Mechanical stress on cells is transmitted through many biological processes, for example, cell shape control, tissue patterning, and axonal homeostasis. Microtubules, a cytoskeletal component, presumably play a significant role in the mechanoregulation of cellular processes. We investigate motor protein-driven transport of quantum dots along mechanically deformed microtubules. We found that microtubule deformation significantly slowed kinesin-driven transport, whereas we previously reported dynein-driven transport was rather robust. Such dualistic modulation of transportation dynamics of the motor proteins by microtubule deformation can be attributed to the altered affinity of the motor proteins for buckled microtubules. Our results may form the basis for understanding microtubules’ role in regulating cellular processes in a mechanically adverse environment through its detection ability and response to mechanical stress.

Cell wall patterning is central to determining the shape and function of plant cells. Protoxylem and metaxylem vessel cells deposit banded and pitted cell walls, respectively, which enable their distinctive water transport capabilities. Here, we show that the pitted cell wall pattern in metaxylem vessels is specified by transcriptional control of actin polymerization. A newly isolated allele of KNOTTED-LIKE HOMEOBOX TRANSCRIPTION FACTOR 7 (KNAT7) was associated with the formation of banded cell walls in metaxylem vessels. Loss of KNAT7 caused misexpression of FORMIN HOMOLOGY DOMAIN CONTAINING PROTEIN11 (FH11) in the metaxylem, which in turn caused rearrangements of ROP GTPases and microtubules in banded patterns. FH11 function required its plasma membrane anchoring and actin polymerization activity. These results suggest that excessive actin polymerization at the plasma membrane abolishes the pitted cell wall formation and promotes banded cell wall formation in metaxylem vessels. This study unveils the importance of proper control of actin polymerization for cell wall pattern determination.

The microtubule-kinesin biomolecular motor system, which is vital for cellular function, holds significant promise for nanotechnological applications. In vitro gliding assays have demonstrated the ability to transport microcargo by propelling microtubules across kinesin-coated surfaces. However, the uncontrolled directional motion of microtubules has posed significant challenges, limiting the system's application for precise cargo delivery. Microfluidic devices provide a means to direct microtubule movement through their geometric features. Norland Optical Adhesive (NOA) is valued for its mold-free application in microfluidic device fabrication; however, microtubules often climb up channel walls, limiting controlled movement. In this study, a surface passivation method for NOA is introduced, using polyethylene glycol via a thiol-ene click reaction. This technique significantly improved the directional control and concentration of microtubules within NOA microchannels. This approach presents new possibilities for the precise application of biomolecular motors in nanotechnology, enabling advancements in the design of microfluidic systems for complex biomolecular manipulations.

In recent years, there has been a growing interest in engineering dynamic and autonomous systems with robotic functionalities using biomolecules. Specifically, the ability of molecular motors to convert chemical energy to mechanical forces and the programmability of DNA are regarded as promising components for these systems. However, current systems rely on the manual addition of external stimuli, limiting the potential for autonomous molecular systems. Here, we show that DNA-based cascade reactions can act as a molecular controller that drives the autonomous assembly and disassembly of DNA-functionalized microtubules propelled by kinesins. The DNA controller is designed to produce two different DNA strands that program the interaction between the microtubules. The gliding microtubules integrated with the controller autonomously assemble to bundle-like structures and disassemble into discrete filaments without external stimuli, which is observable by fluorescence microscopy. We believe this approach to be a starting point toward more autonomous behavior of motor protein–based multicomponent systems with robotic functionalities.

Properly patterned deposition of cell wall polymers is prerequisite for the morphogenesis of plant cells. A cortical microtubule array guides the two-dimensional pattern of cell wall deposition. Yet, the mechanism underlying the three-dimensional patterning of cell wall deposition is poorly understood. In metaxylem vessels, cell wall arches are formed over numerous pit membranes, forming highly organized three-dimensional cell wall structures. Here, we show that the microtubule-associated proteins, MAP70-5 and MAP70-1, regulate arch development. The map70-1 map70-5 plants formed oblique arches in an abnormal orientation in pits. Microtubules fit the aperture of developing arches in wild-type cells, whereas microtubules in map70-1 map70-5 cells extended over the boundaries of pit arches. MAP70 caused the bending and bundling of microtubules. These results suggest that MAP70 confines microtubules within the pit apertures by altering the physical properties of microtubules, thereby directing the growth of pit arches in the proper orientation. This study provides clues to understanding how plants develop three-dimensional structure of cell walls.

