Next stop for the CRISPR revolution: RNA‐guided epigenetic regulators

Abstract

Clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins offer a breakthrough platform for cheap, programmable, and effective sequence-specific DNA targeting. The CRISPR-Cas system is naturally equipped for targeted DNA cutting through its native nuclease activity. As such, groups researching a broad spectrum of biological organisms have quickly adopted the technology with groundbreaking applications to genomic sequence editing in over 20 different species. However, the biological code of life is not only encoded in genetics but also in epigenetics as well. While genetic sequence editing is a powerful ability, we must also be able to edit and regulate transcriptional and epigenetic code. Taking inspiration from work on earlier sequencespecific targeting technologies such as zinc fingers (ZFs) and transcription activator-like effectors (TALEs), researchers quickly expanded the CRISPR-Cas toolbox to include transcriptional activation, repression, and epigenetic modification. In this review, we highlight advances that extend the CRISPR-Cas toolkit for transcriptional and epigenetic regulation, as well as best practice guidelines for these tools, and a perspective on future applications.

In Vivo Target Gene Activation via CRISPR/Cas9-Mediated Trans-epigenetic Modulation

“…This system can be used to express genes to compensate for disease-associated genetic mutations, or to overexpress long non-coding RNAs oas well as GC-rich genes to reveal their biological functions, a difficult feat until now (La Russa and Qi, 2015; Vora et al, 2016). Finally, combined loss- and gain-of-function manipulations can be applied to rapidly establish epistatic relationships between genes in vivo .…”

“…This enabled the CRISPR/Cas9 system to transcriptionally activate target genes within the native chromosomal context. This transformative technology has the potential to provide the foundation for many scientific and medical applications, including: 1) performing functional genetic screens, 2) creating synthetic gene circuits, 3) developing therapeutic interventions to compensate for genetic defects, and 4) redirecting cell fate by epigenetic reprogramming for regenerative medicine (Chen and Qi, 2017; Thakore et al, 2016; Vora et al, 2016). …”

“…To our knowledge, current CRISPR/Cas9-mediated epigenetic editing systems have not yet been able to induce a physiologically relevant phenotype in a postnatal mammal (Jurkowski et al, 2015; Vora et al, 2016). This limits the utility of these tools for performing experiments and for developing targeted epigenetic therapies.…”

Interaction between epigenetic and metabolism in aging stem cells

“…How these different epigenetic marks are affected in aging stem cells is not yet known. It will be important to develop methods to modify the epigenetic state of specific genetic loci to test for causal effects on stem cell function [29,30] to determine if the epigenome of old stem cells can be “reset” to a youthful state [31]. …”

Probability, odds and random chance: the difficult task of modulating the epigenetic profile of cloned embryos

“…Such application can benefit the treatment of human epigenetic diseases, such as the Angelman Syndrome, in which a functional parental allele is silenced due to genomic imprinting, whereas the other allele is mutant. In such cases, it is possible to use the CRISPR/Cas9 system as an epigenetic activator of silenced genes, allowing expression of an intact copy of a missing gene (Vora et al, 2016). For instance, Hilton et al (2015) fused Cas9 to the core catalytic domain of the histone acetyltransferase (HAT) of the human E1A-associated protein p300, which allowed the acetylation of the lysine residue at position 27 of Histone 3 (H3K27), activating gene expression.…”