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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
Characterization of ejecta in shock experiments with multiple light scattering
Upon impact, the free surface of a solid metal may eject a cloud of fast and
fine particles. Photon Doppler Velocimetry (PDV) is one of the optical
diagnostics used to characterize these ejecta. Although the technique provides
a direct way to estimate the particle velocities in the single scattering
regime, it has been shown that multiple scattering cannot be neglected in real
ejecta. Here we derive a model for PDV measurements starting from first
principles of wave scattering. We establish rigorously the relationship between
the specific intensity and the measured signal, as well as the radiative
transport equation (RTE) that describes the evolution of the specific intensity
upon scattering and absorption in a dynamic ejecta, including the effects of
inelastic scattering and inhomogenities in the optical properties. We also
establish rigorously the connection between the Monte-Carlo scheme used for
numerical simulations and the solution to the RTE. Using numerical simulations,
we demonstrate the crucial role of multiple scattering and inhomogeneities in
the particle density and size-velocity distribution. These results could
substantially impact the analysis of ejecta by PDV
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
Wet Granular Materials
Most studies on granular physics have focused on dry granular media, with no
liquids between the grains. However, in geology and many real world
applications (e.g., food processing, pharmaceuticals, ceramics, civil
engineering, constructions, and many industrial applications), liquid is
present between the grains. This produces inter-grain cohesion and drastically
modifies the mechanical properties of the granular media (e.g., the surface
angle can be larger than 90 degrees). Here we present a review of the
mechanical properties of wet granular media, with particular emphasis on the
effect of cohesion. We also list several open problems that might motivate
future studies in this exciting but mostly unexplored field.Comment: review article, accepted for publication in Advances in Physics;
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Cell Nucleus-Targeting Zwitterionic Carbon Dots
An innovative nucleus-targeting zwitterionic carbon dot (CD) vehicle has been developed for anticancer drug delivery and optical monitoring. The zwitterionic functional groups of the CDs introduced by a simple one-step synthesis using beta-alanine as a passivating and zwitterionic ligand allow cytoplasmic uptake and subsequent nuclear translocation of the CDs. Moreover, multicolor fluorescence improves the accuracy of the CDs as an optical code. The CD-based drug delivery system constructed by non-covalent grafting of doxorubicin, exhibits superior antitumor efficacy owing to enhanced nuclear delivery in vitro and tumor accumulation in vivo, resulting in highly effective tumor growth inhibition. Since the zwitterionic CDs are highly biocompatible and effectively translocated into the nucleus, it provides a compelling solution to a multifunctional nanoparticle for substantially enhanced nuclear uptake of drugs and optical monitoring of translocation.open
Staged decline of neuronal function in vivo in an animal model of Alzheimer's disease
The accumulation of amyloid-β in the brain is an essential feature of Alzheimer's disease. However, the impact of amyloid-β-accumulation on neuronal dysfunction on the single cell level in vivo is poorly understood. Here we investigate the progression of amyloid-β load in relation to neuronal dysfunction in the visual system of the APP23×PS45 mouse model of Alzheimer's disease. Using in vivo two-photon calcium imaging in the visual cortex, we demonstrate that a progressive deterioration of neuronal tuning for the orientation of visual stimuli occurs in parallel with the age-dependent increase of the amyloid-β load. Importantly, we find this deterioration only in neurons that are hyperactive during spontaneous activity. This impairment of visual cortical circuit function also correlates with pronounced deficits in visual-pattern discrimination. Together, our results identify distinct stages of decline in sensory cortical performance in vivo as a function of the increased amyloid-β-load
Mitogen- and Stress-Activated Kinase 1 (MSK1) Regulates Cigarette Smoke-Induced Histone Modifications on NF-κB-dependent Genes
Cigarette smoke (CS) causes sustained lung inflammation, which is an important event in the pathogenesis of chronic obstructive pulmonary disease (COPD). We have previously reported that IKKα (I kappaB kinase alpha) plays a key role in CS-induced pro-inflammatory gene transcription by chromatin modifications; however, the underlying role of downstream signaling kinase is not known. Mitogen- and stress-activated kinase 1 (MSK1) serves as a specific downstream NF-κB RelA/p65 kinase, mediating transcriptional activation of NF-κB-dependent pro-inflammatory genes. The role of MSK1 in nuclear signaling and chromatin modifications is not known, particularly in response to environmental stimuli. We hypothesized that MSK1 regulates chromatin modifications of pro-inflammatory gene promoters in response to CS. Here, we report that CS extract activates MSK1 in human lung epithelial (H292 and BEAS-2B) cell lines, human primary small airway epithelial cells (SAEC), and in mouse lung, resulting in phosphorylation of nuclear MSK1 (Thr581), phospho-acetylation of RelA/p65 at Ser276 and Lys310 respectively. This event was associated with phospho-acetylation of histone H3 (Ser10/Lys9) and acetylation of histone H4 (Lys12). MSK1 N- and C-terminal kinase-dead mutants, MSK1 siRNA-mediated knock-down in transiently transfected H292 cells, and MSK1 stable knock-down mouse embryonic fibroblasts significantly reduced CS extract-induced MSK1, NF-κB RelA/p65 activation, and posttranslational modifications of histones. CS extract/CS promotes the direct interaction of MSK1 with RelA/p65 and p300 in epithelial cells and in mouse lung. Furthermore, CS-mediated recruitment of MSK1 and its substrates to the promoters of NF-κB-dependent pro-inflammatory genes leads to transcriptional activation, as determined by chromatin immunoprecipitation. Thus, MSK1 is an important downstream kinase involved in CS-induced NF-κB activation and chromatin modifications, which have implications in pathogenesis of COPD
The changing form of Antarctic biodiversity
Antarctic biodiversity is much more extensive, ecologically diverse and biogeographically structured than previously thought. Understanding of how this diversity is distributed in marine and terrestrial systems, the mechanisms underlying its spatial variation, and the significance of the microbiota is growing rapidly. Broadly recognizable drivers of diversity variation include energy availability and historical refugia. The impacts of local human activities and global environmental change nonetheless pose challenges to the current and future understanding of Antarctic biodiversity. Life in the Antarctic and the Southern Ocean is surprisingly rich, and as much at risk from environmental change as it is elsewher
Serotonergic chemosensory neurons modify the <i>C. elegans</i> immune response by regulating G-protein signaling in epithelial cells
The nervous and immune systems influence each other, allowing animals to rapidly protect themselves from changes in their internal and external environment. However, the complex nature of these systems in mammals makes it difficult to determine how neuronal signaling influences the immune response. Here we show that serotonin, synthesized in Caenorhabditis elegans chemosensory neurons, modulates the immune response. Serotonin released from these cells acts, directly or indirectly, to regulate G-protein signaling in epithelial cells. Signaling in these cells is required for the immune response to infection by the natural pathogen Microbacterium nematophilum. Here we show that serotonin signaling suppresses the innate immune response and limits the rate of pathogen clearance. We show that C. elegans uses classical neurotransmitters to alter the immune response. Serotonin released from sensory neurons may function to modify the immune system in response to changes in the animal's external environment such as the availability, or quality, of food
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