| 1. |
- Abdalla, H., et al.
(författare)
-
A very-high-energy component deep in the gamma-ray burst afterglow
- 2019
-
Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 575:7783, s. 464-467
-
Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray bursts (GRBs) are brief flashes of gamma-rays and are considered to be the most energetic explosive phenomena in the Universe(1). The emission from GRBs comprises a short (typically tens of seconds) and bright prompt emission, followed by a much longer afterglow phase. During the afterglow phase, the shocked outflow-produced by the interaction between the ejected matter and the circumburst medium-slows down, and a gradual decrease in brightness is observed(2). GRBs typically emit most of their energy via.-rays with energies in the kiloelectronvolt-to-megaelectronvolt range, but a few photons with energies of tens of gigaelectronvolts have been detected by space-based instruments(3). However, the origins of such high-energy (above one gigaelectronvolt) photons and the presence of very-high-energy (more than 100 gigaelectronvolts) emission have remained elusive(4). Here we report observations of very-high-energy emission in the bright GRB 180720B deep in the GRB afterglow-ten hours after the end of the prompt emission phase, when the X-ray flux had already decayed by four orders of magnitude. Two possible explanations exist for the observed radiation: inverse Compton emission and synchrotron emission of ultrarelativistic electrons. Our observations show that the energy fluxes in the X-ray and gamma-ray range and their photon indices remain comparable to each other throughout the afterglow. This discovery places distinct constraints on the GRB environment for both emission mechanisms, with the inverse Compton explanation alleviating the particle energy requirements for the emission observed at late times. The late timing of this detection has consequences for the future observations of GRBs at the highest energies.
|
|
| 2. |
- Hibar, Derrek P., et al.
(författare)
-
Novel genetic loci associated with hippocampal volume
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (r(g) = -0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness.
|
|
| 3. |
- Segelbacher, Gernot, et al.
(författare)
-
Analyses of historical and current populations of black grouse in Central Europe reveal strong effects of genetic drift and loss of genetic diversity
- 2014
-
Ingår i: Conservation Genetics. - : Springer Science and Business Media LLC. - 1566-0621 .- 1572-9737. ; 15:5, s. 1183-1195
-
Tidskriftsartikel (refereegranskat)abstract
- Black grouse (Tetrao tetrix) in Central Europe have undergone a severe contraction of their range in recent decades with only a few small isolated remaining populations. Here we compare genetic diversity of two contemporary isolated populations (Sallandse Heuvelrug, Netherlands and Lüneburger Heide, Germany) with historical samples from the same region collected within the last one hundred years. We use markers with both putatively neutral and functional variation to test whether the present small and highly fragmented populations hold lower genetic diversity compared to the former larger population. For this we applied three different types of genetic markers: nine microsatellites and 21 single nucleotide polymorphisms (SNPs), both sets which have been found to be neutral, and two functional major histocompatibility complex (MHC) genes for which there is evidence they are under selection. The contemporary small isolated populations displayed lower neutral genetic diversity compared to the corresponding historical samples. Furthermore, samples from Denmark showed that this now extinct population displayed lower genetic variation in the period immediately prior to the local extinction. Population structure was more pronounced among contemporary populations compared to historical populations for microsatellites and SNPs. This effect was not as distinct for MHC which is consistent with the possibility that MHC has been subjected to balancing selection in the past, a process which maintains genetic variation and may minimize population structure for such markers. Genetic differentiation among the present populations highlights the strong effects of population decline on the genetic structure of natural populations, which can be ultimately attributed to habitat loss following anthropogenic land use changes.
|
|
| 4. |
- Segelbacher, Gernot, et al.
(författare)
-
Historic and current populations of black grouse in central Europe – evidence for rapid loss of genetic diversity
- 2011
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Black grouse (Tetrao tetrix) in central Europe have undergone a severe contraction of their range with only a few small isolated remaining populations. We here compare genetic diversity of two contemporary populations (Sallandse Heuvelrug, Netherlands and Lüneburger Heide, Germany) with historic samples from the same range collected decades ago. We use both neutral and MHC markers to test whether present small and highly fragmented populations hold lower genetic diversity compared to the former larger population. For this we applied three different types of genetic markers: nine microsatellites and 21 SNPs (Single Nucleotide Polymorphisms) which both have been found to be neutral, and two functional MHC (Major Histocompatibility Complex) genes that are presumably under selection. The contemporary small isolated populations displayed lower neutral genetic diversity compared to the historic samples. A similar trend was found for genotypes at MHC class II loci. Furthermore, population structure was more pronounced among contemporary populations compared to historic populations for microsatellites and SNPs. This effect was not as distinct for MHC which suggests that MHC has been subjected to balancing selection in the past, a process upholding genetic variation and minimizing population structure for such markers. As predicted from theory, drift is the most potent evolutionary processes affecting genetic variation at small population sizes. Genetic differentiation among present populations highlights the strong affects of population decline and habitat loss due to anthropogenic land use changes on genetic structure of natural populations.
|
|
| 5. |
- Strand, Tanja, 1978-, et al.
