Structure of the native γ-tubulin ring complex capping spindle microtubules.

Microtubule (MT) filaments, composed of α/ß-tubulin dimers, are fundamental to cellular architecture, function and organismal development. They are nucleated from MT organizing centers by the evolutionarily conserved γ-tubulin ring complex (γTuRC). However, the molecular mechanism of nucleation remains elusive. Here we used cryo-electron tomography to determine the structure of the native γTuRC capping the minus end of a MT in the context of enriched budding yeast spindles. In our structure, γTuRC presents a ring of γ-tubulin subunits to seed nucleation of exclusively 13-protofilament MTs, adopting an active closed conformation to function as a perfect geometric template for MT nucleation. Our cryo-electron tomography reconstruction revealed that a coiled-coil protein staples the first row of α/ß-tubulin of the MT to alternating positions along the γ-tubulin ring of γTuRC. This positioning of α/ß-tubulin onto γTuRC suggests a role for the coiled-coil protein in augmenting γTuRC-mediated MT nucleation. Based on our results, we describe a molecular model for budding yeast γTuRC activation and MT nucleation.

Device innovation in cardiovascular medicine: a report from the European Society of Cardiology Cardiovascular Round Table.

Research performed in Europe has driven cardiovascular device innovation. This includes, but is not limited to, percutaneous coronary intervention, cardiac imaging, transcatheter heart valve implantation, and device therapy of cardiac arrhythmias and heart failure. An important part of future medical progress involves the evolution of medical technology and the ongoing development of artificial intelligence and machine learning. There is a need to foster an environment conducive to medical technology development and validation so that Europe can continue to play a major role in device innovation while providing high standards of safety. This paper summarizes viewpoints on the topic of device innovation in cardiovascular medicine at the European Society of Cardiology Cardiovascular Round Table, a strategic forum for high-level dialogue to discuss issues related to the future of cardiovascular health in Europe. Devices are developed and improved through an iterative process throughout their lifecycle. Early feasibility studies demonstrate proof of concept and help to optimize the design of a device. If successful, this should ideally be followed by randomized clinical trials comparing novel devices vs. accepted standards of care when available and the collection of post-market real-world evidence through registries. Unfortunately, standardized procedures for feasibility studies across various device categories have not yet been implemented in Europe. Cardiovascular imaging can be used to diagnose and characterize patients for interventions to improve procedural results and to monitor devices long term after implantation. Randomized clinical trials often use cardiac imaging-based inclusion criteria, while less frequently trials randomize patients to compare the diagnostic or prognostic value of different modalities. Applications using machine learning are increasingly important, but specific regulatory standards and pathways remain in development in both Europe and the USA. Standards are also needed for smart devices and digital technologies that support device-driven biomonitoring. Changes in device regulation introduced by the European Union aim to improve clinical evidence, transparency, and safety, but they may impact the speed of innovation, access, and availability. Device development programmes including dialogue on unmet needs and advice on study designs must be driven by a community of physicians, trialists, patients, regulators, payers, and industry to ensure that patients have access to innovative care.

Platinum incorporation into titanate perovskites to deliver emergent active and stable platinum nanoparticles.

Platinum functions exceptionally well as a nanoparticulate catalyst in many important fields, such as in the removal of atmospheric pollutants, but it is scarce, expensive and not always sufficiently durable. Here, we report a perovskite system in which 0.5 wt% Pt is integrated into the support and its subsequent conversion through exsolution to achieve a resilient catalyst. Owing to the instability of most Pt oxides at high temperatures, a thermally stable platinum oxide precursor, barium platinate, was used to preserve the platinum as an oxide during the solid-state synthesis in an approach akin to the Trojan horse legend. By tailoring the procedure, it is possible to produce a uniform equilibrated structure with active emergent Pt nanoparticles strongly embedded in the perovskite surface that display better CO oxidation activity and stability than those of conventionally prepared Pt catalysts. This catalyst was further evaluated for a variety of reactions under realistic test environments-CO and NO oxidation, diesel oxidation catalysis and ammonia slip reactions were investigated.

Centriolar satellites are acentriolar assemblies of centrosomal proteins.

