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July 19, 2019

Detection and whole genome sequencing of carbapenemase-producing Aeromonas hydrophila isolated from routine perirectal surveillance culture.

Perirectal surveillance cultures and a stool culture grew Aeromonas species from three patients over a six-week period without epidemiological links. Detection of the blaKPC-2 gene in one isolate prompted inclusion of non-Enterobacteriaceae in our surveillance culture workup. Whole genome sequencing confirmed isolates were unrelated, and provided data for Aeromonas reference genomes. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

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July 19, 2019

Mitotic intragenic recombination: A mechanism of survival for several congenital disorders of glycosylation.

Congenital disorders of glycosylation (CDGs) are disorders of abnormal protein glycosylation that affect multiple organ systems. Because most CDGs have been described in only a few individuals, our understanding of the associated phenotypes and the mechanisms of individual survival are limited. In the process of studying two siblings, aged 6 and 11 years, with MOGS-CDG and biallelic MOGS (mannosyl-oligosaccharide glucosidase) mutations (GenBank: NM_006302.2; c.[65C>A; 329G>A] p.[Ala22Glu; Arg110His]; c.[370C>T] p.[Gln124(*)]), we noted that their survival was much longer than the previous report of MOGS-CDG, in a child who died at 74 days of age. Upon mutation analysis, we detected multiple MOGS genotypes including wild-type alleles in their cultured fibroblast and peripheral blood DNA. Further analysis of DNA from cultured fibroblasts of six individuals with compound heterozygous mutations of PMM2 (PMM2-CDG), MPI (MPI-CDG), ALG3 (ALG3-CDG), ALG12 (ALG12-CDG), DPAGT1 (DPAGT1-CDG), and ALG1 (ALG1-CDG) also identified multiple genotypes including wild-type alleles for each. Droplet digital PCR showed a ratio of nearly 1:1 wild-type to mutant alleles for most, but not all, mutations. This suggests that mitotic recombination contributes to the survival and the variable expressivity of individuals with compound heterozygous CDGs. This also provides an explanation for prior observations of a reduced frequency of homozygous mutations and might contribute to increased levels of residual enzyme activity in cultured fibroblasts of individuals with MPI- and PMM2-CDGs. Copyright © 2016 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

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July 19, 2019

Large deletions at the SHOX locus in the pseudoautosomal region are associated with skeletal atavism in Shetland ponies.

Skeletal atavism in Shetland ponies is a heritable disorder characterized by abnormal growth of the ulna and fibula that extend the carpal and tarsal joints, respectively. This causes abnormal skeletal structure, impaired movements, and affected foals are usually euthanized. In order to identify the causal mutation we subjected six confirmed Swedish cases and a DNA pool consisting of 21 control individuals to whole genome resequencing. We screened for polymorphisms where the cases and the control pool were fixed for opposite alleles and observed this signature for only 25 SNPs, most of which were scattered on genome assembly unassigned scaffolds. Read depth analysis at these loci revealed homozygosity or compound heterozygosity for two partially overlapping large deletions in the pseudoautosomal region (PAR) of chromosome X/Y in cases but not in the control pool. One of these deletions removes the entire coding region of the SHOX gene and both deletions remove parts of the CRLF2 gene located downstream of SHOX. The horse reference assembly of the PAR is highly fragmented, and in order to characterize this region we sequenced bacterial artificial chromosome (BAC) clones by single-molecule real-time (SMRT) sequencing technology. This considerably improved the assembly and enabled size estimations of the two deletions to 160-180 kb and 60-80 kb, respectively. Complete association between the presence of these deletions and disease status was verified in eight other affected horses. The result of the present study is consistent with previous studies in humans showing crucial importance of SHOX for normal skeletal development. Copyright © 2016 Author et al.

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July 19, 2019

Development and clinical application of an integrative genomic approach to personalized cancer therapy.

Personalized therapy provides the best outcome of cancer care and its implementation in the clinic has been greatly facilitated by recent convergence of enormous progress in basic cancer research, rapid advancement of new tumor profiling technologies, and an expanding compendium of targeted cancer therapeutics.We developed a personalized cancer therapy (PCT) program in a clinical setting, using an integrative genomics approach to fully characterize the complexity of each tumor. We carried out whole exome sequencing (WES) and single-nucleotide polymorphism (SNP) microarray genotyping on DNA from tumor and patient-matched normal specimens, as well as RNA sequencing (RNA-Seq) on available frozen specimens, to identify somatic (tumor-specific) mutations, copy number alterations (CNAs), gene expression changes, gene fusions, and also germline variants. To provide high sensitivity in known cancer mutation hotspots, Ion AmpliSeq Cancer Hotspot Panel v2 (CHPv2) was also employed. We integrated the resulting data with cancer knowledge bases and developed a specific workflow for each cancer type to improve interpretation of genomic data.We returned genomics findings to 46 patients and their physicians describing somatic alterations and predicting drug response, toxicity, and prognosis. Mean 17.3 cancer-relevant somatic mutations per patient were identified, 13.3-fold, 6.9-fold, and 4.7-fold more than could have been detected using CHPv2, Oncomine Cancer Panel (OCP), and FoundationOne, respectively. Our approach delineated the underlying genetic drivers at the pathway level and provided meaningful predictions of therapeutic efficacy and toxicity. Actionable alterations were found in 91 % of patients (mean 4.9 per patient, including somatic mutations, copy number alterations, gene expression alterations, and germline variants), a 7.5-fold, 2.0-fold, and 1.9-fold increase over what could have been uncovered by CHPv2, OCP, and FoundationOne, respectively. The findings altered the course of treatment in four cases. These results show that a comprehensive, integrative genomic approach as outlined above significantly enhanced genomics-based PCT strategies.

