Scientists who require confident resolution of heterogeneous populations across complex regions have been unable to transition to short-read sequencing methods. They continue to depend on Sanger Sequencing despite its cost and time inefficiencies. Here we present a new redesigned algorithm that allows the generation of circular consensus sequences (CCS) from individual SMRT Sequencing reads. With this new algorithm, dubbed CCS2, it is possible to reach arbitrarily high quality across longer insert lengths at a lower cost and higher throughput than Sanger Sequencing. We apply this new algorithm, dubbed CCS2, to the characterization of the HIV-1 K103N drug-resistance associated mutation, which…
With the increasing availability of whole-genome sequencing, haplotype reconstruction of individual genomes, or haplotype assembly, remains unsolved. Like the de novo genome assembly problem, haplotype assembly is greatly simplified by having more long-range information. The Targeted Locus Amplification (TLA) technology from Cergentis has the unique capability of targeting a specific region of the genome using a single primer pair and yielding ~2 kb DNA circles that are comprised of ~500 bp fragments. Fragments from the same circle come from the same haplotype and follow an exponential decay in distance from the target region, with a span that reaches the multi-megabase…
Early detection of colorectal cancer (CRC) and its precursor lesions (adenomas) is crucial to reduce mortality rates. The fecal immunochemical test (FIT) is a non-invasive CRC screening test that detects the blood-derived protein hemoglobin. However, FIT sensitivity is suboptimal especially in detection of CRC precursor lesions. As adenoma-to-carcinoma progression is accompanied by alternative splicing, tumor-specific proteins derived from alternatively spliced RNA transcripts might serve as candidate biomarkers for CRC detection.
Bipolar disorder (BD) is a phenotypically and genetically complex and debilitating neurological disorder that affects 1% of the worldwide population. There is compelling evidence from family, twin and adoption studies supporting the involvement of a genetic predisposition in BD with estimated heritability up to ~ 80%. The risk in first-degree relatives is ten times higher than in the general population. Linkage and association studies have implicated multiple putative chromosomal loci for BP susceptibility, however no disease genes have been identified to date.
Targeted sequencing has proven to be an economical means of obtaining sequence information for one or more defined regions of a larger genome. However, most target enrichment methods are reliant upon some form of amplification. Amplification removes the epigenetic marks present in native DNA, and some genomic regions, such as those with extreme GC content and repetitive sequences, are recalcitrant to faithful amplification. Yet, a large number of genetic disorders are caused by expansions of repeat sequences. Furthermore, for some disorders, methylation status has been shown to be a key factor in the mechanism of disease. We have developed a…
Determining compositions and functional capabilities of complex populations is often challenging, especially for sequencing technologies with short reads that do not uniquely identify organisms or genes. Long-read sequencing improves the resolution of these mixed communities, but adoption for this application has been limited due to concerns about throughput, cost and accuracy. The recently introduced PacBio Sequel System generates hundreds of thousands of long and highly accurate single-molecule reads per SMRT Cell. We investigated how the Sequel System might increase understanding of metagenomic communities. In the past, focus was largely on taxonomic classification with 16S rRNA sequencing. Recent expansion to WGS…
Whole-sample shotgun sequencing can provide a more detailed view of a metagenomic community than 16S sequencing, but its use in multi-sample experiments is limited by throughput, cost and analysis complexity. While short-read sequencing technologies offer higher throughput, read lengthss less fewer than 500 bp will rarely cover a gene of interest, and necessitate assembly before further analysis. Assembling large fragments requires sampling each community member at a high depth, significantly increasing the amount of sequencing needed, and limiting the analysis of rare community members. Assembly methods also risk It is also possible to incorrectly combine combining sequences from different community…
Aedes aegypti is a tropical and subtropical mosquito vector for Zika, yellow fever, dengue fever, and chikungunya. We describe the first diploid assembly of an insect genome, using SMRT Sequencing and the open-source assembler FALCON-Unzip. This assembly has high contiguity (contig N50 1.3 Mb), is more complete than previous assemblies (Length 1.45 Gb with 87% BUSCO genes complete), and is high quality (mean base >QV30 after polishing). Long-range haplotype structure, in some cases encompassing more than 4 Mb of extremely divergent homologous sequence with dramatic differences in coding sequence content, is resolved using a combination of the FALCON-Unzip assembler, genome…
To test the impact of high-quality genome assemblies on biological research, we applied PacBio long-read sequencing in conjunction with the new, diploid-aware FALCON-Unzip assembler to a number of bird species. These included: the zebra finch, for which a consortium-generated, Sanger-based reference exists, to determine how the FALCON-Unzip assembly would compare to the current best references available; Anna’s hummingbird genome, which had been assembled with short-read sequencing methods as part of the Avian Phylogenomics phase I initiative; and two critically endangered bird species (kakapo and ‘alala) of high importance for conservations efforts, whose genomes had not previously been sequenced and assembled.
