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Auto Tag: Epigenetics

July 7, 2019

The characterization of goat genetic diversity: Towards a genomic approach

The investigation of genetic diversity at molecular level has been proposed as a valuable complement and sometimes proxy to phenotypic diversity of local breeds and is presently considered as one of the FAO priorities for breed characterization. By recommending a set of selected molecular markers for each of the main livestock species, FAO has promoted the meta-analysis of local datasets, to achieve a global view of molecular genetic diversity. Analysis within the EU Globaldiv project of two large goat microsatellite datasets produced by the Econogene Consortium and the IAEA CRP–Asia Consortium, respectively, has generated a picture of goat diversity across continents. This indicates a gradient of decreasing diversity from the domestication centre towards Europe and Asia, a clear phylogeographic structure at the continental and regional levels, and in Asia a limited genetic differentiation among local breeds. The development of SNP panels that assay thousands of markers and the whole genome sequencing of livestock permit an affordable use of genomic technologies in all livestock species, goats included. Preliminary data from the Italian Goat Consortium indicate that the SNP panel developed for this species is highly informative. The existing panel can be improved by integrating additional SNPs identified from the whole genome sequence alignment of goats adapted to extreme climates. Part of this effort is being achieved by international projects (e.g. EU FP7 NextGen and 3SR projects), but a fair representation of the global diversity in goats requires a large panel of samples (i.e. as in the recently launched 1000 cattle genomes initiative). Genomic technologies offer new strategies to investigate complex traits difficult to measure. For example, the comparison of patterns of diversity among the genomes in selected groups of animals (e.g. adapted to different environments) and the integration of genome-wide diversity with new GIScience-based methods are able to identify molecular markers associated with genomic regions of putative importance in adaptation and thus pave the way for the identification of causative genes. Goat breeds adapted to different production systems in extreme and harsh environments will play an important role in this process. The new sequencing technologies also permit the analysis of the entire mitochondrial genome at maximum resolution. The complete mtDNA sequence is now the common standard format for the investigation of human maternal lineages. A preliminary analysis of the complete goat mtDNA genome supports a single Neolithic origin of domestic goats rather than multiple domestication events in different geographic areas.

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July 7, 2019

Diversification of bacterial genome content through distinct mechanisms over different timescales.

Bacterial populations often consist of multiple co-circulating lineages. Determining how such population structures arise requires understanding what drives bacterial diversification. Using 616 systematically sampled genomes, we show that Streptococcus pneumoniae lineages are typically characterized by combinations of infrequently transferred stable genomic islands: those moving primarily through transformation, along with integrative and conjugative elements and phage-related chromosomal islands. The only lineage containing extensive unique sequence corresponds to a set of atypical unencapsulated isolates that may represent a distinct species. However, prophage content is highly variable even within lineages, suggesting frequent horizontal transmission that would necessitate rapidly diversifying anti-phage mechanisms to prevent these viruses sweeping through populations. Correspondingly, two loci encoding Type I restriction-modification systems able to change their specificity over short timescales through intragenomic recombination are ubiquitous across the collection. Hence short-term pneumococcal variation is characterized by movement of phage and intragenomic rearrangements, with the slower transfer of stable loci distinguishing lineages.

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July 7, 2019

Expansion of the genetic toolkit for metabolic engineering of Clostridium pasteurianum: chromosomal gene disruption of the endogenous CpaAI restriction enzyme.

