Symmetric or asymmetric positioning of intracellular structures including the nucleus and mitotic spindle steers various biological processes such as cell migration, division, and embryogenesis. In typical animal cells, both a sparse actomyosin meshwork in the cytoplasm and a dense actomyosin cortex underneath the cell membrane participate in the intracellular positioning. However, it remains unclear how these coexisting actomyosin structures regulate the positioning symmetry. To reveal the potential mechanism, we construct an in vitro model composed of cytoplasmic extracts and nucleus-like clusters confined in droplets. Here we find that periodic centripetal actomyosin waves contract from the droplet boundary push clusters to the center in large droplets, while network percolation of bulk actomyosin pulls clusters to the edge in small droplets. An active gel model quantitatively reproduces molecular perturbation experiments, which reveals that the tug-of-war between two distinct actomyosin networks with different maturation timescales determines the positioning symmetry.
The stress fiber composed of actin filaments, myosin motors, and α-actinin is essential to maintain a cell shape. To investigate the self-assembly mechanism of the stress fiber, we constructed 2D actin networks crosslinked by α-actinin in vitro, and observed the network contraction by the addition of myosin with ATP. At high [myosin], the network collapsed, forming large clusters. At the intermediate [myosin], we found that the thin actin bundles were fused and straightened, resulting in the formation of thick bundle networks. We confirmed that the successful thick bundle network formation was determined by the myosin vs. actinin molar ratio. Our results suggest that the local density ratio of α-actinin and active myosin in cytoplasm regulates the stress fiber assembly. 2P170 微小管ネットワークの対称性の破れによって引き起こされる 細胞質回転流動 Cytoplasmic rotational flow induced by symmetry breaking of active microtubule networks Cytoskeletal networks are essential for cellular functions. While properties of actin networks are well understood, it remains unclear how microtubule (MT) networks behave in cytoplasm. Here, we employed Xenopus egg extracts encapsulated in droplets as a model system to examine the behavior of cytoplasmic MT networks. After the encapsulation, the networks spontaneously contracted, accumulating cytoplasmic materials to the droplet center. In contrast, when dynein was inactive, extensile MT bundles pushed the droplet boundary, resulting in a rotational vortex. This vortex induced cytoplasmic rotational flow, which seems useful for dispersing organelles. Our results suggest that cellular MT networks have two different modes, and cells utilize dynein activity as a switch. 2P171 二種類の固定子を持つシュードモナス・シリンゲの運動解析 Motility analysis of Pseudomonas syringae possessing two different stator systems Takuto Tensaka, Shuichi Nakamura, Seishi Kudo (Grad. Sch. Eng., Tohoku. Univ.)The bacterial flagellar motor consists of a rotor and a stator, which convert the flow of ions, such as proton and sodium ion, to rotation. Pseudomonas syringae is known to possess two sets of stators, MotA/B and MotC/D. In this study, to elucidate how the dual stator system functions in the P. syringae flagellar motor, we tested the motilities of P. syringae mutants lacking motA/B or motC/D at various viscous conditions. Both ΔmotA/B and ΔmotC/D cells showed motility in a low viscous medium. However, in a high viscous medium containing 20% Ficoll, the ΔmotA/B cells swam as fast as the wild-type cell, while the ΔmotC/D cells were non-motile. These suggest that the MotC/D complex rather than the MotA/B one would play a major role in highly viscous environments. 2P172MotA に点変異を持つ細菌べん毛モーターの出力特性解析 Rotation analysis of the bacterial flagellar motor with a point mutation in MotAThe bacterial flagellar motor converts the energy of proton flow through the stator into the mechanical work. The stator complex consists of MotA and MotB. Though it has been proposed that the electrostatic interaction between MotA and a rotor protein FliG generates the torque, the mechanism of tor...
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.