102 research outputs found
User acceptability of saliva and gargle samples for identifying COVID-19 positive high-risk workers
N-body Models of Rotating Globular Clusters
We have studied the dynamical evolution of rotating globular clusters with
direct -body models. Our initial models are rotating King models; we
obtained results for both equal-mass systems and systems composed out of two
mass components. Previous investigations using a Fokker-Planck solver have
revealed that rotation has a noticeable influence on stellar systems like
globular clusters, which evolve by two-body relaxation. In particular, it
accelerates their dynamical evolution through the gravogyro instability. We
have validated the occurence of the gravogyro instability with direct -body
models. In the case of systems composed out of two mass components, mass
segregation takes place, which competes with the rotation in the acceleration
of the core collapse. The "accelerating" effect of rotation has not been
detected in our isolated two-mass -body models. Last, but not least, we have
looked at rotating -body models in a tidal field within the tidal
approximation. It turns out that rotation increases the escape rate
significantly. A difference between retrograde and prograde rotating star
clusters occurs with respect to the orbit of the star cluster around the
Galaxy, which is due to the presence of a ``third integral'' and chaotic
scattering, respectively.Comment: 16 pages, 17 figures, accepted by MNRA
Radial velocities in the globular cluster omega Centauri
We have used the ARGUS multi-object spectrometer at the CTIO 4m Blanco
telescope to obtain 2756 radial velocity measurements for 1966 individual stars
in the globular cluster omega Centauri brighter than blue photographic
magnitude of about 16.5. Of these, 1589 stars are cluster members. A comparison
with two independent radial velocity studies, carried out by Suntzeff & Kraft
and by Mayor et al., demonstrates that the median error of our measurements is
below 2 km/s for the stars brighter than B-magnitude 15, which constitute the
bulk of the sample. The observed velocity dispersion decreases from about 15
km/s in the inner few arcmin to about 6 km/s at a radius of 25 arcmin. The
cluster shows significant rotation, with a maximum amplitude of about 6 km/s in
the radial zone between 6 and 10 arcmin. In a companion paper by van de Ven et
al., we correct these radial velocities for the perspective rotation caused by
the space motion of the cluster, and combine them with the internal proper
motions of nearly 8000 cluster members measured by van Leeuwen et al., to
construct a detailed dynamical model of omega Centauri and to measure its
distance.Comment: 10 pages (7 figures), accepted for publication in A&
RNase H2, mutated in Aicardi-GoutiĆØres syndrome, promotes LINE-1 retrotransposition
Long INterspersed Element class 1 (LINE-1) elements are a type of
abundant retrotransposons active in mammalian genomes. An
average human genome contains ~100 retrotransposition-competent
LINE-1s, whose activity is influenced by the combined action
of cellular repressors and activators. TREX1, SAMHD1 and ADAR1
are known LINE-1 repressors and when mutated cause the autoinflammatory
disorder Aicardi-GoutiĆØres syndrome (AGS). Mutations
in RNase H2 are the most common cause of AGS, and its activity
was proposed to similarly control LINE-1 retrotransposition. It has
therefore been suggested that increased LINE-1 activity may be
the cause of aberrant innate immune activation in AGS. Here, we
establish that, contrary to expectations, RNase H2 is required for
efficient LINE-1 retrotransposition. As RNase H1 overexpression
partially rescues the defect in RNase H2 null cells, we propose a
model in which RNase H2 degrades the LINE-1 RNA after reverse
transcription, allowing retrotransposition to be completed. This
also explains how LINE-1 elements can retrotranspose efficiently
without their own RNase H activity. Our findings appear to be at
odds with LINE-1-derived nucleic acids driving autoinflammation
in AGS.M.B.-G. is funded by a āFormacion Profesorado
Universitarioā (FPU) PhD fellowship from the Government of Spain (MINECO,
Ref FPU15/03294), and this paper is part of her thesis project (āEpigenetic
control of the mobility of a human retrotransposonā). R.V.-A. is funded by a
PFIS Fellowship from the Government of Spain (ISCiii, FI16/00413). O.M. is
funded by an EMBO Long-Term Fellowship (ALTF 7-2015), the European
Commission FP7 (Marie Curie Actions, LTFCOFUND2013, GA-2013-609409) and
the Swiss National Science Foundation (P2ZHP3_158709). S.R.H. is funded by
the Government of Spain (MINECO, RYC-2016-21395 and SAF2015-71589-P).
