384 research outputs found
Parameter estimation for robust HMM analysis of ChIP-chip data
Tiling arrays are an important tool for the study of transcriptional activity, protein-DNA interactions and chromatin structure on a genome-wide scale at high resolution. Although hidden Markov models have been used successfully to analyse tiling array data, parameter estimation for these models is typically ad hoc. Especially in the context of ChIP-chip experiments, no standard procedures exist to obtain parameter estimates from the data. Common methods for the calculation of maximum likelihood estimates such as the Baum-Welch algorithm or Viterbi training are rarely applied in the context of tiling array analysis. Results: Here we develop a hidden Markov model for the analysis of chromatin structure ChIP-chip tiling array data, using t emission distributions to increase robustness towards outliers. Maximum likelihood estimates are used for all model parameters. Two different approaches to parameter estimation are investigated and combined into an efficient procedure. Conclusion: We illustrate an efficient parameter estimation procedure that can be used for HMM based methods in general and leads to a clear increase in performance when compared to the use of ad hoc estimates. The resulting hidden Markov model outperforms established methods like TileMap in the context of histone modification studies.13 page(s
Association of Trauma Molecular Endotypes With Differential Response to Transfusion Resuscitation Strategies
IMPORTANCE: It is not clear which severely injured patients with hemorrhagic shock may benefit most from a 1:1:1 vs 1:1:2 (plasma:platelets:red blood cells) resuscitation strategy. Identification of trauma molecular endotypes may reveal subgroups of patients with differential treatment response to various resuscitation strategies.
OBJECTIVE: To derive trauma endotypes (TEs) from molecular data and determine whether these endotypes are associated with mortality and differential treatment response to 1:1:1 vs 1:1:2 resuscitation strategies.
DESIGN, SETTING, AND PARTICIPANTS: This was a secondary analysis of the Pragmatic, Randomized Optimal Platelet and Plasma Ratios (PROPPR) randomized clinical trial. The study cohort included individuals with severe injury from 12 North American trauma centers. The cohort was taken from the participants in the PROPPR trial who had complete plasma biomarker data available. Study data were analyzed on August 2, 2021, to October 25, 2022.
EXPOSURES: TEs identified by K-means clustering of plasma biomarkers collected at hospital arrival.
MAIN OUTCOMES AND MEASURES: An association between TEs and 30-day mortality was tested using multivariable relative risk (RR) regression adjusting for age, sex, trauma center, mechanism of injury, and injury severity score (ISS). Differential treatment response to transfusion strategy was assessed using an RR regression model for 30-day mortality by incorporating an interaction term for the product of endotype and treatment group adjusting for age, sex, trauma center, mechanism of injury, and ISS.
RESULTS: A total of 478 participants (median [IQR] age, 34.5 [25-51] years; 384 male [80%]) of the 680 participants in the PROPPR trial were included in this study analysis. A 2-class model that had optimal performance in K-means clustering was found. TE-1 (n = 270) was characterized by higher plasma concentrations of inflammatory biomarkers (eg, interleukin 8 and tumor necrosis factor α) and significantly higher 30-day mortality compared with TE-2 (n = 208). There was a significant interaction between treatment arm and TE for 30-day mortality. Mortality in TE-1 was 28.6% with 1:1:2 treatment vs 32.6% with 1:1:1 treatment, whereas mortality in TE-2 was 24.5% with 1:1:2 treatment vs 7.3% with 1:1:1 treatment (P for interaction = .001).
