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Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex
Get PDFDynamic reorganization of the actomyosin cytoskeleton allows fast modulation of the cell surface, which is vital for many cellular functions. Myosin-II motors generate the forces required for this remodeling by imparting contractility to actin networks. However, myosin-II activity might also have a more indirect contribution to cytoskeletal dynamics; it has been proposed that myosin activity increases actin turnover in various cellular contexts, presumably by enhancing disassembly. In vitro reconstitution of actomyosin networks has confirmed the role of myosin in actin network disassembly, but the reassembly of actin in these assays was limited by factors such as diffusional constraints and the use of stabilized actin filaments. Here, we present the reconstitution of a minimal dynamic actin cortex, where actin polymerization is catalyzed on the membrane in the presence of myosin-II activity. We demonstrate that myosin activity leads to disassembly and redistribution in this simplified cortex. Consequently, a new dynamic steady state emerges in which the actin network undergoes constant turnover. Our findings suggest a multifaceted role of myosin-II in the dynamics of the eukaryotic actin cortex
More from less – bottom-up reconstitution of cell biology
Get PDFThe ultimate goal of bottom-up synthetic biology is recreating life in its simplest form. However, in its quest to find the minimal functional units of life, this field contributes more than its main aim by also offering a range of tools for asking, and experimentally approaching, biological questions. This Review focusses on how bottom-up reconstitution has furthered our understanding of cell biology. Studying cell biological processes in vitro has a long tradition, but only recent technological advances have enabled researchers to reconstitute increasingly complex biomolecular systems by controlling their multi-component composition and their spatiotemporal arrangements. We illustrate this progress using the example of cytoskeletal processes. Our understanding of these has been greatly enhanced by reconstitution experiments, from the first in vitro experiments 70 years ago to recent work on minimal cytoskeleton systems (including this Special Issue of Journal of Cell Science). Importantly, reconstitution approaches are not limited to the cytoskeleton field. Thus, we also discuss progress in other areas, such as the shaping of biomembranes and cellular signalling, and prompt the reader to add their subfield of cell biology to this list in the future
Snooping on cells in worms and mini-organs
No full textThroughout their lifetime, animals face a wide variety of biological chal-
lenges. Starting out as single cells, their first challenge is to undergo devel-
opment and become fully grown and functional adults. Remarkably, this
incredibly complex process occurs in a highly reproducible manner despite
the huge variability in environmental, genetic and molecular fluctuations
they encounter during their journey through development. However, the
challenges do not end here; once animals become adults, their tissues are
constantly subject to damage, either by external sources such as disease, or
due to intrinsic causes such as cellular aging. Thus, adult tissues are con-
stantly renewing themselves, and must do so in a tightly controlled manner
in order to maintain homeostasis. In this thesis, we explore how animals
cope with a few of such challenges with the help of two model systems, C.
elegans worms and stem cell-derived organoids
Perovskite Thin Film Materials Stabilized and Enhanced by Zinc(II) Doping
Get PDFFeatured Application Doping lead perovskite materials with a few percent of zinc-halides increases their stability at ambient conditions, enhances their properties and improves the efficiency of the corresponding solar cell devices.