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July 19, 2019

Single-molecule sequencing reveals complex genomic variation of hepatitis B virus during 15 years of chronic infection following liver transplantation.

Chronic hepatitis B (CHB) is prevalent worldwide. The infectious agent, hepatitis B virus (HBV) replicates via an RNA intermediate and is error-prone, leading to rapid generation of closely related but not identical viral variants, including those that can escape host immune responses and antiviral treatments. The complexity of CHB can be further enhanced by the presence of HBV variants with large deletions in the genome, generated via splicing (spHBV). Although spHBV variants are incapable of autonomous replication, their replication is rescued by wild-type HBV. SpHBV variants have been shown to enhance wild-type virus replication, and their prevalence increases with liver disease progression. Single-molecule deep sequencing was performed on whole HBV genomes extracted from longitudinal samples of a post-liver transplant CHB subject, collected over a 15-year period that included the liver explant. By employing novel bioinformatics methods, this analysis showed a complex dynamics of the viral population across a period of changing treatment regimens. The spHBV detected in the liver explant remained present post-transplantation, along with emergence of a highly diverse novel spHBV population as well as variants with multiple deletions in the preS genes. The identification of novel mutations outside the HBV reverse transcriptase gene that co-occur with known drug resistant mutations, highlight the relevance of using full genome deep sequencing and support the hypothesis that drug resistance involves interactions across the full-length HBV genome.Single-molecule sequencing allowed characterising, in unprecedented detail, the evolution of HBV populations and offered unique insights into the dynamics of defective and spHBV variants following liver transplantation and complex treatment regimes. This analysis also showed rapid adaptation of HBV populations to treatment regimens with evolving drug resistance phenotypes and evidence of purifying selection across the whole genome. Finally, the new open source bioinformatics tools are freely available, with the capacity to easily identify potential spliced variants from deep sequencing data. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

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July 19, 2019

Towards precision medicine.

There is great potential for genome sequencing to enhance patient care through improved diagnostic sensitivity and more precise therapeutic targeting. To maximize this potential, genomics strategies that have been developed for genetic discovery – including DNA-sequencing technologies and analysis algorithms – need to be adapted to fit clinical needs. This will require the optimization of alignment algorithms, attention to quality-coverage metrics, tailored solutions for paralogous or low-complexity areas of the genome, and the adoption of consensus standards for variant calling and interpretation. Global sharing of this more accurate genotypic and phenotypic data will accelerate the determination of causality for novel genes or variants. Thus, a deeper understanding of disease will be realized that will allow its targeting with much greater therapeutic precision.

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July 19, 2019

Variation and evolution in the glutamine-rich repeat region of Drosophila argonaute-2.

RNA interference pathways mediate biological processes through Argonaute-family proteins, which bind small RNAs as guides to silence complementary target nucleic acids . In insects and crustaceans Argonaute-2 silences viral nucleic acids, and therefore acts as a primary effector of innate antiviral immunity. Although the function of the major Argonaute-2 domains, which are conserved across most Argonaute-family proteins, are known, many invertebrate Argonaute-2 homologs contain a glutamine-rich repeat (GRR) region of unknown function at the N-terminus . Here we combine long-read amplicon sequencing of Drosophila Genetic Reference Panel (DGRP) lines with publicly available sequence data from many insect species to show that this region evolves extremely rapidly and is hyper-variable within species. We identify distinct GRR haplotype groups in Drosophila melanogaster, and suggest that one of these haplotype groups has recently risen to high frequency in a North American population. Finally, we use published data from genome-wide association studies of viral resistance in D. melanogaster to test whether GRR haplotypes are associated with survival after virus challenge. We find a marginally significant association with survival after challenge with Drosophila C Virus in the DGRP, but we were unable to replicate this finding using lines from the Drosophila Synthetic Population Resource panel. Copyright © 2016 Palmer and Obbard.

