Biology subjects

Schaedel, L.

Publications and source records attributed to Schaedel, L..

11 recordsLinked to original sources

bioRxiv2026

Cytosolic factors govern vimentin network architecture and mechanics

Vimentin intermediate filaments are key cytoskeletal components forming networks with architectures distinct from other intermediate filament types, enabling specialized functions. Although assembly of individual filaments from soluble subunits is well characterized, dissecting how vimentin networks are organized has been challenging, as existing in vitro systems do not mimic the structures observed in cells. Thus, how cells establish higher-order vimentin organization remains unclear. Here, we reconstitute cell-like vimentin networks in vitro, using purified vimentin and extracts from mammalian and non-mammalian cells. Systematic variation of parameters reveals that cytosolic biomolecules, rather than intrinsic filament properties or generic ionic components, are the primary determinants of network architecture and mechanical behaviour. Importantly, network architecture is not universal but varies strongly according to the cell type from which the extract is derived, indicating that vimentin assemblies are tailored in a cell type-specific manner. Thus, this extract-based reconstitution system enables mechanistic dissection of intermediate filament regulation under near-native biochemical conditions, bridging the current gap between purified systems and the cellular environment. Our findings show that vimentin architecture and mechanics emerge primarily from cytosolic biomolecular factors that organize filaments into cell type-specific networks. These results establish cytosolic regulation as a central mechanism specifying intermediate filament network architecture and function.

cell biology↗

bioRxiv2025

MAP65-1/PRC1 reinforces microtubules through nucleation

Microtubules are dynamic cytoskeletal filaments that help shape cells and guide their response to external cues, including mechanical stress. How cells reorganize and reinforce microtubule arrays under stress remains poorly understood. Here, we show that MAP65-1/PRC1 promotes microtubule nucleation on pre-existing lattices in vitro, particularly on microtubules with lattice defects and damage sites associated with mechanical stress. MAP65-1 preferentially binds bent microtubules both in vitro and in cells, likely because bending induces lattice damage, enhancing nucleation on and bundling of these microtubules in vitro. This creates a potential feedback loop where mechanical stress promotes MAP65-1 binding, which in turn stabilizes microtubules by nucleation and bundling and reinforces the alignment of the array with mechanical stress. Thus, we reveal a previously unknown role for MAP65/PRC1 proteins in lattice-based nucleation and suggest a mechanism by which cells record and respond to mechanical stress through microtubule reorganization.

cell biology↗

bioRxiv2025

Kinesin-induced buckling reveals the limits of microtubule self-repair

Microtubules are stiff cytoskeletal polymers whose ability to rapidly switch between growth and disassembly relies on a metastable lattice. This metastability is also reflected in their sensitivity to environmental conditions and in intrinsic lattice dynamics, where spontaneous tubulin loss is balanced by tubulin incorporation from solution - a process that also enables microtubules to self-repair when damaged. Whether such intrinsic self-repair is sufficient to preserve microtubule integrity during dynamic molecular-motor induced buckling, which frequently occurs in cells, remains unclear. Here, we show that kinesin-driven microtubule buckling in vitro induces severe lattice damage, leading to extensive tubulin incorporation. In many cases, however, the damage exceeds the microtubules capacity for self-repair, resulting in breakage. In contrast, microtubules survive continuous buckling substantially longer in the presence of intracellular factors. Our results identify the limits of intrinsic microtubule self-repair and demonstrate that additional cellular mechanisms are essential to maintain microtubule integrity under sustained mechanical load.

biophysics↗

bioRxiv2025

The mechanism how Pretubulysin-induced microtubule disassembly improves T cell search efficiency

To clean tissue from tumorigenic and infected cells, cytotoxic T lymphocytes (CTLs) must navigate confined environments in vivo, locate the infected cells and eliminate them. Impaired CTL migration towards the tumor can limit the efficacy of immunotherapy. Microtubules (MTs) have emerged as promising targets, because destabilizing MTs enhances T-cell migration and subsequent killing, yet the underlying mechanisms are poorly understood. Here, we use pretubulysin, a potent MT depolymerizer, to uncover how MT dynamics regulate CTL motility. Complete MT disassembly markedly increased CTL infiltration and migration in 3D matrices. To investigate how altered migration affects target elimination, we employed a persistent random-walk model parameterized solely with experimental motility data. The model shows that the increase in speed and persistence induced by pretubulysin explains enhanced search efficiency increasing the encounter rate of CTLs with target cells. The simulations also predict how these gains in search efficiency scale with tissue thickness and CTL density. Mechanistically, MT depolymerization in activated CTLs triggers localized actomyosin accumulation at the uropod. This enhances rear contraction forces and promotes faster, more persistent migration and efficient search. Our findings clarify how MT dynamics influence CTL ability to eliminate targets in 3D environments and highlights the potential of MT-targeting agents such as pretubulysin to optimize T cell-based immunotherapies.

