UBC Theses and Dissertations
Epigenetic heterogeneity revealed through single-cell DNA methylation sequencing Hui, Zhao Kun (Tony)
Increasing evidence of functional and transcriptional heterogeneity in phenotypically similar single-cells has prompted interest in protocols for obtaining parallel methylome data. Despite appreciable advancements in experimental protocols for single-cell DNA methylation measurements, methods for analyzing the resulting data are still immature. To address the challenge of stochastic data loss associated with single cell measurements, current strategies average methylation in windows or region sets. However previous studies have demonstrated that single CpGs are functional and our analysis of single cell methylation measurements revealed a rapid decay in concordance neighbouring CpG states beyond 1kb. To leverage the information content of individual CpGs in the context of single cell methylation measurements we developed an analytical strategy for deriving single-cell DNA methylation states using individual CpGs, which we term PDclust. We validated PDclust on existing datasets and on data we generated from single index-sorted murine and human hematopoietic stem cells (HSCs) that are highly enriched in functionally defined stem cells. Using PDClust, we identified epigenetically distinct subpopulations within these HSC populations. Strikingly, human cord blood derived HSC populations were separable by donor specific methylation states whereas more differentiated hematopoietic cells separated solely by cell type. Interestingly, removal of methylation sites near genetic variants did not impact this separation, suggesting that these epigenetic states may be a consequence of environmental differences. Finally, through protocol optimization and deep sequencing we generated one of the most comprehensive sets of single cell methylome profiles (20% of CpGs on average) and from these were able to generate genomewide profiles from as little as 6 epigenetically related HSCs to derive subtype-specific regulatory states.
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