Biology subjects

Nishizawa, K.

Publications and source records attributed to Nishizawa, K..

9 recordsLinked to original sources

bioRxiv2025

Enhancing structural heterogeneity in managed forest landscapes promotes gamma but not beta diversity in understorey plant communities

O_LIAlthough habitat heterogeneity is known to enhance local species diversity, the effects of management-driven structural heterogeneity on understorey plant communities across spatial scales remain poorly understood, despite their crucial role for forest biodiversity and ecosystem functioning. C_LIO_LITo analyse how forest understorey plant communities respond to an enhancement of structural heterogeneity in managed forests, we established 11 experimental sites consisting of two paired forest landscapes, an untreated homogenous control and a treatment district (ESBC). In treatment districts, structural heterogeneity was enhanced through different combinations of local patch-scale manipulations of light and deadwood features, leading to greater between-patch heterogeneity at the landscape scale. We performed a meta-analysis across these 11 sites using a Hill-Chao number and sample coverage standardisation framework. C_LIO_LIGamma diversity increased across taxonomic, functional and phylogenetic facets in structurally heterogeneous forests (ESBC districts) via higher alpha diversity. This effect was positively associated with heterogeneity in light availability between forest patches, but not with their mean light availability. In contrast, we found no support that species turnover among patches (i.e., beta diversity) significantly contributes on average to the observed increase in gamma diversity. However, both the direction and magnitude of beta diversity responses varied substantially among landscapes. C_LIO_LIOn average, structurally heterogeneous forests supported higher species richness for both open and closed forest habitat species. C_LIO_LISynthesis and applications: Our findings highlight the benefits of enhancing structural heterogeneity for understorey plant diversity in managed forest landscapes. Specifically, management strategies that create a spatial mosaic of interventions, such as combining single-tree removal with group felling, can increase the variety of light niches among forest patches, thereby supporting the conservation of a wide range of understorey plant species, including forest specialists. C_LI

ecology↗

bioRxiv2023

Acquisition of Auditory Discrimination Mediated by Different Processes through Two Distinct Circuits Linked to the Lateral Striatum

The striatum, the central hub of cortico-basal ganglia loops, contains functionally heterogeneous subregions distinguished by the topographic patterns of structural connectivity. These subregions mediate various processes of procedural learning. However, it remains unclear when and how striatal subregions engage in the acquisition of sensory stimulus-based decision-making. A neuroimaging of regional brain activity shows that the anterior dorsolateral striatum (aDLS) and posterior ventrolateral striatum (pVLS) in rats are activated in a different temporal pattern during the acquisition phase of auditory discrimination. Chronic and transient pharmacologic manipulations show that the aDLS promotes the behavioral strategy driven by the stimulus- response association while suppressing that by the response-outcome association, and that the pVLS contributes to forming and maintaining the stimulus-response strategy. Electrophysiological recording indicates that subpopulations of aDLS neurons predominantly represent the outcome of specific behaviors at the initial period of discrimination learning, and that pVLS subpopulations encode the beginning and ending of each behavior according to the progress of learning. In addition, other subpopulations of striatal neurons indicate sustained activation after obtaining reward with distinct patterns reflecting the stimulus-response associations. Our findings demonstrate that aDLS and pVLS neurons integrate the new learning of auditory discrimination in spatiotemporally and functionally different manners.

animal behavior and cognition↗

bioRxiv2023

Bark traits affect epiphytic bryophyte community assembly in a temperate forest

Bark traits of trees often serve as a key factor determining the community structure of epiphytes. However, the extent to which barks modulate the relative importance of abiotic and biotic assembly processes of epiphytes is poorly understood. Here, using a community phylogenetic approach, we aimed to infer the assembly processes of epiphytic mosses and liverworts on tree species with varying bark traits in a temperate forest of central Japan. We observed a total of 56 moss and 35 liverwort species on 150 trees. Moss communities showed decreasing species richness and a tendency toward phylogenetic overdispersion, that is, higher phylogenetic diversity than expected by chance, in relation to increasing bark roughness, acidity, and wetness. Along the same bark gradients, liverwort communities became phylogenetically clustered. Species richness of both mosses and liverworts increased with the nitrogen content of barks. The results indicate non-random assembly processes such as interspecific competition on resource-rich barks and abiotic filtering associated with environmental harshness and microhabitat variety determined by barks. Our findings imply that bark traits modulate community assembly processes through which epiphyte diversity is maintained.

