985 research outputs found

    The Forces behind Directed Cell Migration

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    Directed cell migration is an essential building block of life, present when an embryo develops, a dendritic cell migrates toward a lymphatic vessel, or a fibrotic organ fails to restore its normal parenchyma. Directed cell migration is often guided by spatial gradients in a physicochemical property of the cell microenvironment, such as a gradient in chemical factors dissolved in the medium or a gradient in the mechanical properties of the substrate. Single cells and tissues sense these gradients, establish a back-to-front polarity, and coordinate the migration machinery accordingly. Central to these steps we find physical forces. In some cases, these forces are integrated into the gradient sensing mechanism. Other times, they transmit information through cells and tissues to coordinate a collective response. At any time, they participate in the cellular migratory system. In this review, we explore the role of physical forces in gradient sensing, polarization, and coordinating movement from single cells to multicellular collectives. We use the framework proposed by the molecular clutch model and explore to what extent asymmetries in the different elements of the clutch can lead to directional migration

    Proteomická architektura interakcí gamet

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    Nedávné pokroky v proteomických metodách poskytují nové poznatky pro biologický výzkum a to včetně oblasti reprodukční biologie. Stanovení proteomického základu spermií je klíčové pro pochopení komplexního procesu interakcí gamet během oplození zahrnující akrozomální reakci. Napříč živočišnými taxony lze pozorovat značné rozdíly ve velikosti, tvaru a molekulárním složení spermií způsobené postkopulačním pohlavním výběrem a fylogenezí. První cílem této disertační práce je characterizovat proteinové složení akrozomu a zjistit tak jeho další funkční význam v interakci spermie a vajíčka. Dále se zaměřujeme na možné souvislosti mezi proteinovým složením spermií a morfologickou diverzifikací spermií, mírou výskytu kompetice spermií a fylogenetickou příbuzností zkoumaných druhů. Pro analýzy byli použiti samci odchycení v přírodě z přirozených populací druhů Mus musculus musculus, Apodemus flavicollis, Microtus arvalis (řád Hlodavci), Acrocephalus palustris, Chloris chloris, Phylloscopus collybita, Cinclus cinclus, Hirundo rustica a Taeniopygia guttata chovaní v zajetí (řád Pěvci). Jako hlavní metodologický přístup byla v celé práci použita nano kapalinová chromatografie spojená s tandemovou hmotnostní spektrometrií. Naše data ukazují, že biologické role akrozomu hlodavců nespočívají pouze v usnadňování...Recent advances in proteomic methods provide new insights for biological research including the field of reproductive biology. Determination of the proteomic basis of spermatozoa is pivotal for understanding the complex process of gamete interactions during fertilization such as acrosome reaction. Great differences imposed by postcopulatory sexual selection and phylogeny can be observed regarding the size, shape, and molecular composition of sperm across animal taxa. The first objective of this doctoral thesis is to characterize the protein contents of the acrosome to ascertain its further functional significance in sperm-egg interaction. Also, we aim to investigate the potential relationships between sperm protein composition and sperm morphology diversification, risk of sperm competition, and species phylogenetic background. Wild-caught males from natural populations of species of Mus musculus musculus, Apodemus flavicollis, Microtus arvalis (order Rodentia), Acrocephalus palustris, Chloris chloris, Phylloscopus collybita, Cinclus cinclus, Hirundo rustica, and Taeniopygia guttata from a captive population (order Passeriformes) were subject to the analyses. Nano-liquid chromatography with tandem mass spectrometry was applied as the main methodological approach in this thesis. Our data implicate...Katedra zoologieDepartment of ZoologyPřírodovědecká fakultaFaculty of Scienc

    Biomaterials for Bone Tissue Engineering 2020

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    This book presents recent advances in the field of bone tissue engineering, including molecular insights, innovative biomaterials with regenerative properties (e.g., osteoinduction and osteoconduction), and physical stimuli to enhance bone regeneration

    Unraveling Molecular Mechanisms of Gecko Adhesion: Multi-Scale Molecular Dynamics