Clostridium pasteurianum is one of the most promising biofuel producers within the genus Clostridium owing to its unique metabolic ability to ferment glycerol into butanol. Although an efficient means is available for introducing foreign DNA to C. pasteurianum, major genetic tools, such as gene knockout, knockdown, or genome editing, are lacking, preventing metabolic engineering of C. pasteurianum.Here we present a methodology for performing chromosomal gene disruption in C. pasteurianum using the programmable lactococcus Ll.ltrB group II intron. Gene disruption was initially found to be impeded by inefficient electrotransformation of Escherichia coli-C. pasteurianum shuttle vectors, presumably due to host restriction. By assessing the ability of various vector deletion derivatives to electrotransform C. pasteurianum and probing the microorganism’s methylome using next-generation sequence data, we identified a new C. pasteurianum Type I restriction-methylation system, CpaAII, with a predicted recognition sequence of 5′-AAGNNNNNCTCC-3′ (N?=?A, C, G, or T). Following rescue of high-level electrotransformation via mutation of the sole CpaAII site within the shuttle vectors, we retargeted the intron to the cpaAIR gene encoding the CpaAI Type II restriction endonuclease (recognition site of 5′-CGCG-3′). Intron insertion was potentially hindered by low retrohoming efficiency, yet this limitation could be overcome by a procedure for enrichment of the intron insertion. The resulting ?cpaAIR mutant strain was efficiently electrotransformed with M.FnuDII-unmethylated plasmid DNA.The markerless and plasmidless ?cpaAIR mutant strain of C. pasteurianum developed in this study can serve as a general host strain for future genetic and metabolic manipulation. Further, the associated gene disruption protocol should not only serve as a guide for chromosomal gene inactivation studies involving mobile group II introns, but also prove invaluable for applying metabolic engineering strategies to C. pasteurianum.

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July 7, 2019

Simultaneous sequencing of oxidized methylcytosines produced by TET/JBP dioxygenases in Coprinopsis cinerea.

TET/JBP enzymes oxidize 5-methylpyrimidines in DNA. In mammals, the oxidized methylcytosines (oxi-mCs) function as epigenetic marks and likely intermediates in DNA demethylation. Here we present a method based on diglucosylation of 5-hydroxymethylcytosine (5hmC) to simultaneously map 5hmC, 5-formylcytosine, and 5-carboxylcytosine at near-base-pair resolution. We have used the method to map the distribution of oxi-mC across the genome of Coprinopsis cinerea, a basidiomycete that encodes 47 TET/JBP paralogs in a previously unidentified class of DNA transposons. Like 5-methylcytosine residues from which they are derived, oxi-mC modifications are enriched at centromeres, TET/JBP transposons, and multicopy paralogous genes that are not expressed, but rarely mark genes whose expression changes between two developmental stages. Our study provides evidence for the emergence of an epigenetic regulatory system through recruitment of selfish elements in a eukaryotic lineage, and describes a method to map all three different species of oxi-mCs simultaneously.

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July 7, 2019

Genome annotation provides insight into carbon monoxide and hydrogen metabolism in Rubrivivax gelatinosus.

We report here the sequencing and analysis of the genome of the purple non-sulfur photosynthetic bacterium Rubrivivax gelatinosus CBS. This microbe is a model for studies of its carboxydotrophic life style under anaerobic condition, based on its ability to utilize carbon monoxide (CO) as the sole carbon substrate and water as the electron acceptor, yielding CO2 and H2 as the end products. The CO-oxidation reaction is known to be catalyzed by two enzyme complexes, the CO dehydrogenase and hydrogenase. As expected, analysis of the genome of Rx. gelatinosus CBS reveals the presence of genes encoding both enzyme complexes. The CO-oxidation reaction is CO-inducible, which is consistent with the presence of two putative CO-sensing transcription factors in its genome. Genome analysis also reveals the presence of two additional hydrogenases, an uptake hydrogenase that liberates the electrons in H2 in support of cell growth, and a regulatory hydrogenase that senses H2 and relays the signal to a two-component system that ultimately controls synthesis of the uptake hydrogenase. The genome also contains two sets of hydrogenase maturation genes which are known to assemble the catalytic metallocluster of the hydrogenase NiFe active site. Collectively, the genome sequence and analysis information reveals the blueprint of an intricate network of signal transduction pathways and its underlying regulation that enables Rx. gelatinosus CBS to thrive on CO or H2 in support of cell growth.

