Samuel Myllykangas

Efficient targeted resequencing of human germline and cancer genomes by oligonucleotide-selective sequencing

We describe an approach for targeted genome resequencing, called oligonucleotide-selective sequencing (OS-Seq), in which we modify the immobilized lawn of oligonucleotide primers of a next-generation DNA sequencer to function as both a capture and sequencing substrate. We apply OS-Seq to resequence the exons of either 10 or 344 cancer genes from human DNA samples. In our assessment of capture performance, >87% of the captured sequence originated from the intended target region with sequencing coverage falling within a tenfold range for a majority of all targets. Single nucleotide variants (SNVs) called from OS-Seq data agreed with >95% of variants obtained from whole-genome sequencing of the same individual. We also demonstrate mutation discovery from a colorectal cancer tumor sample matched with normal tissue. Overall, we show the robust performance and utility of OS-Seq for the resequencing analysis of human germline and cancer genomes.

Overview of Sequencing Technology Platforms

The high-throughput DNA sequencing technologies are based on xadimmobilization of the DNA samples onto a solid support, cyclic sequencing reactions using automated fluidics devices, and detection of molecular events by imaging. Featured sequencing technologies include: GS FLX by 454 Life Technologies/Roche, Genome Analyzer by Solexa/Illumina, SOLiD by Applied Biosystems, CGA Platform by Complete Genomics, and PacBio RS by Pacific Biosciences. In addition, emerging technologies are discussed.

Targeted sequencing library preparation by genomic dna circularization

BackgroundFor next generation DNA sequencing, we have developed a rapid and simple approach for preparing DNA libraries of targeted DNA content. Current protocols for preparing DNA for next-generation targeted sequencing are labor-intensive, require large amounts of starting material, and are prone to artifacts that result from necessary PCR amplification of sequencing libraries. Typically, sample preparation for targeted NGS is a two-step process where (1) the desired regions are selectively captured and (2) the ends of the DNA molecules are modified to render them compatible with any given NGS sequencing platform.ResultsIn this proof-of-concept study, we present an integrated approach that combines these two separate steps into one. Our method involves circularization of a specific genomic DNA molecule that directly incorporates the necessary components for conducting sequencing in a single assay and requires only one PCR amplification step. We also show that specific regions of the genome can be targeted and sequenced without any PCR amplification.ConclusionWe anticipate that these rapid targeted libraries will be useful for validation of variants and may have diagnostic application.

Dependency detection with similarity constraints

Unsupervised two-view learning, or detection of dependencies between two paired data sets, is typically done by some variant of canonical correlation analysis (CCA). CCA searches for a linear projection for each view, such that the correlations between the projections are maximized. The solution is invariant to any linear transformation of either or both of the views; for tasks with small sample size such flexibility implies overfitting, which is even worse for more flexible nonparametric or kernel-based dependency discovery methods. We develop variants which reduce the degrees of freedomby assuming constraints on similarity of the projections in the two views. A particular example is provided by a cancer gene discovery application where chromosomal distance affects the dependencies between gene copy number and activity levels. Similarity constraints are shown to improve detection performance of known cancer genes.

Serial analysis of gene expression in the chicken otocyst.

The inner ear arises from multipotent placodal precursors that are gradually committed to the otic fate and further differentiate into all inner ear cell types, with the exception of a few immigrating neural crest-derived cells. The otocyst plays a pivotal role during inner ear development: otic progenitor cells sub-compartmentalize into non-sensory and prosensory domains, giving rise to individual vestibular and auditory organs and their associated ganglia. The genes and pathways underlying this progressive subdivision and differentiation process are not entirely known. The goal of this study was to identify a comprehensive set of genes expressed in the chicken otocyst using the serial analysis of gene expression (SAGE) method. Our analysis revealed several hundred transcriptional regulators, potential signaling proteins, and receptors. We identified a substantial collection of genes that were previously known in the context of inner ear development, but we also found many new candidate genes, such as SOX4, SOX5, SOX7, SOX8, SOX11, and SOX18, which previously were not known to be expressed in the developing inner ear. Despite its limitation of not being all-inclusive, the generated otocyst SAGE library is a practical bioinformatics tool to study otocyst gene expression and to identify candidate genes for developmental studies.

Targeted deep resequencing of the human cancer genome using next-generation technologies.

Abstract Next-generation sequencing technologies have revolutionized our ability to identify genetic variants, either germline or somatic point mutations, that occur in cancer. Parallelization and miniaturization of DNA sequencing enables massive data throughput and for the first time, large-scale, nucleotide resolution views of cancer genomes can be achieved. Systematic, large-scale sequencing surveys have revealed that the genetic spectrum of mutations in cancers appears to be highly complex with numerous low frequency bystander somatic variations, and a limited number of common, frequently mutated genes. Large sample sizes and deeper resequencing are much needed in resolving clinical and biological relevance of the mutations as well as in detecting somatic variants in heterogeneous samples and cancer cell sub-populations. However, even with the next-generation sequencing technologies, the overwhelming size of the human genome and need for very high fold coverage represents a major challenge for up-scaling cancer genome sequencing projects. Assays to target, capture, enrich or partition disease-specific regions of the genome offer immediate solutions for reducing the complexity of the sequencing libraries. Integration of targeted DNA capture assays and next-generation deep resequencing improves the ability to identify clinically and biologically relevant mutations.

Abstract 1160: Whole genome amplification and high-throughput sequencing of formalin-fixed paraffin-embedded colorectal cancer

Formalin-fixed paraffin-embedded (FFPE) tumors represent a valuable resource for translational cancer genomic research. However, genetic analysis of the FFPE material is challenging, as archived tissues are often small biopsies and the fixation process damages DNA. In researching a solution to this, we have evaluated the performance of different whole genome amplification methods for obtaining DNA samples from archived tumors and their use as a template in high-throughput sequencing. Two whole genome amplification methods were applied using 20 μm sections of FFPE colorectal cancer tissue and normal human genome DNA samples. Genomic DNA was amplified using Multiple Displacement Amplification (MDA) method and a modified version of Degenerate Oligonucleotide PCR (DOP) assay. Non-amplified human genomic DNA was used as a reference when genomic coverage, linearity and uniformity of the amplified products were assessed. Paired-end sequencing libraries were prepared from the DOP amplified templates while the MDA samples underwent single read library preparation. Sequencing was performed using an Illumina Genome Analyzer II. 2.5 million 54-mer reads mapping to the human genome were generated for each sample. Whole genome amplification was shown to produce artifacts when compared to non-amplified genomic DNA sequences. The modified DOP method preferentially amplified non-repetitive sequences in the human genome. Using the MDA-based method, genomic sequence coverage was generally more even between regions of repetitive and non-repetitive DNA. However, spread of the sequence read counts was greater in the MDA method and MDA amplification offered less dynamic range to identify copy number aberrations. Using whole genome amplification methods with the FFPE colorectal tumor sample we were able to generate 130 Mb of genomic sequence data and identify DNA copy number gains in chromosomes 13 and 20q. Whole genome amplification and high-throughput sequencing can be used to generate sequence data from minute amounts of FFPE material and identify DNA copy number aberrations in the archived tumors. Nonetheless, whole genome amplification produces artifacts by introducing bias towards specific regions of the genome, generating artificial and random DNA fragment assemblies (MDA) and introducing universal primer sequence in the ends of the amplified DNA fragments (DOP). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1160.