A.P.Jās laboratory is supported by the UK Medical Research Council (MRC University Unit grant U127527202). J.L.G.Pās laboratory is supported by CICEFEDER-
P12-CTS-2256, Plan Nacional de I+D+I 2008-2011 and 2013-2016 (FISFEDER-
PI14/02152), PCIN-2014-115-ERA-NET NEURON II, the European
Research Council (ERC-Consolidator ERC-STG-2012-233764), by an International
Early Career Scientist grant from the Howard Hughes Medical Institute
(IECS-55007420), by The Wellcome Trust-University of Edinburgh Institutional
Strategic Support Fund (ISFF2) and by a private donation from Ms Francisca
Serrano (Trading y Bolsa para Torpes, Granada, Spain)
When TADs go bad: chromatin structure and nuclear organisation in human disease
Chromatin in the interphase nucleus is organised as a hierarchical series of structural domains, including self-interacting domains called topologically associating domains (TADs). This arrangement is thought to bring enhancers into closer physical proximity with their target genes, which often are located hundreds of kilobases away in linear genomic distance. TADs are demarcated by boundary regions bound by architectural proteins, such as CTCF and cohesin, although much remains to be discovered about the structure and function of these domains. Recent studies of TAD boundaries disrupted in engineered mouse models show that boundary mutations can recapitulate human developmental disorders as a result of aberrant promoter-enhancer interactions in the affected TADs. Similar boundary disruptions in certain cancers can result in oncogene overexpression, and CTCF binding sites at boundaries appear to be hyper-mutated across cancers. Further insights into chromatin organisation, in parallel with accumulating whole genome sequence data for disease cohorts, are likely to yield additional valuable insights into the roles of noncoding sequence variation in human disease
The non-peculiar velocity dispersion profile of the stellar system omega Centauri
We present the results of a survey of radial velocities over a wide region
extending from r~10 arcmin out to r~80 arcmin (~1.5 tidal radii) within the
massive star cluster omega Centauri. The survey was performed with FLAMES@VLT,
to study the velocity dispersion profile in the outer regions of this stellar
system. We derived accurate radial velocities for a sample of 2557 newly
observed stars, identifying 318 bona-fide cluster red giants. Merging our data
with those provided by Pancino et al. (2007), we assembled a final homogeneous
sample of 946 cluster members that allowed us to trace the velocity dispersion
profile from the center out to r~32 arcmin. The velocity dispersion appears to
decrease monotonically over this range, from a central value of sigma_{v}~17.2
Km/s down to a minimum value of sigma_{v}~5.2 Km/s. The observed surface
brightness profile, rotation curve, velocity dispersion profile and ellipticity
profile are simultaneously well reproduced by a simple dynamical model in which
mass follows light, within the classical Newtonian theory of gravitation. The
comparison with an N-body model of the evolution of a system mimicking omega
Cen during the last 10 orbits into the Galactic potential suggests that (a) the
rotation of stars lying in the inner ~20 arcmin of the clusters is not due to
the effects of the tidal field of the Milky Way, as hypothized by other
authors, and (b) the overall observational scenario is still compatible with
the possibility that the outer regions of the cluster are subject to some tidal
stirring.Comment: 12 pages, 12 figures, accepted for publication by MNRA
PCNA directs type 2 RNase H activity on DNA replication and repair substrates
Ribonuclease H2 is the major nuclear enzyme degrading cellular RNA/DNA hybrids in eukaryotes and the sole nuclease known to be able to hydrolyze ribonucleotides misincorporated during genomic replication. Mutation in RNASEH2 causes AicardiāGoutiĆØres syndrome, an auto-inflammatory disorder that may arise from nucleic acid byproducts generated during DNA replication. Here, we report the crystal structures of Archaeoglobus fulgidus RNase HII in complex with PCNA, and human PCNA bound to a C-terminal peptide of RNASEH2B. In the archaeal structure, three binding modes are observed as the enzyme rotates about a flexible hinge while anchored to PCNA by its PIP-box motif. PCNA binding promotes RNase HII activity in a hinge-dependent manner. It enhances both cleavage of ribonucleotides misincorporated in DNA duplexes, and the comprehensive hydrolysis of RNA primers formed during Okazaki fragment maturation. In addition, PCNA imposes strand specificity on enzyme function, and by localizing RNase H2 and not RNase H1 to nuclear replication foci in vivo it ensures that RNase H2 is the dominant RNase H activity during nuclear replication. Our findings provide insights into how type 2 RNase H activity is directed during genome replication and repair, and suggest a mechanism by which RNase H2 may suppress generation of immunostimulatory nucleic acids