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July 7, 2019

Genomic mapping of phosphorothioates reveals partial modification of short consensus sequences.

Bacterial phosphorothioate (PT) DNA modifications are incorporated by Dnd proteins A-E and often function with DndF-H as a restriction-modification (R-M) system, as in Escherichia coli B7A. However, bacteria such as Vibrio cyclitrophicus FF75 lack dndF-H, which points to other PT functions. Here we report two novel, orthogonal technologies to map PTs across the genomes of B7A and FF75 with >90% agreement: single molecule, real-time sequencing and deep sequencing of iodine-induced cleavage at PT (ICDS). In B7A, we detect PT on both strands of GpsAAC/GpsTTC motifs, but with only 12% of 40,701 possible sites modified. In contrast, PT in FF75 occurs as a single-strand modification at CpsCA, again with only 14% of 160,541 sites modified. Single-molecule analysis indicates that modification could be partial at any particular genomic site even with active restriction by DndF-H, with direct interaction of modification proteins with GAAC/GTTC sites demonstrated with oligonucleotides. These results point to highly unusual target selection by PT-modification proteins and rule out known R-M mechanisms.

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July 7, 2019

Complete genome sequence of Bifidobacterium longum 105-A, a strain with high transformation efficiency.

Bifidobacterium longum 105-A shows high transformation efficiency and allows for the generation of gene knockout mutants through homologous recombination. Here, we report the complete genome sequence of strain 105-A. Genes encoding at least four putative restriction-modification systems were found in this genome, which might contribute to its transformation efficiency. Copyright © 2014 Kanesaki et al.

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July 7, 2019

Draft genome sequence of a metabolically diverse Antarctic supraglacial stream organism, Polaromonas sp. strain CG9_12, determined using Pacific Biosciences Single-Molecule Real-Time Sequencing Technology.

Polaromonas species are found in a diversity of environments and are particularly common in icy ecosystems. Polaromonas sp. strain CG9_12 is an aerobic, Gram-negative, catalase-positive, white-pigmented bacterium of the Proteobacteria phylum. Here, we present the draft genome sequence of Polaromonas sp. strain CG9_12, isolated from an Antarctic supraglacial stream. Copyright © 2014 Smith et al.

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July 7, 2019

Inconsistency of phenotypic and genomic characteristics of Campylobacter fetus subspecies requires reevaluation of current diagnostics.

Classifications of the Campylobacter fetus subspecies fetus and venerealis were first described in 1959 and were based on the source of isolation (intestinal versus genital) and the ability of the strains to proliferate in the genital tract of cows. Two phenotypic assays (1% glycine tolerance and H2S production) were described to differentiate the subspecies. Multiple molecular assays have been applied to differentiate the C. fetus subspecies, but none of these tests is consistent with the phenotypic identification methods. In this study, we defined the core genome and accessory genes of C. fetus, which are based on the closed genomes of five C. fetus strains. Phylogenetic analysis of the core genomes of 23 C. fetus strains of the two subspecies showed a division into two clusters. The phylogenetic core genome clusters were not consistent with the phenotypic classifications of the C. fetus subspecies. However, they were consistent with the molecular characteristics of the strains, which were determined by multilocus sequence typing, sap typing, and the presence/absence of insertion sequences and a type I restriction modification system. The similarity of the genome characteristics of three of the phenotypically defined C. fetus subsp. fetus strains to C. fetus subsp. venerealis strains, when considering the core genome and accessory genes, requires a critical evaluation of the clinical relevance of C. fetus subspecies identification by phenotypic assays. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

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July 7, 2019

Comparative genomics of the Campylobacter lari group.

