Biology subjects

Osswald, M.

Publications and source records attributed to Osswald, M..

13 recordsLinked to original sources

bioRxiv2026

Elevated MPS1 converts the fibrous corona into a source of chromosomal instability in colon cancer

Chromosomal instability (CIN), characterised by recurrent chromosome mis-segregation, fuels intratumour heterogeneity and tumour evolution. Yet, its proximal molecular causes remain ill-defined. Tumour-scale genomic and transcriptomic analyses associate MPS1 overexpression with CIN in colon carcinomas. Consistently, CIN+ patient-derived colon cancer cells (PCCCs) display elevated MPS1, frequent merotelic kinetochore-microtubule attachments and lagging chromosomes that are suppressed by partial MPS1 inhibition. Conversely, ectopic MPS1 overexpression in otherwise stable near-diploid cells phenocopies these defects, inducing micronuclei formation and karyotypic divergence. Mechanistically, MPS1 overactivity maintains ROD phosphorylation at Thr13/Ser15, continuously sustaining fibrous corona assembly despite mature end-on attachments. 3D-STED microscopy reveals split-interface configurations in which microtubules from opposing poles engage the canonical outer-kinetochore surface and a spatially distinct corona domain, explaining how merotely forms and persists into anaphase. Disrupting corona assembly restores chromosome segregation fidelity in MPS1-overexpressing RPE-1 cells and in CIN+ PCCCs. Together, our findings establish MPS1 overexpression as a driver of CIN and uncover how oncogenic transcriptional rewiring of mitotic signalling converts a transient microtubule-capture structure into a pathological source of merotely and chromosome mis-segregation in colon cancer.

cell biology↗

bioRxiv2026

Curated Residual Decomposition for Increased MU Yield from HD-sEMG

High-density surface electromyography (HD-sEMG) decomposition algorithms identify motor units (MUs) from non-invasive recordings, yet even gold-standard methods typically decompose only a subset of all physiologically active MUs and preferentially extract higher-amplitude units, leaving low-amplitude MUs underrepresented. We propose Curated Residual Decomposition (CRD): Through decomposition of the residual signal remaining from a manually edited initial decomposition, we identify additional, mainly lower amplitude MUs that were previously undetected due to action potential superposition and preferential convergence to larger MUs. We applied this approach to three datasets: concurrent HD-sEMG and HD-iEMG recordings from three muscles for two-source validation, and two publicly available datasets. Across all datasets, CRD substantially increased MU yield. In the two-source validation dataset, the first CRD iteration increased yield by 31-50% (FDI: 46.9%, TA: 49.8%, VL: 31.1%), with validation via intramuscular recordings confirming comparable identification accuracy of the CRD compared to the original MUs (RoA original: 0.994 {+/-} 0.005; RoA CRD: 0.992 {+/-} 0.009). In public datasets, yield increases ranged from 35-142% per muscle in the first iteration. Correspondingly, the explained signal power ratio increased, with the first iteration accounting for most gains. A second CRD iteration resulted in an additional, yet smaller yield increase (0-26.7%). Additionally identified MUs had smaller action potential amplitudes and lower recruitment thresholds, indicating the recovery of smaller, lower-threshold MUs. CRD reliably increased MU yield and explained signal power across diverse muscles, datasets, and decomposition implementations. The approach provides an optional, validated step for more complete decomposition results across the full recruitment range in offline analyses.

neuroscience↗

bioRxiv2025

Spatial inhibition of RhoA by RhoGAP15B promotes protrusive activity during collective cell migration

The Rho family GTPases RhoA, Rac1 and Cdc42 are well established regulators of collective migration by driving the formation of cellular protrusions and by regulating actomyosin contraction and adhesion. However, how their activation and inhibition are spatially and temporally coordinated remains unclear. Using GFP knock-in lines, we systematically characterized the localization patterns of all Drosophila RhoGEFs (activators) and RhoGAPs (inhibitors) in border cells, an in vivo model of collective migration. We have further combined RNAi screening with GFP-based validation of depletion efficiency to assess the functional significance of those RhoGEF/GAPs expressed in border cells. This identified RhoGAP15B as a localized inhibitor of RhoA activity at the border cell cortex. RhoGAP15B regulates cluster morphology and is enriched at the leading cell front, where it restrains actomyosin contractility to promote protrusive behavior. Our findings reveal RhoGAP15B as a key spatial RhoA regulator and highlight that patterned RhoGAP and RhoGEF activities are essential for coordinating cortical contraction and protrusion dynamics during collective migration.