ecology↗

bioRxiv2023

Plant-mycorrhizal associations may explain the latitudinal gradient of plant community assembly

Biogeographical variation in community assembly patterns forms the basis of large-scale biodiversity gradients. Previous studies on community assembly have suggested the dominant role of environmental filtering at higher latitudes. However, recent evidence indicates that plant community distributions at higher latitudes exhibit more spatial clustering, suggesting the importance of spatial assembly processes. In this study, we propose a hypothesis that resolves this paradox by incorporating biogeographic variations in dominant mycorrhizal types: the increasing prevalence of ectomycorrhizal (EcM) trees with latitude contributes to the spatially clustered distribution of plants, as EcM trees tend to exhibit positive plant-soil feedback. We analyzed a large-scale standardized dataset of Japanese forests covering a latitudinal gradient of >10{degrees} and found that (i) the proportion of EcM trees was higher at higher latitudes, and (ii) EcM tree-rich communities exhibited more spatially clustered distributions. Consequently, (iii) the tree species composition at higher latitudes was better explained by spatial variables. Moreover, consistent with predictions derived from the plant-soil feedback theory, these findings were particularly evident in the understory rather than the canopy communities. This study demonstrates that plant-soil feedback influences plant community distributions at metacommunity scales, thereby giving rise to a paradox within the latitudinal gradient of plant community assembly.

ecology↗

bioRxiv2022

Activity-dependent glassy cell mechanics : Mechanical properties measured with active microrheology

Active microrheology was conducted in living cells by applying an optical-trapping force to vigorously-fluctuating tracer beads with feedback-tracking technology. The complex shear viscoelastic modulus G({omega}) = G'({omega}) - iG''({omega}) was measured in HeLa cells in an epithelial-like confluent monolayer. We found that G({omega}) {propto} (-i{omega})1/2 over a wide range of frequencies (1 Hz <{omega} /2{pi}<10 kHz). Actin disruption and cell-cycle progression from G1 to S and G2 phases only had a limited effect on G({omega}) in living cells. On the other hand, G ({omega}) was found to be dependent on cell metabolism; ATP-depleted cells showed an increased elastic modulus G'({omega}) at low frequencies, giving rise to a constant plateau such that G({omega}) = G0 + A(-i{omega})1/2. Both the plateau and the additional frequency dependency {propto} (-i{omega})1/2 of ATP-depleted cells are consistent with a rheological response typical of colloidal jamming. On the other hand, the plateau G0 disappeared in ordinary metabolically active cells, implying that living cells fluidize their internal states such that they approach the critical jamming point. Statement of SignificanceIntracellular mechanical properties were measured using optical-trap-based microrheology. Despite expectations to the contrary, shear viscoelasticity was hardly affected by reorganization of cytoskeletal structures during cell-cycle progression (G1 to S and G2 phases), nor by artificial disruption of the actin cytoskeleton induced by chemical inhibitors. Rather, the mechanics of cell interiors is governed by the glassy cytoplasm. Cells depleted of ATP solidified, whereas living cells that maintained metabolic activities were more fluid-like. Instead of a completely fluid response, however, we observed a characteristic power-law viscoelasticity G({omega}) {propto} (-i{omega})1/2 over the whole range of frequencies measured. Based on our current understanding of jamming rheology, we discuss how cells fluidize their internal state in a way that pushes the system towards the critical jamming transition.

biophysics↗

bioRxiv2022

Two-point optical manipulation reveals mechanosensitive remodeling of cell-cell contacts in vivo

