429 research outputs found
Cooperative Emission of a Coherent Superflash of Light
We investigate the transient coherent transmission of light through an
optically thick cold stron-tium gas. We observe a coherent superflash just
after an abrupt probe extinction, with peak intensity more than three times the
incident one. We show that this coherent superflash is a direct signature of
the cooperative forward emission of the atoms. By engineering fast transient
phenomena on the incident field, we give a clear and simple picture of the
physical mechanisms at play.Comment: 4 Fig., 5 page
Dynamic force spectroscopy on multiple bonds: experiments and model
We probe the dynamic strength of multiple biotin-streptavidin adhesion bonds
under linear loading using the biomembrane force probe setup for dynamic force
spectroscopy. Measured rupture force histograms are compared to results from a
master equation model for the stochastic dynamics of bond rupture under load.
This allows us to extract the distribution of the number of initially closed
bonds. We also extract the molecular parameters of the adhesion bonds, in good
agreement with earlier results from single bond experiments. Our analysis shows
that the peaks in the measured histograms are not simple multiples of the
single bond values, but follow from a superposition procedure which generates
different peak positions.Comment: to appear in Europhysics Letter
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The exon junction complex senses energetic stress and regulates contractility and cell architecture in cardiac myocytes
The exon junction complex (EJC) is the main mechanism by which cells select specific mRNAs
for translation into protein. We hypothesized that the EJC is involved in the regulation
of gene expression during the stress response in cardiac myocytes, with implications for
the failing heart. In cultured rat neonatal myocytes, we examined the cellular distribution
of two EJC components eukaryotic translation initiation factor 4A isoform 3 (eIF4A3) and
mago nashi homologue (Mago) in response to metabolic stress. There was significant relocalization
of eIF4A3 and Mago from the nucleus to cytoplasm following 18 h of hypoxia.
Treating myocytes with 50 mM NaN3 for 4 h to mimic the metabolic stress induced by hypoxia
also resulted in significant relocalization of eIF4A3 and Mago to the cytoplasm. To
examine whether the effects of metabolic stress on the EJC proteins were dependent on
the metabolic sensor AMP kinase (AMPK), we treated myocytes with 1 μM dorsomorphin
(DM) in combination with NaN3. DM augmented the translocation of Mago and eIF4A3 from
the nucleus to the cytoplasm. Knockdown of eIF4A3 resulted in cessation of cell contractility
96 h post-treatment and a significant reduction in the number of intact sarcomeres.
Cell area was significantly reduced by both hypoxia and eIF4A3 knockdown, whilst eIF4A3
knockdown also significantly reduced nuclear size. The reduction in nuclear size is unlikely
to be related to apoptosis as it was reversed in combination with hypoxia. These data suggest
for the first time that eIF4A3 and potentially other EJC members play an important role
in the myocyte stress response, cell contractility and morphology
Light in correlated disordered media
The optics of correlated disordered media is a fascinating research topic
emerging at the interface between the physics of waves in complex media and
nanophotonics. Inspired by photonic structures in nature and enabled by
advances in nanofabrication processes, recent investigations have unveiled how
the design of structural correlations down to the subwavelength scale could be
exploited to control the scattering, transport and localization of light in
matter. From optical transparency to superdiffusive light transport to photonic
gaps, the optics of correlated disordered media challenges our physical
intuition and offers new perspectives for applications. This article reviews
the theoretical foundations, state-of-the-art experimental techniques and major
achievements in the study of light interaction with correlated disorder,
covering a wide range of systems -- from short-range correlated photonic
liquids, to L\'evy glasses containing fractal heterogeneities, to hyperuniform
disordered photonic materials. The mechanisms underlying light scattering and
transport phenomena are elucidated on the basis of rigorous theoretical
arguments. We overview the exciting ongoing research on mesoscopic phenomena,
such as transport phase transitions and speckle statistics, and the current
development of disorder engineering for applications such as light-energy
management and visual appearance design. Special efforts are finally made to
identify the main theoretical and experimental challenges to address in the
near future.Comment: Submitted to Reviews of Modern Physics. Feedbacks are welcom
eIF4A RNA Helicase Associates with Cyclin-Dependent Protein Kinase A in Proliferating Cells and is Modulated by Phosphorylation