T-cells play a central part in the immune response in humans and related species. T-cell receptors (TCRs), heterodimers located on the T-cell surface, specifically bind foreign antigens displayed on the MHC complex of antigen-presenting cells. The wide spectrum of potential antigens is addressed by the diversity of TCRs created by V(D)J recombination. Profiling this repertoire of TCRs could be useful from, but not limited to, diagnosis, monitoring response to treatments, and examining T-cell development and diversification.
Alzheimer’s disease (AD) is a devastating neurodegenerative disease that is genetically complex. Although great progress has been made in identifying fully penetrant mutations in genes such as APP, PSEN1 and PSEN2 that cause early-onset AD, these still represent a very small percentage of AD cases. Large-scale, genome-wide association studies (GWAS) have identified at least 20 additional genetic risk loci for the more common form of late-onset AD. However, the identified SNPs are typically not the actual causal variants, but are in linkage disequilibrium with the presumed causative variant (Van Cauwenberghe C, et al., The genetic landscape of Alzheimer disease: clinical…
Despite amazing progress over the past quarter century in the technology to detect genetic variants, intermediate-sized structural variants (50 bp to 50 kb) have remained difficult to identify. Such variants are too small to detect with array comparative genomic hybridization, but too large to reliably discover with short-read DNA sequencing. Recent de novo assemblies of human genomes have demonstrated the power of PacBio Single Molecule, Real-Time (SMRT) Sequencing to fill this technology gap and sensitively identify structural variants in the human genome. While de novo assembly is the ideal method to identify variants in a genome, it requires high depth…
Mitochondrial DNA (mtDNA) is a compact, double-stranded circular genome of 16,569 bp with a cytosine-rich light (L) chain and a guanine-rich heavy (H) chain. mtDNA mutations have been increasingly recognized as important contributors to an array of human diseases such as Parkinson’s disease, Alzheimer’s disease, colorectal cancer and Kearns–Sayre syndrome. mtDNA mutations can affect all of the 1000-10,000 copies of the mitochondrial genome present in a cell (homoplasmic mutation) or only a subset of copies (heteroplasmic mutation). The ratio of normal to mutant mtDNAs within cells is a significant factor in whether mutations will result in disease, as well as…
Microbes play an important role in nearly every part of our world, as they affect human health, our environment, agriculture, and aid in waste management. Complete closed genome sequences, which have become the gold standard with PacBio long-read sequencing, can be key to understanding microbial functional characteristics. However, input requirements, consumables costs, and the labor required to prepare and sequence a microbial genome have in the past put PacBio sequencing out of reach for some larger projects. We have developed a multiplexed library prep approach that is simple, fast, and cost-effective, and can produce 4 to 16 closed bacterial genomes…
The kakapo (Strigops habroptila) is a large, flightless parrot endemic to New Zealand. It is highly endangered with only ~150 individuals remaining, and intensive conservation efforts are underway to save this iconic species from extinction. These include genetic studies to understand critical genes relevant to fertility, adaptation and disease resistance, and genetic diversity across the remaining population for future breeding program decisions. To aid with these efforts, we have generated a high-quality de novo genome assembly using PacBio long-read sequencing. Using the new diploid-aware FALCON-Unzip assembler, the resulting genome of 1.06 Gb has a contig N50 of 5.6 Mb (largest…