The Campylobacter lari group is a phylogenetic clade within the epsilon subdivision of the Proteobacteria and is part of the thermotolerant Campylobacter spp., a division within the genus that includes the human pathogen Campylobacter jejuni. The C. lari group is currently composed of five species (C. lari, Campylobacter insulaenigrae, Campylobacter volucris, Campylobacter subantarcticus, and Campylobacter peloridis), as well as a group of strains termed the urease-positive thermophilic Campylobacter (UPTC) and other C. lari-like strains. Here we present the complete genome sequences of 11 C. lari group strains, including the five C. lari group species, four UPTC strains, and a lari-like strain isolated in this study. The genome of C. lari subsp. lari strain RM2100 was described previously. Analysis of the C. lari group genomes indicates that this group is highly related at the genome level. Furthermore, these genomes are strongly syntenic with minor rearrangements occurring only in 4 of the 12 genomes studied. The C. lari group can be bifurcated, based on the flagella and flagellar modification genes. Genomic analysis of the UPTC strains indicated that these organisms are variable but highly similar, closely related to but distinct from C. lari. Additionally, the C. lari group contains multiple genes encoding hemagglutination domain proteins, which are either contingency genes or linked to conserved contingency genes. Many of the features identified in strain RM2100, such as major deficiencies in amino acid biosynthesis and energy metabolism, are conserved across all 12 genomes, suggesting that these common features may play a role in the association of the C. lari group with coastal environments and watersheds. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution 2014. This work is written by US Government employees and is in the public domain in the US.

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July 7, 2019

Reversible positioning of single molecules inside zero-mode waveguides.

We have developed a hybrid nanopore/zero-mode waveguide device for single-molecule fluorescence and DNA sequencing applications. The device is a freestanding solid-state membrane with sub-5 nm nanopores that reversibly delivers individual biomolecules to the base of 70 nm diameter waveguides for interrogation. Rapid and reversible molecular loading is achieved by controlling the voltage across the device. Using this device we demonstrate protein and DNA loading with efficiency that is orders of magnitude higher than diffusion-based molecular loading.

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July 7, 2019

In transition: primate genomics at a time of rapid change.

The field of nonhuman primate genomics is undergoing rapid change and making impressive progress. Exploiting new technologies for DNA sequencing, researchers have generated new whole-genome sequence assemblies for multiple primate species over the past 6 years. In addition, investigations of within-species genetic variation, gene expression and RNA sequences, conservation of non-protein-coding regions of the genome, and other aspects of comparative genomics are moving at an accelerating speed. This progress is opening a wide array of new research opportunities in the analysis of comparative primate genome content and evolution. It also creates new possibilities for the use of nonhuman primates as model organisms in biomedical research. This transition, based on both new technology and the new information being generated in regard to human genetics, provides an important justification for reevaluating the research goals, strategies, and study designs used in primate genetics and genomics.

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July 7, 2019

Feasibility of real time next generation sequencing of cancer genes linked to drug response: results from a clinical trial.

The successes of targeted drugs with companion predictive biomarkers and the technological advances in gene sequencing have generated enthusiasm for evaluating personalized cancer medicine strategies using genomic profiling. We assessed the feasibility of incorporating real-time analysis of somatic mutations within exons of 19 genes into patient management. Blood, tumor biopsy and archived tumor samples were collected from 50 patients recruited from four cancer centers. Samples were analyzed using three technologies: targeted exon sequencing using Pacific Biosciences PacBio RS, multiplex somatic mutation genotyping using Sequenom MassARRAY and Sanger sequencing. An expert panel reviewed results prior to reporting to clinicians. A clinical laboratory verified actionable mutations. Fifty patients were recruited. Nineteen actionable mutations were identified in 16 (32%) patients. Across technologies, results were in agreement in 100% of biopsy specimens and 95% of archival specimens. Profiling results from paired archival/biopsy specimens were concordant in 30/34 (88%) patients. We demonstrated that the use of next generation sequencing for real-time genomic profiling in advanced cancer patients is feasible. Additionally, actionable mutations identified in this study were relatively stable between archival and biopsy samples, implying that cancer mutations that are good predictors of drug response may remain constant across clinical stages. Copyright © 2012 UICC.

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