cell biology↗

bioRxiv2024

Tau accelerates tubulin exchange in the microtubule lattice

Microtubules are cytoskeletal filaments that exhibit dynamic tip instability and, as recent discoveries reveal, possess a dynamic lattice undergoing continuous tubulin loss and incorporation. In this study, we investigate the role of tau, a neuronal microtubule-associated protein (MAP) known for its stabilizing effects on microtubules, in modulating lattice dynamics. Using in vitro reconstitution, kinetic Monte Carlo modeling, and molecular dynamics simulations, we reveal that tau, despite lacking enzymatic activity, accelerates tubulin exchange within the lattice, particularly at topological defect sites. Tau appears to stabilize longitudinal tubulin-tubulin interactions while destabilizing lateral ones, thereby enhancing the mobility and repair of lattice defects. These results challenge the traditional view of tau as merely a stabilizer, uncovering its active role in dynamically modulating microtubule lattice structure.

biophysics↗

bioRxiv2024

Multiple clustered centrosomes in antigen-presenting cells foster T cell activation without MTOC polarization

Cellular polarization plays a pivotal role in regulating immunological processes and is often associated with centrosome reorientation. During immune synapse (IS) formation centrosome repositioning in lymphocytes assists in T cell activation. While a single centrosome, consisting of two centrioles, is present in T cells, antigen-presenting cells (APCs) such as dendritic cells (DCs) amplify centrioles during maturation leading to increased centrosome numbers upon immune activation. How centrosome amplification in DCs affects IS formation and T cell activation is unclear. In this study, we combine experimental data with mathematical and computational modelling to provide evidence that centrosome amplification in DCs enhances antigen-specific T cell activation. Extra centrioles in DCs form active centrosomes, which cluster during DC-T cell interactions and unlike in T cells, localize close to the cell center. Perturbing either centriole numbers or centrosome configuration in DCs results in impaired T cell activation. Collectively, our results highlight a crucial role for centrosome amplification and optimal centrosome positioning in APCs for controlling T cell responses.

cell biology↗

bioRxiv2023

Vimentin intermediate filaments structure and mechanically support microtubules in cells

The eukaryotic cytoskeleton is an intricate network of three types of mechanically distinct biopolymers - actin filaments, microtubules and intermediate filaments (IFs). These filamentous networks determine essential cellular functions and properties. Among them, microtubules are important for intracellular transport and establishing cell polarity during migration. Despite their intrinsic stiffness, they exhibit characteristic bending and buckling in cells due to non thermal forces acting on them. Interactions between cytoskeletal filaments have been found but are complex and diverse with respect to their effect on the mechanical behavior of the filaments and the architecture of networks. We systematically study how actin and vimentin IFs influence the network structure and local bending of microtubules by analyzing fluorescence microscopy images of mouse fibroblasts on protein micropatterns. Our automated analysis averages over large amounts of data to mitigate the effect of the considerable natural variance in biological cell data. We find that the radial orientation of microtubules in circular cells is robust and is established independently of vimentin and actin networks. Observing the local curvature of microtubules, we find highly similar average bending of microtubules in the entire cell regardless of the cytoskeletal surrounding. Small systematic differences cannot be attributed directly to vimentin and actin densities. Our results suggest that, on average, microtubules in unpolarized mouse fibroblasts are unexpectedly independent of the rest of the cytoskeleton in their global network structure and their local response to forces.

biophysics↗

bioRxiv2020

Vimentin Intermediate Filaments Stabilize Dynamic Microtubules by Direct Interactions

