828 research outputs found
The vimentin-tubulin binding site peptide (Vim-TBS.58-81) crosses the plasma membrane and enters the nuclei of human glioma cells
Cell-penetrating peptides (CPPs) can translocate through the plasma membrane and localize in different cell compartments providing a promising delivery system for peptides, proteins, nucleic acids, and other products. Here we describe features of a novel cell-penetrating peptide derived from the intermediate filament protein vimentin, called Vim-TBS.58-81. We show that it enters cells from a glioblastoma line via endocytosis where it distributes throughout the cytoplasm and nucleus. Moreover, when coupled to the pro-apoptogenic peptide P10, it localizes to the nucleus inhibiting cell proliferation. Thus, the Vim-TBS.58-81 peptide represents an effective vector for delivery of peptides and potentially a broad range of cargos to the nucleus
Stable tubule only polypeptides (STOP) proteins co-aggregate with spheroid neurofilaments in amyotrophic lateral sclerosis
A major cytopathological hallmark of amyotrophic lateral sclerosis (ALS) is the presence of axonal spheroids containing abnormally accumulated neurofilaments. The mechanism of their formation, their contribution to the disease, and the possibility of other co-aggregated components are still enigmatic. Here we analyze the composition of such lesions with special reference to stable tubule only polypeptide (STOP), a protein responsible for microtubule cold stabilization. In normal human brain and spinal cord, the distribution of STOP proteins is uniform between the cytoplasm and neurites of neurons. However, all the neurofilament-rich spheroids present in the tissues of affected patients are intensely labeled with 3 different anti-STOP antibodies. Moreover, when neurofilaments and microtubules are isolated from spinal cord and brain, STOP proteins are systematically co-purified with neurofilaments. By SDS-PAGE analysis, no alteration of the migration profile of STOP proteins is observed in pathological samples. Other microtubular proteins, like tubulin or kinesin, are inconstantly present in spheroids, suggesting that a microtubule destabilizing process may be involved in the pathogenesis of ALS. These results indicate that the selective co-aggregation of neurofilament and STOP proteins represent a new cytopathological marker for spheroids
Investigating Cepheid Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry
Baade-Wesselink-type (BW) techniques enable geometric distance measurements
of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading
uncertainties involved concern projection factors required to translate
observed radial velocities (RVs) to pulsational velocities and recently
discovered modulated variability. We carried out an unprecedented observational
campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy
(Euler/Coralie) to search for modulated variability in the long-period (P
35.5 d) Cepheid Carinae. We determine highly precise angular diameters
from squared visibilities and investigate possible differences between two
consecutive maximal diameters, . We characterize the
modulated variability along the line-of-sight using 360 high-precision RVs.
Here we report tentative evidence for modulated angular variability and confirm
cycle-to-cycle differences of Carinae's RV variability. Two successive
maxima yield = 13.1 0.7 (stat.) {\mu}as for
uniform disk models and 22.5 1.4 (stat.) {\mu}as (4% of the total angular
variation) for limb-darkened models. By comparing new RVs with 2014 RVs we show
modulation to vary in strength. Barring confirmation, our results suggest the
optical continuum (traced by interferometry) to be differently affected by
modulation than gas motions (traced by spectroscopy). This implies a previously
unknown time-dependence of projection factors, which can vary by 5% between
consecutive cycles of expansion and contraction. Additional interferometric
data are required to confirm modulated angular diameter variations. By
understanding the origin of modulated variability and monitoring its long-term
behavior, we aim to improve the accuracy of BW distances and further the
understanding of stellar pulsations.Comment: Accepted for publication in MNRAS. 19 pages, 13 figures, 10 table
Neurofilament high molecular weight-green fluorescent protein fusion is normally expressed in neurons and transported in axons: a neuronal marker to investigate the biology of neurofilaments
