Stationary shapes of deformable particles moving at low Reynolds numbers

Lecture Notes of the Summer School ``Microswimmers -- From Single Particle Motion to Collective Behaviour'', organised by the DFG Priority Programme SPP 1726 (Forschungszentrum J{\"{u}}lich, 2015).Comment: Pages C7.1-16 of G. Gompper et al. (ed.), Microswimmers - From Single Particle Motion to Collective Behaviour, Lecture Notes of the DFG SPP 1726 Summer School 2015, Forschungszentrum J\"ulich GmbH, Schriften des Forschungszentrums J\"ulich, Reihe Key Technologies, Vol 110, ISBN 978-3-95806-083-

Transcriptional and Linkage Analyses Identify Loci that Mediate the Differential Macrophage Response to Inflammatory Stimuli and Infection

Macrophages display flexible activation states that range between pro-inflammatory (classical activation) and anti-inflammatory (alternative activation). These macrophage polarization states contribute to a variety of organismal phenotypes such as tissue remodeling and susceptibility to infectious and inflammatory diseases. Several macrophage- or immune-related genes have been shown to modulate infectious and inflammatory disease pathogenesis. However, the potential role that differences in macrophage activation phenotypes play in modulating differences in susceptibility to infectious and inflammatory disease is just emerging. We integrated transcriptional profiling and linkage analyses to determine the genetic basis for the differential murine macrophage response to inflammatory stimuli and to infection with the obligate intracellular parasite Toxoplasma gondii. We show that specific transcriptional programs, defined by distinct genomic loci, modulate macrophage activation phenotypes. In addition, we show that the difference between AJ and C57BL/6J macrophages in controlling Toxoplasma growth after stimulation with interferon gamma and tumor necrosis factor alpha mapped to chromosome 3, proximal to the Guanylate binding protein (Gbp) locus that is known to modulate the murine macrophage response to Toxoplasma. Using an shRNA-knockdown strategy, we show that the transcript levels of an RNA helicase, Ddx1, regulates strain differences in the amount of nitric oxide produced by macrophage after stimulation with interferon gamma and tumor necrosis factor. Our results provide a template for discovering candidate genes that modulate macrophage-mediated complex traits

Subjective assessment of frequency distribution histograms and consequences on reference interval accuracy for small sample sizes: A computer-simulated study

BACKGROUND: Inaccuracy in estimating reference intervals (RIs) is a problem with small sample sizes. OBJECTIVES: This study aimed to identify the most accurate statistical methods to estimate RIs based on sample size and population distribution shape. We also studied the accuracy of sample frequency distribution histograms to retrieve the original population distribution and compared strategies based on the histogram and goodness-of-fit test. METHODS: The statistical methods that best enhanced accuracy were determined for various sample sizes (n = 20-60) and population distributions (Gaussian, log-normal, and left-skewed) were determined by repeated-measures ANOVA and posthoc analyses. Frequency distribution histograms were built from 900 samples of five different sizes randomly extracted from six simulated populations. Three reviewers classified the population distributions from visual assessments of a sample histogram, and the classification error rate was calculated. RI accuracy was compared among the strategies based on the histograms and goodness-of-fit tests. RESULTS: The parametric, nonparametric, and robust methods enhanced lower reference limit estimation accuracy for Gaussian, log-normal, and left-skewed distributions, respectively. The parametric, nonparametric bootstrap, and nonparametric methods enhanced the upper limit estimation accuracy for Gaussian, log-normal, and left-skewed distributions, respectively. Regardless of sample size, sample histogram assessments properly classified the original population distribution 71% to 93.9% of the time, depending on the reviewers. In this study, the strategy based on histograms assessed by the statistician was significantly more precise and accurate than the strategy based on the goodness-of-fit test (P \u3c 0.001). CONCLUSIONS: A strategy based on histograms might enhance the accuracy of RI estimations. However, relevant inter-reviewer variations in histogram interpretation were detected. Factors affecting inter-reviewer variations should be further explored

Dynamics of pearling instability in polymersomes: the role of shear membrane viscosity and spontaneous curvature

International audienceThe stability of copolymer tethers is investigated theoretically. Self-assembly of diblockor triblock copolymers can lead to tubular polymersomes which are known experimentallyto undergo shape instability under thermal, chemical and tension stresses. It leads to aperiodic modulation of the radius which evolves to assembly-line pearls connected by tinytethers. We study the contributions of shear surface viscosity and spontaneous curvatureand their interplay to understand the pearling instability. The performed linear analysisof stability of this cylinder-to-pearls transition shows that such systems are unstable if themembrane tension is larger than a finite critical value contrary to the Rayleigh-Plateauinstability, an already known result or if the spontaneous curvature is in a specific rangewhich depends on membrane tension. For the case of spontaneous curvature-induced shapeinstability, two dynamical modes are identified. The first one is analog to the tension-induced instability with a marginal mode. Its wavenumber associated with the most un-stable mode decreases continuously to zero as membrane viscosity increases. The secondone has a finite range of unstable wavenumbers. The wavenumber of the most unstablemode tends redto be constant as membrane viscosity increases. In this mode, its growthrate becomes independent of the bulk viscosity in the limit of high membrane viscosity andbehaves as a pure viscous surface

Dynamics of pearling instability in polymersomes: the role of shear membrane viscosity and spontaneous curvature

The stability of copolymer tethers is investigated theoretically. Self-assembly of diblockor triblock copolymers can lead to tubular polymersomes which are known experimentallyto undergo shape instability under thermal, chemical and tension stresses. It leads to aperiodic modulation of the radius which evolves to assembly-line pearls connected by tinytethers. We study the contributions of shear surface viscosity and spontaneous curvatureand their interplay to understand the pearling instability. The performed linear analysisof stability of this cylinder-to-pearls transition shows that such systems are unstable if themembrane tension is larger than a finite critical value contrary to the Rayleigh-Plateauinstability, an already known result or if the spontaneous curvature is in a specific rangewhich depends on membrane tension. For the case of spontaneous curvature-induced shapeinstability, two dynamical modes are identified. The first one is analog to the tension-induced instability with a marginal mode. Its wavenumber associated with the most un-stable mode decreases continuously to zero as membrane viscosity increases. The secondone has a finite range of unstable wavenumbers. The wavenumber of the most unstablemode tends redto be constant as membrane viscosity increases. In this mode, its growthrate becomes independent of the bulk viscosity in the limit of high membrane viscosity andbehaves as a pure viscous surface