Biology subjects

Higashitani, A.

Publications and source records attributed to Higashitani, A..

8 recordsLinked to original sources

bioRxiv2026

Microgravity affects the nervous system and aging in C. elegans through reduced tactile stimulation

Space travel is becoming accessible, yet our understanding of how space environment and microgravity ({micro}G) affect biology, physiology, and health remains incomplete. We investigated {micro}G effects on neuromuscular development and aging in Caenorhabditis elegans. Nematodes in {micro}G showed downregulation of genes related to synaptic signaling, dopamine response, locomotion, and cuticle development, with impaired synaptic vesicle dynamics, reduced motility, and shorter body lengths. Aged worms in {micro}G showed decreased collagen gene expression, increased motor neuron defects, synaptic vesicle accumulation and decreased release, and mitochondrial morphology collapse in body wall muscles, indicating accelerated aging. MEC-4 mechanoreceptor was identified as a key mediator of {micro}G-induced body length reduction and changes in extracellular matrix gene expression. {micro}G conditions suppressed mechanoreceptor genes, suggesting multiple mechanosensory systems are affected. Physical stimulation through culture medium with small beads in space mitigated many {micro}G-induced expression changes, including mechanoreceptors, neuromuscular defects, and aging-related phenotypes. These results highlight mechanical stimulis role in maintaining neuromuscular integrity during spaceflight and suggest restoring tactile input could counter health risks from reduced stimulation in long-term space missions. SIGNIFICACEWe found that microgravity ({micro}G) conditions suppress the expression of multiple mechanoreceptor genes in Caenorhabditis elegans, indicating that several mechanosensory systems are affected during spaceflight. Importantly, reintroducing physical stimulation by adding small beads to the culture medium in space partially reversed many of these {micro}G-induced gene expression changes. This intervention also mitigated neuromuscular defects and aging-related phenotypes observed under {micro}G conditions. Collectively, these findings underscore the essential role of mechanical stimuli in preserving neuromuscular integrity during space missions and suggest that restoring tactile input may be a promising strategy to counteract the health risks associated with reduced tactile stimulation during prolonged spaceflights.

systems biology↗

bioRxiv2025

Actin cytoskeletal remodeling requires the interaction between Solo and LARG in response to substrate stiffness

In response to external mechanical stimuli, cells remodel their actin cytoskeleton. Solo, a Rho guanine nucleotide exchange factor (RhoGEF), is involved in mechanical stress responses. Using BioID, we identified PDZ-RhoGEF (PRG), a member of the RGS-RhoGEF family (regulator of G protein signaling domain-containing RhoGEFs, as a Solo-interacting protein. Moreover, we found that Solo regulates PRG during the mechanical stress response. Furthermore, we identified leukemia-associated RhoGEF (LARG), another RGS-RhoGEF member, as a Solo-interacting protein; however, the functional role of this interaction remains unknown. Therefore, in this study, we investigated the interaction between Solo and LARG and found that LARG localizes to Solo accumulation sites at the basal plane and that LARG is required for Solo-induced actin polymerization. Additionally, Solo is required to maintain LARG activity in cells, and this interaction is related to actin regulation in response to substrate stiffness. We further investigated the relationship between LARG and PRG as a function of Solo. We noted that although they did not competitively localize at Solo accumulation sites, knockdown of either PRG or LARG suppressed Solo-induced actin polymerization to the same extent as double knockdown, indicating that these signaling pathways cooperatively regulate Solo-induced actin polymerization.

cell biology↗

bioRxiv2023

Interaction between Solo and PDZ-RhoGEF is involved in actin cytoskeletal remodeling and response to substrate stiffness