The cytoskeleton determines cell mechanics and lies at the heart of important cellular functions. Growing evidence suggests that the manifold tasks of the cytoskeleton rely on the interactions between its filamentous components - actin filaments, intermediate filaments and microtubules. However, the nature of these interactions and their impact on cytoskeletal dynamics are largely unknown. Here, we show in a reconstituted in vitro system that vimentin intermediate filaments stabilize microtubules against depolymerization and support microtubule rescue. To understand these stabilizing effects, we directly measured the interaction forces between individual microtubules and vimentin filaments. Combined with numerical simulations, our observations provide detailed insight into the physical nature of the interactions and how they affect microtubule dynamics. Thus, we describe an additional, direct mechanism for cells to establish the fundamental cross-talk of cytoskeletal components alongside linker proteins. Moreover, we suggest a novel strategy to estimate the binding energy of tubulin dimers within the microtubule lattice.

biophysics↗

bioRxiv2019

CLASP mediates microtubule repair by promoting tubulin incorporation into damaged lattices

Microtubule network plays a key role in cell division, motility and intracellular trafficking. Microtubule lattices are generally regarded as stable structures that undergo turnover through dynamic instability of their ends [1]. However, recent evidence suggests that microtubules also exchange tubulin dimers at the sites of lattice defects, which can either be induced by mechanical stress or occur spontaneously during polymerization [2-4]. Tubulin incorporation can restore microtubule integrity; moreover, \"islands\" of freshly incorporated GTP-tubulin can inhibit microtubule disassembly and promote rescues [3-7]. Microtubule repair occurs in vitro in the presence of tubulin alone [2-4, 8]. However, in cells, it is likely to be regulated by specific factors, the nature of which is currently unknown. CLASP is an interesting candidate for microtubule repair, because it induces microtubule nucleation, stimulates rescue and suppresses catastrophes by stabilizing incomplete growing plus ends with lagging protofilaments and promoting their conversion into complete ones [9-16]. Here, we used in vitro reconstitution assays combined with laser microsurgery and microfluidics to show that CLASP2 indeed stimulates microtubule lattice repair. CLASP2 promoted tubulin incorporation into damaged lattice sites thereby restoring microtubule integrity. Furthermore, it induced the formation of complete tubes from partial protofilament assemblies and inhibited microtubule softening caused by hydrodynamic flow-induced bending. A single CLASP2 domain, TOG2, which suppresses catastrophes when tethered to microtubules, was sufficient to stimulate microtubule repair, indicating that catastrophe suppression and lattice repair are mechanistically similar. Our results suggest that the cellular machinery controlling microtubule nucleation and growth can also help to maintain microtubule integrity.

cell biology↗

bioRxiv2018

Self-repair protects microtubules from their destruction by molecular motors

Microtubules are dynamic polymers that are used for intracellular transport and chromosome segregation during cell division. Their instability stems from the low energy of tubulin dimer interactions, which sets the growing polymer close to its disassembly conditions. Microtubules function in coordination with kinesin and dynein molecular motors, which use ATP hydrolysis to produce mechanical work and move on microtubules. This raises the possibility that the forces produced by walking motors can break dimer interactions and trigger microtubule disassembly. We tested this hypothesis by studying the interplay between microtubules and moving molecular motors in vitro. Our results show that the mechanical work of molecular motors can remove tubulin dimers from the lattice and rapidly destroy microtubules. This effect was not observed when free tubulin dimers were present in the assay. Using fluorescently labelled tubulin dimers we found that dimer removal by motors was compensated for by the insertion of free tubulin dimers into the microtubule lattice. This self-repair mechanism allows microtubules to survive the damage induced by molecular motors as they move along their tracks. Our study reveals the existence of coupling between the motion of kinesin and dynein motors and the renewal of the microtubule lattice.

cell biology↗

bioRxiv2018

Lattice defects induce microtubule self-renewal

The dynamic instability of microtubules is powered by the addition and removal of tubulin dimers at the ends of the microtubule. Apart from the end, the microtubule shaft is not considered to be dynamic. However recent evidence suggests that free dimers can be incorporated into the shaft of a microtubule damaged by mechanical stress. Here we explored whether dimer exchange was a core property of the microtubule lattice independently of any external constraint. We found that dimers can be removed from and incorporated into the lattice at sites along the microtubule shaft. Furthermore, we showed by experiment and by modeling that rapid dimer renewal requires structural defects in the lattice, which occur in fast growing microtubules. Hence long-lived microtubules have the capacity to self-renew despite their apparent stability and thereby can potentially regulate signaling pathways and structural rearrangements associated with tubulin-dimer exchange at sites along their entire length.

cell biology↗