(författare)
-
Can balancing selection on MHC loci counteract genetic drift in small fragmented populations of black grouse?
- 2012
-
Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 2:2, s. 341-353
-
Tidskriftsartikel (refereegranskat)abstract
- The ability of natural populations to adapt to new environmental conditions is crucial for their survival and partly determined by the standing genetic variation in each population. Populations with higher genetic diversity are more likely to contain individuals that are better adapted to new circumstances than populations with lower genetic diversity. Here we use both neutral and MHC markers to test whether small and highly fragmented populations hold lower genetic diversity than large ones. We use black grouse as it is distributed across Europe and found in populations with varying degrees of isolation and size. We sampled eleven different populations; five continuous, three isolated and three small and isolated. We tested patterns of genetic variation in these populations using three different types of genetic markers: nine microsatellites and 21 SNPs (Single Nucleotide Polymorphisms) which both were found to be neutral, and two functional MHC (Major Histocompatibility Complex) genes that are presumably under selection. The small isolated populations displayed significantly lower neutral genetic diversity compared to continuous populations. A similar trend, but not as pronounced, was found for genotypes at MHC class II loci. Populations were less divergent at MHC genes compared to neutral markers. Measures of genetic diversity and population genetic structure were positively correlated among microsatellites and SNPs, but none of them were correlated to MHC when comparing all populations. Our results suggest that balancing selection at MHC loci does not counteract the power of genetic drift when populations get small and fragmented.
|
|
| 6. |
|
|
| 7. |
- Ivanov, Maxim, et al.
(författare)
-
Single base resolution analysis of 5-hydroxymethylcytosine in 188 human genes : implications for hepatic gene expression
- 2016
-
Ingår i: Nucleic Acids Research. - : Oxford University Press. - 0305-1048 .- 1362-4962. ; 44:14, s. 6756-6769
-
Tidskriftsartikel (refereegranskat)abstract
- To improve the epigenomic analysis of tissues rich in 5-hydroxymethylcytosine (hmC), we developed a novel protocol called TAB-Methyl-SEQ, which allows for single base resolution profiling of both hmC and 5-methylcytosine by targeted next-generation sequencing. TAB-Methyl-SEQ data were extensively validated by a set of five methodologically different protocols. Importantly, these extensive cross-comparisons revealed that protocols based on Tet1-assisted bisulfite conversion provided more precise hmC values than TrueMethyl-based methods. A total of 109 454 CpG sites were analyzed by TAB-Methyl-SEQ for mC and hmC in 188 genes from 20 different adult human livers. We describe three types of variability of hepatic hmC profiles: (i) sample-specific variability at 40.8% of CpG sites analyzed, where the local hmC values correlate to the global hmC content of livers (measured by LC-MS), (ii) gene-specific variability, where hmC levels in the coding regions positively correlate to expression of the respective gene and (iii) site-specific variability, where prominent hmC peaks span only 1 to 3 neighboring CpG sites. Our data suggest that both the gene-and site-specific components of hmC variability might contribute to the epigenetic control of hepatic genes. The protocol described here should be useful for targeted DNA analysis in a variety of applications.
|
|
| 8. |
|
|
| 9. |
- Kamae, Tuneyoshi, et al.
(författare)
-
PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter
- 2008
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 30:2, s. 72-84
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.
|
|
| 10. |
- Penell, Johanna, et al.
(författare)
-
Genetic variation in the CYP2B6 Gene is related to circulating 2,2 ',4,4 '-tetrabromodiphenyl ether (BDE-47) concentrations : an observational population-based study
- 2014
-
Ingår i: Environmental Health. - London : BioMed Central (BMC). - 1476-069X. ; 13, s. 34-
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Since human CYP2B6 has been identified as the major CYP enzyme involved in the metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and that human 2B6 is a highly polymorphic CYP, with known functional variants, we evaluated if circulating concentrations of a major brominated flame retardant, BDE-47, were related to genetic variation in the CYP2B6 gene in a population sample.Methods: In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (men and women all aged 70), 25 single nucleotide polymorphisms (SNPs) in the CYP2B6 gene were genotyped. Circulating concentrations of BDE-47 were analyzed by high-resolution gas chromatography coupled to high-resolution mass spectrometry (HRGC/HRMS).Results: Several SNPs in the CYP2B6 gene were associated with circulating concentrations of BDE-47 (P = 10(- 4) to 10(-9)). The investigated SNPs came primarily from two haplotypes, although the correlation between the haplotypes was rather high. Conditional analyses adjusting for the SNP with the strongest association with the exposure (rs2014141) did not provide evidence for independent signals.Conclusion: Circulating concentrations of BDE-47 were related to genetic variation in the CYP2B6 gene in an elderly population.
|
|
