CRISPR System Developed for Dose-Dependent Gene Expression

CRISPR is renowned for its precise gene-editing ability, but is gaining ground in alternative applications; namely the control of selected gene expression. In an exciting new development, researchers have now developed a CRISPR-Cas9 system complexed with Chemical Epigenetic Modifiers (CEMs) that allowed dose-dependent activation of gene expression.

Unlike in gene editing systems where Cas9 is used; the endonuclease that cleaves DNA complementary to its guide RNA sequence, this study employed a catalytically inactive form of Cas9 called dCas9. This system allows manipulation of gene expression rather than gene editing. In a two-part system, the group at the University of North Carolina Eshelman School of Pharmacy, complexed dCas9 and CEMs that interact with cellular epigenetic apparatus.

CEMs are molecules that can induce heritable gene expression (or transcriptional) modifications, without altering the genotype. However, for these molecules to have effect there must be complementary transcriptional regulatory proteins present in the cell. Previous studies have had to recruit exogenous transcriptional activators, meaning lower specificity and efficacy in the manipulation of gene expression. The CEMs employed by this study were designed in such a way that target genes were activated by recruiting components of the host cell’s chromatin-activating machinery.

This is not the first-time scientists have combined CRISPR-Cas9 and CEMs to control gene expression, but the study published this week is the first to demonstrate dose-dependent control of gene upregulation. In addition, the group have achieved controlled transcriptional activation across multiple genes, diversely located in the genome, and, were able to reverse those effects.

The authors finally highlighted the versatility of the system and its potential, with modifications, to target any gene in the genome. With results of up to 20-fold upregulation in human embryonic kidney cells, the implications of this work are potentially huge for gene therapy applications, as transcriptional mis-regulation results in a broad spectrum of often severe and hereditary human diseases. These conditions include Huntington’s Disease and recessive autosomal diseases such as Cystic Fibrosis; both of which are progressive and incurable. Addressing transcriptional mis-regulation in a dose-dependent fashion holds exciting possibilities for personalised medicine across many therapeutic areas.