Ultrafine heat-induced structural perturbations of bone mineral at the individual nanocrystal level

International audienc

UtpA and UtpB chaperone nascent pre-ribosomal RNA and U3 snoRNA to initiate eukaryotic ribosome assembly

Early eukaryotic ribosome biogenesis involves large multi-protein complexes, which co-transcriptionally associate with pre-ribosomal RNA to form the small subunit processome. The precise mechanisms by which two of the largest multi-protein complexes—UtpA and UtpB—interact with nascent pre-ribosomal RNA are poorly understood. Here, we combined biochemical and structural biology approaches with ensembles of RNA–protein cross-linking data to elucidate the essential functions of both complexes. We show that UtpA contains a large composite RNA-binding site and captures the 5′ end of pre-ribosomal RNA. UtpB forms an extended structure that binds early pre-ribosomal intermediates in close proximity to architectural sites such as an RNA duplex formed by the 5′ ETS and U3 snoRNA as well as the 3′ boundary of the 18S rRNA. Both complexes therefore act as vital RNA chaperones to initiate eukaryotic ribosome assembly

Combination of Nanoindentation and Quantitative Backscattered Electron Imaging Revealed Altered Bone Material Properties Associated with Femoral Neck Fragility

Osteoporotic fragility fractures were hypothesized to be related to changes in bone material properties and not solely to reduction in bone mass. We studied cortical bone from the superior and inferior sectors of whole femoral neck sections from five female osteoporotic hip fracture cases (74–92 years) and five nonfractured controls (75–88 years). The typical calcium content (CaPeak) and the mineral particle thickness parameter (T) were mapped in large areas of the superior and inferior regions using quantitative backscattered electron imaging (qBEI) and scanning small-angle X-ray scattering, respectively. Additionally, indentation modulus (E) and hardness (H) (determined by nanoindentation) were compared at the local level to the mineral content (CaInd) at the indent positions (obtained from qBEI). CaPeak (−2.2%, P = 0.002), CaInd (−1.8%, P = 0.048), E (−5.6%, P = 0.040), and H (−6.0%, P = 0.016) were significantly lower for the superior compared to the inferior region. Interestingly, CaPeak as well as CaInd were also lower (−2.6%, P = 0.006, and –3.7%, P = 0.002, respectively) in fracture cases compared to controls, while E and H did not show any significant reduction. T values were in the normal range, independent of region (P = 0.181) or fracture status (P = 0.551). In conclusion, it appears that the observed femoral neck fragility is associated with a reduced mineral content, which was not accompanied by a reduction in stiffness and hardness of the bone material. This pilot study suggests that a stiffening process in the organic matrix component contributes to bone fragility independently of mineral content

Investigation of Structural Processes During Indentation of Polymers by Synchrotron Radiation Microdiffraction

International audienc

Hardness testing under a different light: combining synchrotron X-ray microdiffraction and indentation techniques for polymer fibres studies

International audienceDeformation mechanisms occurring on the nanometer scale during indentation of bulk polymer fibres were investigated by means of scanning wide-angle diffraction scattering (WAXS) using beams of micrometer size at the ESRF microfocus beamline (ID13). Elastic processes could be evidenced in-situ using a dedicated microindenter device. The most important changes appear in the form of local crystalline reorientation which can be quantified by analysis of the azimuthal profiles of the WAXS reflections. The texture and phase-transitions induced by plastic deformation at higher loads was also measured and the differences between high performance fibres and a more traditional semicrystalline polymer are emphasized

Combined Microindentation and Synchrotron Radiation Microdiffraction Applied to Polymers

International audienc

Towards a better understanding of alteration phenomena of archaeological bone by a closer look at the organic mineral association at micro and nanoscale. Preliminary results on neolithic samples from Chalain lake site 19, Jura, France

International audienceIn this paper we present the extension of existing analytical schemes for the precise evaluation of archaeological bone preservation states. The new methodological developments concerning the study of the morphological and structural features of archaeological bones at micro- and nanoscale are emphasized in order to elucidate fine diagenetic modifications and to better understand the underlying alteration mechanisms. A combination of synchrotron X-ray microtomography, infrared micro-spectroscopy imaging and quantitative scanning small-angle X-ray scattering (sSAXS) imaging allowed studying micromorphological changes and the distribution of the organic and mineral components of bone at a histological level. Transmission electron microscopy gives precise information on changes of apatite crystal dimensions, orientations, periodicity of collagen fiber arrangement and crystal distributions within the fibers in archaeological bone. It allows establishing criteria to evaluate more precisely the preservation state of archaeological bone material with respect to modern references. The potential of these methods is highlighted on the basis of the study of some macroscopically well preserved archaeological bone samples from the Chalain lake station 19, Neolithic period, Jura, France. The investigations allowed a differentiation in preservation state between these samples and the postulation of an alteration sequence in such humid chalk-rich burial environments.Dans cet article nous présentons une extension de méthodes analytiques existantes pour évaluer précisément l’état de conversation des os archéologiques. Les nouveaux développements méthodologiques concernent particulièrement l’étude des caractéristiques structurales et morphologiques des ossements archéologiques aux échelles micro- et nanoscopiques afin de pouvoir élucider des modifications diagénetiques fines et de mieux comprendre les mécanismes d’altération sous-jacents. Une combinaison de microtomographie X, de micro-spectroscopie infrarouge et de micro-imagerie SAXS à balayage au synchrotron a permis d’étudier les altérations micromorphologiques et la répartition spatiale des composés organiques et minéraux dans les os à l’échelle histologiques. La microscopie électronique à transmission donne des informations précises sur les modifications de la taille des cristaux, leur orientation, la périodicité des arrangements des fibres collagéniques ainsi que la répartition des cristaux au sein des fibres dans l’os archéologique. Ces observations ont permis d’établir des paramétres permettant l’évaluation fine des modifications diagénetiques de la structure des os archéologiques en comparaison aux références modernes. Le potentiel de ces méthodes est illustré grâce à l’étude d’os archéologiques qui sont bien préservés à l’échelle macroscopique provenant du site néolithique de Chalain 19, Jura, France. Cette investigation a permis de montrer des différences dans l’état de conservation de ces os et permet de proposer une séquence d’altération pour les os enfouis dans des environnements humides et riches en craie