Project description:The physical properties of cell-free DNA fragments in plasma, such as fragment sizes and ends, have attracted much recent interest, leading to the emerging field of fragmentomics. This study attempted to further characterize the end structure of plasma DNA.
Project description:In this study, we compared the two long-read sequencing platforms, namely the single-molecule real-time sequencing by Pacific Biosciences and nanopore sequencing by Oxford Nanopore Technologies, for the analysis of cell-free DNA from plasma. Artificial mixtures of sonicated human and mouse DNA at different sizes were sequenced with the two platforms.
Project description:Background: Cell free DNA (cfDNA) in plasma has received increasing attention and has been studied in a broad range of clinical conditions implicating inflammation, cancer, and aging. However, few studies have focused on mitochondrial DNA (mtDNA) in the cell free form. This study characterized the size distribution and sequence characteristics of plasma cell free mtDNA (cf mtDNA) in humans.Methods and Results: We optimized DNA isolation and next-generation sequencing library preparation protocols to better retain short DNA fragments from plasma, and applied these optimized methods to plasma samples from patients with sepsis. After massive parallel sequencing, we verified that our methods can retain substantially shorter DNA fragments than the standard isolation method, resulting in an average of 11.5 fold increase in short DNA fragments yield (DNA < 100bp). We report that cf mtDNA in plasma is highly enriched in short-size cfDNA (30 ~ 60 bp), which is much shorter than the value previously reported (~140 bp). Motivated by this unique size distribution, we size-selected short cfDNA fragments from the sequencing library, which further increased the mtDNA recovery rate by an average of 10.4 fold. Using this approach we detected mixtures of different mtDNA sequences, termed heteroplasmy, in plasma from 3 patients. In one patient who previously received bone marrow transplantation, different minor allele frequencies were observed between plasma and white blood cells (WBC) at heteroplasmic mtDNA sites, consistent with mixed-tissue origin for plasma DNA.Conclusion: mtDNA in plasma exists as very short fragments that exhibit mtDNA heteroplasmy distribution differences from that found in a single organ/tissue. This study is the first report of genome wide identification of mtDNA heteroplasmy in human plasma. Our optimized method can be used to investigate the potential utility of cf mtDNA fragments and heteroplasmy as biomarkers in various diseases.
Project description:We discovered that the cell-free chromatin assembly system senses free DNA ends and mounts a DNA double-strand break response. DNA ends are first recognized by the Ku complex and later resected. The phosphorylation of H2A.V (homologous to gH2A.X) initiates at DNA breaks and spreads over ten thousands of base pairs of DNA within a few minutes. The phosphorylation of gH2A.V remains tightly associated with the damaged DNA in cis and does not transfer to intact DNA circles in the same reaction. Our descriptions of the damage-related proteome and phospho-proteome provide a rich resource for in-depth mechanistic analyses of the DNA chromosome break response in this model system.