Biology subjects

Hauschild, R.

Publications and source records attributed to Hauschild, R..

16 recordsLinked to original sources

bioRxiv2025

Dynamic protrusions mediate unique crawling motility in Asgard Archaea (Promethearchaeota)

Crawling motility is a hallmark of eukaryotic cells and requires a dynamic actin cytoskeleton, regulated adhesion, and spatially organized signalling pathways1-3. Asgard archaea (phylum Promethearchaeota) which are considered the closest known prokaryotic relatives of eukaryotes potentially encode these functions within their large set of eukaryotic signature proteins4-9. The few cultivated members show a complex cell morphology, consisting of a central cell body from which several protrusions extend, filled with an actin-based cytoskeleton10,11. Here, live cell microscopy of two organisms of the Loki- and Hodarchaea lineages10,12 showed that they dynamically and drastically change their cell shape on a minute time scale and grow and retract their extensive protrusions with a speed of 1.5 to 5.3 {micro}m/min, respectively. After adhering to a glass surface, cells employ their protrusions to undergo active crawling motion. In the presence of selected actin inhibitors however, the observed dynamics were arrested, suggesting a central role of actin in these processes. The observed cellular plasticity and motility are unique features among prokaryotes and might have been crucial for the emergence of the first eukaryotic cells that are thought to have formed through the association of a member of the Promethearchaeota and an alphaproteobacterium, the ancestor of mitochondria.

microbiology↗

bioRxiv2024

Pulsatile basal gene expression as a fitness determinant in bacteria

Active regulation of gene expression, orchestrated by complex interactions of activators and repressors at promoters, controls the fate of organisms. In contrast, basal expression at uninduced promoters is considered to be a dynamically inert mode of non-functional "promoter leakiness", merely a byproduct of transcriptional regulation. Here, we investigate the basal expression mode of the mar operon, the main regulator of intrinsic multiple antibiotic resistance in Escherichia coli, and link its dynamic properties to the non-canonical, yet highly conserved start codon of marR across Enterobacteriaceae. Real-time single-cell measurements across tens of generations, reveal that basal expression consists of rare stochastic gene expression pulses, which maximize variability in wildtype and, surprisingly, transiently accelerate cellular elongation rates. Competition experiments show that basal expression confers fitness advantages to wildtype across several transitions between exponential and stationary growth by shortening lag times. The dynamically rich basal expression of the mar operon, has likely been evolutionarily maintained for its role in growth homeostasis of Enterobacteria within the gut environment, thereby allowing other ancillary gene regulatory roles to evolve, e.g. control of costly-to-induce multi-drug efflux pumps. Understanding the complex selection forces governing genetic systems involved in intrinsic multi-drug resistance is crucial for effective public health measures.

systems biology↗

bioRxiv2024

Mechanical Centrosome Fracturing during Cell Navigation

The centrosome is the primary microtubule orchestrator in most eukaryotic cells, nucleating and anchoring microtubules that grow radially and exert forces on cargos. At the same time, mechanical stresses from the microenvironment and cellular shape changes compress and bend microtubules. Yet, centrosomes are membrane-less organelles, raising the question of how centrosomes withstand mechanical forces. Here we discover that centrosomes in non-dividing cells can mechanically fracture. We reveal that centrosomes experience mechanical deformations during microenvironmental confinement and navigational pathfinding by motile cells. Coherence of the centrosome is maintained by Dyrk3, preventing fracturing by mechanical forces. Centrosome fracturing impedes cellular function by generating coexisting microtubule organizing centers that compete during path navigation and thereby cause cellular entanglement in the microenvironment. Our findings show that non-dividing cells actively maintain the integrity of the centrosome to withstand mechanical forces. Given that almost all cells in multicellular organism experience forces, these results suggest that centrosome stability preservation is fundamental during development, tissue maintenance, immunology, and disease. One-Sentence SummaryPathfinding during cellular motility causes centrosome breakage counteracted by Dyrk3 activity.

cell biology↗

bioRxiv2024

Spinal neuron diversity scales exponentially with swim-to-limb transformation during frog metamorphosis

Vertebrates exhibit a wide range of motor behaviors, ranging from swimming to complex limb-based movements. Here we take advantage of frog metamorphosis, which captures a swim-to-limb-based movement transformation during the development of a single organism, to explore changes in the underlying spinal circuits. We find that the tadpole spinal cord contains small and largely homogeneous populations of motor neurons (MNs) and V1 interneurons (V1s) at early escape swimming stages. These neuronal populations only modestly increase in number and subtype heterogeneity with the emergence of free swimming. In contrast, during frog metamorphosis and the emergence of limb movement, there is a dramatic expansion of MN and V1 interneuron number and transcriptional heterogeneity, culminating in cohorts of neurons that exhibit striking molecular similarity to mammalian motor circuits. CRISPR/Cas9-mediated gene disruption of the limb MN and V1 determinants FoxP1 and Engrailed-1, respectively, results in severe but selective deficits in tail and limb function. Our work thus demonstrates that neural diversity scales exponentially with increasing behavioral complexity and illustrates striking evolutionary conservation in the molecular organization and function of motor circuits across species.

