene expression. The CRISPR system has been shown previously to target exogenous DNA, but new research from Emory shows that it can specifically target an endogenous transcript to silence expression.
Researchers at Emory identified that the CRISPR pathway modulates specific bacterial transcripts to promote replication in the host cell without stimulating an immune response. The intracellular pathogen, Francisella novicida, uses CRISPR to repress its endogenous transcript, bacterial lipoprotein (BLP). By reducing BLP expression, F. novicida circumvents toll-like receptor 2 activation to prevent initiation of host defenses and pro-inflammatory pathways. Our researchers propose the use of this system to decrease translation of proteins by targeting specific mRNA transcripts in both prokaryotic and eukaryotic cells.
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