Biology subjects

Broedersz, C.

Publications and source records attributed to Broedersz, C..

5 recordsLinked to original sources

bioRxiv2026

Mechanical characterization of human centromeres

Centromeres must withstand high pulling forces in metaphase, yet allow rapid and complete chromosome segregation in anaphase. Using optical tweezers measurements on isolated human metaphase chromosomes, we find that centromeres are stiffer at low forces and more frequently exhibit pronounced softening compared to whole chromosomes, while displaying a similar stiffening response at high forces. We capture these mechanical properties by establishing a softened hierarchical worm-like chain model. Cohesin cleavage alters the mechanical properties of centromeres but does not lead to chromosome segregation in vitro. Topoisomerase II is recruited to centromeric regions under significant tension, likely to resolve the persistent centromeric DNA entanglements that provide additional sister chromatid cohesion. These findings advance our understanding of the mechanical resilience and regulation of centromeres during mitosis.

biophysics↗

bioRxiv2024

An alternative mechanism for activation of innate immune signaling by MDA5

Long double-stranded (ds) RNA in the cytosol acts as a potent inflammatory molecule recognized by the receptor MDA5, triggering the innate immune response. Mutations affecting MDA5 ATPase activity lead to severe pathological conditions. MDA5 nucleoprotein filament assembly-disassembly dynamic is proposed to regulate dsRNA recognition, though the exact mechanism remains unclear. Here, we employed magnetic tweezers to monitor the assembly and manipulate MDA5 filaments at the single dsRNA level. Following a slow nucleation event, MDA5 assembles cooperatively and directionally into (partial) filaments and utilizes ATP hydrolysis to compact dsRNA via single-stranded (ss) RNA loop extrusion, even against a significant opposing force. This compacted state is further stabilized by oligomerization of MDA5s caspase recruitment domain (CARD) and requires high force to be disrupted. ssRNA gaps impaired compaction, suggesting a new mechanism for dsRNA recognition. We propose that MDA5 mediated dsRNA compaction captures viral dsRNA, preventing further usage for viral replication.

biophysics↗

bioRxiv2024

Resolving interface structure and local internal mechanics of mitotic chromosomes

The interface of chromosomes enables them to interact with the cell environment and is crucial for their mechanical stability during mitosis. Here, we use Atomic Force Microscopy (AFM) to probe the interface and local micromechanics of the highly condensed and complex chromatin network of native human mitotic chromosomes. Our AFM images provide detailed snapshots of chromatin loops and Sister-Chromatids Intertwines. A scaling analysis of these images reveals that the chromatin surface has fractal nature. AFM-based Force Spectroscopy and microrheology further show that chromosomes can resist severe deformations, elastically recovering their initial shape following two characteristic timescales. Localized indentations over the chromatids reveal that the spatially varying micromechanics of the chromatin network is largely governed by chromatin density. Together, our AFM investigation provides new insights into the structure and local mechanics of mitotic chromosomes, offering a toolbox for further characterization of complex biological structures, such as chromosomes, down to the nanoscale.

biophysics↗

bioRxiv2023

Nuclear deformation and dynamics of migrating cells in 3D confinement reveal adaptation of pulling and pushing forces

Eukaryotic cells show an astounding ability to migrate through pores and constrictions smaller than their nuclear diameter. However, the forces engaged in nuclear deformation and their effect on confined cell dynamics remain unclear. Here, we study the mechanics and dynamics of nuclei of mesenchymal cancer cells as they spontaneously and repeatedly transition through 3D compliant hydrogel channels. We find a biphasic dependence of migration speed and transition frequency on channel width, revealing maximal transition rates at widths comparable to the nuclear diameter. Using confocal imaging and hydrogel bead displacement, we determine the nuclear deformation and corresponding forces during spontaneous confined migration. We find the nucleus to reversibly deform with an elastic modulus not adapting to the confinement. Instead, with decreasing channel width, the nuclear shape during transmigration changes biphasically concomitant with the transitioning dynamics. The nucleus exhibits a prolate form along the migration direction in wide channels and a more compressed oblate shape in narrow channels. We propose a physical model for confined cell migration that explains the observed nuclear shapes and slowing down in terms of the cytoskeletal force-generation adapting from a pulling-to a pushing-dominated mechanism with increasing nuclear confinement.

biophysics↗

bioRxiv2020

Single-cell growth inference of Corynebacterium glutamicum reveals asymptotically linear growth

Regulation of growth and cell size is crucial for the optimization of bacterial cellular function. So far, single bacterial cells have been found to grow exponentially, which implies the need for tight regulation to maintain cell size homeostasis. Here, we characterize the growth behavior of the apically growing bacterium Corynebacterium glutamicum using a novel broadly applicable inference method for single-cell growth dynamics. Using this approach, we find that C. glutamicum exhibits asymptotically linear single-cell growth. To explain this growth mode, we model elongation as being rate-limited by the apical growth mechanism. Our model accurately reproduces the inferred cell growth dynamics and is validated with elongation measurements on a transglycosylase deficient{Delta} rodA mutant. Finally, with simulations we show that the distribution of cell lengths is narrower for linear than exponential growth, suggesting that this asymptotically linear growth mode can act as a substitute for tight division length and division symmetry regulation.

microbiology↗