Centrioles are core structural elements of both centrosomes and cilia. Although cytoplasmic granules called centriolar satellites have been observed around these structures, lack of a comprehensive inventory of satellite proteins impedes our understanding of their ancestry. To address this, we performed mass spectrometry (MS)-based proteome profiling of centriolar satellites obtained by affinity purification of their key constituent, PCM1, from sucrose gradient fractions. We defined an interactome consisting of 223 proteins, which showed striking enrichment in centrosome components. The proteome also contained new structural and regulatory factors with roles in ciliogenesis. Quantitative MS on whole-cell and centriolar satellite proteomes of acentriolar cells was performed to reveal dependencies of satellite composition on intact centrosomes. Although most components remained associated with PCM1 in acentriolar cells, reduced cytoplasmic and satellite levels were observed for a subset of centrosomal proteins. These results demonstrate that centriolar satellites and centrosomes form independently but share a substantial fraction of their proteomes. Dynamic exchange of proteins between these organelles could facilitate their adaptation to changing cellular environments during development, stress response and tissue homeostasis.

The relationships between illness and treatment perceptions with adherence to diabetes self-care: A comparison between Arabic-speaking migrants and Caucasian English-speaking patients.

AIMS: To compare illness and treatment perceptions between Arabic-speaking immigrants and Caucasian English-speaking people with type 2 diabetes, and explore the relationships between these beliefs and adherence to self-care activities. METHODS: A cross-sectional study was conducted in healthcare settings with large Arabic populations in metropolitan and rural Victoria, Australia. Adherence to self-care activities, illness and treatment perceptions, and clinical data were recorded. Bivariate associations for continuous normally distributed variables were tested with Pearson's correlation. Non-parametric data were tested using Spearman's rank correlation coefficient. RESULTS: 701 participants were recruited; 392 Arabic-speaking participants (ASPs) and 309 English-speaking participants (ESPs). There were significant relationships between participants' illness and treatment perceptions and adherence to diabetes self-care activities. ASPs' negative beliefs about diabetes were strongly and significantly correlated with poorer adherence to diet recommendations, exercise, blood glucose testing and foot care. ASPs were significantly less adherent to all aspects of diabetes self-care compared with ESPs: dietary behaviours (P=<0.01; 95% confidence interval (CI)=-1.17, -0.84), exercise and physical activity (P=<0.001, 95% CI -1.14, -0.61), blood glucose testing (P=<0.001) and foot-care (P=<0.001). 52.8% of ASPs were sceptical about prescribed diabetes treatment compared with only 11.2% of the ESPs. 88.3% of ASPs were non-adherent to prescribed medication, compared with 45.1% of ESPs. CONCLUSIONS: Arabic-speaking migrants' illness and treatment perceptions were significantly different from the English-speaking group. There is a pressing need to develop new innovative interventions that deliver much-needed improvements in adherence to self-care activities and key health outcomes.

Ring closure activates yeast γTuRC for species-specific microtubule nucleation.

The γ-tubulin ring complex (γTuRC) is the primary microtubule nucleator in cells. γTuRC is assembled from repeating γ-tubulin small complex (γTuSC) subunits and is thought to function as a template by presenting a γ-tubulin ring that mimics microtubule geometry. However, a previous yeast γTuRC structure showed γTuSC in an open conformation that prevents matching to microtubule symmetry. By contrast, we show here that γ-tubulin complexes are in a closed conformation when attached to microtubules. To confirm the functional importance of the closed γTuSC ring, we trapped the closed state and determined its structure, showing that the γ-tubulin ring precisely matches microtubule symmetry and providing detailed insight into γTuRC architecture. Importantly, the closed state is a stronger nucleator, thus suggesting that this conformational switch may allosterically control γTuRC activity. Finally, we demonstrate that γTuRCs have a strong preference for tubulin from the same species.

Lessons from yeast: the spindle pole body and the centrosome.

The yeast spindle pole body (SPB) is the functional equivalent of the centrosome. Most SPB components have been identified and their functions partly established. This involved a large variety of techniques which are described here, and the potential use of some of these in the centrosome field is highlighted. In particular, very useful structural information on the SPB was obtained from a reconstituted complex, the γ-tubulin complex, and also from a sub-particle, SPB cores, prepared by extraction of an enriched SPB preparation. The labelling of SPB proteins with GFP at the N or C termini, using GFP tags inserted into the genome, gave informative electron microscopy localization and fluorescence resonance energy transfer data. Examples are given of more precise functional data obtained by removing domains from one SPB protein, Spc110p, without affecting its essential function. Finally, a structural model for SPB duplication is described and the differences between SPB and centrosome duplication discussed.

