1,898 research outputs found
Replication stress caused by low MCM expression limits fetal erythropoiesis and hematopoietic stem cell functionality
Replicative stress during embryonic development influences ageing and
predisposition to disease in adults. A protective mechanism against
replicative stress is provided by the licensing of thousands of origins
in G1 that are not necessarily activated in the subsequent S-phase.
These `dormant' origins provide a backup in the presence of stalled
forks and may confer flexibility to the replication program in specific
cell types during differentiation, a role that has remained unexplored.
Here we show, using a mouse strain with hypomorphic expression of the
origin licensing factor mini-chromosome maintenance (MCM)3 that limiting
origin licensing in vivo affects the functionality of hematopoietic stem
cells and the differentiation of rapidly-dividing erythrocyte
precursors. Mcm3-deficient erythroblasts display aberrant DNA
replication patterns and fail to complete maturation, causing lethal
anemia. Our results indicate that hematopoietic progenitors are
particularly sensitive to replication stress, and full origin licensing
ensures their correct differentiation and functionality.We thank members of our laboratories for helpful discussions, Marcos
Malumbres (CNIO) for advice on the design of the Mcm3-Lox allele, Isabel
Blanco for her administrative help with mouse work and Soraya Ruiz for
excellent handling of the mouse colony in J.M.'s group. Research was
supported by the Spanish Ministry of Economy and Competitiveness (grants
BFU2013-49153-P and Consolider-Ingenio CSD2007-00015 to J.M.,
SAF2011-23753 to O.F.-C., BFU2012-35892 to J.I.) and RO1 HL092471 to
E.P., S.A. was the recipient of an EMBO short-term fellowship to visit
E.P.'s laboratory at UCSF. We are grateful to Manuel Serrano (CNIO),
Almudena Ramiro (CNIC) and Arkaitz Ibarra (The Salk Institute, USA) for
useful comments on the manuscript.S
New record of Aedes Albopictus in a suburban area of Merida, Yucatan, Mexico
Along with Aedes aegypti (L.), Aedes albopictus has been implicated as a secondary vector for dengue virus, chikungunya virus, and Zika virus in Latin America. The article covers an entomological survey in 2018, in a suburban area of Merida (the largest and capital city in Yucatan). This is the first report of Ae. albopictus in a suburban area of Merida City. A total of 259 specimens were collected. It is important to consider the ecology of Ae. albopictus alongside that of Ae. aegypti when developing vector/disease control programs
MAGIC observations of MWC 656, the only known Be/BH system
Context: MWC 656 has recently been established as the first observationally
detected high-mass X-ray binary system containing a Be star and a black hole
(BH). The system has been associated with a gamma-ray flaring event detected by
the AGILE satellite in July 2010. Aims: Our aim is to evaluate if the MWC 656
gamma-ray emission extends to very high energy (VHE > 100 GeV) gamma rays.
Methods. We have observed MWC 656 with the MAGIC telescopes for 23 hours
during two observation periods: between May and June 2012 and June 2013. During
the last period, observations were performed contemporaneously with X-ray
(XMM-Newton) and optical (STELLA) instruments. Results: We have not detected
the MWC 656 binary system at TeV energies with the MAGIC Telescopes in either
of the two campaigns carried out. Upper limits (ULs) to the integral flux above
300 GeV have been set, as well as differential ULs at a level of 5% of
the Crab Nebula flux. The results obtained from the MAGIC observations do not
support persistent emission of very high energy gamma rays from this system at
a level of 2.4% the Crab flux.Comment: Accepted for publication in A&A. 5 pages, 2 figures, 2 table
The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in
the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent
a series of upgrades, involving the exchange of the MAGIC-I camera and its
trigger system, as well as the upgrade of the readout system of both
telescopes. We use observations of the Crab Nebula taken at low and medium
zenith angles to assess the key performance parameters of the MAGIC stereo
system. For low zenith angle observations, the standard trigger threshold of
the MAGIC telescopes is ~50GeV. The integral sensitivity for point-like sources
with Crab Nebula-like spectrum above 220GeV is (0.66+/-0.03)% of Crab Nebula
flux in 50 h of observations. The angular resolution, defined as the sigma of a
2-dimensional Gaussian distribution, at those energies is < 0.07 degree, while
the energy resolution is 16%. We also re-evaluate the effect of the systematic
uncertainty on the data taken with the MAGIC telescopes after the upgrade. We
estimate that the systematic uncertainties can be divided in the following
components: < 15% in energy scale, 11-18% in flux normalization and +/-0.15 for
the energy spectrum power-law slope.Comment: 21 pages, 25 figures, accepted for publication in Astroparticle
Physic
Limits to dark matter annihilation cross-section from a combined analysis of MAGIC and Fermi-LAT observations of dwarf satellite galaxies
We present the first joint analysis of gamma-ray data from the MAGIC
Cherenkov telescopes and the Fermi Large Area Telescope (LAT) to search for
gamma-ray signals from dark matter annihilation in dwarf satellite galaxies. We
combine 158 hours of Segue 1 observations with MAGIC with 6-year observations
of 15 dwarf satellite galaxies by the Fermi-LAT. We obtain limits on the
annihilation cross-section for dark matter particle masses between 10 GeV and
100 TeV - the widest mass range ever explored by a single gamma-ray analysis.
These limits improve on previously published Fermi-LAT and MAGIC results by up
to a factor of two at certain masses. Our new inclusive analysis approach is
completely generic and can be used to perform a global, sensitivity-optimized
dark matter search by combining data from present and future gamma-ray and
neutrino detectors.Comment: 19 pages, 3 figures. V2: Few typos corrected and references added.