Eukaryotic initiation factor 4A (eIF4A) is a highly conserved RNA-stimulated ATPase and helicase involved in the initiation of messenger RNA translation. Previously, we found that eIF4A interacts with cyclin-dependent kinase A (CDKA), the plant ortholog of mammalian CDK1. Here, we show that this interaction occurs only in proliferating cells where the two proteins coassociate with 5′-cap-binding protein complexes, eIF4F or the plant-specific eIFiso4F. CDKA phosphorylates eIF4A on a conserved threonine residue (threonine-164) within the RNA-binding motif 1b TPGR. In vivo, a phospho-null (APGR) variant of the Arabidopsis (Arabidopsis thaliana) eIF4A1 protein retains the ability to functionally complement a mutant (eif4a1) plant line lacking eIF4A1, whereas a phosphomimetic (EPGR) variant fails to complement. The phospho-null variant (APGR) rescues the slow growth rate of roots and rosettes, together with the ovule-abortion and late-flowering phenotypes. In vitro, wild-type recombinant eIF4A1 and its phospho-null variant both support translation in cell-free wheat germ extracts dependent upon eIF4A, but the phosphomimetic variant does not support translation and also was deficient in ATP hydrolysis and helicase activity. These observations suggest a mechanism whereby CDK phosphorylation has the potential to down-regulate eIF4A activity and thereby affect translation
Control of protein translation by phosphorylation of the mRNA 5′-cap-binding complex,
Abstract Initiation of mRNA translation is a key regulatory step in the control of gene expression. Microarray analysis indicates that total mRNA levels do not always reflect protein levels, since mRNA association with polyribosomes is necessary for protein synthesis. Phosphorylation of translation initiation factors offers a costeffective and rapid way to adapt to physiological and environmental changes, and there is increasing evidence that many of these factors are subject to multiple regulatory phosphorylation events. The present article focuses on the nature of reversible phosphorylation and the function of the 5 -cap-binding complex in plants
Developmental motor problems and health-related quality of life in 5-year-old children born extremely preterm: A European cohort study
Aim To measure the association between cerebral palsy (CP) and non-CP-related movement difficulties and health-related quality of life (HRQoL) among 5-year-old children born extremely preterm (<28 weeks gestational age). Method We included 5-year-old children from a multi-country, population-based cohort of children born extremely preterm in 2011 to 2012 in 11 European countries (n = 1021). Children without CP were classified using the Movement Assessment Battery for Children, Second Edition as having significant movement difficulties (<= 5th centile of standardized norms) or being at risk of movement difficulties (6th-15th centile). Parents reported on a clinical CP diagnosis and HRQoL using the Pediatric Quality of Life Inventory. Associations were assessed using linear and quantile regressions. Results Compared to children without movement difficulties, children at risk of movement difficulties, with significant movement difficulties, and CP had lower adjusted HRQoL total scores (beta [95% confidence interval] = -5.0 [-7.7 to -2.3], -9.1 [-12.0 to -6.1], and - 26.1 [-31.0 to -21.2]). Quantile regression analyses showed similar decreases in HRQoL for all children with CP, whereas for children with non-CP-related movement difficulties, reductions in HRQoL were more pronounced at lower centiles. Interpretation CP and non-CP-related movement difficulties were associated with lower HRQoL, even for children with less severe difficulties. Heterogeneous associations for non-CP-related movement difficulties raise questions for research about mitigating and protective factors.Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Grant/Award Number: SFRH/BPD/117597/2016; Horizon 2020 Framework Programme, Grant/Award Number: No 633724 and No 733280; Seventh Framework Programme, Grant/Award Number: No 25988
Evaluating photosynthetic activity across Arctic-Boreal land cover types using solar-induced fluorescence
Signatures of Le´vy flights with annealed disorder
We present theoretical and experimental results of Le´vy flights of light originating from a random walk of
photons in a hot atomic vapor. In contrast to systems with quenched disorder, this system does not present any
correlations between the position and the step length of the random walk. In an analytical model based on micro-
scopic first principles including Doppler broadening we find anomalous Le´vy-type superdiffusion corresponding
to a single-step size distribution P (x) ∝ x−(1+α), with α ≈ 1. We show that this step size distribution leads to a
violation of Ohm’s law [Tdiff ∝ L−α/2 = L−1], as expected for a Le´vy walk of independent steps. Furthermore,
the spatial profile of the transmitted light develops power-law tails [Tdiff(r) ∝ r−3−α]. In an experiment using a
slab geometry with hot Rb vapor, we measured the total diffuse transmission Tdiff and the spatial profile of the
transmitted light Tdiff(r). We obtained the microscopic Le´vy parameter α under macroscopic multiple scattering
conditions paving the way to investigation of Le´vy flights in different atomic physics and astrophysics systems.We thank Dominique Delande for fruitful discussions and we acknowledge funding for N.M. and Q.B. by the french Direction Generale de l'Armement. R.P acknowledges the support of LABEX WIFI (Laboratory of Excellence ANR-10-LABX-24) within the French Program "Investments for the Future" under reference ANR-10-IDEX-0001-02 PSL*. E.J.N. and R.K. acknowledge the FCT/CNRS exchange program (441.00 CNRS)
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