Kinesin is a biomolecular motor that generates force and motility along microtubule cytoskeletons in cells. Owing to their ability to manipulate cellular nanoscale components, microtubule/kinesin systems show great promise as actuators of nanodevices. However, classical in vivo protein production has some limitations for the design and production of kinesins. Designing and producing kinesins is laborious, and conventional protein production requires specific facilities to create and contain recombinant organisms. Here, we demonstrated the in vitro synthesis and editing of functional kinesins using a wheat germ cell-free protein synthesis system. The synthesized kinesins propelled microtubules on a kinesin-coated substrate and showed a higher binding affinity with microtubules than E. coli-produced kinesins. We also successfully incorporated affinity tags into the kinesins by extending the original sequence of the DNA template by PCR. Our method will accelerate the study of biomolecular motor systems and encourage their wider use in various nanotechnology applications.

Controlling the patterns formed by self-propelled particles through dynamic self-organization is a challenging task. Although varieties of patterns associated with chiral self-propelled particles have been reported, essential factors that determine the morphology of the patterns have remained unclear. Here, we explore theoretically how torque formed upon collision of the particles affects the dynamic self-organization of the particles and determine the patterns. Based on a particle-based model with collision-induced torque and torque associated with self-propulsion, we find that introducing collision-induced torque turns the homogeneous bi-directionally aligned particles into rotating mono-polar flocks, which helps resolve a discrepancy in the earlier observations in microfilament gliding assays.

Bioinformatics applies computer science approaches to the analysis of biological data. It is widely known for its genomics-based analysis approaches that have supported, for example, the 1000 Genomes Project. In addition, bioinformatics relates to many other areas, such as analysis of microscopic images (e.g., organelle localization), molecular modelling (e.g., proteins, biological membranes), and visualization of biological networks (e.g., protein-protein interaction networks, metabolism). Design is a highly interdisciplinary field that incorporates aspects such as aesthetic, economic, functional, philosophical, and/or socio-political considerations into the creative process and is usually determined by context. While visualization plays a critical role in bioinformatics, as reflected in a number of conferences and workshops in the field, design in bioinformatics-related research contexts in particular is not as well studied. With this special issue in conjunction with an international workshop, we aim to bring together bioinformaticians from different fields with designers, design researchers, and medical and scientific illustrators to discuss future challenges in the context of bioinformatics and design.

これまで，微小管のダイナミクスは，その末端でのみ生じると考えられてきたが，最近，格子中心部でも発生することが明らかとなってきた．本稿では，微小管格子内ダイナミクスに関する最近の研究について解説し，その中で，筆者らの生体分子モーターによる微小管格子内ダイナミクスの促進に関する研究について紹介する．

Microtubules are dynamic polymers, permanently assembling and disassembling, that serve as tracks for intra-cellular transport by molecular motors. We recently found that the low energy of tubulin dimer interactions allows for spontaneous loss of tubulin dimers from the microtubule lattice [1]. This raised the possibility that the mechanical work produced by molecular motors as they move on microtubules can break dimer interactions and trigger microtubule disassembly. In a recent study, we tested this hypothesis by studying the interplay between microtubules and moving molecular motors in vitro [2]. Our results show that molecular motors can remove tubulin dimers from the lattice and rapidly destroy microtubules. We also found that dimer removal by motors was compensated by the insertion of free tubulin dimers into the microtubule lattice. This self-repair mechanism allows microtubules to survive the damage induced by molecular motors as they move along their tracks. Our study reveals the existence of coupling between the motion of molecular motors and the renewal of the microtubule lattice.

Self-propelled particles form various patterns through dynamic self-organization like swarming. Here, we explore numerically a new mechanism of mono-polar clustering of self-propelled particles by controlling left-right asymmetry of motility with bidirectional alignment. We apply two types of torque to the particles, resulting in rotation of global orientation and clustering depending on the balance of the two torque. The particles in global orientation exhibit bi-polar motion, while the clusters predominantly exhibit mono-polar motion. This mono-polar cluster actually recapitulates the rotating swarms observed in a microtubule gliding assay.

Microtubule instability stems from the low energy of tubulin dimer interactions, which sets the growing polymer close to its disassembly conditions. Molecular motors use ATP hydrolysis to produce mechanical work and move on microtubules. This raises the possibility that the mechanical work produced by walking motors can break dimer interactions and trigger microtubule disassembly. We tested this hypothesis by studying the interplay between microtubules and moving molecular motors in vitro. Our results show that molecular motors can remove tubulin dimers from the lattice and rapidly destroy microtubules. We also found that dimer removal by motors was compensated for by the insertion of free tubulin dimers into the microtubule lattice. This self-repair mechanism allows microtubules to survive the damage induced by molecular motors as they move along their tracks. Our study reveals the existence of coupling between the motion of molecular motors and the renewal of the microtubule lattice.

