The subclonal structure and genomic evolution of oral squamous cell carcinoma revealed by ultra-deep sequencing.
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ABSTRACT:
SUBMITTER: Tabatabaeifar S
PROVIDER: S-EPMC5369985 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:During the clonal expansion of cancer from an ancestral cell with an initiating oncogenic mutation to symptomatic neoplasm, the occurrence of somatic mutations (both driver and passenger) can be used to track the on-going evolution of the neoplasm. All subclones within a cancer are phylogenetically related, with the prevalence of each subclone determined by its evolutionary fitness and the timing of its origin relative to other subclones. Recently developed massively parallel sequencing platforms promise the ability to detect rare subclones of genetic variants without a priori knowledge of the mutations involved. We used ultra-deep pyrosequencing to investigate intraclonal diversification at the Ig heavy chain locus in 22 patients with B-cell chronic lymphocytic leukemia. Analysis of a non-polymorphic control locus revealed artifactual insertions and deletions resulting from sequencing errors and base substitutions caused by polymerase misincorporation during PCR amplification. We developed an algorithm to differentiate genuine haplotypes of somatic hypermutations from such artifacts. This proved capable of detecting multiple rare subclones with frequencies as low as 1 in 5000 copies and allowed the characterization of phylogenetic interrelationships among subclones within each patient. This study demonstrates the potential for ultra-deep resequencing to recapitulate the dynamics of clonal evolution in cancer cell populations.
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Project description:Patients with advanced oral squamous cell carcinoma (OSCC) have heterogeneous outcomes that limit the implementation of tailored treatment options. Genetic markers for improved prognostic stratification are eagerly awaited.Herein, next-generation sequencing (NGS) was performed in 345 formalin-fixed paraffin-embedded (FFPE) samples obtained from advanced OSCC patients. Genetic mutations on the hotspot regions of 45 cancer-related genes were detected using an ultra-deep (>1000×) sequencing approach. Kaplan-Meier plots and Cox regression analyses were used to investigate the associations between the mutation status and disease-free survival (DFS).We identified 1269 non-synonymous mutations in 276 OSCC samples. TP53, PIK3CA, CDKN2A, HRAS and BRAF were the most frequently mutated genes. Mutations in 14 genes were found to predict DFS. A mutation-based signature affecting ten genes (HRAS, BRAF, FGFR3, SMAD4, KIT, PTEN, NOTCH1, AKT1, CTNNB1, and PTPN11) was devised to predict DFS. Two different resampling methods were used to validate the prognostic value of the identified gene signature. Multivariate analysis demonstrated that presence of a mutated gene signature was an independent predictor of poorer DFS (P = 0.005).Genetic variants identified by NGS technology in FFPE samples are clinically useful to predict prognosis in advanced OSCC patients.
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Project description:BackgroundUltra-deep targeted sequencing (UDT-Seq) has advanced our knowledge on the incidence and functional significance of somatic mutations. However, the utility of UDT-Seq in detecting copy number alterations (CNAs) remains unclear. With the goal of improving molecular prognostication and identifying new therapeutic targets, we designed this study to assess whether UDT-Seq may be useful for detecting CNA in oral cavity squamous cell carcinoma (OSCC).MethodsWe sequenced a panel of clinically actionable cancer mutations in 310 formalin-fixed paraffin-embedded OSCC specimens. A linear model was developed to overcome uneven coverage across target regions and multiple samples. The 5-year rates of secondary primary tumors, local recurrence, neck recurrence, distant metastases, and survival served as the outcome measures. We confirmed the prognostic significance of the CNA signatures in an independent sample of 105 primary OSCC specimens.ResultsThe CNA burden across 10 targeted genes was found to predict prognosis in two independent cohorts. FGFR1 and PIK3CAamplifications were associated with prognosis independent of clinical risk factors. Genes exhibiting CNA were clustered in the proteoglycan metabolism, the FOXO signaling, and the PI3K-AKT signaling pathways, for which targeted drugs are already available or currently under development.ConclusionsUDT-Seq is clinically useful to identify CNA, which significantly improve the prognostic information provided by traditional clinicopathological risk factors in OSCC patients.