Chromatin loop anchors are associated with genome instability in cancer and recombination hotspots in the germline
Abstract Background Chromatin loops form a basic unit of interphase nuclear organization, with chromatin loop anchor points providing contacts between regulatory regions and promoters. However, the mutational landscape at these anchor points remains under-studied. Here, we describe the unusual patterns of somatic mutations and germline variation associated with loop anchor points and explore the underlying features influencing these patterns. Results Analyses of whole genome sequencing datasets reveal that anchor points are strongly depleted for single nucleotide variants (SNVs) in tumours. Despite low SNV rates in their genomic neighbourhood, anchor points emerge as sites of evolutionary innovation, showing enrichment for structural variant (SV) breakpoints and a peak of SNVs at focal CTCF sites within the anchor points. Both CTCF-bound and non-CTCF anchor points harbour an excess of SV breakpoints in multiple tumour types and are prone to double-strand breaks in cell lines. Common fragile sites, which are hotspots for genome instability, also show elevated numbers of intersecting loop anchor points. Recurrently disrupted anchor points are enriched for genes with functions in cell cycle transitions and regions associated with predisposition to cancer. We also discover a novel class of CTCF-bound anchor points which overlap meiotic recombination hotspots and are enriched for the core PRDM9 binding motif, suggesting that the anchor points have been foci for diversity generated during recent human evolution. Conclusions We suggest that the unusual chromatin environment at loop anchor points underlies the elevated rates of variation observed, marking them as sites of regulatory importance but also genomic fragility
Polymerase Ī“ replicates both strands after homologous recombination-dependent fork restart
To maintain genetic stability DNA must be replicated only once and replication completed even when individual replication forks are inactivated. Because fork inactivation is common, the passive convergence of an adjacent fork is insufficient to rescue all inactive forks. Thus, eukaryotic cells have evolved homologous recombination-dependent mechanisms to restart persistent inactive forks. Completing DNA synthesis via Homologous Recombination Restarted Replication (HoRReR) ensures cell survival, but at a cost. One such cost is increased mutagenesis caused by HoRReR being more error prone than canonical replication. This increased error rate implies that the HoRReR mechanism is distinct from that of a canonical fork. Here we exploit the fission yeast Schizosaccharomyces pombe to demonstrate that a DNA sequence duplicated by HoRReR during S phase is replicated semi-conservatively, but that both the leading and lagging strands are synthesised by DNA polymerase delta
Ribonuclease H2 mutations induce a cGAS/STING-dependent innate immune response
AicardiāGoutiĆØres syndrome (AGS) provides a monogenic model of nucleic acidāmediated inflammation relevant to the pathogenesis of systemic autoimmunity. Mutations that impair ribonuclease (RNase) H2 enzyme function are the most frequent cause of this autoinflammatory disorder of childhood and are also associated with systemic lupus erythematosus. Reduced processing of either RNA:DNA hybrid or genomeāembedded ribonucleotide substrates is thought to lead to activation of a yet undefined nucleic acidāsensing pathway. Here, we establish Rnaseh2b (A174T/A174T) knockāin mice as a subclinical model of disease, identifying significant interferonāstimulated gene (ISG) transcript upregulation that recapitulates the ISG signature seen in AGS patients. The inflammatory response is dependent on the nucleic acid sensor cyclic GMPāAMP synthase (cGAS) and its adaptor STING and is associated with reduced cellular ribonucleotide excision repair activity and increased DNA damage. This suggests that cGAS/STING is a key nucleic acidāsensing pathway relevant to AGS, providing additional insight into disease pathogenesis relevant to the development of therapeutics for this childhoodāonset interferonopathy and adult systemic autoimmune disorders
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