neuroscience↗

bioRxiv2024

Global coordination of protrusive forces in migrating immune cells

Efficient immune responses rely on the capacity of leukocytes to traverse diverse and complex tissues. To meet such changing environmental conditions, leukocytes usually adopt an amoeboid configuration, utilizing their forward-positioned nucleus as a probe to identify and follow the path of least resistance among pre-existing pores. We show that in dense environments, where even the largest pores preclude free passage, leukocytes switch polarity and position their nucleus behind centrosome and organelles. In this mesenchymal configuration, local compression of the cell body triggers assembly of a central F-actin pool, located between cell front and nucleus. Central actin pushes outward to transiently dilate a path for organelles and nucleus. Pools of central and front actin are tightly coupled and experimental depletion of the central pool enhances actin accumulation and protrusion formation at the cell front. Although this shifted balance speeds up cells in permissive environments, migration in restrictive environments is impaired, as the unleashed leading edge dissociates from the trapped cell body. Our findings establish an actin regulatory loop that balances path dilation with advancement of the leading edge to maintain cellular coherence.

cell biology↗

bioRxiv2023

Unveiling the ultrastructural landscape of native extracellular matrix via lift-out cryo-FIBSEM and cryo-ET

The extracellular matrix (ECM) is a highly hydrated, three-dimensional network composed of various macromolecules and signaling factors. It serves as a structural scaffold for cells and plays an essential role in the regulation of numerous cellular processes, including cell migration, adhesion, and proliferation. Despite its importance in metazoans, structural knowledge is rudimentary on how the components of the matrisome are secreted, remodeled, and interact with each other and with surrounding cells. Specifically, the exact molecular assembly of important ECM fibers, such as fibronectin fibrils, fibrillin microfibrils, or Collagen-VI filaments has remained enigmatic. This is largely due to methodological limitations in specimen preparation for conventional room-temperature electron microscopy (EM). To overcome these limitations, we have developed a cell culture-based 3D-ECM platform compatible with sample thinning by cryo-lift out focused ion beam (FIB) milling and cryo-electron tomography (cryo-ET). Our workflow involves the implementation of cell-derived matrices (CDMs) grown on EM grids, resulting in a highly adaptable and versatile tool to closely mimic ECM environments. This allows us to visualize native ECM and its components for the first time in their fully hydrated, cellular context. Our data reveals an intricate network of ECM fibers and their positioning with respect to matrix-secreting cells. In addition to D-spaced collagen fibers, we visualize previously unresolved fibrous structures, and an amorphous matrix co-assembling in proximity to ECM fibers and delineating the boundary between ECM and empty extra-cellular space. Intra- and extracellular granules presumably represent assembly intermediates of the ECM. Our results add to the structural atlas of the ECM and provide novel insights into ECM secretion, assembly and maintenance.

cell biology↗

bioRxiv2023

BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation

Cell migration is a fundamental process during embryonic development. Most studies on cell migration in vivo have focussed on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the overlying ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal pole-directed migration of LME cells, while the ectoderm at the animal pole of the gastrula halts animal pole-directed LME migration. These differences in the permissive properties of the ectoderm for LME migration are due to the lateral ectoderm being more cohesive and viscous than the animal ectoderm. Consistently, tuning cell contractility in lateral and animal ectoderm via modulation of the actomyosin cytoskeleton is sufficient to change their permissiveness for LME migration. Finally, we found that BMP signalling is critical for reducing animal ectoderm cohesion and, thus, its capacity to halt LME migration towards the animal pole. Collectively, these findings identify a critical role of ectoderm tissue cohesion and viscosity in guiding LME migration during zebrafish gastrulation.

developmental biology↗

bioRxiv2023

Robust axis elongation by Nodal-dependent restriction of BMP signaling

Embryogenesis is brought about by the coordinated activities of different signaling pathways controlling cell fate specification and morphogenesis. In vertebrate gastrulation, both Nodal and BMP signaling play key roles in germ layer specification and morphogenesis, yet their interplay to coordinate embryo patterning with morphogenesis is still insufficiently understood. Here, we took a reductionist approach using zebrafish embryonic explants to study the coordination of Nodal and BMP signaling for embryo patterning and morphogenesis. We show that Nodal signaling not only triggers explant elongation by inducing mesendodermal progenitors but also by suppressing BMP signaling activity at the site of mesendoderm induction. Ectopic BMP signaling in the mesendoderm blocks cell alignment and oriented mesendoderm intercalations, key processes to drive explant elongation. Translating these ex vivo observations to the intact zebrafish embryo showed that, similar to explants, Nodal signaling renders the dorsal domain less sensitive towards BMP signaling to allow effective cell intercalations and thus robust embryonic axis elongation. These findings suggest a dual function of Nodal signaling in embryonic axis elongation by both inducing mesendoderm and maintaining low levels of BMP signaling activity in the dorsal portion of the mesendoderm.

