707 research outputs found
Genetic characterization of fluoroquinolone-resistant Escherichia coli associated with bovine mastitis in India
Neuroligin1: a cell adhesion molecule that recruits PSD-95 and NMDA receptors by distinct mechanisms during synaptogenesis
<p>Abstract</p> <p>Background</p> <p>The cell adhesion molecule pair neuroligin1 (Nlg1) and β-neurexin (β-NRX) is a powerful inducer of postsynaptic differentiation of glutamatergic synapses <it>in vitro</it>. Because Nlg1 induces accumulation of two essential components of the postsynaptic density (PSD) – PSD-95 and NMDA receptors (NMDARs) – and can physically bind PSD-95 and NMDARs at mature synapses, it has been proposed that Nlg1 recruits NMDARs to synapses through its interaction with PSD-95. However, PSD-95 and NMDARs are recruited to nascent synapses independently and it is not known if Nlg1 accumulates at synapses before these PSD proteins. Here, we investigate how a single type of cell adhesion molecule can recruit multiple types of synaptic proteins to new synapses with distinct mechanisms and time courses.</p> <p>Results</p> <p>Nlg1 was present in young cortical neurons in two distinct pools before synaptogenesis, diffuse and clustered. Time-lapse imaging revealed that the diffuse Nlg1 aggregated at, and the clustered Nlg1 moved to, sites of axodendritic contact with a rapid time course. Using a patching assay that artificially induced clusters of Nlg, the time course and mechanisms of recruitment of PSD-95 and NMDARs to those Nlg clusters were characterized. Patching Nlg induced clustering of PSD-95 via a slow palmitoylation-dependent step. In contrast, NMDARs directly associated with clusters of Nlg1 during trafficking. Nlg1 and NMDARs were highly colocalized in dendrites before synaptogenesis and they became enriched with a similar time course at synapses with age. Patching of Nlg1 dramatically decreased the mobility of NMDAR transport packets. Finally, Nlg1 was biochemically associated with NMDAR transport packets, presumably through binding of NMDARs to MAGUK proteins that, in turn, bind Nlg1. This interaction was essential for colocalization and co-transport of Nlg1 with NMDARs.</p> <p>Conclusion</p> <p>Our results suggest that axodendritic contact leads to rapid accumulation of Nlg1, recruitment of NMDARs co-transported with Nlg1 soon thereafter, followed by a slower, independent recruitment of PSD-95 to those nascent synapses.</p
Characterization of Salmonella Gallinarum isolates from backyard poultry by polymerase chain reaction detection of invasion (invA) and Salmonella plasmid virulence (spvC) genes
The fully connected N-dimensional skeleton: probing the evolution of the cosmic web
A method to compute the full hierarchy of the critical subsets of a density
field is presented. It is based on a watershed technique and uses a probability
propagation scheme to improve the quality of the segmentation by circumventing
the discreteness of the sampling. It can be applied within spaces of arbitrary
dimensions and geometry. This recursive segmentation of space yields, for a
-dimensional space, a succession of -dimensional subspaces that
fully characterize the topology of the density field. The final 1D manifold of
the hierarchy is the fully connected network of the primary critical lines of
the field : the skeleton. It corresponds to the subset of lines linking maxima
to saddle points, and provides a definition of the filaments that compose the
cosmic web as a precise physical object, which makes it possible to compute any
of its properties such as its length, curvature, connectivity etc... When the
skeleton extraction is applied to initial conditions of cosmological N-body
simulations and their present day non linear counterparts, it is shown that the
time evolution of the cosmic web, as traced by the skeleton, is well accounted
for by the Zel'dovich approximation. Comparing this skeleton to the initial
skeleton undergoing the Zel'dovich mapping shows that two effects are competing
during the formation of the cosmic web: a general dilation of the larger
filaments that is captured by a simple deformation of the skeleton of the
initial conditions on the one hand, and the shrinking, fusion and disappearance
of the more numerous smaller filaments on the other hand. Other applications of
the N dimensional skeleton and its peak patch hierarchy are discussed.Comment: Accepted for publication in MNRA
Fractional Action Cosmology with Power Law Weight Function
Motivated by an earlier work on fractional-action cosmology with a periodic
weight function [1], we extend it by choosing a power-law weight function in
the action. In this approach, we obtain a varying gravitational coupling
constant. We then model dark energy in this paradigm and obtain relevant
cosmological parameters.Comment: 12 pages, 9 figures, Contributed talk published in the proceedings of
"3rd Italian-Pakistani Workshop on Relativistic Astrophysics
A four-helix bundle stores copper for methane oxidation
Methane-oxidising bacteria (methanotrophs) require large quantities of copper for the membrane-bound (particulate) methane monooxygenase (pMMO). Certain methanotrophs are also able to switch to using the iron-containing soluble MMO (sMMO) to catalyse methane oxidation, with this switchover regulated by copper. MMOs are Nature’s primary biological mechanism for suppressing atmospheric levels of methane, a potent greenhouse gas. Furthermore, methanotrophs and MMOs have enormous potential in bioremediation and for biotransformations producing bulk and fine chemicals, and in bioenergy, particularly considering increased methane availability from renewable sources and hydraulic fracturing of shale rock. We have discovered and characterised a novel copper storage protein (Csp1) from the methanotroph Methylosinus trichosporium OB3b that is exported from the cytosol, and stores copper for pMMO. Csp1 is a tetramer of 4-helix bundles with each monomer binding up to 13 Cu(I) ions in a previously unseen manner via mainly Cys residues that point into the core of the bundle. Csp1 is the first example of a protein that stores a metal within an established protein-folding motif. This work provides a detailed insight into how methanotrophs accumulate copper for the oxidation of methane. Understanding this process is essential if the wide-ranging biotechnological applications of methanotrophs are to be realised. Cytosolic homologues of Csp1 are present in diverse bacteria thus challenging the dogma that such organisms do not use copper in this location
