The physical basis of self-organization of the mammalian oocyte spindle

To prepare gametes with the appropriate number of chromosomes, mammalian oocytes undergo two sequential cell divisions. During each division, a large, long-lived, microtubule-based organelle called the meiotic spindle assembles around condensed chromosomes. Although meiotic spindles have been intensively studied for several decades, as force-generating mechanical objects, they remain very poorly understood. In materials physics, coarse-grained theories have been essential in understanding the large-scale behavior of systems composed of many interacting particles. It is unclear, however, if this approach can succeed in capturing the properties of active, biochemically complex, living materials like the spindle. Here, we show that a class of models based on nematic liquid crystal theory can describe important aspects of the organelle-scale structure and dynamics of spindles in living mouse oocytes. Using our models to interpret quantitative polarization microscopy data, we measure for the first time material properties relating to stress propagation in living oocytes, including the nematic diffusivities corresponding to splay and bend deformations. Unlike the reconstituted amphibian spindles that were previously studied in vitro, nematic elastic stress is exponentially screened in the microtubule network of living mammalian oocytes, with a screening length of order one micron. This observation can be explained by the relatively high volume fraction of embedded chromosomes in mammalian meiotic spindles, which cause long voids in the microtubule network and so disrupt orientational stress propagation

An inherited duplication at the gene p21 protein-activated Kinase 7 (PAK7) is a risk factor for psychosis

FUNDING Funding for this study was provided by the Wellcome Trust Case Control Consortium 2 project (085475/B/08/Z and 085475/Z/08/Z), the Wellcome Trust (072894/Z/03/Z, 090532/Z/09/Z and 075491/Z/04/B), NIMH grants (MH 41953 and MH083094) and Science Foundation Ireland (08/IN.1/B1916). We acknowledge use of the Trinity Biobank sample from the Irish Blood Transfusion Service; the Trinity Centre for High Performance Computing; British 1958 Birth Cohort DNA collection funded by the Medical Research Council (G0000934) and the Wellcome Trust (068545/Z/02) and of the UK National Blood Service controls funded by the Wellcome Trust. Chris Spencer is supported by a Wellcome Trust Career Development Fellowship (097364/Z/11/Z). Funding to pay the Open Access publication charges for this article was provided by the Wellcome Trust. ACKNOWLEDGEMENTS The authors sincerely thank all patients who contributed to this study and all staff who facilitated their involvement. We thank W. Bodmer and B. Winney for use of the People of the British Isles DNA collection, which was funded by the Wellcome Trust. We thank Akira Sawa and Koko Ishzuki for advice on the PAK7–DISC1 interaction experiment and Jan Korbel for discussions on mechanism of structural variation.Peer reviewedPublisher PD

Common polygenic variation in coeliac disease and confirmation of ZNF335 and NIFA as disease susceptibility loci

Coeliac disease (CD) is a chronic immune-mediated disease triggered by the ingestion of gluten. It has an estimated prevalence of approximately 1% in European populations. Specific HLA-DQA1 and HLA-DQB1 alleles are established coeliac susceptibility genes and are required for the presentation of gliadin to the immune system resulting in damage to the intestinal mucosa. In the largest association analysis of CD to date, 39 non-HLA risk loci were identified, 13 of which were new, in a sample of 12 014 individuals with CD and 12 228 controls using the Immunochip genotyping platform. Including the HLA, this brings the total number of known CD loci to 40. We have replicated this study in an independent Irish CD case–control population of 425 CD and 453 controls using the Immunochip platform. Using a binomial sign test, we show that the direction of the effects of previously described risk alleles were highly correlated with those reported in the Irish population, (P=2.2 × 10−16). Using the Polygene Risk Score (PRS) approach, we estimated that up to 35% of the genetic variance could be explained by loci present on the Immunochip (P=9 × 10−75). When this is limited to non-HLA loci, we explain a maximum of 4.5% of the genetic variance (P=3.6 × 10−18). Finally, we performed a meta-analysis of our data with the previous reports, identifying two further loci harbouring the ZNF335 and NIFA genes which now exceed genome-wide significance, taking the total number of CD susceptibility loci to 42

