Using next-generation sequencing to probe epigenetic landscapes: Although single-base changes in DNA
methylation are clearly relevant to the transcriptional status of individual genes, the true power of this approach
for pharmacotherapeutics comes from understanding DNA methylation principles across the entire genome. This
ability not only enables the determination of potential off-target effects of a DNA methylation–related drug but also
provides the opportunity to screen for and select new genetic or epigenetic targets for drug treatment. The advent of
massively parallel next-generation sequencing platforms has made this idea a concrete reality, and it is now entirely
feasible to sequence the entire methylome and transcriptome from neuronal populations to understand the precise
functional relationship between DNA methylation and gene expression (48–52). As a practical matter, researchers
should consider several issues, both in terms of which sequencing approach to use (53, 54) and how to interpret and
analyze the resulting data (55). For example, sequencing approaches that rely on immunoprecipitation or capture of
methylated DNA have proved to provide good genomic coverage and are relatively cheap, but they lack single-base
resolution. Likewise, approaches that involve bisulfite conversion of DNA provide exquisitely detailed single-
nucleotide methylation maps but can be more expensive to generate and are bioinformatically more challenging
because of the reduced complexity of DNA after conversion. Nevertheless, sequencing-based methylation assays
have yielded enormous insights into the role of DNA methylation in the brain and will be required for therapeutic
targeting of DNA methylation.