The study of genomics has revolutionized our understanding of science, but the field of transcriptomics grew with the need to explore the functional impacts of genetic variation. While different tissues in an organism may share the same genomic DNA, they can differ greatly in what regions are transcribed into RNA and in their patterns of RNA processing. By reviewing the history of transcriptomics, we can see the advantages of RNA sequencing using a full-length transcript approach become clearer.
Bart Weimer, a professor at the University of California, Davis, who is leading the 100K Foodborne Pathogen Genome Project, talks about using PacBio sequencing to produce long reads for microbial genomes as well as to study how bacteria use epigenetics to regulate gene expression.
In this BioConference Live webinar, PacBio CSO Jonas Korlach highlights how multi-kilobase reads from SMRT Sequencing can resolve many of the previously considered ‘difficult-to-sequence’ genomic regions. The long reads also allow phasing of the sequence information along the maternal and paternal alleles, demonstrated by full-length, fully phased HLA class I & II gene sequencing. In addition, characterizing the complex landscape of alternative gene products is currently very difficult with short-read sequencing technologies, and he describes how long-read, full-length mRNA sequencing can be used to describe the diversity of transcript isoforms, with no assembly required. Lastly, in the exciting area of…
PacBio Sequencing is characterized by very long sequence reads (averaging > 10,000 bases), lack of GC-bias, and high consensus accuracy. These features have allowed the method to provide a new gold standard in de novo genome assemblies, producing highly contiguous (contig N50 > 1 Mb) and accurate (> QV 50) genome assemblies. We will briefly describe the technology and then highlight the full workflow, from sample preparation through sequencing to data analysis, on examples of insect genome assemblies, and illustrate the difference these high-quality genomes represent with regard to biological insights, compared to fragmented draft assemblies generated by short-read sequencing.
Michael Lutz, from the Duke University Medical Center, discussed a recently published software tool that can now be used in a pipeline with SMRT Sequencing data to find structural variant biomarkers for neurodegenerative diseases with a focus on Alzheimer’s disease, ALS, and Lewy body dementia. His team is particularly interested in short sequence repeats and short tandem repeats, which have already been implicated in neurodegenerative disease.
In this AGBT 2017 poster, the University of Helsinki’s Petri Auevinen reports on efforts to understand bacteria that grow on, and subsequently spoil, food. This analysis monitored DNA modifications and transcriptomic changes in three species of lactic acid bacteria. Scientists discovered that the organisms’ metabolic profiles change substantially when grown together compared to those cultured individually, and are now studying how Cas protein activity changes under these conditions too.
Targeted sequencing experiments commonly rely on either PCR or hybrid capture to enrich for targets of interest. When using short read sequencing platforms, these amplicons or fragments are frequently targeted to a few hundred base pairs to accommodate the read lengths of the platform. Given PacBio’s long readlength, it is straightforward to sequence amplicons or captured fragments that are multiple kilobases in length. These long sequences are useful for easily visualizing variants that include SNPs, CNVs and other structural variants, often without assembly. We will review methods for the sequencing of long amplicons and provide examples using amplicons that range…
In this PAG 2018 presentation, John Williams of University of Adelaide, presents research on using PacBio SMRT Sequencing to explore the genetic origins of cattle subspecies, Angus (Bos taurus taurus) and Brahman (Bos taurus indicus). He shares RNA sequencing data using the PacBio Iso-Seq method to compare transcriptomes and phase allelic expression and describes how the IsoPhase technique enables evaluation of SNPs through transcriptome mapping back to the single genome of a cross-bred individual. Using a genomic and transcriptomic approach, two high-quality genomes from a single individual and gene isoforms specific to each subspecies are being identified.
In this ASHG workshop presentation, Janet Song of Stanford School of Medicine shared research on resolving a tandem repeat array implicated in bipolar disorder and schizophrenia. These psychiatric diseases share a number of genomic risk variants, she noted, but scientists continue to search for a specific causal variant in the CACNA1C gene suggested by previous genome-wide association studies. SMRT Sequencing of this region in 16 individuals identified a series of 30-mer repeats, containing a total of about 50 variants. Analysis showed that 10 variants were linked to protective or risk haplotypes. Song aims to study the function of these variants…
In this AGBT presentation from AGBT 2019, Jason Underwood, shares information about single-cell isoform sequencing (scIso-Seq), focusing on a collaborative project with the labs of Evan Eichler and Alex Pollen. For this effort, scientists used Drop-seq sample prep and then loaded cDNA products onto the Sequel System. Results from a barnyard experiment using mouse and human cells as well as from cerebral organoids demonstrated that this approach could deliver cell type-specific gene expression data. Underwood also presents data from the Sequel II System comparing chimp and human organoids, resulting in information about 14,000 unique genes with important insights for post-transcriptional…
In this PacBio User Group Meeting presentation, Shawn Trojahn of Washington State University describes transcriptome sequencing and analysis of grizzly bears focused on differential gene expression during hibernation and active cycles, potentially offering human-relevant information about muscle atrophy and insulin resistance. The team was able to identify more unique isoforms just from liver tissue than had been previously characterized in the entire reference genome. Of particular interest: more than 2,000 transcripts differentially expressed between hibernation and active season, including 86 genes that have isoforms expressed in opposite directions.
In this PacBio User Group Meeting lightning talk, Shawn Polson of the University of Delaware speaks about viral metagenomes, which are more challenging to distinguish than their bacterial counterparts because viruses have no 16S equivalent. By using SMRT Sequencing, his team generated higher-resolution data about viral genomes and aims to use this information as a guide to how these genomes function.
In this PacBio User Group Meeting presentation, Ana Conesa Cegarra from the University of Florida spoke about Iso-Seq analysis tools developed by her group, which created the popular SQANTI tools for Iso-Seq data QC. They’re also working on IsoAnnot to perform functional annotation at isoform resolution; validation has already been done on various species. Currently it’s a set of scripts, but her team is working to produce a more user-friendly version. Finally, tappAS is for functional diversity analysis and for prioritizing genes for validation.
In a push to develop insect-based food sources for people, Brenda Oppert from the USDA has been sequencing bug genomes with PacBio technology. Long reads are essential because of the highly repetitive sequences and large genomes. On the Sequel II System, a single SMRT Cell is sufficient to generate 350-fold coverage and produce a high-quality assembly for some of the insects she’s studying.