Biological tissues acquire reproducible shapes during development through dynamic cell behaviors. These events involve the remodeling of cell contacts driven by active cytoskeletal contractile forces. However how cell-cell contacts remodel remains poorly understood because of lack of tools to directly apply forces at cell-cell contacts to produce their remodeling. Here we develop a dual-optical trap manipulation method to impose different force patterns on cell-cell contacts in the early epithelium of the Drosophila embryo. Through different push and pull manipulations at the edges of junctions, the technique allows us to produce junction extension and junction shrinkage. We use these observations to constrain and specify vertex-based models of tissue mechanics, incorporating negative and positive mechanosensitive feedback depending on the type of remodeling. We show that Myosin-II activity responds to junction strain rate and facilitates full junction shrinkage. Altogether our work provides insight into how stress produces efficient deformation of cell-cell contacts in vivo and identifies unanticipated mechanosensitive features of their remodeling. Significance statementThe highly organized tissues and organs that form our body emerge from internal dynamic activities at the cellular level. Among such activities, cell shape changes and cell rearrangement, cell extrusion and cell division sculpt epithelial tissues into elongated sheets, tubes and spherical cavities. Remodeling of cell-cell contacts, powered by actomyosin contractility, is key to all these transformations. Although much is known about the molecular machinery and biochemical signals that regulate remodeling of cell contacts, there is a lack of approaches to directly probe the mechanics of cell contacts and therefore assess their ability to resist or deform in response to mechanical loads. We developed an experimental technique to manipulate and exert contractile and extensile forces to cell-cell junctions. Our results lead to a specific physical model of junctional mechanics, with implications in the modeling of collective cell behavior in epithelial tissues.

biophysics↗

bioRxiv2022

Catecholaminergic cell type-specific expression of Cre recombinase in knock-in transgenic rats generated by the Combi-CRISPR technology

BackgroundCell groups containing catecholamines provide a useful model to study the molecular and cellular mechanisms underlying the morphogenesis, physiology, and pathology of the central nervous system. For this purpose, it is necessary to establish a system to induce catecholaminergic group-specific expression of Cre recombinase. Recently, we introduced a gene cassette encoding 2A peptide fused to Cre recombinase into the site between the C-terminus and translational termination codons of the rat tyrosine hydroxylase (TH) open reading frame by the Combi-CRISPR technology, which is a genomic editing method to enable an efficient knock-in (KI) of long DNA sequence into a target site. However, the expression patterns of the transgene and its function as well as the effect of the mutation on the biochemical and behavioral phenotypes in the KI strains have not been characterized yet. New MethodWe aimed to evaluate the usefulness of TH-Cre KI rats as an experimental model for investigating the structure and function of catecholaminergic neurons in the brain. ResultsWe detected cell type-specific expression of Cre recombinase and site-specific recombination activity in the representative catecholaminergic groups in the TH-Cre KI rat strains. In addition, we measured TH expression level and catecholamine accumulation in the brain regions, and spontaneous locomotion, indicating that catecholamine metabolism and general behavior are apparently normal in these KI rats. ConclusionsTH-Cre KI rat strains produced by the Combi-CRISPR system offer a beneficial model to study the molecular and cellular mechanics for the morphogenesis, physiology, and pathology of catecholamine-containing neurons in the brain.

neuroscience↗

bioRxiv2022

Highly selective transgene expression through double-floxed inverted orientation system by using a unilateral spacer sequence

The double-floxed inverted orientation (DIO) system with adeno-associated viral (AAV) vector provides a beneficial approach to express transgenes in specific cell populations having Cre recombinase. A significant issue with this system is the protection against non-specific expression of transgenes in tissues after vector injection. We here show that Cre-independent recombination in AAV genome carrying the DIO sequence occurs during the production of viral vectors in packaging cells, which results in transgene expression in off-target populations. Introduction of a relatively longer nucleotide sequence between two recognition sites at the unilateral side of the transgene cassette, termed a unilateral spacer sequence (USS), is useful to suppress recombination during the vector production, leading to the protection of non-specific transgene expression with enhanced gene expression selectivity. Our DIO/USS system offers a powerful strategy for highly specific Cre-dependent transgene expression, aiming at various applications for structural and functional analyses of target cell populations.

neuroscience↗

bioRxiv2019

Prediction of prospective leaf morphology in lettuce based on intracellular chloroplast position

In the accumulation response, chloroplasts move toward weak blue light, staying at positions along the periclinal cell wall. By contrast, in the avoidance response, chloroplasts move away from strong blue light, escaping to positions along the anticlinal cell wall. The accumulation response maximizes light capture and the avoidance response reduces photodamage. The intracellular positioning of chloroplasts is important for optimizing photosynthesis and may have common signals with the regulators that determine leaf morphology, another factor that affects photosynthesis. Here, we propose that intracellular chloroplast position can be used to predict prospective leaf morphology in lettuce (Lactuca sativa). To test this, we induced the accumulation or avoidance response in lettuce cells through exposure to the appropriate strength of blue light and observed the growth of the plants. Our results indicated that leaf area increased in response to weak blue light inducing the accumulation response, and leaf thickness increased in response to strong blue light inducing the avoidance response.

plant biology↗