Over the last few years, several advances were implemented in the PacBio RS II System to maximize throughput and efficiency while reducing the cost per sample. The number of useable bases per SMRT Cell now exceeds 1 Gb with the latest P6-C4 chemistry and 6-hour movies. For applications such as microbial sequencing, targeted sequencing, Iso-Seq (full-length isoform sequencing) and Nimblegen’s target enrichment method, current SMRT Cell yields could be an excess relative to project requirements. To this end, barcoding is a viable option for multiplexing samples. For microbial sequencing, multiplexing can be accomplished by tagging sheared genomic DNA during library…
For many of the repeat expansion disorders, the disease gene has been discovered, however the underlying biological mechanisms have not yet been fully understood. This is mainly due to technological limitations that do not allow for the needed base-pair resolution of the long, repetitive genomic regions. We have developed a novel, amplification-free enrichment technique that uses the CRISPR/Cas9 system to target large repeat expansions. This method, in conjunction with PacBio’s long reads and uniform coverage, enables sequencing of these complex genomic regions. By using a PCR-free amplification method, we are able to access not only the repetitive elements and interruption…
We have developed several candidate gene screening applications for both Neuromuscular and Neurological disorders. The power behind these applications comes from the use of long-read sequencing. It allows us to access previously unresolvable and even unsequencable genomic regions. SMRT Sequencing offers uniform coverage, a lack of sequence context bias, and very high accuracy. In addition, it is also possible to directly detect epigenetic signatures and characterize full-length gene transcripts through assembly-free isoform sequencing. In addition to calling the bases, SMRT Sequencing uses the kinetic information from each nucleotide to distinguish between modified and native bases.
The increased sequencing throughput creates a need for multiplexing for several applications. We are here detailing different barcoding strategies for microbial sequencing, targeted sequencing, Iso-Seq full-length isoform sequencing, and Roche NimbleGen’s target enrichment method.
Target enrichment capture methods allow scientists to rapidly interrogate important genomic regions of interest for variant discovery, including SNPs, gene isoforms, and structural variation. Custom targeted sequencing panels are important for characterizing heterogeneous, complex diseases and uncovering the genetic basis of inherited traits with more uniform coverage when compared to PCR-based strategies. With the increasing availability of high-quality reference genomes, customized gene panels are readily designed with high specificity to capture genomic regions of interest, thus enabling scientists to expand their research scope from a single individual to larger cohort studies or population-wide investigations. Coupled with PacBio® long-read sequencing, these…
Genes associated with several neurological disorders have been shown to be highly polymorphic. Targeted sequencing of these genes using NGS technologies is a powerful way to increase the cost-effectiveness of variant discovery and detection. However, for a comprehensive view of these target genes, it is necessary to have complete and uniform coverage across regions of interest. Unfortunately, short-read sequencing technologies are not ideal for these types of studies as they are prone to mis-mapping and often fail to span repetitive regions. Targeted sequencing with PacBio long reads provides the unique advantage of single-molecule observations of complex genomic regions. PacBio long…
Nucleotide repeat expansions are a major cause of neurological and neuromuscular disease in humans, however, the nature of these genomic regions makes characterizing them extremely challenging. Accurate DNA sequencing of repeat expansions using short-read sequencing technologies is difficult, as short-read technologies often cannot read through regions of low sequence complexity. Additionally, these short reads do not span the entire region of interest and therefore sequence assembly is required. Lastly, most target enrichment methods are reliant upon amplification which adds the additional caveat of PCR bias. We have developed a novel, amplification-free enrichment technique that employs the CRISPR/Cas9 system for specific…
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 risk variants, but are in linkage disequilibrium with the presumed causative variant (Van Cauwenberghe C, et al., The genetic landscape of Alzheimer disease: clinical…
Over 40% of males and ~16% of female carriers of a FMR1 premutation allele (55-200 CGG repeats) are at risk for developing Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), an adult onset neurodegenerative disorder while, about 20% of female carriers will develop Fragile X-associated Primary Ovarian Insufficiency (FXPOI), in addition to a number of adult-onset clinical problems (FMR1 associated disorders). Marked elevation in FMR1 mRNA levels have been observed with premutation alleles and the resulting RNA toxicity is believed to be the leading molecular mechanism proposed for these disorders. The FMR1 gene, as many housekeeping genes, undergoes alternative splicing. Using long-read isoform…
Target enrichment is a powerful tool for studies involved in understanding polymorphic SNPs with phasing, tandem repeats, and structural variations. With increasing availability of reference genomes, researchers can easily design a cost-effective targeted investigation with custom probes specific to regions of interest. Using PacBio long-read technology in conjunction with probe capture, we were able to sequence multi-kilobase enriched regions to fully investigate intronic and exonic regions, distinguish haplotypes, and characterize structural variations. Furthermore, we demonstrate this approach is advantageous for studying complex genomic regions previously inaccessible through other sequencing platforms. In the present work, 12 barcoded genomic DNA (gDNA) samples…
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…
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.
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.
Over the past decades neurological disorders have been extensively studied producing a large number of candidate genomic regions and candidate genes. The SNPs identified in these studies rarely represent the true disease-related functional variants. However, more recently a shift in focus from SNPs to larger structural variants has yielded breakthroughs in our understanding of neurological disorders.Here we have developed candidate gene screening methods that combine enrichment of long DNA fragments with long-read sequencing that is optimized for structural variation discovery. We have also developed a novel, amplification-free enrichment technique using the CRISPR/Cas9 system to target genomic regions.We sequenced gDNA and…
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…