Intro to Reduced Representation Bisulfite Sequencing (RRBS)

DNA methylationis well known for its role in regulating genes and their expression. It involves the covalent addition of a methyl group at the 5-carbon position of cytosine rings to form 5-methylcytosine, or 5mC. Aberrancies in DNA methylation can lead to the development and progression of numerous pathologies, including inflammatory, metabolic, infectious, cardiovascular, and neurological disorders, as well as cancers. Consequently, this epigenetic modification has become a major focus of methylome research and an attractive therapeutic target.

A variety of experimental techniques are available to study 5mC, bisulfite sequencingbeing among the more popular methods for genome-wide DNA methylation analysis. This strategy combines bisulfite conversion, a chemical reaction whereby unmethylated cytosine is deaminated to uracil while methylated cytosine is left intact, and sequencing in order to identify 5mC sites at single-base resolution. 

Whole-genome bisulfite sequencing (WGBS), often considered the “gold standard” for DNA methylation profiling, is commonly used to determine the methylation status of single cytosines across the entire genome. Reduced-representation bisulfite sequencing(RRBS) affords a more directed and cost-effective approach, with focused coverage on dense areas of CpG dinucleotides where 5mC is primarily found.

By enriching genomic regions that contain high CpG content, including CpG islands, gene promoters, and repeated sequences, RRBS significantly reduces (down to 1%) the amount of genome sequenced and thereby provides an economical alternative for researchers on a budget. The standard RRBS protocol entails digestion of isolated and purified genomic DNA via a methylation-insensitive restriction enzyme such as MspI, which specifically targets the 5′-CCGG-3′ motif irrespective of CpG methylation status and generates DNA fragments of various sizes. This is followed by end repair and A-tailing, adaptor ligation, fragment size selection, bisulfite conversion, and library amplification and purification, prior to sequencing.

Traditional RRBS has several drawbacks. It requires relatively large amounts of DNA as input material, which is difficult to prepare from limited biological samples such as tumor biopsies, early embryos, embryonic tissues, and ccfDNA. Post-ligation bisulfite conversion causes most of the DNA inserts within the adaptor/DNA fragment constructs to be broken, resulting in the formation of mono-tagged templates that will be removed during library enrichment. Thus, incomplete coverage and bias occur when performing RRBS. It is also a time-consuming process, taking approximately 2 days.

To account for these issues, EpigenTek developed the EpiNext™ RRBS Library Fast Kit(catalog # P-1069), which offers the following features and advantages:

• Convenience. This all-inclusive kit comes equipped with the total essentials for MspI digestion, bisulfite conversion, and Illumina-based library DNA preparation.
• Speed. The entire procedure, from digestion to ready-to-use library, can be finished within just 4 hours.
• Specificity. Complete (>99%) C-to-U conversion, with negligible 5mC-to-T conversion.
• Low input requirement, as low as 10 ng of starting DNA. Innovative direct adaptor ligation of bisulfite DNA minimizes sample loss, making the kit ideal for precious, low-abundant specimens.
• Flexibility, allowing for both non-barcoded (singleplexed) and barcoded (multiplexed) library preparation.