Pertinence et validité de tâches complexes dans l’évaluation de futurs enseignants

Ce chapitre interroge la manière d’assurer la pertinence tâches complexes utilisées dans l’évaluation des compétences de futurs enseignants. En d’autres termes, il s’agit d’assurer que le choix des tâches complexes est adéquat pour produire une information pertinente pour prendre une décision. Il présente une démarche articulée autour de cette exigence qui consiste à exposer ces tâches complexes – les auteurs en ont retenues six élaborées dans les Hautes Ecoles Pédagogiques (HEP) vaudoises et fribourgeoises – à la critique de praticiens et en regard d’un cadre théorique

Role of capsid sequence and immature nucleocapsid proteins p9 and p15 in Human Immunodeficiency Virus type 1 genomic RNA dimerization

AbstractHIV-1 genomic RNA (gRNA) dimerization is important for viral infectivity and is regulated by proteolytic processing of the Gag precursor protein (Pr55gag) under the direction of the viral protease. The processing occurs in successive steps and, to date, the step associated with formation of a wild-type (WT) level of gRNA dimers has not been identified. The primary cleavage divides Pr55gag into two proteins. The C-terminal polypeptide is termed NCp15 (NCp7–p1–p6) because it contains the nucleocapsid protein (NC), a key determinant of gRNA dimerization and packaging. To examine the importance of precursor polypeptides NCp15 and NCp9 (NCp7–p1), we introduced mutations that prevented the proteolytic cleavages responsible for the appearance of NCp9 or NCp7. Using native Northern blot analysis, we show that gRNA dimerization was impaired when both the secondary (p1–p6) and tertiary (p7–p1) cleavage sites of NCp15 were abolished, but unaffected when only one or the other site was abolished. Though processing to NCp9 therefore suffices for a WT level of gRNA dimerization, we also show that preventing cleavage at the p7–p1 site abolished HIV-1 replication. To identify the minimum level of protease activity compatible with a WT level of gRNA dimers, we introduced mutations Thr26Ser and Ala28Ser in the viral protease to partially inactivate it, and we prepared composite HIV-1 resulting from the cotransfection of various ratios of WT and protease-inactive proviral DNAs. The results reveal that a 30% processing of Pr55gag into mature capsid proteins (CA/CA-p2) yielded a WT level of gRNA dimers, while a 10% Pr55gag processing hardly increased gRNA dimerization above the level seen in protease-inactive virions. We found that full gRNA dimerization required less than 50% WT NC in complementation asssays. Finally, we show that if we destroy alpha helix 1 of the capsid protein (CA), gRNA dimerization is impaired to the same extent as when the viral protease is inactivated. Cotransfection studies show that this CA mutation, in contrast to the NC-disabling mutations, has a dominant negative effect on HIV-1 RNA dimerization, viral core formation, and viral replication. This represents the first evidence that a capsid mutation can affect HIV-1 RNA dimerization

Regional differences in the expression of K⁺–Cl⁻ 2 cotransporter in the developing rat cortex

The type 2 potassium–chloride cotransporter (KCC2) is the main regulator of intracellular chloride concentration in CNS neurons, and plays a crucial role in spine development that is independent of its ion cotransport function. The expression pattern of KCC2 is upregulated during postnatal development showing area and layer-specific differences in distinct brain areas. We examined the regional and ultrastructural localisation of KCC2 in various areas of developing neocortex and paleocortex during the first two postnatal weeks. Light-microscopy examination revealed diffuse neuropil and discrete funnel-shaped dendritic labelling in the piriform and entorhinal cortices at birth. Subsequently, during the beginning of the first postnatal week, diffuse KCC2 labelling gradually started to appear in the superficial layers of the neocortex while the punctate-like labelling of dendrites in the piriform, entorhinal and perirhinal cortices become more pronounced. By the end of the first postnatal week, discrete dendritic expression of KCC2 was visible in all neocortical and paleocortical areas. The expression level did not change during the second postnatal week suggesting that, in contrast to hippocampus, adult pattern of KCC2 in the cortical cells is already established by the end of the first postnatal week. Quantitative electron microscopy examination revealed that in superficial layers of both neo- and paleocortex, the majority of KCC2 signal was plasma membrane associated but the number of transport vesicle-associated immunosignal increased with development. In deep layers, KCC2 immunolabeling was evenly distributed in plasma membrane and transport vesicles showing no obvious change with maturation. The number of KCC2 immunogold particles increased in dendritic spines with no association with synapses. This observation points to the dual role of KCC2 in spine genesis and ion cotransport

Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum

We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, New Jersey. Aside from previously-described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability – a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming – drove diversification of magnetite-forming organisms, likely including eukaryotes

Coordinated Rearrangements between Cytoplasmic and Periplasmic Domains of the Membrane Protein Complex ExbB-ExbD of Escherichia coli

SummaryGram-negative bacteria rely on the ExbB-ExbD-TonB system for the import of essential nutrients. Despite decades of research, the stoichiometry, subunit organization, and mechanism of action of the membrane proteins of the Ton system remain unclear. We copurified ExbB with ExbD as an ∼240 kDa protein-detergent complex, measured by light scattering and by native gels. Quantitative Coomassie staining revealed a stoichiometry of ExbB4-ExbD2. Negative stain electron microscopy and 2D analysis showed particles of ∼10 nm diameter in multiple structural states. Nanogold labeling identified the position of the ExbD periplasmic domain. Random conical tilt was used to reconstruct the particles in three structural states followed by sorting of the single particles and refinement of each state. The different states are interpreted by coordinated structural rearrangements between the cytoplasmic domain and the periplasmic domain, concordant with in vivo predictions

