Biology subjects

Nishigami, Y.

Publications and source records attributed to Nishigami, Y..

6 recordsLinked to original sources

bioRxiv2026

Allocation pattern of fruiting bodies in plasmodial slime molds, and threshold size for sporulation of P. polycephalum

The plasmodium of Myxogastria (a group of amoeboid protists) species often crawls around the forest floor to feed while searching for places to form fruiting bodies for reproduction (sporulation). Certain environmental factors that trigger sporulation have been reported; however, other unknown factors are also expected. In this study, we reported field observations of Physarum rigidum and Fuligo septica. Inspired by the field observation, we examined the effects of multiple factors on sporulation in laboratory experiments using Physarum polycephalum. We found that:(1) there was a critical body size below which sporulation did not occur under our experimental conditions and (2) the plasmodium selected its sporulation sites from the available landscape of the experimental arena: dry and low sites for the majority and dry and high sites for the minority. Further analysis revealed that they preferred the edge area at the high site. We discuss the possible ecological importance of the threshold and location preference

animal behavior and cognition↗

bioRxiv2026

Mechanical analysis of spatiotemporal traction stress dynamics in a bleb-driven migrating cell, Amoeba proteus

Many adherent eukaryotic cells exhibit amoeboid locomotion, where traction stress exerted on the substrate is essential for movement. In this study, we investigated the spatiotemporal development of these forces in Amoeba proteus to clarify the mechanical dynamics underlying bleb-driven migration. By performing a multipole analysis of the stress distribution, we characterized the spatiotemporal patterns exhibited by motile cells. Furthermore, we tracked the behavior of individual localized peak structures within these profiles, which are thought to correspond to focal contact sites. These analyses revealed that the front-back asymmetry in the traction distribution correlates with the direction of migration. We also found that A. proteus exhibits a periodic pattern in which inward-directed stresses are alternately strengthened and weakened at the cell poles. Crucially, we identified a distinctive feature not observed in other cell types: the generation of large lateral traction forces at the cell center. Together, these results highlight both the universality and diversity of the biophysical mechanisms driving amoeboid locomotion.

biophysics↗

bioRxiv2026

Image-scanning light-sheet microscopy for high-speed volumetric imaging of complex biological dynamics

Volumetric fluorescence microscopy is a powerful method for studying complex biological systems because it enables comprehensive observation of structural and physiological dynamics. In particular, light-sheet microscopy (LSM) is a leading option for real-time volumetric fluorescence imaging as it combines high imaging speed, low phototoxicity, minimal photobleaching, high spatiotemporal resolution, and low computational burden. To capture fast biological events, various efforts have been made to improve the imaging speed of volumetric fluorescence microscopy, including LSM. However, existing approaches entail significant trade-offs that make routine volumetric imaging at and beyond video rates challenging under practical conditions. Here, we introduce image-scanning LSM, a method that substantially increases the volumetric imaging speed achievable with LSM while preserving key performance metrics, such as spatial resolution and photon efficiency, as well as accessibility. Our implementation, termed image-scanning oblique plane (ISOP) microscopy, enables volumetric fluorescence imaging at up to 1,000 volumes per second with submicrometer lateral spatial resolution. We demonstrate the broad utility of ISOP microscopy by recording and analyzing the dynamics of behaving and rapidly moving organisms.

bioengineering↗

bioRxiv2025

Mathematical modeling for primitive form of habituation in an amoeba

Learning abilities, once thought to be unique to higher animals, have been reported to exist in their primitive form in single-celled organisms. This has triggered a growing interest in carefully examining the nature and mechanisms of the primitive versions of learning abilities, which would provide important clues for understanding the evolution of behavioral capabilities in organisms. In this study, we focused on previous experimental studies showing that the slime mold Physarum polycephalum, a model organism for studying protist behavior, exhibits the ability to adapt to chemical environments. We propose a possible dynamic mechanism underlying this habituation, reproducing reported experimental observations with accuracy. By refining a mathematical model that was as simple as possible and based on non-specific biochemical processes within cells, we clarified a plausible mechanistic framework. Based on these results, we examined the similarities and differences between this framework and previously proposed habituation models of single-cell movement and animal neural-circuit regulation. These findings are significant because they open new avenues for research into the generality and evolutionary origins of acclimation learning.

systems biology↗

bioRxiv2025

Geometrical preference of anchoring sites in the unicellular organism Stentor coeruleus

Organisms often inhabit environments comprising complex structures across various scales. Animals rely on visual information from surrounding geometrical structures for navigation. Even at the microscale, various microsediments form complex structures in microbial habitats. The movement of microorganisms is passively affected by collisions and hydrodynamic interactions with surrounding structures. However, the influence of microenvironmental geometry on behavioral changes of unicellular organisms that lack visual perception remains unclear. Here, we developed geometrically structured chambers to investigate anchoring site preferences in the swimming ciliate Stentor coeruleus. Our experiments revealed that S. coeruleus preferentially anchored in narrow regions characterized by specific geometrical features, including corner angle, depth, and curvature at the corner end. Before anchoring, free-swimming S. coeruleus changed its behavior to move along the boundary wall of the chambers, accompanied by Ca2+-induced asymmetrical body deformation. To further investigate how S. coeruleus moves along the wall continuously, we conducted a hydrodynamic simulation and revealed that the asymmetric morphology causes asymmetric propulsive forces, explaining wall-following behavior through physical interactions with a wall. Thus, morphological change near a wall causes wall-following behavior, facilitating the identification of these narrow anchoring sites. Our findings indicate that environmental geometry drives behavioral transitions in S. coeruleus through simple biophysical processes, enabling spatial selection without visual cues. Overall, these results suggest that microgeometry plays a key role in shaping ecological niches for unicellular microorganisms. Significance StatementAnimals use various natural structures as landmarks for navigation. In microorganism habitats, microsediments also form geometrically complex environments. Is there a relationship between the geometrical features of structures and the behavior in unicellular organisms lacking visual cues? Here we report that the free-swimming unicellular organism Stentor coeruleus selects the anchoring sites based on the surrounding shapes. Further observations and numerical simulations reveal that an asymmetric morphological change causes a temporary switch from ballistic to wall-following exploration, driven by surrounding structures. These results indicate that one simple behavioral response underlies the preference of anchoring sites with specific geometrical features in non-neural unicellular organisms. The findings shed light on the role of microenvironmental geometry in forming ecological niches for microorganisms.

biophysics↗

bioRxiv2023

Linear contraction of stress fibers generates cell body rotation

Wounds are healed by crawling migration of the epidermal cells around the injured area. Fish epidermal keratocytes that rapidly repair wounds comprise a frontal crescent-shaped lamellipodium and a rear rugby ball-shaped cell body. The cell body rotates like a wheel during migration. Stress fibers, which are bundles of contractile actomyosin filaments, are arranged along the seams of the rugby ball. Here we show the linear contraction of stress fibers to be the driving force for rotation. We constructed a mechanical model of the cell body that consisted of a soft cylinder with a contractile coil. From the motion of the model, it was predicted that contraction of the stress fibers would deform the soft cell body, as a result of which the deformed cell body would push against the substrate to generate torque. This prediction was confirmed by the observation of stress fiber dynamics in migrating cells. Linear-to-rotation conversion in migrating keratocytes is realized by simple soft-body mechanics. Conversion from linear motion to rotation is widely used in machines with moving parts, but requires somewhat complicated mechanics. An understanding of linear-to-rotation conversion in keratocytes has potential for use in the design of biomimetic soft robots.

biophysics↗