Biology subjects

Santen, L.

Publications and source records attributed to Santen, L..

7 recordsLinked to original sources

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↗

bioRxiv2024

A floor-field model of tau-taxol competition explains tau envelope dynamics on taxol-stabilized microtubules

Tau is a microtubule-associated protein (MAP) that is highly expressed in neurons. Recent in-vitro studies have shown that tau molecules can segregate into cohesive envelopes on paclitaxel (taxol) stabilized microtubules. These envelopes act as selective barriers gating the motor transport and protecting microtubules against the action of severing enzymes. However, the mechanisms underlying the formation of these envelopes remain unclear. Recent in vitro reconstitution assays revealed that the formation of tau envelopes induces a compaction of the underlying microtubule lattice, whereas taxol binding induces lattice expansion, indicating competitive binding between tau and taxol on microtubules. In this study, we use physical modeling to investigate how this competition between tau and taxol regulates the formation of tau envelopes. Our model includes static and dynamic floor-fields, concepts adapted from pedestrian dynamics. By comparing our simulation results with experimental data, we demonstrate that tau-taxol competition on the microtubule lattice is sufficient to explain the features of the formation and disassembly of tau envelopes. Notably, tau-tau interactions are not necessary to account for the steadiness of these envelopes.

biophysics↗

bioRxiv2024

Tracking the Morphological Evolution of Neuronal Dendrites by First-Passage Analysis

A high degree of structural complexity arises in dynamic neuronal dendrites due to extensive branching patterns and diverse spine morphologies, which enable the nervous system to adjust function, construct complex input pathways and thereby enhance the computational power of the system. Owing to the determinant role of dendrite morphology in the functionality of the nervous system, recognition of pathological changes due to neurodegenerative disorders is of crucial importance. We show that the statistical analysis of a temporary signal generated by cargos that have diffusively passed through the complex dendritic structure yields vital information about dendrite morphology. As a feasible scenario, we propose engineering mRNA-carrying multilamellar liposomes to diffusively reach the soma and release mRNAs, which are translated into a specific protein upon encountering ribosomes. The concentration of this protein over a large population of neurons can be externally measured, as a detectable temporary signal. Using a stochastic coarse-grained approach for first-passage through dendrites, we connect the key morphological properties affected by neurodegenerative diseases--including the density and size of spines, the extent of the tree, and the segmental increase of dendrite diameter towards soma--to the characteristics of the evolving signal. Thus, we establish a direct link between the dendrite morphology and the statistical characteristics of the detectable signal. Our approach provides a fast noninvasive measurement technique to indirectly extract vital information about the morphological evolution of dendrites in the course of neurodegenerative disease progression.

neuroscience↗

bioRxiv2024

Growth of Stress-Responsive Bacteria in 3D Colonies under Confining Pressure

We numerically study three-dimensional colonies of nonmotile stress-responsive bacteria growing under confining isotropic pressure in a nutrient-rich environment. We develop a novel simulation method to demonstrate how imposing an external pressure leads to a denser aggregate and strengthens the mechanical interactions between bacteria. Unlike rigid confinements that prevent bacterial growth, confining pressure acts as a soft constraint and allows colony expansion with a nearly linear long-term population growth and colony size. Enhancing the mechanosensitivity reduces instantaneous bacterial growth rates and the overall colony size, though its impact is modest compared to pressure for our studied set of biologically relevant parameter values. The doubling time grows exponentially at low mechanosensitivity or pressure in our bacterial growth model. We provide an analytical estimate of the doubling time and develop a population dynamics model consistent with our simulations. Our findings align with previous experimental results for E. coli colonies under pressure. Understanding the growth dynamics of stress-responsive bacteria under mechanical stresses provides insight into their adaptive response to varying environmental conditions.

biophysics↗

bioRxiv2022

Vesicles driven by dynein and kinesin exhibit directional reversals without external regulators

Intracellular transport along cytoskeletal filaments propelled by molecular motors ensures the targeted delivery of cargoes to their destinations. Such transport is rarely unidirectional but rather bidirectional, including intermittent pauses and directional reversals owing to the simultaneous presence of opposite-polarity motors. It has been unclear whether such a complex motility pattern results from the sole mechanical interplay between opposite-polarity motors or requires external regulators. Here, we addressed this outstanding question by reconstituting cargo motility along microtubules in vitro by attaching purified Dynein-Dynactin-BICD2 (DDB) and kinesin-3 (KIF16B) to large unilamellar vesicles. Strikingly, we found that this minimal system is sufficient to recapitulate runs, pauses and reversals similar to in vivo cargo motility. In our experiments, reversals were always preceded by vesicle pausing and the transport directionality could be tuned by the relative numbers of opposite-polarity motors on the vesicles. Unexpectedly, during all runs the vesicle velocity was not influenced by the presence of the opposing motors. To gain mechanistic insight into bidirectional transport, we developed a mathematical model which predicts that low numbers of engaged motors are critical to transition between runs and pauses. Taken together, our results suggest that motors diffusively anchored to membranous cargo transiently engage in a tug-of-war during pauses where stochastic motor attachment and detachment events can lead to directional reversals without the necessity of external regulators.

biophysics↗

bioRxiv2021

The adhesion capability of S. aureus cells is heterogeneously distributed over the cell envelope

Understanding and controlling microbial adhesion is an important biomedical problem. However, many properties of the adhesion process of bacteria are still unknown, for example the distribution of adhesive strength over the cell wall. While a patchy colloid model for adhesion has been developed recently for Gram-negative Escherichia coli cells, a comparable model for Grampositive cells is unknown. Here, we use single-cell force spectroscopy to measure the adhesion of Staphylococcus aureus at different positions on tailored surfaces. We find heterogeneous adhesion profiles with varying degrees of intensity. By comparing these results to simulations, we find that locally increased adhesion can be explained by several distinct spots of high adhesion capabilities, similar to the patchy colloid model. Only for the underlying profile without local adhesive spots simple geometric considerations are insufficient. Rather, strong angle-dependent molecule-substratum interactions are necessary to explain the bathtub-like adhesion profiles seen for Staphylococcus aureus on a sinusoidal surface. We discuss implications of our results for the development of new materials and the design and analysis of future studies.

biophysics↗

bioRxiv2020

Stable tug-of-war between kinesin-1 and cytoplasmic dynein upon different ATP and roadblock concentrations

The maintenance of intracellular processes like organelle transport and cell division depend on bidirectional movement along microtubules. These processes typically require kinesin and dynein motor proteins which move with opposite directionality. Because both types of motors are often simultaneously bound to the cargo, regulatory mechanisms are required to ensure controlled directional transport. Recently, it has been shown that parameters like mechanical motor activation, ATP concentration and roadblocks on the microtubule surface differentially influence the activity of kinesin and dynein motors in distinct manners. However, how these parameters affect bidirectional transport systems has not been studied. Here, we investigate the regulatory influence of these three parameter using in vitro gliding motility assays and stochastic simulations. We find that the number of active kinesin and dynein motors determines the transport direction and velocity, but that variations in ATP concentration and roadblock density have no significant effect. Thus, factors influencing the force balance between opposite motors appear to be important, whereas the detailed stepping kinetics and bypassing capabilities of the motors have only little effect.

biophysics↗