The carboxy-terminal side arm of the neurofilament high subunit consists of a highly phosphorylated domain and a negatively charged region. Multiple evidences suggested that these domains are essential for the axonal phosphorylation and transport of neurofilaments and play a role in their abnormal accumulation following chemical intoxication or during neurodegenerative disorders such as amyotrophic lateral sclerosis. In order to investigate the consequences of altering this side arm of neurofilament high subunit we used a fusion protein (neurofilament high subunit-green fluorescent protein) between the mouse neurofilament high subunit missing a major part of the C-terminal domain and the reporter green fluorescent protein. In cell culture and in transgenic mice this fusion protein co-assembles and co-distributes with the endogenous intermediate filament network. Conditions known to disturb the cytoskeleton were also found to alter the distribution of the fusion protein in cell cultures. In transgenic mice the expression of the transgene evaluated by its fluorescent properties was found to be restricted to neurons, where the neurofilament high subunit-green fluorescent protein fusion protein is axonally transported. Biochemical approaches showed that the fusion protein is phosphorylated and co-purified with neurofilaments. Despite the presence of such an neurofilament high subunit-green fluorescent protein fusion protein, the axonal cytoskeletal density and the axonal caliber were not altered. Together these data show that removal of this portion of neurofilament high subunit does not affect the capacity of neurofilament high subunit to assemble and to be transported into axons, suggesting that this sequence is involved in another function. Moreover, the fluorescent properties of this fusion protein represent a useful marker
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
Determination of rotation periods in solar-like stars with irregular sampling: the Gaia case
We present a study on the determination of rotation periods (P) of solar-like
stars from the photometric irregular time-sampling of the ESA Gaia mission,
currently scheduled for launch in 2013, taking into account its dependence on
ecliptic coordinates. We examine the case of solar-twins as well as thousands
of synthetic time-series of solar-like stars rotating faster than the Sun. In
the case of solar twins we assume that the Gaia unfiltered photometric passband
G will mimic the variability of the total solar irradiance (TSI) as measured by
the VIRGO experiment. For stars rotating faster than the Sun, light-curves are
simulated using synthetic spectra for the quiet atmosphere, the spots, and the
faculae combined by applying semi-empirical relationships relating the level of
photospheric magnetic activity to the stellar rotation and the Gaia
instrumental response. The capabilities of the Deeming, Lomb-Scargle, and Phase
Dispersion Minimisation methods in recovering the correct rotation periods are
tested and compared. The false alarm probability (FAP) is computed using Monte
Carlo simulations and compared with analytical formulae. The Gaia scanning law
makes the rate of correct detection of rotation periods strongly dependent on
the ecliptic latitude (beta). We find that for P ~ 1 d, the rate of correct
detection increases with ecliptic latitude from 20-30 per cent at beta ~
0{\deg} to a peak of 70 per cent at beta=45{\deg}, then it abruptly falls below
10 per cent at beta > 45{\deg}. For P > 5 d, the rate of correct detection is
quite low and for solar twins is only 5 per cent on average.Comment: 12 pages, 18 figures, accepted by MNRA
Variability-selected quasars behind the Small Magellanic Cloud
We present followup spectroscopic observations of quasar candidates in the
Small Magellanic Cloud selected by Eyer from the OGLE database. Of twelve
observed objects identified as "QSO Candidate", five are confirmed quasars,
with the emission redshifts ranging from 0.28 to 2.16. Two of those quasars
were also recently identified independently in the MACHO database by Geha et
al. We discuss the prospects of using variability-based selection technique for
quasar searches behind other dense stellar fields. An additional criterion
utilizing the color-color diagram should reduce the number of stars in the
candidate lists.Comment: Revised version, AASTeX, 11 pages, 3 EPS figures, one table, accepted
14 Nov 2002 for publication in the Astronomical Journal, March 2003 issu
Four New Delta Scuti Pulsators from a Variability Survey of 131 Stars
In a photometric variability survey of 131 stars with B < 14 mag, we have
found four new Delta Scuti stars. We were sensitive to oscillation amplitudes
as low as a few mmag. The detection rate of short-period (P < 0.1 d) pulsating
variable stars, which may be relevant for planned large variability surveys
such as GAIA, POI, and even the LSST, was therefore 3%. All four new variable
stars have low pulsation amplitude (tens of mmag), and one has a very short
period (0.0198 d). This star is one of the fastest known Delta Scuti pulsators.
The short period of this variable star makes it observationally tractable, and
it may therefore be a particularly good candidate for asteroseismological
studies. All four new variable stars will add to the cadre of low-amplitude and
relatively short-period Delta Scuti stars that are potentially useful for
learning about the structure of stars on or near the main sequence, slightly
more massive than the Sun.Comment: To appear in the June 2002 issue of PASP, 9 pages, 6 figure
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