Matches published version JCAP 02 (2016) 03
Measurement of the Crab Nebula spectrum over three decades in energy with the MAGIC telescopes
The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between
October 2009 and April 2011. Analysis of this data sample using the latest
improvements in the MAGIC stereoscopic software provided an unprecedented
precision of spectral and night-by-night light curve determination at gamma
rays. We derived a differential spectrum with a single instrument from 50 GeV
up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC
results, combined with Fermi-LAT data, show a flat and broad Inverse Compton
peak. The overall fit to the data between 1 GeV and 30 TeV is not well
described by a log-parabola function. We find that a modified log-parabola
function with an exponent of 2.5 instead of 2 provides a good description of
the data (). Using systematic uncertainties of red the MAGIC and
Fermi-LAT measurements we determine the position of the Inverse Compton peak to
be at (53 3stat + 31syst -13syst) GeV, which is the most precise
estimation up to date and is dominated by the systematic effects. There is no
hint of the integral flux variability on daily scales at energies above 300 GeV
when systematic uncertainties are included in the flux measurement. We consider
three state- of-the-art theoretical models to describe the overall spectral
energy distribution of the Crab Nebula. The constant B-field model cannot
satisfactorily reproduce the VHE spectral measurements presented in this work,
having particular difficulty reproducing the broadness of the observed IC peak.
Most probably this implies that the assumption of the homogeneity of the
magnetic field inside the nebula is incorrect. On the other hand, the
time-dependent 1D spectral model provides a good fit of the new VHE results
when considering a 80 {\mu}G magnetic field. However, it fails to match the
data when including the morphology of the nebula at lower wavelengths.Comment: accepted by JHEAp, 9 pages, 6 figure
Multi-Wavelength Observations of the Blazar 1ES 1011+496 in Spring 2008
The BL Lac object 1ES 1011+496 was discovered at Very High Energy gamma-rays
by MAGIC in spring 2007. Before that the source was little studied in different
wavelengths. Therefore a multi-wavelength (MWL) campaign was organized in
spring 2008. Along MAGIC, the MWL campaign included the Metsahovi radio
observatory, Bell and KVA optical telescopes and the Swift and AGILE
satellites. MAGIC observations span from March to May, 2008 for a total of 27.9
hours, of which 19.4 hours remained after quality cuts. The light curve showed
no significant variability. The differential VHE spectrum could be described
with a power-law function. Both results were similar to those obtained during
the discovery. Swift XRT observations revealed an X-ray flare, characterized by
a harder when brighter trend, as is typical for high synchrotron peak BL Lac
objects (HBL). Strong optical variability was found during the campaign, but no
conclusion on the connection between the optical and VHE gamma-ray bands could
be drawn. The contemporaneous SED shows a synchrotron dominated source, unlike
concluded in previous work based on nonsimultaneous data, and is well described
by a standard one zone synchrotron self Compton model. We also performed a
study on the source classification. While the optical and X-ray data taken
during our campaign show typical characteristics of an HBL, we suggest, based
on archival data, that 1ES 1011+496 is actually a borderline case between
intermediate and high synchrotron peak frequency BL Lac objects.Comment: 13 pages, accepted for publication in MNRA
MAGIC detection of short-term variability of the high-peaked BL Lac object 1ES 0806+524
The high-frequency-peaked BL Lac (HBL) 1ES 0806+524 (z = 0.138) was
discovered in VHE rays in 2008. Until now, the broad-band spectrum of
1ES 0806+524 has been only poorly characterized, in particular at high
energies. We analysed multiwavelength observations from rays to radio
performed from 2011 January to March, which were triggered by the high activity
detected at optical frequencies. These observations constitute the most precise
determination of the broad-band emission of 1ES 0806+524 to date. The
stereoscopic MAGIC observations yielded a -ray signal above 250 GeV of
per cent of the Crab Nebula flux with a statistical
significance of 9.9 . The multiwavelength observations showed
significant variability in essentially all energy bands, including a VHE
-ray flare that lasted less than one night, which provided
unprecedented evidence for short-term variability in 1ES 0806+524. The spectrum
of this flare is well described by a power law with a photon index of between 150 GeV and 1 TeV and an integral flux of
per cent of the Crab Nebula flux above 250 GeV. The spectrum during the
non-flaring VHE activity is compatible with the only available VHE observation
performed in 2008 with VERITAS when the source was in a low optical state. The
broad-band spectral energy distribution can be described with a one-zone
Synchrotron Self Compton model with parameters typical for HBLs, indicating
that 1ES 0806+524 is not substantially different from the HBLs previously
detected.Comment: 12 pages, 8 figures, 3 tables, accepted 2015 April 20 for publication
in Monthly Notices of the Royal Astronomical Society Main Journa
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