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July 19, 2019

Living apart together: crosstalk between the core and supernumerary genomes in a fungal plant pathogen.

Eukaryotes display remarkable genome plasticity, which can include supernumerary chromosomes that differ markedly from the core chromosomes. Despite the widespread occurrence of supernumerary chromosomes in fungi, their origin, relation to the core genome and the reason for their divergent characteristics are still largely unknown. The complexity of genome assembly due to the presence of repetitive DNA partially accounts for this.Here we use single-molecule real-time (SMRT) sequencing to assemble the genome of a prominent fungal wheat pathogen, Fusarium poae, including at least one supernumerary chromosome. The core genome contains limited transposable elements (TEs) and no gene duplications, while the supernumerary genome holds up to 25 % TEs and multiple gene duplications. The core genome shows all hallmarks of repeat-induced point mutation (RIP), a defense mechanism against TEs, specific for fungi. The absence of RIP on the supernumerary genome accounts for the differences between the two (sub)genomes, and results in a functional crosstalk between them. The supernumerary genome is a reservoir for TEs that migrate to the core genome, and even large blocks of supernumerary sequence (>200 kb) have recently translocated to the core. Vice versa, the supernumerary genome acts as a refuge for genes that are duplicated from the core genome.For the first time, a mechanism was determined that explains the differences that exist between the core and supernumerary genome in fungi. Different biology rather than origin was shown to be responsible. A “living apart together” crosstalk exists between the core and supernumerary genome, accelerating chromosomal and organismal evolution.

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July 19, 2019

Standardization and quality management in next-generation sequencing

DNA sequencing continues to evolve quickly even after > 30 years. Many new platforms suddenly appeared and former established systems have vanished in almost the same manner. Since establishment of next-generation sequencing devices, this progress gains momentum due to the continually growing demand for higher throughput, lower costs and better quality of data. In consequence of this rapid development, standardized procedures and data formats as well as comprehensive quality management considerations are still scarce. Here, we listed and summarized current standardization efforts and quality management initiatives from companies, organizations and societies in form of published studies and ongoing projects. These comprise on the one hand quality documentation issues like technical notes, accreditation checklists and guidelines for validation of sequencing workflows. On the other hand, general standard proposals and quality metrics are developed and applied to the sequencing workflow steps with the main focus on upstream processes. Finally, certain standard developments for downstream pipeline data handling, processing and storage are discussed in brief. These standardization approaches represent a first basis for continuing work in order to prospectively implement next-generation sequencing in important areas such as clinical diagnostics, where reliable results and fast processing is crucial. Additionally, these efforts will exert a decisive influence on traceability and reproducibility of sequence data.

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July 19, 2019

Biosynthesis and function of modified bases in bacteria and their viruses.

Naturally occurring modification of the canonical A, G, C, and T bases can be found in the DNA of cellular organisms and viruses from all domains of life. Bacterial viruses (bacteriophages) are a particularly rich but still underexploited source of such modified variant nucleotides. The modifications conserve the coding and base-pairing functions of DNA, but add regulatory and protective functions. In prokaryotes, modified bases appear primarily to be part of an arms race between bacteriophages (and other genomic parasites) and their hosts, although, as in eukaryotes, some modifications have been adapted to convey epigenetic information. The first half of this review catalogs the identification and diversity of DNA modifications found in bacteria and bacteriophages. What is known about the biogenesis, context, and function of these modifications are also described. The second part of the review places these DNA modifications in the context of the arms race between bacteria and bacteriophages. It focuses particularly on the defense and counter-defense strategies that turn on direct recognition of the presence of a modified base. Where modification has been shown to affect other DNA transactions, such as expression and chromosome segregation, that is summarized, with reference to recent reviews.

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July 19, 2019

A distinct class of chromoanagenesis events characterized by focal copy number gains.

Chromoanagenesis is the process by which a single catastrophic event creates complex rearrangements confined to a single or a few chromosomes. It is usually characterized by the presence of multiple deletions and/or duplications, as well as by copy neutral rearrangements. In contrast, an array CGH screen of patients with developmental anomalies revealed three patients in which a single chromosome carries from 8 to 11 large copy number gains confined to a single chromosome or chromosomal arm, but the absence of deletions. Subsequent fluorescence in situ hybiridization and massive parallel sequencing revealed the duplicons to be clustered together in distinct locations across the altered chromosomes. Breakpoint junction sequences showed both microhomology and non-templated insertions of up to 40 bp. Hence, these patients each demonstrate a single altered chromosome of clustered insertional duplications, no deletions, and breakpoint junction sequences showing microhomology and/or non-templated insertions. These observations are difficult to reconcile with current mechanistic descriptions of chromothripsis and chromoanasynthesis. Therefore, we hypothesize those rearrangements to be of a mechanistically different origin. In addition, we suggest that large untemplated insertional sequences observed at breakpoints are driven by a non-canonical non-homologous end joining mechanism.© 2016 WILEY PERIODICALS, INC.