cell biology↗

bioRxiv2025

Task-Dependent Motor Unit Recruitment and Rate Coding Reveal Redistribution of Neural Drive in the Human Hand

Although Henneman's size principle dictates an orderly small-to-large activation for a given common input, evidence suggests a certain level of flexibility in the recruitment of spinal motoneurons depending on task demands. Here, we investigate motor unit (MU) recruitment flexibility in the human first dorsal interosseus (FDI) muscle while controlling for overall muscle activation across two functionally distinct tasks using High-Density intramuscular EMG (HD-iEMG) electrode arrays. Six participants performed isometric index finger abduction where the FDI serves as the prime mover, and flexion with the FDI functioning as a synergist. Recruitment thresholds (RT) and recruitment orders (RO) were highly consistent within the same task, but differed significantly between abduction and flexion. Across participants, 45.3% of MUs showed changes in recruitment above the coefficient of repeatability across tasks compared to only 5.0% within tasks. The spatial distribution of muscle activation did not shift between tasks, confirming that the same muscle region was engaged in both. Changes in RT were accompanied by corresponding adaptations in discharge rate (DR), preserving the inverse RT-DR relationship. Intramuscular coherence analysis revealed no differences in the delta (1-5 Hz) or alpha (5-13 Hz) band, but beta band (13-30 Hz) coherence was significantly lower during flexion than abduction, indicating reduced common input synchronization in this frequency range when FDI serves as a synergist muscle. Together, these results indicate different distributions of net excitatory input to FDI MUs across different functional tasks, potentially involving a stronger contribution of spinal circuits during flexion, as suggested by the reduced intramuscular beta coherence. Moreover, the present findings also demonstrate that common synaptic input and not intrinsic motoneuron properties determines the inverse relation between MU RT and DR.

neuroscience↗

bioRxiv2024

The Dystrophin-Dystroglycan complex ensures cytokinesis efficiency in Drosophila epithelia

Cytokinesis physically separates daughter cells at the end of cell division. This step is particularly challenging for epithelial cells, which are connected to their neighbors and to the extracellular matrix by transmembrane protein complexes. To systematically evaluate the impact of the cell adhesion machinery on epithelial cytokinesis efficiency, we performed an RNAi-based modifier screen in the Drosophila follicular epithelium. Strikingly, this unveiled adhesion molecules and transmembrane receptors that facilitate cytokinesis completion. Among these is Dystroglycan, which connects the extracellular matrix to the cytoskeleton via Dystrophin. Live imaging revealed that Dystrophin and Dystroglycan become enriched in the ingressing membrane, below the cytokinetic ring, during and after ring constriction. Using multiple alleles, including Dystrophin isoform-specific mutants, we show that Dystrophin/Dystroglycan localization is linked with unanticipated roles in regulating cytokinetic ring contraction and in preventing membrane regression during the abscission period. Altogether, we provide evidence that, rather than opposing cytokinesis completion, the machinery involved in cell-cell and cell-matrix interactions has also evolved functions to ensure cytokinesis efficiency in epithelial tissues.

cell biology↗

bioRxiv2023

Mechanical Hand Synergies during Dynamic Hand Movements are Mostly Controlled in a Non-Synergistic Way by Spinal Motor Neurons

Precise control of spinal motor neurons is crucial for voluntary hand and digit movements. However, the specific mechanisms by which motor unit ensembles govern dynamic synergistic and individual digit tasks remain poorly understood. We recorded synchronized 3D hand kinematics and high-density surface EMG (HD-sEMG) data from extrinsic hand muscles of twelve participants during 13 dynamic hand and digit movement tasks, consisting of single-digit flexion/extension and mechanically synergistic grasping tasks. We extracted single motor unit (MU) activity and identified identical MUs across tasks. We extracted 7.8 {+/-} 1.8 MUs per task and participant and found 182 out of 554 total MUs active during multiple movements. Analysis of the MU discharge patterns revealed two groups of motor units that were categorized into prime mover MUs, showing strong correlation between firing rate modulation and digit kinematics, and postural MUs with little modulated activity. We found these motor units could switch between the two modes, showing either postural or movement encoding activation depending on the task. However, MUs acted as prime mover only for one specific digit. We further observed highly task specific recruitment of prime mover MUs. Across participants, we found only 9 {+/-} 8.2 % of prime mover MUs active during a grasp task and any single digit task involved in the grasp motion. We draw three conclusions: (1) Single digits are controlled by distinct groups of MUs. (2) Unexpectedly, mechanically synergistic grasp movements are mostly controlled in a non-synergistic way by distinct groups of MUs. 3) Multiple manifolds construct the movement of the human hand, and each motor unit can flexibly switch between postural and dynamic modes. Significance StatementWe investigated the neural control of motor unit ensembles during single-digit and synergistic grasping tasks in dynamic conditions. We found that motor units exhibited strong movement-correlated activity only for one specific digit. We further observed highly task specific recruitment of motor units during mechanically synergistic grasp movements, showing that on a motor unit level, mechanically synergistic movements are controlled in a non-synergistic way. The findings extend the knowledge of motor unit recruitment strategies in natural movements and have strong implications in the field of neurorehabilitation and control of assistive devices.

