Biology subjects

Igarashi, M.

Publications and source records attributed to Igarashi, M..

11 recordsLinked to original sources

bioRxiv2025

In vitro live cell imaging reveals nuclear dynamics and role of the cytoskeleton during asymmetric division of pollen mitosis I in Nicotiana benthamiana

Pollen is a male gametophyte of angiosperms. Following meiosis, the microspore undergoes an asymmetric division called pollen mitosis I (PMI), which produces two cells of different sizes: a large vegetative cell and a small generative cell. Polarized nuclear migration and positioning during PMI are important for successful pollen development and cell differentiation. However, analyzing the pollen development process in real-time is challenging in many model plants with tricellular pollen, including Arabidopsis and rice. In this study, we established a method for live confocal imaging of microtubule and actin dynamics using suspension cultures with biolistic delivery of plasmid DNAs during PMI in Nicotiana benthamiana (Benthams tobacco), containing bicellular pollen. Pharmacological studies have indicated that actin filaments are crucial for microspore nuclear positioning before PMI, cell plate expansion during cytokinesis, and chromatin dispersion in vegetative cell nucleus after PMI. By contrast, inhibition of microtubule assembly resulted in abnormal chromosome segregation and nuclear behavior after PMI, although nuclear positioning and asymmetric division were observed. Our in vitro live cell imaging system for PMI provides insights into the importance of cytoskeletal regulation in asymmetric division and differentiation during pollen development.

plant biology↗

bioRxiv2025

The pivotal role of a novel free fatty acid receptor GPR164 in the intestinal barrier function

GPR164 is a novel free fatty acid receptor, activated by both short-chain fatty acids and medium-chain fatty acids, and expressed throughout the gastrointestinal tract. Although GPR164 is reported to be involved in the release of gut hormones, the physiological functions of this receptor in the maintenance of intestinal homeostasis remain unclear. In this study, we explored the role of GPR164 in regulating intestinal barrier function using mice lacking Gpr164 gene (Gpr164-/-). A loss-of-function mutation in GPR164 promoted cell proliferation and disrupted the intestinal barrier function in both Caco-2 cell line and mice. Genome-wide RNA-seq analysis revealed that GPR164 deletion caused aberrant wnt/{beta}-catenin signaling, and the intraperitoneal injection of wnt/{beta}-catenin inhibitor ameliorated a series of abnormalities of Gpr164-/- mice. Gpr164-/- mice also exhibited gut microbial dysbiosis and severe inflammation, indicating that deletion of Gpr164 causes similar pathologies observed in patients with inflammation bowel disease (IBD). Thus, our findings uncover the pivotal role of GPR164 in the maintenance of intestinal barrier function, providing an attractive clinical target for IBD.

physiology↗

bioRxiv2025

Identification of an ambisense kolmiovirus from birds

Circular RNA replicons share compact, highly self-complementary genomes that impose severe constraints on genome organization and coding capacity. Recent studies have uncovered a broad diversity of such replicons, but their transcriptional and coding strategies remain inferred largely from sequence analyses. Here we show experimentally that some kolmioviruses (family Kolmioviridae), which have been described as negative-sense circular RNA satellite viruses, use ambisense transcription to expand coding capacity. We identify avian bornaviruses as helper viruses for Serinus canaria kolmiovirus (scKoV) and show that ambisense transcription drives expression of a previously unrecognized gene, open reading frame 2 (ORF2), that promotes helper-dependent transmission. Comparative analyses reveal ambisense gene expression in additional kolmiovirus lineages, suggesting independent acquisition during evolution. These findings provide experimental evidence that circular RNA replicons with highly constrained genomes can acquire additional protein-coding genes through ambisense transcription.

microbiology↗

bioRxiv2024

Nicotine enhances the stemness and tumorigenicity in intestinal stem cells via Hippo-YAP/TAZ and Notch signal pathway

Cigarette smoking is a well-known risk factor inducing the development and progression of various diseases. Nicotine (NIC) is the major constituent of cigarette smoke. However, knowledge of the mechanism underlying the NIC-regulated stem cell functions is limited. In this study, we demonstrate that NIC increases the abundance and proliferative activity of intestinal stem cells (ISCs) in vivo and ex vivo. Moreover, NIC induces Yes-associated protein (YAP) /Transcriptional coactivator with PDZ-binding motif (TAZ) and Notch signaling in ISCs via 7-nicotinic acetylcholine receptor (nAchR) and protein kinase C (PKC) activation; this effect was not detected in Paneth cells. The inhibition of Notch signaling by dibenzazepine (DBZ) nullified the effects of NIC on ISCs. NIC enhances in vivo tumor formation from ISCs after loss of the tumor suppressor gene Apc, DBZ inhibited NIC-induced tumor growth. Hence, this study identifies a NIC-triggered pathway regulating the stemness and tumorigenicity of ISCs and suggests the use of DBZ as a potential therapeutic strategy for treating intestinal tumors.

