Architecture of the chromatin remodeler RSC and insights into its nucleosome engagement.

Eukaryotic DNA is packaged into nucleosome arrays, which are repositioned by chromatin remodeling complexes to control DNA accessibility. The Saccharomyces cerevisiae RSC (Remodeling the Structure of Chromatin) complex, a member of the SWI/SNF chromatin remodeler family, plays critical roles in genome maintenance, transcription, and DNA repair. Here, we report cryo-electron microscopy (cryo-EM) and crosslinking mass spectrometry (CLMS) studies of yeast RSC complex and show that RSC is composed of a rigid tripartite core and two flexible lobes. The core structure is scaffolded by an asymmetric Rsc8 dimer and built with the evolutionarily conserved subunits Sfh1, Rsc6, Rsc9 and Sth1. The flexible ATPase lobe, composed of helicase subunit Sth1, Arp7, Arp9 and Rtt102, is anchored to this core by the N-terminus of Sth1. Our cryo-EM analysis of RSC bound to a nucleosome core particle shows that in addition to the expected nucleosome-Sth1 interactions, RSC engages histones and nucleosomal DNA through one arm of the core structure, composed of the Rsc8 SWIRM domains, Sfh1 and Npl6. Our findings provide structural insights into the conserved assembly process for all members of the SWI/SNF family of remodelers, and illustrate how RSC selects, engages, and remodels nucleosomes

Novel tau filament fold in chronic traumatic encephalopathy encloses hydrophobic molecules

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy that is associated with repetitive head impacts or exposure to blast waves. First described as punch-drunk syndrome and dementia pugilistica in retired boxers1-3, CTE has since been identified in former participants of other contact sports, ex-military personnel and after physical abuse4-7. No disease-modifying therapies currently exist, and diagnosis requires an autopsy. CTE is defined by an abundance of hyperphosphorylated tau protein in neurons, astrocytes and cell processes around blood vessels8,9. This, together with the accumulation of tau inclusions in cortical layers II and III, distinguishes CTE from Alzheimer's disease and other tauopathies10,11. However, the morphologies of tau filaments in CTE and the mechanisms by which brain trauma can lead to their formation are unknown. Here we determine the structures of tau filaments from the brains of three individuals with CTE at resolutions down to 2.3 Å, using cryo-electron microscopy. We show that filament structures are identical in the three cases but are distinct from those of Alzheimer's and Pick's diseases, and from those formed in vitro12-15. Similar to Alzheimer's disease12,14,16-18, all six brain tau isoforms assemble into filaments in CTE, and residues K274-R379 of three-repeat tau and S305-R379 of four-repeat tau form the ordered core of two identical C-shaped protofilaments. However, a different conformation of the β-helix region creates a hydrophobic cavity that is absent in tau filaments from the brains of patients with Alzheimer's disease. This cavity encloses an additional density that is not connected to tau, which suggests that the incorporation of cofactors may have a role in tau aggregation in CTE. Moreover, filaments in CTE have distinct protofilament interfaces to those of Alzheimer's disease. Our structures provide a unifying neuropathological criterion for CTE, and support the hypothesis that the formation and propagation of distinct conformers of assembled tau underlie different neurodegenerative diseases

Mechanical Characterization of Ink-Jet Printed Ag Samples on Different Substrates

Part 6: Computational Systems ApplicationsInternational audienceIn this paper, the main activity was to investigate how different substrates, temperature of sintering and percentage of silver ink containing silver nanoparticles influence on Young’s modulus and hardness of printed silver thin samples. Samples were prepared by low cost ink-jet printing technique using Dimatix Material Printer on polyimide flexible substrate and slide glass. Characterization of these samples was carried out by Nano Indenter using a three sided pyramidal (Berkovich) diamond tip. Measurement results show that the thickness of ink-jet printed silver layer varies for different percent of nanoparticles in silver ink. All measurements were done at same depth of indentation to avoid possibility of perforation of printed layer. The higher temperature of sintering and the higher percent of silver nanoparticles give the bigger Young’s modulus and hardness of printed silver sample. This research provides very useful information about mechanical characterization of the silver layers on flexible substrates for printed-electronics

Adequate immune response ensured by binary IL-2 and graded CD25 expression in a murine transfer model

The IL-2/IL-2Ralpha (CD25) axis is of central importance for the interplay of effector and regulatory T cells. Nevertheless, the question how different antigen loads are translated into appropriate IL-2 production to ensure adequate responses against pathogens remains largely unexplored. Here we find that at single cell level, IL-2 is binary (digital) and CD25 is graded expressed whereas at population level both parameters show graded expression correlating with the antigen amount. Combining in vivo data with a mathematical model we demonstrate that only this binary IL-2 expression ensures a wide linear antigen response range for Teff and Treg cells under real spatiotemporal conditions. Furthermore, at low antigen concentrations binary IL-2 expression safeguards by its spatial distribution selective STAT5 activation only of closely adjacent Treg cells regardless of their antigen specificity. These data show that the mode of IL-2 secretion is critical to tailor the adaptive immune response to the antigen amount

Reconstruction of intricate surfaces from scanning electron microscopy

This PhD thesis is concerned with the reconstruction of intricate shapes from scanning electron microscope (SEM) imagery. Since SEM images bear a certain resemblance to optical images, approaches developed in the wider field of computer vision can to a certain degree be applied to SEM images as well. I focus on two such approaches, namely Multiview Stereo (MVS) and Shape from Shading (SfS) and extend them to the SEM domain. The reconstruction of intricate shapes featuring thin protrusions and sparsely textured curved areas poses a significant challenge for current MVS techniques. The MVS methods I propose are designed to deal with such surfaces in particular, while also being robust to the specific problems inherent in the SEM modality: the absence of a static illumination and the unusually high noise level. I describe two different novel MVS methods aimed at narrow-baseline and medium-baseline imaging setups respectively. Both of them build on the assumption of pixelwise photoconsistency. In the SfS context, I propose a novel empirical reflectance model for SEM images that allows for an efficient inference of surface orientation from multiple observations. My reflectance model is able to model both secondary and backscattered electron emission under an arbitrary detector setup. I describe two additional methods of inferring shape using combinations of MVS and SfS approaches: the first builds on my medium-baseline MVS method, which assumes photoconsistency, and improves on it by estimating the surface orientation using my reflectance model. The second goes beyond photoconsistency and estimates the depths themselves using the reflectance model