PacBio 2013 User Group Meeting Presentation Slides: Lisbeth Guethlein from Stanford University School of Medicine looked at highly repetitive and variable immune regions of the orangutan genome. Guethlein reported that “PacBio managed to accomplish in a week what I have been working on for a couple years” (with Sanger sequencing), and the results were concordant. “Long story short, I was a happy customer.”
The three classes of genes that comprise the MHC gene family are actively involved in determining donor-recipient compatibility for organ transplant, as well as susceptibility to autoimmune diseases via cross-reacting immunization. Specifically, Class I genes HLA-A, -B, -C, and class II genes HLA-DR, -DQ and -DP are considered medically important for genetic analysis to determine histocompatibility. They are highly polymorphic and have thousands of alleles implicated in disease resistance and susceptibility. The importance of full-length HLA gene sequencing for genotyping, detection of null alleles, and phasing is now widely acknowledged. While DNA-sequencing-based HLA genotyping has become routine, only 7% of…
While the identification of individual SNPs has been readily available for some time, the ability to accurately phase SNPs and structural variation across a haplotype has been a challenge. With individual reads of an average length of 9 kb (P5-C3), and individual reads beyond 30 kb in length, SMRT Sequencing technology allows the identification of mutation combinations such as microdeletions, insertions, and substitutions without any predetermined reference sequence. Long- amplicon analysis is a novel protocol that identifies and reports the abundance of differing clusters of sequencing reads within a single library. Graphs generated via hierarchical clustering of individual sequencing reads…
Sequence based typing (SBT) is considered the gold standard method for HLA typing. Current SBT methods are rather laborious and are prone to phase ambiguity problems and genotyping uncertainties. As a result, the NGS community is rapidly seeking to remedy these challenges, to produce high resolution and high throughput HLA sequencing conducive to a clinical setting. Today, second generation NGS technologies are limited in their ability to yield full length HLA sequences required for adequate phasing and identification of novel alleles. Here we present the use of single molecule real time (SMRT) sequencing as a means of determining full length/long…
Allelic-level resolution HLA typing is known to improve survival prognoses post Unrelated Donor (UD) Haematopoietic Stem Cell Transplantation (HSCT). Currently, many commonly used HLA typing methodologies are limited either due to the fact that ambiguity cannot be resolved or that they are not amenable to high-throughput laboratories. Pacific Biosciences’ Single Molecule Real-Time (SMRT) DNA sequencing technology enables sequencing of single molecules in isolation and has read-length capabilities to enable whole gene sequencing for HLA. DNA barcode technology labels samples with unique identifiers that can be traced throughout the sequencing process. The use of DNA barcodes means that multiple samples can…
The correct phasing of genetic variations is a key challenge for many applications of DNA sequencing. Allele-level resolution is strongly preferred for histocompatibility sequencing where recombined genes can exhibit different compatibilities than their parents. In other contexts, gene complementation can provide protection if deleterious mutations are found on only one allele of a gene. These problems are especially pronounced in immunological domains given the high levels of genetic diversity and recombination seen in regions like the Major Histocompatibility Complex. A new tool for analyzing Single Molecule, Real-Time (SMRT) Sequencing data – Long Amplicon Analysis (LAA) – can generate highly accurate,…
Fully phased allele-level sequencing of highly polymorphic HLA genes is greatly facilitated by SMRT Sequencing technology. In the present work, we have evaluated multiple DNA barcoding strategies for multiplexing several loci from multiple individuals, using three different tagging methods. Specifically MHC class I genes HLA-A, -B, and –C were indexed via DNA Barcodes by either tailed primers or barcoded SMRTbell adapters. Eight different 16-bp barcode sequences were used in symmetric & asymmetric pairing. Eight DNA barcoded adapters in symmetric pairing were independently ligated to a pool of HLA-A, -B and –C for eight different individuals, one at a time and…
Determination of unique individual haplotypes is an essential first step toward understanding how identical genotypes having different phases lead to different biological interpretations of function, phenotype, and disease. Genome-wide methods for identifying individual genetic variation have been limited in their ability to acquire phased, extended, and complete genomic sequences that are long enough to assemble haplotypes with high confidence. We explore a recombineering approach for isolation and sequencing of a tiling of targeted fosmids to capture interesting regions from human genome. Each individual fosmid contains large genomic fragments (~35?kb) that are sequenced with long-read SMRT technology to generate contiguous long…