Recent findings indicate that Solo, a RhoGEF, is involved in cellular mechanical stress responses. However, the mechanism of actin cytoskeletal remodeling via Solo remains unclear. Therefore, this study was aimed at identifying Solo-interacting proteins using the BioID, a proximal-dependent labeling method and elucidating the molecular mechanisms of function of Solo. We identified PDZ-RhoGEF (PRG) as a Solo-interacting protein. PRG co-localized with Solo in the basal area of cells, depending on Solo localization, and enhanced actin polymerization at Solo accumulation sites. Additionally, Solo and PRG interaction was necessary for actin cytoskeletal remodeling and RhoA activation. Moreover, overexpression of the binding domains of Solo and PRG had a dominant-negative effect on actin polymerization and actin stress fiber formation in response to substrate stiffness. Therefore, Solo restricts the localization of PRG and regulates actin cytoskeletal remodeling in synergy with PRG in response to the surrounding mechanical environment.

cell biology↗

bioRxiv2023

Gravitational and mechanical forces drive mitochondrial translation through the cell adhesion-FAK axis

Life on Earth has evolved in a form suitable for the gravitational force of 1 x g. Although the pivotal role of gravity in gene expression has been revealed by multiomics approaches in space-flown samples and astronauts, the molecular details of how mammalian cells harness gravity have remained unclear. Here, we showed that mitochondria utilize gravity to activate protein synthesis within the organelle. Genome-wide ribosome profiling revealed reduced mitochondrial translation in mammalian cells and Caenorhabditis elegans under both microgravity at the International Space Station and simulated microgravity in a 3D-clinostat on the ground. We found that attenuation of cell adhesion through laminin-integrin interactions causes the phenotype. The downstream signaling pathway including FAK, RAC1, PAK1, BAD, and Bcl-2 family proteins in the cytosol, and mitochondrial fatty acid synthesis (mtFAS) pathway in the matrix maintain mitochondrial translation at high level. Mechanistically, a decreased level of mitochondrial malonyl-CoA, which is consumed by activated mtFAS, leads to a reduction in the malonylation of the translational machinery and an increase in the initiation and elongation of in organello translation. Consistent with the role of integrin as a mechanosensor, we observed a decrease in mitochondrial translation via the minimization of mechanical stress in mouse skeletal muscle. Our work provides mechanistic insights into how cells convert gravitational and mechanical forces into translation in an energy-producing organelle.

molecular biology↗

bioRxiv2022

A stratagem for primary root elongation under moderate salt stress in the halophyte Schrenkiella parvula

Halophytes are salt-tolerant plants that grow in soil or waters of high salinity. Schrenkiella parvula is one of the halophyte plants that grow around Tuz (Salt) Lake, TURKEY that can survive at 600 mM NaCl. Intriguingly, S. parvula belongs to the same Brassicaceae family as the model plant Arabidopsis thaliana, and its genome is 90% homologous to the Arabidopsis genome. Here, we performed proteomic analysis and physiological studies on the roots of S. parvula seedlings cultivated under a moderate salt condition at 100 mM NaCl. Surprisingly, under 100 mM NaCl conditions, the primary roots elongated much faster than under NaCl-free conditions, although up to 200 mM those were reduced. On the other hand, iso-osmotic mannitol did not promote primary root elongation, suggesting a specific response to NaCl. Epidermal cell elongation was promoted in the elongation zone, but meristem size and DNA replication were decreased. In addition, root hair formation and lateral root elongation were suppressed at moderate salinity. Compared with A. thaliana, the cell death and ROS increase of root tip meristem cells under 100 mM NaCl condition were significantly lower in S. parvula seedlings. The size and starch content of sedimentary amyloplasts/statoliths in columella cells decreased, and gravitropism of primary roots was partially reduced. Gene expression analyses showed that the expression of auxin response and biosynthesis genes IAA1, IAA2, TAA1 and YUC8 were repressed and the SOS1 gene was upregulated two-fold in roots grown under moderate salt conditions. Proteomic analysis showed that co-chaperone and activator of HSPs such as Hop2 and Aha1 domain-containing protein orthologs were upregulated. Moreover, several secondary metabolic process-related proteins, antioxidant proteins, stress response proteins and proline catabolic process-related proteins were also increased. In contrast, enzymes associated with root hair elongation and nucleotide and protein syntheses were downregulated. These changes in auxin-related physiological responses, root architecture, lower ROS signaling, and stress-related protein expression promote primary root penetration into lower-salinity deeper soils as an adaptation of S. parvula.

plant biology↗

bioRxiv2022

Increased mitochondrial Ca2+ contributes to health decline with age and Duchene muscular dystrophy in C. elegans.