CONCLUSIONS AND RELEVANCE: Results of this secondary analysis suggest that endotypes derived from plasma biomarkers in trauma patients at hospital arrival were associated with a differential response to 1:1:1 vs 1:1:2 resuscitation strategies in trauma patients with severe injury. These findings support the concept of molecular heterogeneity in critically ill trauma populations and have implications for tailoring therapy for patients at high risk for adverse outcomes
GW190425: Pan-STARRS and ATLAS coverage of the skymap and limits on optical emission associated with FRB190425
GW190425 is the second of only two binary neutron star (BNS) merger events to
be significantly detected by the LIGO-Virgo- Kagra gravitational wave
detectors. With a detection only in LIGO Livingston, the skymap containing the
source was large and no plausible electromagnetic counterpart was found in real
time searching in 2019. Here we summarise our ATLAS and Pan-STARRS wide-field
optical coverage of the skymap beginning within 1 hour and 3 hours respectively
of the GW190425 merger time. More recently, a potential coincidence between
GW190425 and a fast radio burst FRB 190425 has been suggested, given their
spatial and temporal coincidence. The smaller sky localisation area of FRB
190425 and its dispersion measure have led to the identification of a likely
host galaxy, UGC 10667 at a distance of 141 +/- 10 Mpc. Our optical imaging
covered the galaxy 6.0 hrs after GW190425 was detected and 3.5 hrs after the
FRB 190425. No optical emission was detected and further imaging at +1.2 and
+13.2 days also revealed no emission. If the FRB 190425 and GW190425
association were real, we highlight our limits on kilonova emission from a BNS
merger in UGC 10667. The model for producing FRB 190425 from a BNS merger
involves a supramassive magnetised neutron star spinning down by dipole
emission on the timescale of hours. We show that magnetar enhanced kilonova
emission is ruled out by optical upper limits. The lack of detected optical
emission from a kilonova in UGC 10667 disfavours, but does not disprove, the
FRB-GW link for this source.Comment: Submitted to MNRAS, 20th Sept 2023, 9 page
ChIPseqR: analysis of ChIP-seq experiments
<p>Abstract</p> <p>Background</p> <p>The use of high-throughput sequencing in combination with chromatin immunoprecipitation (ChIP-seq) has enabled the study of genome-wide protein binding at high resolution. While the amount of data generated from such experiments is steadily increasing, the methods available for their analysis remain limited. Although several algorithms for the analysis of ChIP-seq data have been published they focus almost exclusively on transcription factor studies and are usually not well suited for the analysis of other types of experiments.</p> <p>Results</p> <p>Here we present ChIPseqR, an algorithm for the analysis of nucleosome positioning and histone modification ChIP-seq experiments. The performance of this novel method is studied on short read sequencing data of <it>Arabidopsis thaliana </it>mononucleosomes as well as on simulated data.</p> <p>Conclusions</p> <p>ChIPseqR is shown to improve sensitivity and spatial resolution over existing methods while maintaining high specificity. Further analysis of predicted nucleosomes reveals characteristic patterns in nucleosome sequences and placement.</p
Modulation of enhancer looping and differential gene targeting by Epstein-Barr virus transcription factors directs cellular reprogramming
Epstein-Barr virus (EBV) epigenetically reprogrammes B-lymphocytes to drive immortalization and facilitate viral persistence. Host-cell transcription is perturbed principally through the actions of EBV EBNA 2, 3A, 3B and 3C, with cellular genes deregulated by specific combinations of these EBNAs through unknown mechanisms. Comparing human genome binding by these viral transcription factors, we discovered that 25% of binding sites were shared by EBNA 2 and the EBNA 3s and were located predominantly in enhancers. Moreover, 80% of potential EBNA 3A, 3B or 3C target genes were also targeted by EBNA 2, implicating extensive interplay between EBNA 2 and 3 proteins in cellular reprogramming. Investigating shared enhancer sites neighbouring two new targets (WEE1 and CTBP2) we discovered that EBNA 3 proteins repress transcription by modulating enhancer-promoter loop formation to establish repressive chromatin hubs or prevent assembly of active hubs. Re-ChIP analysis revealed that EBNA 2 and 3 proteins do not bind simultaneously at shared sites but compete for binding thereby modulating enhancer-promoter interactions. At an EBNA 3-only intergenic enhancer site between ADAM28 and ADAMDEC1 EBNA 3C was also able to independently direct epigenetic repression of both genes through enhancer-promoter looping. Significantly, studying shared or unique EBNA 3 binding sites at WEE1, CTBP2, ITGAL (LFA-1 alpha chain), BCL2L11 (Bim) and the ADAMs, we also discovered that different sets of EBNA 3 proteins bind regulatory elements in a gene and cell-type specific manner. Binding profiles correlated with the effects of individual EBNA 3 proteins on the expression of these genes, providing a molecular basis for the targeting of different sets of cellular genes by the EBNA 3s. Our results therefore highlight the influence of the genomic and cellular context in determining the specificity of gene deregulation by EBV and provide a paradigm for host-cell reprogramming through modulation of enhancer-promoter interactions by viral transcription factors
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
PS18kh: A New Tidal Disruption Event with a Non-Axisymmetric Accretion Disk
We present the discovery of PS18kh, a tidal disruption event (TDE) discovered
at the center of SDSS J075654.53+341543.6 ( Mpc) by the Pan-STARRS
Survey for Transients. Our dataset includes pre-discovery survey data from
Pan-STARRS, the All-Sky Automated Survey for Supernovae (ASAS-SN), and the
Asteroid Terrestrial-impact Last Alert System (ATLAS) as well as high-cadence,
multi-wavelength follow-up data from ground-based telescopes and Swift,
spanning from 56 days before peak light until 75 days after. The optical/UV
emission from PS18kh is well-fit as a blackbody with temperatures ranging from
K to K and it peaked at a luminosity of
ergs s. PS18kh radiated
ergs over the period of observation, with
ergs being released during the rise to peak.
