Supernumerary B chromosomes (Bs) are extra karyotype units in addition to A chromosomes, and are found in some fungi and thousands of animals and plant species. Bs are uniquely characterized due to their non-Mendelian inheritance, and represent one of the best examples of genomic conflict. Over the last decades, their genetic composition, function and evolution have remained an unresolved query, although a few successful attempts have been made to address these phenomena. A classical concept based on cytogenetics and genetics is that Bs are selfish and abundant with DNA repeats and transposons, and in most cases, they do not carry…
In the past several years, single-molecule sequencing platforms, such as those by Pacific Biosciences and Oxford Nanopore Technologies, have become available to researchers and are currently being tested for clinical applications. They offer exceptionally long reads that permit direct sequencing through regions of the genome inaccessible or difficult to analyze by short-read platforms. This includes disease-causing long repetitive elements, extreme GC content regions, and complex gene loci. Similarly, these platforms enable structural variation characterization at previously unparalleled resolution and direct detection of epigenetic marks in native DNA. Here, we review how these technologies are opening up new clinical avenues that…
In this AGBT 2017 talk, PacBio CSO Jonas Korlach provided a technology roadmap for the Sequel System, including plans the continue performance and throughput increases through early 2019. Per SMRT Cell throughput of the Sequel System is expected to double this year and again next year. Together with a new higher-capacity SMRT Cell expected to be released by the end of 2018, these improvements result in a ~30-fold increase or ~150 Gb / SMRT Cell allowing a real $1000 real de novo human genome assembly. Also discussed: Additional application protocol improvements, new chemistry and software updates, and a look at…
SMRT Sequencing is a DNA sequencing technology characterized by long read lengths and high consensus accuracy, regardless of the sequence complexity or GC content of the DNA sample. These characteristics can be harnessed to address medically relevant genes, mRNA transcripts, and other genomic features that are otherwise difficult or impossible to resolve. I will describe examples for such new clinical research in diverse areas, including full-length gene sequencing with allelic haplotype phasing, gene/pseudogene discrimination, sequencing extreme DNA contexts, high-resolution pharmacogenomics, biomarker discovery, structural variant resolution, full-length mRNA isoform cataloging, and direct methylation detection.
Past large scale cancer genome sequencing efforts, including The Cancer Genome Atlas and the International Cancer Genome Consortium, have utilized short-read sequencing, which is well-suited for detecting single nucleotide variants (SNVs) but far less reliable for detecting variants larger than 20 base pairs, including insertions, deletions, duplications, inversions and translocations. Recent same-sample comparisons of short- and long-read human reference genome data have revealed that short-read resequencing typically uncovers only ~4,000 structural variants (SVs, =50 bp) per genome and is biased towards deletions, whereas sequencing with PacBio long-reads consistently finds ~20,000 SVs, evenly balanced between insertions and deletions. This discovery has…
Transcriptome sequencing has proven to be an important tool for understanding the biological changes in cancer genomes including the consequences of structural rearrangements. Short read sequencing has been the method of choice, as the high throughput at low cost allows for transcript quantitation and the detection of even rare transcripts. However, the reads are generally too short to reconstruct complete isoforms. Conversely, long-read approaches can provide unambiguous full-length isoforms, but lower throughput has complicated quantitation and high RNA input requirements has made working with cancer samples challenging. Recently, the COLO 829 cell line was sequenced to 50-fold coverage with PacBio…
Colorectal cancer (CRC) represents one of the most prevalent and lethal malignant neoplasms and every individual of age 50 and above should undergo regular CRC screening. Currently, the most effective procedure to detect adenomas, the precursors to CRC, is colonoscopy, which reduces CRC incidence by 80%. However, it is an invasive approach that is unpleasant for the patient, expensive, and poses some risk of complications such as colon perforation. A non-invasive screening approach with detection rates comparable to those of colonoscopy has not yet been established. The current study applies Pacific Biosciences third generation, single molecule sequencing to the inspection…
The comprehensive characterization of cancer genomes and epigenomes for understanding drug resistance remains an important challenge in the field of oncology. For example, PC-9, a non-small cell lung cancer (NSCL) cell line, contains a deletion mutation in exon 19 (DelE746A750) of EGRF that renders it sensitive to erlotinib, an EGFR inhibitor. However, sustained treatment of these cells with erlotinib leads to drug-tolerant cell populations that grow in the presence of erlotinib. However, the resistant cells can be resensitized to erlotinib upon treatment with methyltransferase inhibitors, suggesting a role of epigenetic modification in development of drug resistance. We have characterized for…
In addition to the genome and transcriptome, epigenetic information is essential to understand biological processes and their regulation, and their misregulation underlying disease. Traditionally, epigenetic DNA modifications are detected using upfront sample preparation steps such as bisulfite conversion, followed by sequencing. Bisulfite sequencing has provided a wealth of knowledge about human epigenetics, however it does not access the entire genome due to limitations in read length and GC- bias of the sequencing technologies used. In contrast, Single Molecule, Real-Time (SMRT) DNA Sequencing is unique in that it can detect DNA base modifications as part of the sequencing process. It can…