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Tracking of dCas9-methyltransferase footprints

ABSTRACT: In normal mammalian development cytosine methylation is essential, and is directed to specific regions of the genome. Despite notable advances in mapping the genome-wide distribution, studying the direct contribution of DNA methylation to gene regulation has been limited by the lack of tools for its precise manipulation. Thus, combining the targeting capability of CRISPR/Cas9 systems with an epigenetic modifier has attracted interest in the scientific community. In contrast to profiling the genome-wide cleavage of a nuclease competent Cas9, tracing the global activity of a dead Cas9-methyltransferase is challenging within a highly modified genome. To overcome this, we utilized an engineered, methylation depleted but maintenance competent mouse ES cell line and find a surprisingly ubiquitous nuclear activity of dCas9-methyltransferases. Our results provide new insights into the targeted regulation of DNA methylation and point to an important difference between genetic and epigenetic editing tools that require unique experimental considerations.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE87757 | GEO | 2018/03/12

REPOSITORIES: GEO

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Project description:DNA methylation is a covalent modification of the genome that plays important roles in genome regulation and vertebrate development. Although detection of this modification in the genome has been possible for several decades, the ability to deliberately and specifically manipulate local DNA methylation states in the genome has been extremely limited. Consequently, this has impeded the direct determination of the consequence of DNA methylation on transcriptional regulation and transcription factor binding in the native chromatin context. Thus, highly specific targeted epigenome editing tools are needed to address this outstanding question. Recent adaptations of genome editing technologies, such as the fusion of the DNMT3A methyltransferase catalytic domain to catalytically inactive Cas9 (dC9-D3A), have aimed to provide new tools for altering DNA methylation at desired loci. Here, we performed a deeper analysis of the performance of the tools at a genome wide level which revealed consistent off-target binding events and DNA methylation deposition throughout the genome, limiting the capacity of these tools to generate unambiguous determination of the functional consequences of DNA methylation. To address this issue, we developed a modular dCas9-SunTag (dC9Sun-D3A) system that can recruit multiple DNMT3A catalytic domains to a target site for editing DNA-methylation. dC9Sun-D3A is tunable, specific and exhibits much higher induction of DNA methylation at target sites than the dC9-D3A direct fusion protein. Importantly, genome-wide characterization of dC9Sun-D3A binding sites and DNA methylation revealed minimal off-target protein binding and induction of DNA methylation with dC9Sun-D3A, compared to pervasive off-target binding and methylation by the dC9-D3A direct fusion construct. Furthermore, we used dC9Sun-D3A to test the impact of DNA methylation upon the DNA binding of CTCF and NRF1 upon targeted methylation of their core binding sites, demonstrating the binding sensitivity of these proteins to DNA methylation in situ. Overall, this modular dC9Sun-D3A system enables precise DNA methylation deposition with the least amount of off-target DNA methylation reported to date, allowing accurate functional determination of the role of DNA methylation at single loci.

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Tracking of dCas9-methyltransferase footprints

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