The structural basis of actin filament branching by the Arp2/3 complex

The actin-related protein 2/3 (Arp2/3) complex mediates the formation of branched actin filaments at the leading edge of motile cells and in the comet tails moving certain intracellular pathogens. Crystal structures of the Arp2/3 complex are available, but the architecture of the junction formed by the Arp2/3 complex at the base of the branch was not known. In this study, we use electron tomography to reconstruct the branch junction with sufficient resolution to show how the Arp2/3 complex interacts with the mother filament. Our analysis reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation. The Arp2 and Arp3 subunits reorganize into a dimer, providing a short-pitch template for elongation of the daughter filament. Two subunits of the mother filament undergo conformational changes that increase stability of the branch. These data provide a rationale for why branch formation requires cooperative interactions among the Arp2/3 complex, nucleation-promoting factors, an actin monomer, and the mother filament

Effects of Arp2 and Arp3 nucleotide-binding pocket mutations on Arp2/3 complex function

Contributions of actin-related proteins (Arp) 2 and 3 nucleotide state to Arp2/3 complex function were tested using nucleotide-binding pocket (NBP) mutants in Saccharomyces cerevisiae. ATP binding by Arp2 and Arp3 was required for full Arp2/3 complex nucleation activity in vitro. Analysis of actin dynamics and endocytosis in mutants demonstrated that nucleotide-bound Arp3 is particularly important for Arp2/3 complex function in vivo. Severity of endocytic defects did not correlate with effects on in vitro nucleation activity, suggesting that a critical Arp2/3 complex function during endocytosis may be structural rather than catalytic. A separate class of Arp2 and Arp3 NBP mutants suppressed phenotypes of mutants defective for actin nucleation. An Arp2 suppressor mutant increased Arp2/3 nucleation activity. Electron microscopy of Arp2/3 complex containing this Arp2 suppressor identified a structural change that also occurs upon Arp2/3 activation by nucleation promoting factors. These data demonstrate the importance of Arp2 and Arp3 nucleotide binding for nucleating activity, and Arp3 nucleotide binding for maintenance of cortical actin cytoskeleton cytoarchitecture

Full-length structural model of RET3 and SEC21 in COPI: identification of binding sites on the appendage for accessory protein recruitment motifs

COPI, a 600 kD heptameric complex (consisting of subunits α, β, γ, δ, ε, ζ, and β′) “coatomer,” assembles non-clathrin-coated vesicles and is responsible for intra-Golgi and Golgi-to-ER protein trafficking. Here, we report the three-dimensional structures of the entire sequences of yeast Sec21 (γ-COPI mammalian ortholog), yeast Ret3 (ζ-COPI mammalian ortholog), and the results of successive molecular dynamics investigations of the subunits and assembly based on a protein–protein docking experiment. The three-dimensional structures of the subunits in their complexes indicate the residues of the two subunits that impact on assembly, the conformations of Ret3 and Sec21, and their binding orientations in the complexed state. The structure of the appendage domain of Sec21, with its two subdomains—the platform and the β-sandwich, was investigated to explore its capacity to bind to accessory protein recruitment motifs. Our study shows that a binding site on the platform is capable of binding the Eps15 DPF and epsin DPW2 peptides, whereas the second site on the platform and the site on the β-sandwich subdomain were found to selectively bind to the amphiphysin FXDXF and epsin DPW1 peptides, respectively. Identifying the regions of both the platform and sandwich subdomains involved in binding each peptide motif clarifies the mechanism through which the appendage domain of Sec21 engages with the accessory proteins during the trafficking process of non-clathrin-coated vesicles

Évaluer l'apport des nouvelles technologies dans la sécurisation de la prise en charge médicamenteuse en établissement de santé (une expérience d'implantation d'armoires automatisées au CHU Sainte-Justine de Montréal)

Le processus complexe du circuit du médicament en établissement de santé est à l'origine d'un risque iatrogène désormais bien mesuré et réel. Les objectifs de qualité de la prise en charge médicamenteuse suggèrent l'informatisation et l'automatisation comme outils pour son amélioration. Toutefois, l'utilisation de ces solutions technologiques est à l'origine de changements importants au niveau organisationnel et leur déploiement doit être organisé et sécurisé. À partir de lignes directrices publiées, une auto-évaluation des processus entourant l'implantation et l'utilisation d'armoires automatisées dans les unités de soins a été menée au centre hospitalier universitaire Sainte-Justine de Montréal. Cette analyse de conformité des pratiques a permis d'orienter les actions, tant sur le plan technologique qu'organisationnel, dans le but d'atteindre une sécurisation optimale de la prise en charge médicamenteuse. En parallèle, plusieurs études mettent en évidence l'apparition d'erreurs médicamenteuses générées par l'implantation d'une nouvelle technologie. Il est donc nécessaire d'identifier les non-conformités à des lignes directrices publiées afin de connaître, prévenir et limiter les risques associés. Les outils disponibles pour les évaluer sont actuellement insuffisants. A cet effet, établir un cadre optimal d'utilisation parait indispensable pour chacune des solutions d'informatisation et d'automatisation du circuit du médicament.NANTES-BU Médecine pharmacie (441092101) / SudocSudocFranceF