Phase behavior of charged hydrophobic colloids on flat and spherical surfaces

For a broad class of two-dimensional (2D) materials, the transition from isotropic fluid to crystalline solid is described by the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY). According to this theory, long-range order is achieved via elimination of the topological defects which proliferate in the fluid phase. However, many natural and man-made 2D systems posses spatial curvature and/or non-trivial topology, which require the presence of topological defects, even at T=0. In principle, the presence of these defects could profoundly affect the phase behavior of such a system. In this thesis, we develop and characterize an experimental system of charged colloidal particles that bind electrostatically to the interface between an oil and an aqueous phase. Depending on how we prepare the sample, this fluid interface may be flat, spherical, or have a more complicated geometry. Focusing on the cases where the interface is flat or spherical, we measure the interactions between the particles, and probe various aspects of their phase behavior. On flat interfaces, this phase behavior is well-described by KTHNY theory. In spherical geometries, however, we observe spatial structures and inhomogeneous dynamics that cannot be captured by the measures traditionally used to describe flat-space phase behavior. We show that, in the spherical system, ordering is achieved by a novel mechanism: sequestration of topological defects into freely-terminating grain boundaries (“scars”), and simultaneous spatial organization of the scars themselves on the vertices of an icosahedron. The emergence of icosahedral order coincides with the localization of mobility into isolated “lakes” of fluid or glassy particles, situated at the icosahedron vertices. These lakes are embedded in a rigid, connected “continent” of locally crystalline particles

Freezing on a Sphere

Data files used in the paper "Freezing on a Sphere" by Rodrigo E Guerra, Colm P Kelleher, Andrew D Hollingsworth, and Paul M Chaiki

Olsalazine is not superior to placebo in maintaining remission of inactive Crohn\u27s colitis and ileocolitis: a double blind, parallel, randomised, multicentre study

peer-reviewedBACKGROUND AND AIMS: The benefit of 5-aminosalicylic acid therapy for maintenance of remission in Crohn\u27s disease is controversial. The primary aim of this study was to evaluate the prophylactic properties of olsalazine in comparison with placebo for maintenance of remission in quiescent Crohn\u27s colitis and/or ileocolitis. METHODS: In this randomised, double blind, parallel group study of olsalazine versus placebo, 328 patients with quiescent Crohn\u27s colitis and/or ileocolitis were recruited. Treatment consisted of olsalazine 2.0 g daily or placebo for 52 weeks. The primary end point of efficacy was relapse, as defined by the Crohn\u27s disease activity index (CDAI) and by clinical relapse. Laboratory and clinical disease activity indicators were also measured. Safety analysis consisted of documentation of adverse events and laboratory values. RESULTS: No differences in the frequency of termination due to relapse or time to termination due to relapse were noted between the two treatment groups (olsalazine 48.5% v placebo 45%) for either colitis or ileocolitis. The failure rate, defined as not completing the study, was significantly higher in olsalazine treated patients compared with placebo treated patients for the overall population (colitis and/or ileocolitis: olsalazine 65.4% v 53.9%; p=0.038). Similar failure rates were seen for patients with colitis. A significantly higher percentage of olsalazine treated patients experienced adverse gastrointestinal events. Drug attributed adverse events were reported more frequently in the olsalazine treated group with gastrointestinal symptoms being causally related to olsalazine treatment (olsalazine 40.7% v placebo 26.9%; p=0.010). Back pain was reported significantly more often by the placebo treated group. However, serious medical events did not differ between the two groups. Adverse events led to more early withdrawals in the olsalazine treated group than in the placebo treated group; thus average time in the study for patients in the olsalazine treatment group was significantly shorter than that of patients in the placebo group. CONCLUSIONS: Patients treated with olsalazine were more likely to terminate their participation in the trial than those taking placebo. This difference was not related to relapse of disease, as measured by CDAI and clinical measures, but rather was due to the development of intolerable adverse medical events of a non-serious nature related to the gastrointestinal tract. The gastrointestinal related events in the olsalazine treated group may be due to the difference in gastrointestinal status at baseline which favoured the placebo treatment group

Mechanical Mechanisms of Chromosome Segregation

Chromosome segregation—the partitioning of genetic material into two daughter cells—is one of the most crucial processes in cell division. In all Eukaryotes, chromosome segregation is driven by the spindle, a microtubule-based, self-organizing subcellular structure. Extensive research performed over the past 150 years has identified numerous commonalities and contrasts between spindles in different systems. In this review, we use simple coarse-grained models to organize and integrate previous studies of chromosome segregation. We discuss sites of force generation in spindles and fundamental mechanical principles that any understanding of chromosome segregation must be based upon. We argue that conserved sites of force generation may interact differently in different spindles, leading to distinct mechanical mechanisms of chromosome segregation. We suggest experiments to determine which mechanical mechanism is operative in a particular spindle under study. Finally, we propose that combining biophysical experiments, coarse-grained theories, and evolutionary genetics will be a productive approach to enhance our understanding of chromosome segregation in the future