Abstract Recent work of ten different groups shows that the application of zinc-halides in lead perovskite materials results in a contraction of the d-space, stronger interaction with the organic cation, improved crystallization with larger crystal domains, a Goldschmidt factor closer to unity, smoother and denser thin films and an even distribution of Zn(II) (at the Pb(II) sites) throughout the material. These combined effects may lead to: (1) a substantially higher stability (even at ambient or high humidity conditions); (2) enhanced luminescent properties; (3) a higher power conversion efficiency (PCE) of the corresponding solar cell devices (up to PCE similar to 20%, with enhancement factors of 1.07 to 1.33 relative to undoped material)
Observation of Distinct Carboxylic Acid Conformers in Aqueous Solution
Get PDFWe investigate the molecular geometry of the carboxyl group of formic acid in acetonitrile and aqueous solutions at room temperature with two-dimensional infrared spectroscopy (2D-IR). We found that the carboxyl group adopts two distinct configurations: a configuration in which the carbonyl group is oriented anti-parallel to the hydroxyl (anti-conformer), and a configuration in which the carbonyl group is oriented at an angle of ~60° with respect to the hydroxyl (syn-conformer). These results constitute the first experimental evidence that carboxyl groups exist as two distinct and long-living conformational isomers in aqueous solution at room temperature
A Monolithic Immersion Metalens for Imaging Solid-State Quantum Emitters
Get PDFQuantum emitters such as the diamond nitrogen-vacancy (NV) center are the basis for a wide range of quantum technologies. However, refraction and reflections at material interfaces impede photon collection, and the emitters’ atomic scale necessitates the use of free space optical measurement setups that prevent packaging of quantum devices. To overcome these limitations, we design and fabricate a metasurface composed of nanoscale diamond pillars that acts as an immersion lens to collect and collimate the emission of an individual NV center. The metalens exhibits a numerical aperture greater than 1.0, enabling efficient fiber-coupling of quantum emitters. This flexible design will lead to the miniaturization of quantum devices in a wide range of host materials and the development of metasurfaces that shape single-photon emission for coupling to optical cavities or route photons based on their quantum state
Synthetic cell division via membrane-transforming molecular assemblies
Get PDFReproduction, i.e. the ability to produce new individuals from a parent organism, is a hallmark of living matter. Even the simplest forms of reproduction require cell division: attempts to create a designer cell therefore should include a synthetic cell division machinery. In this review, we will illustrate how nature solves this task, describing membrane remodelling processes in general and focusing on bacterial cell division in particular. We discuss recent progress made in their in vitro reconstitution, identify open challenges, and suggest how purely synthetic building blocks could provide an additional and attractive route to creating artificial cell division machineries
Caffeine and taurine slow down water molecules
Get PDFIn this work we study the effect of caffeine and taurine on the mobility of water molecules at 298 K using femtosecond mid-infrared and dielectric relaxation spectroscopy. We observe both molecules to have a slowing down effect on the mobility of surrounding water molecules: a single caffeine molecule slows down ~9 water molecules, a single taurine molecule slows down ~4 water molecules. The reorientation time constant of these slow water molecules is 4–5 times longer than the reorientation time constant of 2.5 ps of water molecules in bulk liquid water
From plasmodesma geometry to effective symplastic permeability through biophysical modelling
Get PDFRegulation of molecular transport via intercellular channels called plasmodesmata (PDs) is important for both, the coordination of developmental and environmental responses among neighbouring cells and the isolation of cell domains to execute specific developmental or stress-induced programs. PD transport capacity (i.e. effective symplastic permeability) has been determined experimentally, at a tissue level, by assessing the mobility of different fluorescent molecules, or predicted from PD ultrastructural features using electron-microscopy. Values obtained from these approaches are often very different. Here, we build a theoretical bridge between the two experimental approaches by calculating the effective symplastic permeability from a geometrical description of individual PDs, considering the flow towards them and including the impact of PD clustering into pit fields. Our open source multi-level model allows us to link measured permeabilities with realistic PD dimensions, predict how typical PD features affect transport properties and add a functional interpretation to recent experimental observations
Long‐term expanding human airway organoids for disease modeling
Get PDFOrganoids are self-organizing 3D structures grown from stem cells that recapitulate essential aspects of organ structure and function. Here, we describe a method to establish long-term-expanding human airway organoids from broncho-alveolar resections or lavage material. The pseudostratified airway organoids consist of basal cells, functional multi-ciliated cells, mucus-producing secretory cells, and CC10-secreting club cells. Airway organoids derived from cystic fibrosis (CF) patients allow assessment of CFTR function in an organoid swelling assay. Organoids established from lung cancer resections and metastasis biopsies retain tumor histopathology as well as cancer gene mutations and are amenable to drug screening. Respiratory syncytial virus (RSV) infection recapitulates central disease features, dramatically increases organoid cell motility via the non-structural viral NS2 protein, and preferentially recruits neutrophils upon co-culturing. We conclude that human airway organoids represent versatile models for the in vitro study of hereditary, malignant, and infectious pulmonary disease