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Project description:Human noroviruses (NoVs) are a major cause of gastroenteritis worldwide. It is thought that, similar to other RNA viruses, high mutation rates allow NoVs to evolve fast and to undergo rapid immune escape at the population level. However, the rate and spectrum of spontaneous mutations of human NoVs have not been quantified previously. Here, we analyzed the intra-patient diversity of the NoV capsid by carrying out RT-PCR and ultra-deep sequencing with 100,000-fold coverage of 16 stool samples from symptomatic patients. This revealed the presence of low-frequency sequences carrying large numbers of U-to-C or A-to-G base transitions, suggesting a role for hyper-mutation in NoV diversity. To more directly test for hyper-mutation, we performed transfection assays in which the production of mutations was restricted to a single cell infection cycle. This confirmed the presence of sequences with multiple U-to-C/A-to-G transitions, and suggested that hyper-mutation contributed a large fraction of the total NoV spontaneous mutation rate. The type of changes produced and their sequence context are compatible with ADAR-mediated editing of the viral RNA.
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Project description:Most studies on PRRSV evolution have been limited to a particular region of the viral genome. A thorough genome-wide understanding of the impact of different mechanisms on shaping PRRSV genetic diversity is still lacking. To this end, deep sequencing was used to obtain genomic sequences of a diverse set of 16 isolates from a region of Hong Kong with a complex PRRSV epidemiological record. Genome assemblies and phylogenetic typing indicated the co-circulation of strains of both genotypes (type 1 and type 2) with varying Nsp2 deletion patterns and distinct evolutionary lineages ("High Fever"-like and local endemic type). Recombination analyses revealed genomic breakpoints in structural and non-structural regions of genomes of both genotypes with evidence of many recombination events originating from common ancestors. Additionally, the high fold of coverage per nucleotide allowed the characterization of minor variants arising from the quasispecies of each strain. Overall, 0.56-2.83% of sites were found to be polymorphic with respect to cognate consensus genomes. The distribution of minor variants across each genome was not uniform indicating the influence of selective forces. Proportion of variants capable of causing an amino acid change in their respective codons ranged between 25-67% with many predicted to be non-deleterious. Low frequency deletion variants were also detected providing one possible mechanism for their sudden emergence as cited in previous reports.
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Project description:BackgroundGenome and transcriptome sequencing applications that rely on variation in sequence depth can be negatively affected if there are systematic biases in coverage. We have investigated patterns of local variation in sequencing coverage by utilising ultra-deep sequencing (>100,000X) of mtDNA obtained during sequencing of two vertebrate genomes, wolverine (Gulo gulo) and collared flycatcher (Ficedula albicollis). With such extreme depth, stochastic variation in coverage should be negligible, which allows us to provide a very detailed, fine-scale picture of sequence dependent coverage variation and sequencing error rates.ResultsSequencing coverage showed up to six-fold variation across the complete mtDNA and this variation was highly repeatable in sequencing of multiple individuals of the same species. Moreover, coverage in orthologous regions was correlated between the two species and was negatively correlated with GC content. We also found a negative correlation between the site-specific sequencing error rate and coverage, with certain sequence motifs "CCNGCC" being particularly prone to high rates of error and low coverage.ConclusionsOur results demonstrate that inherent sequence characteristics govern variation in coverage and suggest that some of this variation, like GC content, should be controlled for in, for example, RNA-Seq and detection of copy number variation.
| S-EPMC4070552 | biostudies-literature
Project description:Accurate assessment of tumour heterogeneity is an important issue that influences prognosis and therapeutic decision in molecular pathology. Due to the shortage of protective histones and a limited DNA repair capacity, the mitochondrial (mt)-genome undergoes high variability during tumour development. Therefore, screening of mt-genome represents a useful molecular tool for assessing precise cell lineages and tracking tumour history. Here, we describe a highly specific and robust multiplex PCR-based ultra-deep sequencing technology for analysis of the whole mt-genome (wmt-seq) on low quality-DNA from formalin-fixed paraffin-embedded tissues. As a proof of concept, we applied the wmt-seq technology to characterize the clonal relationship of non-small cell lung cancer (NSCLC) specimens with multiple lesions (N = 43) that show either different histological subtypes (group I) or pulmonary adenosquamous carcinoma as striking examples of a mixed-histology tumour (group II). The application of wmt-seq demonstrated that most samples bear common mt-mutations in each lesion of an individual patient, indicating a single cell progeny and clonal relationship. Hereby we show the monoclonal origin of histologically heterogeneous NSCLC and demonstrate the evolutionary relation of NSCLC cases carrying heteroplasmic mt-variants.