developmental biology↗

bioRxiv2023

Adaptive Pathfinding by Nucleokinesis during Amoeboid Migration

Motile cells moving in multicellular organisms encounter microenvironments of locally heterogeneous mechanochemical composition. Individual compositional parameters like chemotactic signals, adhesiveness, and pore sizes are well known to be sensed by motile cells, providing individual guidance cues for cellular pathfinding. However, motile cells encounter diverse mechanochemical signals at the same time, raising the question of how cells respond to locally diverse and potentially competing signals on their migration routes. Here, we reveal that motile amoeboid cells require nuclear repositioning, termed nucleokinesis, for adaptive pathfinding in heterogeneous mechanochemical microenvironments. Using mammalian immune cells and the amoeba Dictyostelium discoideum, we discover that frequent, rapid and long-distance nucleokinesis is a basic component of amoeboid pathfinding, enabling cells to reorientate quickly between locally competing cues. Amoeboid nucleokinesis comprises a two-step cell polarity switch and is driven by myosin II-forces, sliding the nucleus from a losing to the winning leading edge to re-adjust the nuclear to the cellular path. Impaired nucleokinesis distorts fast path adaptions and causes cellular arrest in the microenvironment. Our findings establish that nucleokinesis is required for amoeboid cell navigation. Given that motile single-cell amoebae, many immune cells, and some cancer cells utilize an amoeboid migration strategy, these results suggest that amoeboid nucleokinesis underlies cellular navigation during unicellular biology, immunity, and disease.

cell biology↗

bioRxiv2021

Multi-tier mechanics control stromal adaptations in swelling lymph nodes

Lymph nodes (LNs) comprise two main structural elements: Fibroblastic reticular cells (FRCs) that form dedicated niches for immune cell interaction and capsular fibroblasts that build a shell around the organ. While LNs are fairly stable in size during homeostatic conditions, immunological challenge causes more than 10-fold increase in size within only a few days. How a solid organ can accommodate such extreme volumetric changes is poorly understood. Here, we characterize the biomechanics of LN swelling on the cellular and organ scale. We identify lymphocyte trapping by influx and proliferation as drivers of an outward pressure force, causing FRCs and their associated conduits to stretch. After an initial phase of relaxation, FRCs sense the resulting strain via cell matrix adhesions, which coordinates local growth and remodeling of the stromal network. While the expanded FRC network adopts its typical configuration, a massive fibrotic reaction of the organ capsule sets in and counters further organ expansion. Thus, different fibroblast populations mechanically control LN swelling in a multi-tier fashion.

immunology↗

bioRxiv2021

Mechanosensitivity of amoeboid cells crawling in 3D

Efficient immune-responses require migrating leukocytes to be in the right place at the right time. When crawling through the body amoeboid leukocytes must traverse complex three-dimensional tissue-landscapes obstructed by extracellular matrix and other cells, raising the question how motile cells adapt to mechanical loads to overcome these obstacles. Here we reveal the spatio-temporal configuration of cortical actin-networks rendering amoeboid cells mechanosensitive in three-dimensions, independent of adhesive interactions with the microenvironment. In response to compression, Wiskott-Aldrich syndrom protein (WASp) assembles into dot-like structures acting as nucleation sites for actin spikes that in turn push against the external load. High precision targeting of WASp to objects as delicate as collagen fibers allows the cell to locally and instantaneously deform its viscoelastic surrounding in order to generate space for forward locomotion. Such pushing forces are essential for fast and directed leukocyte migration in fibrous and cell-packed tissues such as skin and lymph nodes. In BriefWASp-driven actin spikes counter compressive loads of crowded tissue-landscapes.

cell biology↗

bioRxiv2020

Dendritic cell actin dynamics controls T cell priming efficiency at the immunological synapse

