Reduced representation optical methylation mapping (R2OM2).
Reduced representation methylation analysis utilizes a subset of CpGs in order to report the overall methylation status of the probed genomic regions. Here, we use this concept in order to create fluorescent optical methylation profiles along chromosomal DNA molecules for epigenetic profiling. Reduced representation optical methylation mapping (R2OM2) in combination with Bionano Genomics next generation genome mapping (NGM) technology provides a hybrid genetic/epigenetic genome map of individual chromosome segments spanning hundreds of kilobase pairs (kbp). These long reads, along with the single-molecule resolution, allow for epigenetic variation calling and methylation analysis of large structural aberrations such as pathogenic macrosatellite arrays not accessible to single-cell next generation sequencing (NGS). We show that in addition to the inherent long-read benefits of R2OM2, it provides genomic methylation patterns comparable to whole genome bisulfite sequencing (WGBS) while retaining single-molecule information. The method is applied here to detect methylation along genes, around regulatory histone marks and to study facioscapulohumeral muscular dystrophy (FSHD), simultaneously recording the haplotype, copy number and methylation status of the disease-associated, highly repetitive locus onchromosome 4q.