neuroscience↗

bioRxiv2022

Systematic characterization of Drosophila RhoGEF/GAP localizations uncovers regulators of mechanosensing and junction formation during epithelial cell division.

Cell proliferation is central to epithelial tissue development, repair and homeostasis. During cell division, small RhoGTPases control both actomyosin dynamics and cell-cell junction remodelling to faithfully segregate the duplicated genome while maintaining tissue polarity and integrity. To decipher the mechanisms of RhoGTPases spatiotemporal regulation during epithelial cell division, we generated a transgenic fluorescently tagged library for Drosophila Rho Guanine exchange factors (GEF) and GTPase activating proteins (GAP), and systematically characterized their endogenous distributions by time- lapse microscopy. Thereby, we unveiled candidate regulators of the interplay between actomyosin and junctional dynamics during epithelial cell division. Building on these findings, we uncovered that during cytokinesis, Cysts and RhoGEF4 play sequential roles in mechanosensing and de novo junction formation, respectively. We foresee that the RhoGEF/GAP library will be a key resource to understand the broad range of biological processes regulated by RhoGTPases.

developmental biology↗

bioRxiv2022

Sensing the Full Dynamics of the Human Hand with a Neural Interface and Deep Learning

Theories about the neural control of movement are largely based on movement-sensing devices that capture the dynamics of predefined anatomical landmarks. However, neuromuscular interfaces such as surface electromyography (sEMG) can potentially overcome the limitations of these technologies by directly sensing the motor commands transmitted to the muscles. This allows for the continuous, real-time prediction of kinematics and kinetics without being limited by the biological and physical constraints that affect motion-based technologies. In this work, we present a deep learning method that can decode and map the electrophysiological activity of the forearm muscles into movements of the human hand. We recorded the kinematics and kinetics of the human hand during a wide range of grasping and individual digit movements covering more than 20 degrees of freedom of the hand at slow (0.5 Hz) and fast (1.5 Hz) movement speeds in healthy participants. The input of the model consists of three-hundred EMG sensors placed only on the extrinsic hand muscles. We demonstrate that our neural network can accurately predict the kinematics and contact forces of the hand even during unseen movements and with simulated real-time resolution. By examining the latent space of the network, we find evidence that it has learned the underlying anatomical and neural features of the sEMG that drive all hand motor behaviours.

neuroscience↗

bioRxiv2022

Apical constriction induces tissue rupture in a proliferative epithelium

Apical-basal polarity is an essential epithelial trait controlled by the evolutionarily conserved PAR-aPKC polarity network. Deregulation of polarity proteins disrupts tissue organization during development and in disease, but the underlying mechanisms are unclear due to the broad implications of polarity loss. Here, we uncovered how Drosophila aPKC maintains epithelial architecture by directly observing tissue disorganization after fast optogenetic inactivation in living adult flies and ovaries cultured ex vivo. We show that fast aPKC perturbation in the proliferative follicular epithelium produces large epithelial gaps that result from increased apical constriction, rather than loss of apical-basal polarity. Accordingly, we could modulate the incidence of epithelial gaps by increasing and decreasing actomyosin-driven contractility. We traced the origin of epithelial gaps to tissue rupture next to dividing cells. Live imaging shows that aPKC perturbation rapidly induces apical constriction in non-mitotic cells, producing pulling forces that ultimately detach dividing and neighbouring cells. We further demonstrate that epithelial rupture requires a global increase of apical constriction, since it was prevented by the presence of non-constricting cells. Conversely, a global induction of apical tension through light-induced recruitment of RhoGEF2 to the apical side was sufficient to produce tissue rupture. Hence, our work reveals that the roles of aPKC in polarity and actomyosin regulation are separable and provides the first in vivo evidence that excessive tissue stress can break the epithelial barrier during proliferation.