cell biology↗

bioRxiv2023

Evasion of APOBEC1-mediated Intrinsic Immunity by a Herpesvirus Uracil DNA Glycosylase Is a Determinant of Viral Encephalitis

Herpes simplex virus 1 (HSV-1) is the most common cause of viral encephalitis, which can be lethal or result in severe neurological defects, even when treated with antiviral therapy. We demonstrated that activation of HSV-1 uracil-DNA glycosylase (vUNG) by phosphorylation, essential for its enzymatic activity, counteracted APOBEC1 to promote viral replication and encephalitis in the central nervous system (CNS) of mice. The activation of vUNG protected HSV-1 genomes from APOBEC1-mediated DNA editing, allowing efficient viral replication to occur. The presence of APOBEC1 markedly improved lethal encephalitis in mice infected with an HSV-1 mutant carrying a mutation in the phosphorylation site and an UNG inhibitor protected wild-type HSV-1-infected mice from lethal encephalitis. These findings re-define vUNG as an important factor that allows evasion from intrinsic anti-viral immunity mediated by APOBEC1 in the CNS, and suggest a new therapeutic approach for the treatment of fetal and critical HSV-1 encephalitis.

microbiology↗

bioRxiv2022

A land plant specific VPS13 mediates polarized vesicle trafficking in germinating pollen

Pollen has an extraordinary ability to convert from a dry state to an extremely rapidly growing state. During pollination, pollen receives water and Ca2+ from the contacting pistil, which will be a directional cue for pollen tube germination. The subsequent rapid activation of directional vesicular transport must support the pollen tube growth, but the molecular mechanism leading to this process is largely unknown. Here we show that a plant-specific VPS13, AtVPS13a, mediates vesicle trafficking during the polarization process in Arabidopsis pollen. AtVPS13a knockout severely affected pollen germination and lipid droplet discharge, while Ca2+-dynamics after pollination was unchanged. Cellular distribution patterns of AtVPS13a and a secretory vesicle marker were synchronized, with a slight delay to the Ca2+-dynamics in polarizing pollen. The absence of AtVPS13a led to reduced cell wall deposition during pollen germination. These results suggest that AtVPS13a mediates pollen polarization, by regulating proper directional vesicular transport following Ca2+-signaling.

plant biology↗

bioRxiv2022

Influenza A virus agnostic receptor tropism revealed using a novel biological system with terminal sialic acid-knockout cells

Avian or human influenza A viruses bind preferentially to avian- or human-type sialic acid receptors, respectively, indicating that receptor tropism is an important factor for determining the viral host range. However, there are currently no reliable methods for analyzing receptor tropism biologically under physiological conditions. Here, we established a novel system using MDCK cells with avian- or human-type sialic acid receptors and with both sialic acid receptors knocked out (KO). When we examined the replication of human and avian influenza viruses in these KO cells, we observed unique viral receptor tropism that could not be detected using a conventional solid-phase sialylglycan binding assay, which directly assesses physical binding between the virus and sialic acids. Furthermore, we serially passaged an engineered avian-derived H4N5 influenza virus, whose PB2 gene was deleted, in avian-type receptor-KO cells stably expressing PB2 to select a mutant with enhanced replication in KO cells; however, its binding to human-type sialylglycan was undetectable using the solid-phase binding assay. These data indicate that a panel of sialic acid receptor-KO cells could be a useful tool for determining the biological receptor tropism of influenza A viruses. Moreover, the PB2-KO virus experimental system could help to safely and efficiently identify the mutations required for avian influenza viruses to adapt to human cells that could trigger a new influenza pandemic. Author summaryInfluenza A virus initiates infection via hemagglutinin by binding to avian- or human-type receptors. The acquisition of mutations that allow avian virus hemagglutinins (HAs) to recognize human-type receptors is mandatory for the transmission of avian influenza viruses to humans, which could lead to a pandemic. Therefore, it is important to detect such mutation(s) in animal influenza viruses for pandemic surveillance and risk assessment. In this study, we established a novel system using a set of genetically engineered MDCK cells with knocked out sialic acid receptors to biologically evaluate the receptor tropism for influenza A viruses. Using this system, we observed unique receptor tropism in several virus strains that was undetectable using conventional solid-phase binding assays that measure physical binding between the virus and artificially synthesized sialylglycans. This study makes a significant contribution to the literature because our findings suggest the pitfall of conventional receptor binding assay and the existence of a sialic acid-independent pathway for viral infection. In addition, our system could be safely used to identify mutations that could acquire human-type receptor tropism. Thus, this system could contribute not only toward basic analyses, such as elucidating the mechanism of influenza virus host range determination, but also the surveillance of viruses of animal origin that could be capable of infecting via human-type receptors, triggering a new influenza pandemic.