The Size Distribution of Void Filaments in a LCDM Cosmology
The size distribution of mini-filaments in voids has been derived from the
Millennium Run halo catalogs at redshifts z=0,0.5,1 and 2. It is assumed that
the primordial tidal field originated the presence of filamentary substructures
in voids and that the void filaments have evolved only little, keeping the
initial memory of the primordial tidal field. Applying the filament-finding
algorithm based on the minimal spanning tree (MST) technique to the Millennium
voids, we identify the mini-filaments running through voids and measure their
sizes at each redshift. Then, we calculate the comoving number density of void
filaments as a function of their sizes in the logarithmic interval and
determine an analytic fitting function for it. It is found that the size
distribution of void mini-filaments in the logarithmic interval has an almost
universal shape, insensitive to the redshift: In the short-size section it is
well approximated as a power-law, while in the long-size section it decreases
exponentially. We expect that the universal size distribution of void filaments
may provide a useful cosmological probe without resorting to the rms density
fluctuations.Comment: MNRAS in press, revised version, two different definitions of void
size considered, chi^2 tests of the universality included, more discussions
on the universality of the void size distribution adde
Chaotic Friedmann-Robertson-Walker Cosmology
We show that the dynamics of a spatially closed Friedmann - Robertson -
Walker Universe conformally coupled to a real, free, massive scalar field, is
chaotic, for large enough field amplitudes. We do so by proving that this
system is integrable under the adiabatic approximation, but that the
corresponding KAM tori break up when non adiabatic terms are considered. This
finding is confirmed by numerical evaluation of the Lyapunov exponents
associated with the system, among other criteria. Chaos sets strong limitations
to our ability to predict the value of the field at the Big Crunch, from its
given value at the Big Bang. (Figures available on request)Comment: 28 pages, 11 figure
Inflation and late time acceleration in braneworld cosmological models with varying brane tension
Braneworld models with variable brane tension introduce a new
degree of freedom that allows for evolving gravitational and cosmological
constants, the latter being a natural candidate for dark energy. We consider a
thermodynamic interpretation of the varying brane tension models, by showing
that the field equations with variable can be interpreted as
describing matter creation in a cosmological framework. The particle creation
rate is determined by the variation rate of the brane tension, as well as by
the brane-bulk energy-matter transfer rate. We investigate the effect of a
variable brane tension on the cosmological evolution of the Universe, in the
framework of a particular model in which the brane tension is an exponentially
dependent function of the scale factor. The resulting cosmology shows the
presence of an initial inflationary expansion, followed by a decelerating
phase, and by a smooth transition towards a late accelerated de Sitter type
expansion. The varying brane tension is also responsible for the generation of
the matter in the Universe (reheating period). The physical constraints on the
model parameters, resulted from the observational cosmological data, are also
investigated.Comment: 25 pages, 8 figures, accepted for publication in European Physical
Journal
Reheating the Universe in Braneworld Cosmological Models with bulk-brane energy transfer
The emergence of the cosmological composition (the reheating era) after the
inflationary period is analyzed in the framework of the braneworld models, in
which our Universe is a three-brane embedded in a five-dimensional bulk, by
assuming the possibility of the brane-bulk energy exchange. The inflaton field
is assumed to decay into normal matter only, while the dark matter is injected
into the brane from the bulk. To describe the reheating process we adopt a
phenomenological approach, by describing the decay of the inflaton field by a
friction term proportional to the energy density of the field. After the
radiation dominated epoch the model reduces to the standard four dimensional
cosmological model. The modified field equations are analyzed analytically and
numerically in both the extra-dimensions dominate reheating phase (when the
quadratic terms in energy density dominate the dynamics), and in the general
case. The evolution profiles of the matter, of the scalar field and of the
scale factor of the universe are obtained for different values of the
parameters of the model, and of the equations of state of the normal and dark
matter, respectively. The equation describing the time evolution of the ratio
of the energy density of the dark and of the normal matter is also obtained.
The ratio depends on the rate of the energy flow between the bulk and the
brane. The observational constraint of an approximately constant ratio of the
dark and of the baryonic matter requires that the dark matter must be
non-relativistic (cold). The model predicts a reheating temperature of the
order of GeV, a brane tension of the order of GeV,
and the obtained composition of the universe is consistent with the
observational data.Comment: 29 pages, 9 figures, accepted for publication in JCA
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