An official website of the United States government
The spontaneous formation of contractile asters is ubiquitous in reconstituted active materials composed of biopolymers and molecular motors. Asters are radially oriented biopolymers or biopolymer bundles with a dense motor-rich core. The microscopic origins of their material properties and their stability are unknown. Recent efforts highlighted how motor-filament and filament-filament interactions control the formation of asters composed of microtubules and kinesin motors. However, the impact of motor-motor interactions is less understood, despite growing evidence that molecular motors often spontaneously aggregate, both and . In this article, we combine experiments and simulations to reveal the origin of the arrested coarsening, aging, and stability of contractile asters composed of microtubules, clusters of adenosine triphosphate (ATP)-powered kinesin-1 motors, and a depletant. Asters coalesce into larger asters upon collision. We show that the spontaneous aggregation of motor clusters drives the solidification of aster cores, arresting their coalescence. We detect aggregation of motor clusters at the single microtubule level, where the uncaging of additional ATP drives the delayed but sudden detachment of large motor aggregates from isolated microtubules. Computer simulations of cytoskeletal assemblies demonstrate that decreasing the motors' unbinding rate slows down the aster's coalescence. Changing the motors' binding rate did not impact the aster's coalescence dynamics. Finally, we show that the aggregation of motor clusters and aster aging result from the combined effects of depletion forces and nonspecific binding of the clusters to themselves. We propose alternative formulations that mitigate these effects, and prevent aster aging. The resulting self-organized structures have a finite lifetime, which reveals that motor aggregation is crucial for maintaining aster's stability. Overall, these experiments and simulations enhance our understanding of how to rationally design long-lived and stable contractile materials from cytoskeletal proteins. Published by the American Physical Society2025
more »
« less
This content will become publicly available on March 1, 2026
Cluster formation and phase separation driven by mobile myosin motors in the motility assay
Interactions between actin filaments (F-actin) and myosin are critically important for a wide range of biological processes, including cell migration, cytokinesis, and morphogenesis. The motility assay with myosin motors fixed on a surface has been utilized for understanding various phenomena emerging from the interactions between F-actin and myosin. For example, F-actin in the motility assay exhibited distinct collective behaviors when actin concentration was above a critical threshold. Recent studies have performed the myosin motility assay on a lipid bilayer, meaning that myosin motors anchored on the fluidlike membrane have mobility. Interestingly, mobile motors led to very different collective behaviors of F-actin compared to those induced by stationary motors. However, the dynamics and mechanism of the unique collective behaviors have remained elusive. In this study, we employed our cutting-edge computational model to simulate the motility assay with mobile myosin motors. We reproduced the formation of actin clusters observed in experiments and showed that F-actin within clusters exhibits strong polar ordering and leads to phase separation between myosin motors and F-actin. The cluster formation was highly dependent on the average length and concentration of F-actin. Our study provides insights into understanding the collective behaviors of F-actins that could emerge under more physiological conditions. Published by the American Physical Society2025
more »
« less
- Award ID(s):
- 2120200
- PAR ID:
- 10589645
- Publisher / Repository:
- The American Physical Society (APS)
- Date Published:
- Journal Name:
- Physical Review Research
- Volume:
- 7
- Issue:
- 1
- ISSN:
- 2643-1564
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We investigate the quantum many-body dynamics of bosonic atoms hopping in a two-leg ladder with strong on-site contact interactions. We observe that when the atoms are prepared in a staggered pattern with pairs of atoms on every other rung, singlon defects, i.e., rungs with only one atom, can localize due to an emergent topological model, even though the underlying model in the absence of interactions admits only topologically trivial states. This emergent topological localization results from the formation of a zero-energy edge mode in an effective lattice formed by two adjacent chains with alternating strong and weak hoping links (Su-Schrieffer-Heeger chains) and opposite staggering which interface at the defect position. Our findings open the opportunity to dynamically generate nontrivial topological behaviors without the need for complex Hamiltonian engineering. Published by the American Physical Society2025more » « less
-
Multiphase field models have emerged as an important computational tool for understanding biological tissue while resolving single-cell properties. While they have successfully reproduced many experimentally observed behaviors of living tissue, the theoretical underpinnings have not been fully explored. We show that a two-dimensional version of the model, which is commonly employed to study tissue monolayers, can be derived from a three-dimensional version in the presence of a substrate. We also show how viscous forces, which arise from friction between different cells, can be included in the model. Finally, we numerically simulate a tissue monolayer and find that intercellular friction tends to solidify the tissue. Published by the American Physical Society2024more » « less
-
Chirality, or handedness, is a geometrical property denoting a lack of mirror symmetry. Chirality is ubiquitous in nature and is associated with the nonreciprocal interactions observed in complex systems ranging from biomolecules to topological materials. Here, we demonstrate that chiral arrangements of dipole-coupled atoms or molecules can facilitate the helicity-dependent superradiant emission of light. We show that the collective modes of these systems experience an emergent spin-orbit coupling that leads to chirality-dependent photon transport and nontrivial topological properties. These phenomena are fully described within the electric dipole approximation, resulting in very strong optical responses. Our results demonstrate an intimate connection between chirality, superradiance, and photon helicity and provide a comprehensive framework for studying electron transport dynamics in chiral molecules using cold atom quantum simulators. Published by the American Physical Society2024more » « less
