384 research outputs found
Skin and bones: the bacterial cytoskeleton, cell wall, and cell morphogenesis
The bacterial world is full of varying cell shapes and sizes, and individual species perpetuate a defined morphology generation after generation. We review recent findings and ideas about how bacteria use the cytoskeleton and other strategies to regulate cell growth in time and space to produce different shapes and sizes
THC Exposure is Reflected in the Microstructure of the Cerebral Cortex and Amygdala of Young Adults
The endocannabinoid system serves a critical role in homeostatic regulation through its influence on processes underlying appetite, pain, reward, and stress, and cannabis has long been used for the related modulatory effects it provides through tetrahydrocannabinol (THC). We investigated how THC exposure relates to tissue microstructure of the cerebral cortex and subcortical nuclei using computational modeling of diffusion magnetic resonance imaging data in a large cohort of young adults from the Human Connectome Project. We report strong associations between biospecimen-defined THC exposure and microstructure parameters in discrete gray matter brain areas, including frontoinsular cortex, ventromedial prefrontal cortex, and the lateral amygdala subfields, with independent effects in behavioral measures of memory performance, negative intrusive thinking, and paternal substance abuse. These results shed new light on the relationship between THC exposure and microstructure variation in brain areas related to salience processing, emotion regulation, and decision making. The absence of effects in some other cannabinoid-receptor-rich brain areas prompts the consideration of cellular and molecular mechanisms that we discuss. Further studies are needed to characterize the nature of these effects across the lifespan and to investigate the mechanistic neurobiological factors connecting THC exposure and microstructural parameters
Dislocation-mediated growth of bacterial cell walls
Recent experiments have illuminated a remarkable growth mechanism of
rod-shaped bacteria: proteins associated with cell wall extension move at
constant velocity in circles oriented approximately along the cell
circumference (Garner et al., Science (2011), Dominguez-Escobar et al. Science
(2011), van Teeffelen et al. PNAS (2011). We view these as dislocations in the
partially ordered peptidoglycan structure, activated by glycan strand extension
machinery, and study theoretically the dynamics of these interacting defects on
the surface of a cylinder. Generation and motion of these interacting defects
lead to surprising effects arising from the cylindrical geometry, with
important implications for growth. We also discuss how long range elastic
interactions and turgor pressure affect the dynamics of the fraction of
actively moving dislocations in the bacterial cell wall.Comment: to appear in PNA
Mutations in the Lipopolysaccharide Biosynthesis Pathway Interfere with Crescentin-Mediated Cell Curvature in Caulobacter crescentus
Bacterial cell morphogenesis requires coordination among multiple cellular systems, including the bacterial
cytoskeleton and the cell wall. In the vibrioid bacterium Caulobacter crescentus, the intermediate filament-like
protein crescentin forms a cell envelope-associated cytoskeletal structure that controls cell wall growth to
generate cell curvature. We undertook a genetic screen to find other cellular components important for cell
curvature. Here we report that deletion of a gene (wbqL) involved in the lipopolysaccharide (LPS) biosynthesis
pathway abolishes cell curvature. Loss of WbqL function leads to the accumulation of an aberrant Opolysaccharide
species and to the release of the S layer in the culture medium. Epistasis and microscopy
experiments show that neither S-layer nor O-polysaccharide production is required for curved cell morphology
per se but that production of the altered O-polysaccharide species abolishes cell curvature by apparently
interfering with the ability of the crescentin structure to associate with the cell envelope. Our data suggest that
perturbations in a cellular pathway that is itself fully dispensable for cell curvature can cause a disruption of
cell morphogenesis, highlighting the delicate harmony among unrelated cellular systems. Using the wbqL
mutant, we also show that the normal assembly and growth properties of the crescentin structure are
independent of its association with the cell envelope. However, this envelope association is important for
facilitating the local disruption of the stable crescentin structure at the division site during cytokinesis
Frontoinsular cortical microstructure is linked to life satisfaction in young adulthood
Life satisfaction is a component of subjective wellbeing
that reflects a global judgement of the quality of life
according to an individualās own needs and expectations.