Loss of centrioles causes chromosomal instability in vertebrate somatic cells.

Most animal cells contain a centrosome, which comprises a pair of centrioles surrounded by an ordered pericentriolar matrix (PCM). Although the role of this organelle in organizing the mitotic spindle poles is well established, its precise contribution to cell division and cell survival remains a subject of debate. By genetically ablating key components of centriole biogenesis in chicken DT40 B cells, we generated multiple cell lines that lack centrioles. PCM components accumulated in acentriolar microtubule (MT)-organizing centers but failed to adopt a higher-order structure, as shown by three-dimensional structured illumination microscopy. Cells without centrioles exhibited both a delay in bipolar spindle assembly and a high rate of chromosomal instability. Collectively, our results expose a vital role for centrosomes in establishing a mitotic spindle geometry that facilitates correct kinetochore-MT attachments. We propose that centrosomes are essential in organisms in which rapid segregation of a large number of chromosomes needs to be attained with fidelity.

CDK5RAP2 functions in centrosome to spindle pole attachment and DNA damage response.

The centrosomal protein, CDK5RAP2, is mutated in primary microcephaly, a neurodevelopmental disorder characterized by reduced brain size. The Drosophila melanogaster homologue of CDK5RAP2, centrosomin (Cnn), maintains the pericentriolar matrix (PCM) around centrioles during mitosis. In this study, we demonstrate a similar role for CDK5RAP2 in vertebrate cells. By disrupting two evolutionarily conserved domains of CDK5RAP2, CNN1 and CNN2, in the avian B cell line DT40, we find that both domains are essential for linking centrosomes to mitotic spindle poles. Although structurally intact, centrosomes lacking the CNN1 domain fail to recruit specific PCM components that mediate attachment to spindle poles. Furthermore, we show that the CNN1 domain enforces cohesion between parental centrioles during interphase and promotes efficient DNA damage-induced G2 cell cycle arrest. Because mitotic spindle positioning, asymmetric centrosome inheritance, and DNA damage signaling have all been implicated in cell fate determination during neurogenesis, our findings provide novel insight into how impaired CDK5RAP2 function could cause premature depletion of neural stem cells and thereby microcephaly.

Structural role of Sfi1p-centrin filaments in budding yeast spindle pole body duplication.

Centrins are calmodulin-like proteins present in centrosomes and yeast spindle pole bodies (SPBs) and have essential functions in their duplication. The Saccharomyces cerevisiae centrin, Cdc31p, binds Sfi1p on multiple conserved repeats; both proteins localize to the SPB half-bridge, where the new SPB is assembled. The crystal structures of Sfi1p-centrin complexes containing several repeats show Sfi1p as an alpha helix with centrins wrapped around each repeat and similar centrin-centrin contacts between each repeat. Electron microscopy (EM) shadowing of an Sfi1p-centrin complex with 15 Sfi1 repeats and 15 centrins bound showed filaments 60 nm long, compatible with all the Sfi1 repeats as a continuous alpha helix. Immuno-EM localization of the Sfi1p N and C termini showed Sfi1p-centrin filaments spanning the length of the half-bridge with the Sfi1p N terminus at the SPB. This suggests a model for SPB duplication where the half-bridge doubles in length by association of the Sfi1p C termini, thereby providing a new Sfi1p N terminus to initiate SPB assembly.

Architecture of the human ndc80-hec1 complex, a critical constituent of the outer kinetochore.

