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Direct Transposition of Native DNA for Sensitive Multimodal Single-Molecule Sequencing

STUDY GOALS: This study focuses on elucidating the epigenetic modulators of prostate cancer progression and metastasis at high resolution. This is achieved by applying a novel, high-sensitivity single molecule sequencing assay that measures chromatin state on single DNA molecules (SMRT-Tag) to matched primary and metastatic tumor samples from the same patient. Samples are obtained from patient derived xenograft (PDX) models.

STUDY DESIGN: Individuals diagnosed with primary and metastatic prostate cancer in the course of routine care were consented and enrolled, and biopsies of primary and/or metastatic lesions performed to obtain sample material used for generating PDX models. Samples collected from these models were processed with a novel strategy developed for highly-sensitive multimodal profiling of single chromatin fibers using the third generation long-read sequencing. The resulting data indicates genetic variants, chromatin organization, and m5dCpG methylation status across the genome.

PRINCIPLE FINDINGS: We determined characteristic single-molecule patterns of chromatin organization (spacing of nucleosomes, presence and absence of m5dCpG marks, etc.) that were altered in the transition from primary malignancy to metastasis. Broadly, global chromatin organization was severely disrupted in metastatic samples, resulting in increased accessibility at CTCF motifs, which may be relevant for disease progression. We further identified specific genomic domains including constitutive heterochromatin significantly enriched for irregular or hyper-accessible chromatin. Together, these findings suggest the involvement of ATP-dependent chromatin remodelers in evicting nucleosomes as a facet of metastatic prostate cancer.

DATA AVAILABILITY: SAMOSA-Tag, the assay used in this study, is a sequencing assay that uses the third generation long read sequencing, specifically the SMRT sequencing platform from Pacific Biosciences. Demultiplexed raw SMRT sequencing BAM files generated in this study are deposited. Individual raw subread BAM files correspond to replicate sequencing assays performed on either primary or metastatic PDX prostate tumors.