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July 19, 2019

ARTISAN PCR: rapid identification of full-length immunoglobulin rearrangements without primer binding bias.

B cells recognize specific antigens by their membrane-bound B-cell receptor (BCR). Functional BCR genes are assembled in pre-B cells by recombination of the variable (V), diversity (D) and joining (J) genes [V(D)J recombination]. When B cells participate in germinal centre reactions, non-templated point mutations are introduced into BCR genes by somatic hypermutation (SHM) (Rajewsky, 1996). V(D)J recombination and SHM create virtually unlimited BCR repertoires.

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July 19, 2019

Multiple origins of the pathogenic yeast Candida orthopsilosis by separate hybridizations between two parental species.

Mating between different species produces hybrids that are usually asexual and stuck as diploids, but can also lead to the formation of new species. Here, we report the genome sequences of 27 isolates of the pathogenic yeast Candida orthopsilosis. We find that most isolates are diploid hybrids, products of mating between two unknown parental species (A and B) that are 5% divergent in sequence. Isolates vary greatly in the extent of homogenization between A and B, making their genomes a mosaic of highly heterozygous regions interspersed with homozygous regions. Separate phylogenetic analyses of SNPs in the A- and B-derived portions of the genome produces almost identical trees of the isolates with four major clades. However, the presence of two mutually exclusive genotype combinations at the mating type locus, and recombinant mitochondrial genomes diagnostic of inter-clade mating, shows that the species C. orthopsilosis does not have a single evolutionary origin but was created at least four times by separate interspecies hybridizations between parents A and B. Older hybrids have lost more heterozygosity. We also identify two isolates with homozygous genomes derived exclusively from parent A, which are pure non-hybrid strains. The parallel emergence of the same hybrid species from multiple independent hybridization events is common in plant evolution, but is much less documented in pathogenic fungi.

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July 19, 2019

Single-molecule sequencing revealing the presence of distinct JC polyomavirus populations in patients with progressive multifocal leukoencephalopathy.

Progressive multifocal leukoencephalopathy (PML) is a fatal disease caused by reactivation of JC polyomavirus (JCPyV) in immunosuppressed individuals and lytic infection by neurotropic JCPyV in glial cells. The exact content of neurotropic mutations within individual JCPyV strains has not been studied to our knowledge.We exploited the capacity of single-molecule real-time sequencing technology to determine the sequence of complete JCPyV genomes in single reads. The method was used to precisely characterize individual neurotropic JCPyV strains of 3 patients with PML without the bias caused by assembly of short sequence reads.In the cerebrospinal fluid sample of a 73-year-old woman with rapid PML onset, 3 distinct JCPyV populations could be identified. All viral populations were characterized by rearrangements within the noncoding regulatory region (NCCR) and 1 point mutation, S267L in the VP1 gene, suggestive of neurotropic strains. One patient with PML had a single neurotropic strain with rearranged NCCR, and 1 patient had a single strain with small NCCR alterations.We report here, for the first time, full characterization of individual neurotropic JCPyV strains in the cerebrospinal fluid of patients with PML. It remains to be established whether PML pathogenesis is driven by one or several neurotropic strains in an individual.

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July 19, 2019

Rapid functional and sequence differentiation of a tandemly repeated species-specific multigene family in Drosophila.

Gene clusters of recently duplicated genes are hotbeds for evolutionary change. However, our understanding of how mutational mechanisms and evolutionary forces shape the structural and functional evolution of these clusters is hindered by the high sequence identity among the copies, which typically results in their inaccurate representation in genome assemblies. The presumed testis-specific, chimeric gene Sdic originated, and tandemly expanded in Drosophila melanogaster, contributing to increased male-male competition. Using various types of massively parallel sequencing data, we studied the organization, sequence evolution, and functional attributes of the different Sdic copies. By leveraging long-read sequencing data, we uncovered both copy number and order differences from the currently accepted annotation for the Sdic region. Despite evidence for pervasive gene conversion affecting the Sdic copies, we also detected signatures of two episodes of diversifying selection, which have contributed to the evolution of a variety of C-termini and miRNA binding site compositions. Expression analyses involving RNA-seq datasets from 59 different biological conditions revealed distinctive expression breadths among the copies, with three copies being transcribed in females, opening the possibility to a sexually antagonistic effect. Phenotypic assays using Sdic knock-out strains indicated that should this antagonistic effect exist, it does not compromise female fertility. Our results strongly suggest that the genome consolidation of the Sdic gene cluster is more the result of a quick exploration of different paths of molecular tinkering by different copies than a mere dosage increase, which could be a recurrent evolutionary outcome in the presence of persistent sexual selection. © The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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