The actomyosin cytoskeleton generates mechanical forces that power important cellular processes, such as cell migration, cell division, and mechanosensing. Actomyosin self-assembles into contractile networks and bundles that underlie force generation and transmission in cells. A central step is the assembly of the myosin II filament from myosin monomers, regulation of which has been extensively studied. However, myosin filaments are almost always found as clusters within the cell cortex. While recent studies characterized cluster nucleation dynamics at the cell periphery, how myosin clusters grow on stress fibers remains poorly characterized. Here, we utilize a U2OS osteosarcoma cell line with endogenously tagged myosin II to measure the myosin cluster size distribution in the lamella of adherent cells. We find that myosin clusters can grow with Rho-kinase (ROCK) activity alone in the absence of myosin motor activity. Time-lapse imaging reveals that myosin clusters grow via increased myosin association to existing clusters, which is potentiated by ROCK-dependent myosin filament assembly. Enabling myosin motor activity allows further myosin cluster growth through myosin association that is dependent on F-actin architecture. Using a toy model, we show that myosin self-affinity is sufficient to recapitulate the experimentally observed myosin cluster size distribution, and that myosin cluster sizes are determined by the pool of myosin available for cluster growth. Together, our findings provide new insights into the regulation of myosin cluster sizes within the lamellar actomyosin cytoskeleton.
The spindle is the force-generating structure that drives chromosome segregation at cell division. In mammalian spindles, bundles of spindle microtubules called kinetochore-fibers (k-fibers) pull on chromosomes to move them. While we know nearly all components necessary for spindle function, how k-fibers respond to force and maintain themselves under force remains poorly understood. Our recent ability to exert local force on the mammalian spindle with microneedles provides key information to answering this question. Here, we use a modeling approach based on Euler-Bernoulli beam theory to identify the minimal mechanical features of the spindle necessary to recapitulate how k-fibers deform under external load. First, we find that force and moment generation at spindle poles are needed to recapitulate observed k-fiber shapes, both with and without external load. Then, we find that crosslinking near kinetochores, which has been experimentally observed, is necessary and sufficient to recapitulate observed k-fiber shapes, assuming no moment generation at kinetochores. By probing the limits of our model under large k-fiber deformations, we infer conditions under high external load beyond which the mechanical integrity of the k-fiber appears compromised, suggesting that structural changes occur under such forces. Finally, we assess the possibility of using our modeling formalism to learn about the applied loads based purely on k-fiber shape analysis. The modeling framework we developed not only helps us understand the mechanisms underlying the spindle's response to force, but will serve as a quantitative framework for probing how the architecture and dynamics of the k-fiber and its surrounding network give rise to mechanics and function.
A DNA G-quadruplex structure is one of the higher-order DNA structures found in a telomere region of chromosomes and suppresses enzymatic telomere-elongation reactions which frequently occur in cancer cells. Therefore, ligand compounds stabilizing such a DNA G-quadruplex structure is expected as a new-type of anti-cancer agents. To evaluate the interaction of the ligand with DNA G-quadruplexes in an aqueous solution, the examined ligands must be highly water-soluble. Such ligands have been usually substituted with hydrophilic substituents in a molecule. Here we report synthesis of several chlorophyll-a derivatives, in which their inner nitrogen is methylated, to enable their complexation and stabilization with a DNA G-quadruplex in an aqueous solution. Their binding constants with the DNA G-quadruplex structure were determined by optical spectroscopic techniques. The values using cationic N-methylated chlorophyll-a derivatives were larger than those using neutral unmethylated analogs. In addition, the thermodynamic stabilities of several G-quadruplexes with the synthetic ligands were analyzed by CD spectroscopy and will be discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.