microbiology↗

bioRxiv2021

Structural insight into Marburg virus nucleoprotein-RNA complex formation

The nucleoprotein (NP) of Marburg virus (MARV), a close relative of Ebola virus (EBOV), encapsidates the single-stranded, negative-sense viral genomic RNA (vRNA) to form the helical NP-RNA complex. The NP-RNA complex serves as a scaffold for the assembly of the nucleocapsid that is responsible for viral RNA synthesis. Although appropriate interactions among NPs and RNA are required for the formation of nucleocapsid, the structural basis of the helical assembly remains largely elusive. Here, we show the structure of the MARV NP-RNA complex determined using cryo-electron microscopy at a resolution of 3.1 [A]. The structures of the asymmetric unit, a complex of an NP and six RNA nucleotides, was very similar to that of EBOV, suggesting that both viruses share common mechanisms for the nucleocapsid formation. Structure-based mutational analysis of both MARV and EBOV NPs identified key residues for the viral RNA synthesis as well as the helical assembly. Importantly, most of the residues identified were conserved in both viruses. These findings provide a structural basis for understanding the nucleocapsid formation and contribute to the development of novel antivirals against MARV and EBOV.

microbiology↗

bioRxiv2021

Modulation of tactile feedback for the execution of dexterous movement

While dexterity relies on the constant transmission of sensory information, unchecked feedback can be disruptive to behavior. Yet how somatosensory feedback from the hands is regulated as it first enters the brain, and whether this modulation exerts any influence on movement, remain unclear. Leveraging molecular-genetic access in mice, we find that tactile afferents from the hand recruit neurons in the brainstem cuneate nucleus whose activity is modulated by distinct classes of local inhibitory neurons. Selective manipulation of these inhibitory circuits can suppress or enhance the transmission of tactile information, affecting behaviors that rely on movement of the hands. Investigating whether these local circuits are subject to top-down control, we identify distinct descending cortical pathways that innervate cuneate in a complementary pattern. Somatosensory cortical neurons target the core tactile region of cuneate, while a large rostral cortical population drives feed-forward inhibition of tactile transmission through an inhibitory shell. These findings identify a circuit basis for tactile feedback modulation, enabling the effective execution of dexterous movement.

neuroscience↗

bioRxiv2020

Collection of 2429 constrained headshots of 277 volunteers for deep learning

Deep learning has rapidly been filtrating many aspects of human lives. In particular, image recognition by convolutional neural networks has inspired numerous studies in this area. Hardware and software technologies as well as large quantities of data have contributed to the drastic development of the field. However, the application of deep learning is often hindered by the need for big data and the laborious manual annotation thereof. To experience deep learning using the data compiled by us, we collected 2429 constrained headshot images of 277 volunteers. The collection of face photographs is challenging in terms of protecting personal information; we established an online procedure in which both the informed consent and image data could be obtained. We did not collect personal information, but issued agreement numbers to deal with withdrawal requests. Gender and smile labels were manually and subjectively annotated only from the appearances, and final labels were determined by majority among our team members. Rotated, trimmed, resolution-reduced, decolorized, and matrix-formed data were allowed to be publicly released. Moreover, simplified feature vectors for data sciences were released. We performed gender recognition by building convolutional neural networks based on the Inception V3 model with pre-trained ImageNet data to demonstrate the usefulness of our dataset.

animal behavior and cognition↗

bioRxiv2019

Anterior corpus callosum modulates symmetric forelimb movements during spontaneous food handling behavior of rats.

Bimanual motor actions, such as threading a needle, require coordination of the movements of each hand according to the state of the other hand. By connecting homologous cortical regions between the two cerebral hemispheres, the corpus callosum is thought to play a key role in such bimanual coordination. However, direct experimental evidence of the contribution of the corpus callosum to natural behaviors requiring bimanual coordination, such as feeding, is lacking. We investigated the hypothesis that the corpus callosum mediates bimanual movements during food-handling behavior. We first traced the forelimb-related components of the motor corpus callosum in Long-Evans rats, and found that the callosal fiber bundle from the forelimb motor areas passes through the anterior part of the corpus callosum. We then confirmed by electrophysiological recordings that blocking the axonal conduction of fibers in the anterior corpus callosum reduced neural transmission between cortical forelimb areas. The causal role of corpus callosum in bimanual coordination was then tested by analyzing forelimb kinematics during object manipulation, before and after blocking axonal conduction in the anterior corpus callosum. We found the frequency of occurrence of symmetric bimanual movements was reduced by inhibition of anterior corpus callosum. In contrast, asymmetric bimanual movement was increased. Our findings suggest that the anterior corpus callosum coordinates the direction of bimanual movement.

neuroscience↗