Dendritic cells (DCs) are crucial for the priming of naive T cells and the initiation of adaptive immunity. Priming is initiated at a heterologous cell-cell contact, the immunological synapse (IS). While it is established that actin dynamics regulates signalling at the T cell side of the contact, little is known about the cytoskeletal contribution on the DC side. We show that that the DC cytoskeleton is decisive for the formation of a multifocal synaptic structure, which correlates with T cell priming efficiency. We demonstrate that DC actin appears in transient foci at the IS and that these foci are dynamized by the WAVE complex. Absence of WAVE in DCs leads to stabilized contacts with T cells, caused by an increase in ICAM1-integrin mediated cell-cell adhesions. This results in a lower number of activated and proliferating T cells. Our results reveal an important role of DC actin in the regulation of synaptic contacts with crucial relevance for full T cell expansion.

cell biology↗

bioRxiv2020

3D printed cell culture grid holders for improved cellular specimen preparation in cryo-electron microscopy

Cryo-electron microscopy (cryo-EM) of cellular specimens provides insights into biological processes and structures within a native context. However, a major challenge still lies in the efficient and reproducible preparation of adherent cells for subsequent cryo-EM analysis. This is due to the sensitivity of many cellular specimens to the varying seeding and culturing conditions required for EM experiments, the often limited amount of cellular material and also the fragility of EM grids and their substrate. Here, we present low-cost and reusable 3D printed grid holders, designed to improve specimen preparation when culturing challenging cellular samples directly on grids. The described grid holders increase cell culture reproducibility and throughput, and reduce the resources required for cell culturing. We show that grid holders can be integrated into various cryo-EM workflows, including micro-patterning approaches to control cell seeding on grids, and for generating samples for cryo-focused ion beam milling and cryo-electron tomography experiments. Their adaptable design allows for the generation of specialized grid holders customized to a large variety of applications.

cell biology↗

bioRxiv2019

Adhesion-free cell migration by topography-based force transduction

Eukaryotic cells migrate by coupling the intracellular force of the actin cytoskeleton to the environment. While force-coupling is usually mediated by transmembrane adhesion receptors, especially these of the integrin family, amoeboid cells like leukocytes can migrate extremely fast despite very low adhesive forces1. We show that leukocytes cannot only migrate under low adhesion but indeed can transduce forces in the complete absence of transmembrane force coupling. When confined within three-dimensional environments, they use the topographic features of the substrate to propel themselves. Here, the retrograde flow of the actin cytoskeleton follows the texture of the substrate, creating shear forces sufficient to drive deformations towards the back of the cell. Notably, adhesion dependent and adhesion independent migration are not exclusive but rather variants of the same principle of coupling retrograde actin flow to the environment and thus can potentially operate simultaneously. As adhesion free migration is independent of the chemical composition of the environment it renders cells completely autonomous in their locomotive behavior.

cell biology↗

bioRxiv2019

Microtubules coordinate protrusion-retraction dynamics in migrating dendritic cells

Cells navigating through tissues face a fundamental challenge: while multiple cellular protrusions explore different paths through the complex geometry of an interstitial matrix the cell needs to avoid becoming too long or ramified, which might ultimately lead to a loss of physical coherence. How a cell surveys its own shape to inform the actomyosin system to retract entangled or stretched protrusions is not understood. Here, we demonstrate that spatially distinct microtubule (MT) dynamics regulate amoeboid cell migration by locally specifying the retraction of explorative protrusions. In migrating dendritic cells (DCs), the microtubule organizing center (MTOC) guides the path through a three dimensional (3D) interstitium and local MT depolymerization in protrusions remote from the MTOC triggers myosin II dependent contractility via the RhoA exchange factor Lfc. Depletion of Lfc leads to aberrant myosin localization, thereby causing two effects that rate-limit locomotion: i) impaired cell edge coordination during path-finding and ii) defective adhesion-resolution. Such compromised cell shape control is particularly hindering when cells navigate through geometrically complex microenvironments, where it leads to entanglement and ultimately fragmentation of the cell body. Our data demonstrate that MTs control cell shape and coherence by locally controlling protrusion-retraction dynamics of the actomyosin system.

cell biology↗

bioRxiv2017

Live Tracking Of Moving Samples In Confocal Microscopy For Vertically Grown Plant Roots

Roots navigate through soil integrating environmental signals to orient their growth. The Arabidopsis root is a widely used model for developmental, physiological and cell biological studies. Live imaging greatly aids these efforts, but the horizontal sample position and continuous root tip displacement present significant difficulties. Here, we develop a confocal microscope setup for vertical sample mounting and integrated directional illumination. We present TipTracker - a custom software for automatic tracking of diverse moving objects usable on various microscope setups. Combined, this enables observation of root tips growing along the natural gravity vector over prolonged periods of time, as well as the ability to induce rapid gravity or light stimulation. We also track migrating cells in the developing zebrafish embryo, demonstrating the utility of this system in the acquisition of high resolution data sets of dynamic samples. We provide detailed descriptions of the tools enabling the easy implementation on other microscopes.

plant biology↗