As a psychological construct, it has attracted attention due
to its relationship to mental health, resilience to stress, and other factors. Neuroimaging studies have identified neurobiological correlates of life satisfaction; however, they are limited to functional connectivity and gray matter morphometry. We explored features of gray matter microstructure obtained through compartmental modeling of multi-shell diffusion MRI data, and we examined cortical microstructure in frontoinsular cortex in a cohort of 807 typical young adults scanned as part of the Human Connectome Project. Our experiments identified the orientation dispersion index (ODI), and analogously fractional anisotropy (FA), of frontoinsular cortex as a robust set of anatomically-specific lateralized diffusion MRI microstructure features that are linked to life satisfaction, independent of other demographic, socioeconomic, and behavioral factors. We further validated
our findings in a secondary test-retest dataset and found high reliability of our imaging metrics and reproducibility of outcomes. In our analysis of twin and non-twin siblings, we found basic microstructure in frontoinsular cortex to be strongly genetically determined. We also found a more moderate but still very significant genetic role in determining microstructure as it relates to life satisfaction in frontoinsular cortex. Our findings suggest a potential linkage between well-being and microscopic features of frontoinsular cortex, which may reflect cellular morphology and architecture and may more broadly implicate the integrity of the homeostatic processing performed by frontoinsular cortex as an important component of an individualās judgements of life satisfaction
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Fauxvea: Crowdsourcing Gaze Location Estimates for Visualization Analysis Tasks
We present the design and evaluation of a method for estimating gaze locations during the analysis of static visualizations using crowdsourcing. Understanding gaze patterns is helpful for evaluating visualizations and user behaviors, but traditional eye-tracking studies require specialized hardware and local users. To avoid these constraints, we developed a method called Fauxvea, which crowdsources visualization tasks on the Web and estimates gaze fixations through cursor interactions without eye-tracking hardware. We ran experiments to evaluate how gaze estimates from our method compare with eye-tracking data. First, we evaluated crowdsourced estimates for three common types of information visualizations and basic visualization tasks using Amazon Mechanical Turk (MTurk). In another, we reproduced findings from a previous eye-tracking study on tree layouts using our method on MTurk. Results from these experiments show that fixation estimates using Fauxvea are qualitatively and quantitatively similar to eye tracking on the same stimulus-task pairs. These findings suggest that crowdsourcing visual analysis tasks with static information visualizations could be a viable alternative to traditional eye-tracking studies for visualization research and design
Christine Jacobs-Wagner: Drawing the bacterial organizational chart
Jacobs-Wagner has been at the forefront of a revolution in bacterial cell biology
Application of a Novel Quantitative Tractography Based Analysis of Diffusion Tensor Imaging to Examine Fiber Bundle Length in Human Cerebral White Matter
This paper reviews basic methods and recent applications of length-based fiber bundle analysis of cerebral white matter using diffusion magnetic resonance imaging (dMRI). Diffusion weighted imaging (DWI) is a dMRI technique that uses the random motion of water to probe tissue microstructure in the brain. Diffusion tensor imaging (DTI) is an extension of DWI that measures the magnitude and direction of water diffusion in cerebral white matter, using either voxel-based scalar metrics or tractography-based analyses. More recently, quantitative tractography based on diffusion tensor imaging (qtDTI) technology has been developed to help quantify aggregate structural anatomical properties of white matter fiber bundles, including both scalar metrics of bundle diffusion and more complex morphometric properties, such as fiber bundle length (FBL). Unlike traditional scalar diffusion metrics, FBL reflects the direction and curvature of white matter pathways coursing through the brain and is sensitive to changes within the entire tractography model. In this paper, we discuss applications of this approach to date that have provided new insights into brain organization and function. We also discuss opportunities for improving the methodology through more complex anatomical models and potential areas of new application for qtDTI
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