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    Gecko adhesion has attracted considerable scientific and public attention over the past two decades. Much effort is going into developing mimetics and gecko-inspired adhesives to replicate the gecko's adhesive mechanisms. Although much research has focused on the hierarchical micrometer and submicrometer structures of the gecko foot leading to the extraordinary gecko adhesion, the molecular-level mechanisms have remained largely unexplored. This work presents a novel multiscale simulation approach that allows us to study gecko adhesion at multiple length scales, from the atomistic to the mesoscale. We investigate the effect of humidity, the role of electrostatic interactions, and the impact of surface roughness on gecko adhesion. Finally, we reconcile a long-standing scientific debate regarding the primary mechanism of gecko adhesion under humid conditions, providing clarity and confirming the significant role of a previously undiscovered molecular mechanism in enhancing adhesion. Our simulations go beyond previous computational and theoretical studies of gecko adhesion, which treated the spatula and surface as continuum bodies and modeled their interaction using the Hamaker theory. Instead, we bridge the gap in our understanding of gecko adhesion by using molecular dynamics simulations to investigate the molecular mechanism, uncovering a previously unknown effect called water-mediation. This mechanism involves small numbers of water molecules filling the gaps between keratin and the surface and increasing the number of keratin-surface contacts by partially absorbing into the keratin at the interface, thereby increasing the local density and the effective surface energy of the spatula. Parallel to the endeavor of designing synthetic gecko-inspired adhesives, the remarkable impact of relative humidity (or the presence of water) on the stickiness of gecko spatulae and setae has been discovered. Through single-spatula atomic force microscopy experiments, it was found that the pull-off forces required to separate two surfaces increased with the relative humidity and decreased with the water contact angle of the surface. Despite years of investigation into the adhesion phenomena, the molecular mechanisms behind humidity-enhanced adhesion had remained elusive due to limitations in resolution and length scale. This work addresses this gap by combining molecular dynamics simulations, a true multiscale protocol, with experimental literature, providing a deeper understanding of the molecular mechanisms in gecko adhesion and its response to relative humidity. The present work extends the understanding of attachment to rough surfaces. It shows that the stickiness decreases as the size of the surface features falls below the spatula contact area. We demonstrate that spatula-softening, the process by which the stiffness of the spatula decreases due to the presence of water, only assists adhesion at near saturation, meaning that the ambient relative humidity is close to 100%. While previous studies have suggested capillary forces as an alternative mechanism to spatula-softening, superhydrophobic surfaces lack attractive capillary forces. Nevertheless, we still observe increased adhesion under humid conditions compared to dry conditions on superhydrophobic surfaces. We conclude that water-mediation determines humidity-enhanced adhesion on hydrophobic flat and rough surfaces and that spatula-softening assists adhesion when the surface is rough and the ambient relative humidity is well above 80%. Unlike on hydrophobic surfaces, keratin shows a remarkable difference on hydrophilic surfaces. The folding of polar and charged amino acids towards the hydrophilic surface maximizes electrostatic and van-der-Waals interactions, leading to a stronger attachment, even in dry conditions. The keratin attaches closer to flat hydrophilic surfaces than hydrophobic surfaces, even in dry conditions. These observations suggest that the keratin exhibits a functional-polymer-like ability to selectively change its tertiary structure upon contacting a hydrophilic surface. Moreover, we find that the presence of water enhances adhesion to hydrophilic surfaces due to water-mediated interactions between the keratin and the surface. Overall, this work provides new insights into the molecular mechanisms of gecko adhesion and may be useful in finding new directions for developing gecko-inspired adhesives that can function effectively under a wide range of humidity conditions, by optimizing for water-mediated adhesion. Our work highlights the importance of considering the molecular-level interactions and the role of water in adhesion and provides a new direction for future research in this field

    Maintaining the Integrity Over Wear Time of a Hydrocolloid-based Ostomy Adhesive Whilst Maintaining Skin Barrier Function

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    In this extensive body of work, a thorough exploration delves into hydrocolloid based adhesives, with a focus on addressing challenges faced by stoma patients, particularly the susceptibility of ostomy adhesives to breakdown upon exposure to liquids. Stoma patients, compelled to wear pouching systems continuously, encounter issues like the compromise of skin barrier integrity, leading to medical adhesive-related skin injuries. The primary objective of this thesis is to reinforce the structural integrity of ostomy adhesives while preserving the skin barrier during pouching system use, an aspect often overlooked in current literature due to the hydrophilic nature of hydrocolloid based adhesives. The study introduces novel aims, examining the potential link between handedness and the preferred direction of adhesive removal, and its impact on peristomal skin complications as well as a novel skin capacitive imagery stitching technique. Another goal involves developing hierarchical structures on adhesive surfaces to enhance integrity, initial tack, and minimize skin contact for optimal skin health. The introduction provides a detailed breakdown of hydrocolloid-based ostomy adhesives, stoma anatomy, and the purpose of pouching systems. A comprehensive literature review, utilizing the PICO approach, encompasses stoma anatomy, physiology, indications for stoma surgery, and methods for assessing skin health. The review explores various methodologies to improve the durability of hydrocolloid-based adhesives, incorporating hydrodynamics, crosslinking, and layering systems. The potential influence of handedness on adhesive removal techniques is examined, considering its impact on peristomal skin complications. Results reveal the consistent performance of Welland Medical Ltd.'s hydrocolloid based adhesive but highlight the need for improved integrity over wear time. Strategies include modifying sodium-carboxymethylcellulose degree of substitution and increasing pectin degree of esterification, resulting in enhanced fluid handling capabilities and reduced susceptibility to degradation. Residual testing indicates that residual particles on the skin can impair the barrier function, remedied by a silicone-based adhesive remover. Surveys show that a patient's dominant hand and following the skin's natural langer lines during adhesive removal may minimize skin trauma. The results also show that structured surface profiles on hydrocolloid-based adhesive surfaces impact the skin's functional barrier recovery time. The research goal of this project and its objectives have been reached, the approaches have been explained clearly and implementations have been assessed using experimental findings. This project's findings contribute to advancements in ostomy care by enhancing adhesive performance, understanding patient behaviour, and improving the overall user experience. It also facilitates the efficient detachment of the adhesive from the skin surface