| S-EPMC5593826 | biostudies-literature
Project description:Head and neck squamous cell carcinoma (HNSCC) is characterized by significant genomic instability that could lead to clonal diversity. Intratumor clonal heterogeneity has been proposed as a major attribute underlying tumor evolution, progression, and resistance to chemotherapy and radiation. Understanding genetic heterogeneity could lead to treatments specific to resistant and metastatic tumor cells. To characterize the degree of intratumor genetic heterogeneity within a single tumor, we performed whole-genome sequencing on three separate regions of an human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma and two separate regions from one corresponding cervical lymph node metastasis. This approach achieved coverage of approximately 97.9% of the genome across all samples. In total, 5701 somatic point mutations (SPMs) and 4347 small somatic insertions and deletions (indels)were detected in at least one sample. Ninety-two percent of SPMs and 77% of indels were validated in a second set of samples adjacent to the discovery set. All five tumor samples shared 41% of SPMs, 57% of the 1805 genes with SPMs, and 34 of 55 cancer genes. The distribution of SPMs allowed phylogenetic reconstruction of this tumor's evolutionary pathway and showed that the metastatic samples arose as a late event. The degree of intratumor heterogeneity showed that a single biopsy may not represent the entire mutational landscape of HNSCC tumors. This approach may be used to further characterize intratumor heterogeneity in more patients, and their sample-to-sample variations could reveal the evolutionary process of cancer cells, facilitate our understanding of tumorigenesis, and enable the development of novel targeted therapies.
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Project description:Listeria monocytogenes, a gram-positive pathogen, and causative agent of listeriosis, has become a widely used model organism for intracellular infections. Recent studies have identified small non-coding RNAs (sRNAs) as important factors for regulating gene expression and pathogenicity of L. monocytogenes. Increased speed and reduced costs of high throughput sequencing (HTS) techniques have made RNA sequencing (RNA-Seq) the state-of-the-art method to study bacterial transcriptomes. We created a large transcriptome dataset of L. monocytogenes containing a total of 21 million reads, using the SOLiD sequencing technology. The dataset contained cDNA sequences generated from L. monocytogenes RNA collected under intracellular and extracellular condition and additionally was size fractioned into three different size ranges from <40 nt, 40-150 nt and >150 nt. We report here, the identification of nine new sRNAs candidates of L. monocytogenes and a reevaluation of known sRNAs of L. monocytogenes EGD-e. Automatic comparison to known sRNAs revealed a high recovery rate of 55%, which was increased to 90% by manual revision of the data. Moreover, thorough classification of known sRNAs shed further light on their possible biological functions. Interestingly among the newly identified sRNA candidates are antisense RNAs (asRNAs) associated to the housekeeping genes purA, fumC and pgi and potentially their regulation, emphasizing the significance of sRNAs for metabolic adaptation in L. monocytogenes.
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Project description:Viruses rely on widespread genetic variation and large population size for adaptation. Large DNA virus populations are thought to harbor little variation though natural populations may be polymorphic. To measure the genetic variation present in a dsDNA virus population, we deep sequenced a natural strain of the baculovirus Autographa californica multiple nucleopolyhedrovirus. With 124,221X average genome coverage of our 133,926 bp long consensus, we could detect low frequency mutations (0.025%). K-means clustering was used to classify the mutations in four categories according to their frequency in the population. We found 60 high frequency non-synonymous mutations under balancing selection distributed in all functional classes. These mutants could alter viral adaptation dynamics, either through competitive or synergistic processes. Lastly, we developed a technique for the delimitation of large deletions in next generation sequencing data. We found that large deletions occur along the entire viral genome, with hotspots located in homologous repeat regions (hrs). Present in 25.4% of the genomes, these deletion mutants presumably require functional complementation to complete their infection cycle. They might thus have a large impact on the fitness of the baculovirus population. Altogether, we found a wide breadth of genomic variation in the baculovirus population, suggesting it has high adaptive potential.
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