Sarcopenia is a geriatric syndrome characterized by an age-related decline in skeletal muscle mass and strength. Here, we show that suppression of mitochondrial calcium uniporter (MCU)-mediated Ca2+ influx into mitochondria in the body wall muscles of the nematode Caenorhabditis elegans improved the sarcopenic phenotypes, blunting movement and mitochondrial structural and functional decline with age. We found that normally aged muscle cells exhibited elevated resting mitochondrial Ca2+ levels and increased mitophagy to eliminate damaged mitochondria. Similar to aging muscle, we found that suppressing MCU function in muscular dystrophy improved movement via reducing elevated resting mitochondrial Ca2+ levels. Taken together, our results reveal that elevated resting mitochondrial Ca2+ levels contribute to muscle decline with age and in muscular dystrophy. Further, modulation of MCU activity may act as a potent pharmacological target in various conditions involving muscle loss.

cell biology↗

bioRxiv2021

Global landscape of replicative DNA polymerase usage in the human genome

The division of labour among DNA polymerase underlies the accuracy and efficiency of replication. However, the roles of replicative polymerases have not been directly established in human cells. We developed polymerase usage sequence (Pu-seq) in HCT116 cells and mapped Pol{varepsilon} and Pol usage genome wide. The polymerase usage profiles show Pol{varepsilon} synthesises the leading strand and Pol contributes mainly to lagging strand synthesis. Combining the Pol{varepsilon} and Pol profiles, we accurately predict the genome-wide pattern of fork directionality plus zones of replication initiation and termination. We confirm that transcriptional activity contributes to the pattern of initiation and termination and, by separately analysing the effect of transcription on both co-directional and converging forks, demonstrate that coupled DNA synthesis of leading and lagging strands in both co- directional and convergent forks is compromised by transcription. Polymerase uncoupling is particularly evident in the vicinity of large genes, including the two most unstable common fragile sites, FRA3B and FRA3D, thus linking transcription-induced polymerase uncoupling to chromosomal instability.

molecular biology↗

bioRxiv2016

Autophagy mitigates high-temperature injury during microsporogenesis in Arabidopsis thaliana

Autophagy is one of the cellular processes that break down cellular components during senescence, starvation, and stress. The susceptibility of plant pollen development to high-temperature (HT) stress is well known, but the involvement of autophagy in HT injury is yet to be clarified. Here, we found that following transfer to 30 {degrees}C, all autophagy-deficient (atg) mutants (atg2-1, 5-1, 7-2, and 10-1) of Arabidopsis thaliana tested displayed visibly impaired pollen development and anther dehiscence. HT-induced male sterility significantly increased in the atg mutants, but the degree of HT-induced obstacles did not change between the wild type (WT) and mutants from the seedling stage to the bolting stage. Cytological analyses showed that 30 {degrees}C promoted autophagy and autolysosome formation in both anther wall cells and microspores in developing anthers of WT, but the atg5-1 mutant did not show completion of tapetum degeneration and microspore maturation. HT upregulated hydrogen peroxide and dehydroascorbate reductase 1 production in both WT and atg5-1 anthers, but the basal levels were already higher in the mutant. HT repressed expression of UNDEAD and its regulator MYB80, which are required for tapetal programmed cell death (PCD) for proper pollen development. Taken together, our results suggest that autophagy functions in tapetum degeneration and pollen development during HT-caused tapetal PCD abortion.\n\nHighlightsO_LIIn Arabidopsis, autophagy is not essential for completion of the life cycle under normal temperatures.\nC_LIO_LIHigh temperature (HT) stress induces autophagy in developing anther wall cells and microspores.\nC_LIO_LIAutophagy deficient atg mutants become almost completely male-sterile at moderate HT.\nC_LIO_LIAutophagy plays a role in tapetum degeneration and pollen development during HT-caused abortion of tapetal program cell death.\nC_LI

plant biology↗