    Bidirectional Mechanical Response Between Cells and Their Microenvironment

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    Cell migration and invasion play a role in many physiological and pathological processes and are therefore subject of intensive research efforts. Despite of the intensively investigated biochemical processes associated with the migration and invasion of cells, such as cancer cells, the contribution ofmechanobiological processes to themigratory capacity of cells as well as the role of physical polymeric phase transitions is not yet clearly understood. Unfortunately, these experiments are not very informative because they completely disregard the influence of the three-dimensional cell environment. Despite this data situation, it was possible to adequately demonstrate that there exists a direct mechanical interplay between cells and theirmicroenvironment in both directions, where both elements can bemechanically altered by one another. In line with these results, it has turned out that the mechanobiological molecular processes through which cells interact with each other and additionally sense their nearby microenvironment have an impact on cellular functions such as cellular motility. The mechanotransduction processes have become the major focus of biophysical research and thereby, diverse biophysical approaches have been developed and improved to analyze the mechanical properties of individual cells and extracellular matrix environments. Both, the cell mechanics and matrix environmentmechanics regulate the cellmigration types in confined microenvironments and hence it seems to be suitable to identify and subsequently present a common bidirectional interplay between cells and their matrix environment. Moreover, hallmarks of the mechanophenotype of invasive cells and extracellular matrices can be defined. This review will point out how on the one hand the intracellular cytoskeletal architecture and on the other hand the matrix architecture contribute to cellular stiffness or contractility and thereby determines the migratory phenotype and subsequently the emergence of a distinct migration mode. Finally, in this review it is discussed whether universal hallmarks of the migratory phenotype can be defined

    Investigating the role of microtubules on pro-invasive factor secretion and intracellular organisation in cells with extra centrosomes

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    The presence of extra centrosomes can drive aneuploidy and invasiveness, thus contributing to tumorigenesis. We previously showed that cells with extra centrosomes induce extra centrosomes-associated secretory pathway (ECASP) that leads to pro-invasive factor secretion, such as IL-8, and drives paracrine invasion. The exact mechanism of how the presence of supernumerary centrosomes promotes ECASP is unclear, but it requires reactive oxygen species (ROS) generated by p22phox-dependent NADPH oxidases(s) (NOXs) and microtubules. Furthermore, we recently observed that cells with amplified centrosomes exhibit higher nuclear deformability and these cells are capable of migrating through small pores faster than cells with a normal number of centrosomes. Therefore, these phenotypes induced by centrosome amplification may facilitate the metastatic potential of cancer cells. In this work, I investigated the mechanism of how centrosome amplification drives these processes. I found that centrosome amplification increases microtubule modifications (PTMs), in particular acetylation. The increased levels of acetylated tubulin are known to enhance kinesin-1 motility and promote the periphery-directed trafficking of proteins, which may be important for secretion. Thus, I examined whether IL-8, one of the key pro-invasive factors, was affected by acetylated tubulin. When acetylated tubulin was depleted in cells with extra centrosomes, however, the secretion of IL-8 was not affected. This suggests that alternative mechanisms exist. Lastly, I examined alterations in the intracellular organisation that may promote nuclear deformation and allows extra centrosomes to migrate faster. Vimentin intermediate filament is known to act as a protective cage around the nucleus and resists nuclear deformation while migrating through small interstitial spaces. Strikingly, the vimentin intermediate filament, which is known to be transported by kinesin-1, was displaced away from the nucleus upon centrosome amplification induction. This implies that the loss of the vimentin cage around the nucleus may be responsible for increased nuclear deformation and allow cells to squeeze through small pores faster. Along with vimentin, extra centrosomes induced a global change in the intracellular organisation where various organelles: centrosomes, Golgi, mitochondria, and endosomes are displaced towards the cell periphery. Depletion of the acetylated tubulin prevented the displacement of vimentin intermediate filaments, centrosomes, and mitochondria. Conversely, increasing tubulin acetylation by H2O2 treatment was sufficient to drive the displacement of the same organelles. This work demonstrates that changes in the intracellular organisation, in particular vimentin intermediate filament, may promote the migratory speed of cells with amplified centrosomes
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