Spectra of PS18kh show a changing, boxy/double-peaked H emission
feature, which becomes more prominent over time. We use models of
non-axisymmetric accretion disks to describe the profile of the H line
and its evolution. We find that at early times the high accretion rate leads
the disk to emit a wind which modifies the shape of the line profile and makes
it bell-shaped. At late times, the wind becomes optically thin, allowing the
non-axisymmetric perturbations to show up in the line profile. The
line-emitting portion of the disk extends from to
an outer radius of and the perturbations can be
represented either as an eccentricity in the outer rings of the disk or as a
spiral arm in the inner disk.Comment: 27 pages, 13 figures, 8 tables. Updated to reflect changes made in
the published version. A table containing the host-subtracted photometry
presented in this manuscript is included in machine-readable format as an
ancillary fil
A 220-nucleotide deletion of the intronic enhancer reveals an epigenetic hierarchy in immunoglobulin heavy chain locus activation
A tissue-specific transcriptional enhancer, Eμ, has been implicated in developmentally regulated recombination and transcription of the immunoglobulin heavy chain (IgH) gene locus. We demonstrate that deleting 220 nucleotides that constitute the core Eμ results in partially active locus, characterized by reduced histone acetylation, chromatin remodeling, transcription, and recombination, whereas other hallmarks of tissue-specific locus activation, such as loss of H3K9 dimethylation or gain of H3K4 dimethylation, are less affected. These observations define Eμ-independent and Eμ-dependent phases of locus activation that reveal an unappreciated epigenetic hierarchy in tissue-specific gene expression
The Insulator Binding Protein CTCF Positions 20 Nucleosomes around Its Binding Sites across the Human Genome
Chromatin structure plays an important role in modulating the accessibility of genomic DNA to regulatory proteins in eukaryotic cells. We performed an integrative analysis on dozens of recent datasets generated by deep-sequencing and high-density tiling arrays, and we discovered an array of well-positioned nucleosomes flanking sites occupied by the insulator binding protein CTCF across the human genome. These nucleosomes are highly enriched for the histone variant H2A.Z and 11 histone modifications. The distances between the center positions of the neighboring nucleosomes are largely invariant, and we estimate them to be 185 bp on average. Surprisingly, subsets of nucleosomes that are enriched in different histone modifications vary greatly in the lengths of DNA protected from micrococcal nuclease cleavage (106–164 bp). The nucleosomes enriched in those histone modifications previously implicated to be correlated with active transcription tend to contain less protected DNA, indicating that these modifications are correlated with greater DNA accessibility. Another striking result obtained from our analysis is that nucleosomes flanking CTCF sites are much better positioned than those downstream of transcription start sites, the only genomic feature previously known to position nucleosomes genome-wide. This nucleosome-positioning phenomenon is not observed for other transcriptional factors for which we had genome-wide binding data. We suggest that binding of CTCF provides an anchor point for positioning nucleosomes, and chromatin remodeling is an important component of CTCF function
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