As a cost-effective alternative to whole genome human sequencing, targeted sequencing of specific regions, such as exomes or panels of relevant genes, has become increasingly common. These methods typically include direct PCR amplification of the genomic DNA of interest, or the capture of these targets via probe-based hybridization. Commonly, these approaches are designed to amplify or capture exonic regions and thereby result in amplicons or fragments that are a few hundred base pairs in length, a length that is well-addressed with short-read sequencing technologies. These approaches typically provide very good coverage and can identify SNPs in the targeted region, but…
Human MHC class I genes HLA-A, -B, -C, and class II genes HLA-DR, -DP and -DQ, play a critical role in the immune system as major factors responsible for organ transplant rejection. The have a direct or linkage-based association with several diseases, including cancer and autoimmune diseases, and are important targets for clinical and drug sensitivity research. HLA genes are also highly polymorphic and their diversity originates from exonic combinations as well as recombination events. A large number of new alleles are expected to be encountered if these genes are sequenced through the UTRs. Thus allele-level resolution is strongly preferred…
Whole genome sequencing can provide comprehensive information important for determining the biochemical and genetic nature of all elements inside a genome. The high-quality genome references produced from past genome projects and advances in short-read sequencing technologies have enabled quick and cheap analysis for simple variants. However even with the focus on genome-wide resequencing for SNPs, the heritability of more than 50% of human diseases remains elusive. For non-human organisms, high-contiguity references are deficient, limiting the analysis of genomic features. The long and unbiased reads from single molecule, real-time (SMRT) Sequencing and new de novo assembly approaches have demonstrated the ability…
A longstanding goal of genomic analysis is the identification of causal genetic factors contributing to disease. While the common disease/common variant hypothesis has been tested in many genome-wide association studies, few advancements in identifying causal variation have been realized, and instead recent findings point away from common variants towards aggregate rare variants as causal. A challenge is obtaining complete phased genomic sequences over extended genomic regions from sufficient numbers of cases and controls to identify all potential variation causal of a disease. To address this, we modified methods for targeted DNA isolation using fosmid technology and single-molecule, long-sequence-read generaton that…
We show that linearizing and directly sequencing full-length fosmids simplifies the assembly problem such that it is possible to unambiguously assemble individual haplotypes for the highly repetitive 100-200 kb killer Ig-like receptor (KIR) gene loci of chromosome 19. A tiling of targeted fosmids can be used to clone extended lengths of genomic DNA, 100s of kb in length, but repeat complexity in regions of particular interest, such as the KIR locus, means that sequence assembly of pooled samples into complete haplotypes is difficult and in many cases impossible. The current maximum read length generated by SMRT Sequencing exceeds the length…
The long reads, random error, and unbiased sampling of SMRT Sequencing enables high quality, de novo assembly of the human genome. PacBio long reads are capable of resolving genomic variations at all size scales, including SNPs, insertions, deletions, inversions, translocations, and repeat expansions, all of which are important in understanding the genetic basis for human disease and difficult to access via other technologies. In demonstration of this, we report a new high-quality, diploid aware de novo assembly of Craig Venter’s well-studied genome.
Aim: In contrast to exon-based HLA-typing approaches, whole gene genotyping crucially depends on full-length sequences submitted to the IMGT/HLA Database. Currently, full-length sequences are provided for only 7 out of 520 HLA-DPB1 alleles. Therefore, we developed a fully phased whole-gene sequencing approach for DPB1, to facilitate further exploration of the allelic structure at this locus. Methods: Primers were developed flanking the UTR-regions of DPB1 resulting in a 12 kb amplicon. Using a 4-primer approach, secondary primers containing barcodes were combined with the gene-specific primers to obtain barcoded full-gene amplicons in a single amplification step. Amplicons were pooled, purified, and ligated…