Tetsuya Hiraiwa, 2, ∗ Ryo Akiyama, Daisuke Inoue, and Arif Md. Rashedul Kabir, Akira Kakugo Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore Universal Biology Institute, The University of Tokyo, Hongo, Tokyo 113-0033, Japan. Department of Chemistry, Kyushu University, Fukuoka 819-0395, Japan Faculty of Design, Kyushu University, Fukuoka 815-0032, Japan Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan (Dated: January 7, 2021)

Flocking is a fascinating coordinated behavior of living organisms or self-propelled particles (SPPs). Particularly, monopolar flocking has been attractive due to its potential applications in various fields. However, the underlying mechanism behind flocking and emergence of monopolar motion in flocking of SPPs has remained obscured. Here, we demonstrate monopolar flocking of kinesin-driven microtubules, a self-propelled biomolecular motor system. Microtubules with an intrinsic structural chirality preferentially move towards counter-clockwise direction. At high density, the CCW motion of microtubules facilitates monopolar flocking and formation of a spiral pattern. The monopolar flocking of microtubules is accounted for by a torque generated when the motion of microtubules was obstructed due to collisions. Our results shed light on flocking and emergence of monopolar motion in flocking of chiral active matters. This work will help regulate the polarity in collective motion of SPPs which in turn will widen their applications in nanotechnology, materials science and engineering.

Recent advancements in molecular robotics have been greatly contributed by the progress in various fields of science and technology, particularly in supramolecular chemistry, bio- and nanotechnology, and informatics. Yet one of the biggest challenges in molecular robotics has been controlling a large number of robots at a time and employing the robots for any specific task as flocks in order to harness emergent functions. Swarming of molecular robots has emerged as a new paradigm with potentials to overcome this hurdle in molecular robotics. In this review article, we comprehensively discuss the latest developments in swarm molecular robotics, particularly emphasizing the effective utilization of bio- and nanotechnology in swarming of molecular robots. Importance of tuning the mutual interaction among the molecular robots in regulation of their swarming is introduced. Successful utilization of DNA, photoresponsive molecules, and natural molecular machines in swarming of molecular robots to provide them with processing, sensing, and actuating ability is highlighted. The potentials of molecular swarm robots for practical applications by means of their ability to participate in logical operations and molecular computations are also discussed. Prospects of the molecular swarm robots in utilizing the emergent functions through swarming are also emphasized together with their future perspectives.

We report the formation of spherulites from droplets of highly concentrated tubulin solution via nucleation and subsequent polymerization to microtubules (MTs) under water evaporation by heating. Radial alignment of MTs in the spherulites was confirmed by the optical properties of the spherulites observed using polarized optical microscopy and fluorescence microscopy. Temperature and concentration of tubulins were found as important parameters to control the spherulite pattern formation of MTs where evaporation plays a significant role. The alignment of MTs was regulated reversibly by temperature induced polymerization and depolymerization of tubulins. The formation of the MTs patterns was also confirmed at the molecular level from the small angle X-ray measurements. This work provides a simple method for obtaining radially aligned arrays of MTs.

Biomolecular motors are the smallest natural machines that can convert chemical energy into mechanical work with much higher energy efficiencies compared to man-made machineries. Nowadays, reconstructed biomolecular motors, such as microtubules-kinesin, are successfully utilized for nanotechnological applications, e.g., in nanotransportation, parallel computation, molecular robotics, and so on. However, stochastic nature of their motion poses a limitation to their applications, which is difficult to control particularly under spatial constraints. In this work, top-down and bottom-up approaches are combined to address this problem in a gliding assay of microtubules. Through mechanical stimulation of the motile microtubule filaments, parallelization of the filaments is demonstrated concurrently in hundreds of microwells. The orientation of plenty of motile microtubules in confined space should further accelerate nanotechnological applications of biomolecular motors.

Mechanical stress on cells has profound influences on biological processes, such as cell shape regulation, the formation of tissue patterns, and development. Recently, mechanosensing properties of the microtubule, an important cytoskeletal component, have drawn attention. In this work, we studied cargo transport by dynein, a microtubule-associated motor protein, along microtubules deformed under mechanical stress. We reveal that the microtubule deformation took place as a response to the applied stress and that the deformation of microtubules facilitated the transport of dynein-driven quantum dots. This finding will provide opportunities to explore the role of microtubules as molecular mechanotransducers in cellular processes.

Parallelization of an active matter, microtubules propelled by kinesins, in confined microwells, is demonstrated through mechanical stimulation of the microtubules. This method will be useful in studying dynamics of active biological materials in response to spatiotemporal change of boundary conditions and time-evolving asymmetry. This work will also lead to potential applications of active matters in microfluidics and biomimetics. More details can be found in article number 1902013 by Akira Kakugo and co-workers.