developmental biology↗

bioRxiv2020

Substrate-induced clustering activates Trim-Away of pathogens and proteins

Trim-Away is a powerful new technology that exploits off-the-shelf antibodies and the E3 RING ligase and cytosolic antibody receptor TRIM21 to carry out rapid protein depletion. How TRIM21 is catalytically-activated upon substrate engagement during either its normal immune function or when re-purposed for targeted protein degradation is unknown. Here we show that a mechanism of substrate-induced clustering triggers intermolecular dimerization of the RING domain to switch on the ubiquitination activity of TRIM21 and induce an antiviral response or drive Trim-Away. We harness this mechanism to expand the Trim-Away toolbox with highly-active TRIM21-nanobody chimeras that can also be controlled optogenetically. This work provides a mechanism for cellular activation of TRIM RING ligases and has important implications for targeted protein degradation technologies.

molecular biology↗

bioRxiv2020

Microtubule poleward flux in human cells is driven by the coordinated action of four kinesins

Mitotic spindle microtubules (MTs) undergo continuous poleward flux, whose driving force and function in humans remain unclear. Here, we combined loss-of-function screenings with analysis of MT dynamics in human cells to investigate the molecular mechanisms underlying MT-flux. We report that kinesin-7/CENP-E at kinetochores (KTs) is the predominant driver of MT-flux in early prometaphase, while kinesin-4/KIF4A on chromosome arms facilitates MT-flux during late prometaphase and metaphase. We show that both of these activities work in coordination with MT-crosslinking motors kinesin-5/EG5 and kinesin-12/KIF15. Our data further indicate that MT-flux driving force is transmitted from non-KT MTs to KT-MTs via MT-coupling by HSET and NuMA. Moreover, we found that MT-flux rate correlates with spindle size and this correlation depends on the establishment of stable end-on KT-MT attachments. Strikingly, we revealed that flux is required to counteract the kinesin 13/MCAK-dependent MT-depolymerization to regulate spindle length. Thus, our study demonstrates that MT-flux in human cells is driven by the coordinated action of four kinesins, and is required to regulate mitotic spindle size in response to MCAK-mediated MT-depolymerizing activity at KTs.

cell biology↗

bioRxiv2019

Lgl cortical dynamics are independent of binding to the Scrib-Dlg complex but require Dlg-dependent restriction of aPKC

Apical-basal polarity underpins the formation of specialized epithelial barriers that are critical for metazoan physiology. Although apical-basal polarity is long known to require the basolateral determinants Lethal Giant Larvae (Lgl), Discs Large (Dlg) and Scribble (Scrib), mechanistic understanding of their function is limited. Lgl plays a role as an aPKC inhibitor, but it remains unclear whether Lgl also forms a complex with Dlg or Scrib. Using fluorescence recovery after photobleaching, we show that Lgl does not form immobile complexes at the lateral domain of Drosophila follicle cells. Optogenetic depletion of plasma membrane phosphatidylinositol 4,5-biphosphate (PIP2) or Dlg removal accelerate Lgl cortical dynamics. However, whereas Lgl turnover relies on PIP2 binding, Dlg and Scrib are only required for Lgl localization and dynamic behavior in the presence of aPKC function. Furthermore, light-induced oligomerization of basolateral proteins indicate that Lgl is not part of the Scrib-Dlg complex in vivo. Thus, Scrib-Dlg are necessary to repress aPKC activity in the lateral domain but do not provide cortical binding sites for Lgl. Our work therefore highlights that Lgl does not act in a complex but in parallel with Scrib-Dlg to antagonize apical determinants.

developmental biology↗

bioRxiv2019

Mps1 releases Mad1 from nuclear pores to ensure a robust mitotic checkpoint and accurate chromosome segregation

The strength of the Spindle Assembly Checkpoint (SAC) depends on the amount of the Mad1-C-Mad2 heterotetramer at kinetochores but also on its binding to Megator/Tpr at nuclear pore complexes (NPCs) during interphase. However, the molecular underpinnings controlling the spatiotemporal redistribution of Mad1-C-Mad2 as cells progress into mitosis remain elusive. Here, we show that Mps1-mediated phosphorylation of Megator/Tpr abolishes its interaction with Mad1 in vitro and in Drosophila cells. Timely activation of Mps1 during prophase triggers Mad1 release from NPCs, which we find to be required for competent kinetochore recruitment of Mad1-C-Mad2 and robust checkpoint response. Importantly, preventing Mad1 binding to Megator/Tpr rescues the fidelity of chromosome segregation and aneuploidy in larval neuroblasts of Drosophila mps1-null mutants. Our findings demonstrate that the subcellular localization of Mad1 is stringently coordinated with cell cycle progression by kinetochore-extrinsic activity of Mps1. This ensures that both NPCs in interphase and kinetochores in mitosis can generate anaphase inhibitors to efficiently preserve genomic stability.

cell biology↗