The Ndc80 complex is a constituent of the outer plate of the kinetochore and plays a critical role in establishing the stable kinetochore-microtubule interactions required for chromosome segregation in mitosis. The Ndc80 complex is evolutionarily conserved and contains the four subunits Spc24, Spc25, Nuf2, and Ndc80 (whose human homologue is called Hec1). All four subunits are predicted to contain globular domains and extensive coiled coil regions. To gain an insight into the organization of the human Ndc80 complex, we reconstituted it using recombinant methods. The hydrodynamic properties of the recombinant Ndc80 complex are identical to those of the endogenous HeLa cell complex and are consistent with a 1:1:1:1 stoichiometry of the four subunits and a very elongated shape. Two tight Hec1-Nuf2 and Spc24-Spc25 subcomplexes, each stabilized by a parallel heterodimeric coiled coil, maintain this organization. These subcomplexes tetramerize via an interaction of the C- and N-terminal portions of the Hec1-Nuf2 and Spc24-Spc25 coiled coils, respectively. The recombinant complex displays normal kinetochore localization upon injection in HeLa cells and is therefore a faithful copy of the endogenous Ndc80 complex.

Interactions between centromere complexes in Saccharomyces cerevisiae.

We have purified two new complexes from Saccharomyces cerevisiae, one containing the centromere component Mtw1p together with Nnf1p, Nsl1p, and Dsn1p, which we call the Mtw1p complex, and the other containing Spc105p and Ydr532p, which we call the Spc105p complex. Further purifications using Dsn1p tagged with protein A show, in addition to the other components of the Mtw1p complex, the two components of the Spc105p complex and the four components of the previously described Ndc80p complex, suggesting that all three complexes are closely associated. Fluorescence microscopy and immunoelectron microscopy show that Nnf1p, Nsl1p, Dsn1p, Spc105p, and Ydr532p all localize to the nuclear side of the spindle pole body and along short spindles. Chromatin immunoprecipitation assays show that all five proteins are associated with centromere DNA. Homologues of Nsl1p and Spc105p in Schizosaccharomyces pombe also localize to the centromere. Temperature-sensitive mutations of Nsl1p, Dsn1p, and Spc105p all cause defects in chromosome segregation. Synthetic-lethal interactions are found between temperature-sensitive mutations in proteins from all three complexes, in agreement with their close physical association. These results show an increasingly complex structure for the S. cerevisiae centromere and a probable conservation of structure between parts of the centromeres of S. cerevisiae and S. pombe.

Sfi1p has conserved centrin-binding sites and an essential function in budding yeast spindle pole body duplication.

Centrins are calmodulin-like proteins present in microtubule-organizing centers. The Saccharomyces cerevisiae centrin, Cdc31p, was functionally tagged with a single Z domain of protein A, and used in pull-down experiments to isolate Cdc31p-binding proteins. One of these, Sfi1p, localizes to the half-bridge of the spindle pole body (SPB), where Cdc31p is also localized. Temperature-sensitive mutants in SFI1 show a defect in SPB duplication and genetic interactions with cdc31-1. Sfi1p contains multiple internal repeats that are also present in a Schizosaccharomyces pombe protein, which also localizes to the SPB, and in several human proteins, one of which localizes close to the centriole region. Cdc31p binds directly to individual Sfi1 repeats in a 1:1 ratio, so a single molecule of Sfi1p binds multiple molecules of Cdc31p. The centrosomal human protein containing Sfi1 repeats also binds centrin in the repeat region, showing that this centrin-binding motif is conserved.

hNuf2 inhibition blocks stable kinetochore-microtubule attachment and induces mitotic cell death in HeLa cells.

Identification of proteins that couple kinetochores to spindle microtubules is critical for understanding how accurate chromosome segregation is achieved in mitosis. Here we show that the protein hNuf2 specifically functions at kinetochores for stable microtubule attachment in HeLa cells. When hNuf2 is depleted by RNA interference, spindle formation occurs normally as cells enter mitosis, but kinetochores fail to form their attachments to spindle microtubules and cells block in prometaphase with an active spindle checkpoint. Kinetochores depleted of hNuf2 retain the microtubule motors CENP-E and cytoplasmic dynein, proteins previously implicated in recruiting kinetochore microtubules. Kinetochores also retain detectable levels of the spindle checkpoint proteins Mad2 and BubR1, as expected for activation of the spindle checkpoint by unattached kinetochores. In addition, the cell cycle block produced by hNuf2 depletion induces mitotic cells to undergo cell death. These data highlight a specific role for hNuf2 in kinetochore-microtubule attachment and suggest that hNuf2 is part of a molecular linker between the kinetochore attachment site and tubulin subunits within the lattice of attached plus ends.