Biology subjects

Okamoto, N.

Publications and source records attributed to Okamoto, N..

13 recordsLinked to original sources

bioRxiv2025

Steroid hormone-dependent glial-neuronal interaction promotes brain development during Drosophila metamorphosis

Steroid hormones regulate various aspects of brain development in metazoans. In the fruit fly Drosophila melanogaster, the primary steroid hormone ecdysone enters the central nervous system (CNS) via Ecdysone Importer (EcI) in the blood-brain barrier (BBB) and induces brain development during metamorphosis. However, our understanding of the exact cell types that require ecdysone during CNS transformation is still limited. Here, we report that ecdysone-dependent glial-neuronal interaction promotes brain development during Drosophila metamorphosis. Unexpectedly, disrupting ecdysone signaling in glial cells caused more severe defects in CNS transformation than in neurons, suggesting an essential role of glia in ecdysone-dependent brain development. When ecdysone receptor was knocked down in mushroom body (MB) neurons, pruning of their larval-specific axonal lobes was disrupted as reported previously. In contrast, knockdown of EcI in the MB did not induce any discernible deficiency in neuronal remodeling, suggesting dispensability of EcI-mediated ecdysone entry into the MB. Consistent with this, the neuronal remodeling defects induced by EcI knockdown in the BBB were rescued by glial cell-specific overexpression of a transforming growth factor-{beta} ligand myoglianin and an engulfment receptor draper, both of which are upregulated in glial cells in an ecdysone-dependent manner. Collectively, our findings suggest that ecdysone is primarily required in glial cells for CNS transformation during metamorphosis, elucidating a hormone-dependent glial-neuronal interaction that drives brain development.

developmental biology↗

bioRxiv2025

Ion transport peptide regulates body water balance via a receptor guanylyl cyclase in the Drosophila hindgut

Maintaining internal water balance, including ionic and osmotic balance, is critical for animal development and survival. In insects, internal water balance is regulated through the Malpighian tubules and the hindgut, which transport water and ions across their epithelia under the regulation of multiple peptide hormones. One of these, ion transport peptide (ITP), a member of the highly conserved crustacean hyperglycemic hormone superfamily among ecdysozoans, is an anti-diuretic hormone in insects, but its mechanism of action remains largely unclear. Here, we show that the short amidated isoform of ITP (saITP), secreted from brain neurosecretory cells, regulates water absorption via the receptor guanylyl cyclase (rGC) Gyc76C in the hindgut of the fruit fly Drosophila melanogaster. Both ITP and Gyc76C are evolutionarily conserved and are essential for larval survival in D. melanogaster, as mutation or knockdown of either gene results in early larval lethality. In Drosophila S2 cells, synthetic saITP increases intracellular cyclic GMP (cGMP) in a Gyc76C-dependent manner, an effect abolished by deletion of its putative ligand-binding domain. Using the fluorescent cGMP biosensor RedcGull in ex vivo-cultured hindguts, we found that saITP increases epithelial cGMP levels, and this response requires Gyc76C. Consistently, saITP promotes hindgut water reabsorption via Gyc76C. Thus, saITP acts via Gyc76C in a brain-hindgut neuroendocrine axis that regulates internal water balance during development. Our study provides new insight into the neuroendocrine control of osmoregulation in ecdysozoans and supports a broader role for rGCs in peptide-hormone signaling.

physiology↗

bioRxiv2025

Two Cytochrome P450 epoxidases mediate juvenile hormone biosynthesis in Drosophila melanogaster

Juvenile hormones (JHs) mediate various biological processes such as development and reproduction in insects. Although pleiotropic functions of JHs are well investigated in the fruit fly Drosophila melanogaster, their biosynthetic mechanisms are less well understood, partly because many JH biosynthetic enzymes still remain unidentified in this important model species. Here we report that two cytochrome P450 (CYP) epoxidases mediate JH biosynthesis in D. melanogaster. In addition to previously reported Cyp6g2, a second epoxidase, Cyp6a13, also functions in the corpus allatum, the major JH biosynthetic endocrine gland. Combined mutations of the genes encoding these enzymes cause developmental and reproductive defects, which can be rescued by JH application. JH biosynthetic functions of these genes were further confirmed by using a heterologous expression system and ex vivo tissue culture. Collectively, our results indicate that these two CYP epoxidases function cooperatively to mediate JH biosynthesis in D. melanogaster. HighlightsO_LIDrosophila Cyp6g2 and Cyp6a13 are highly expressed in the corpus allatum. C_LIO_LICombined knockout mutants of the CYP genes exhibit developmental and reproductive defects. C_LIO_LIMutant phenotypes were rescued by feeding juvenile hormones. C_LIO_LIBoth Cyp6g2 and Cyp6a13 catalyze epoxidation of juvenile hormone precursors. C_LI

developmental biology↗

bioRxiv2025

NudC moonlights in ribosome biogenesis and homeostasis in Drosophila melanogaster polyploid cells

Ribosomes, the cellular machinery responsible for protein synthesis, are fundamental across all kingdoms of life. Disruption in ribosome biogenesis (RiBi) can cause severe ribosomopathies, underscoring the critical need for precise regulatory mechanisms governing RiBi. In this study, we identified the gene NudC (nuclear distribution C, dynein complex regulator), a previously unrecognized regulator of RiBi in polyploid cells of Drosophila melanogaster larvae. RNAi-mediated depletion of NudC in polyploid salivary gland cells led to a significant reduction in ribosome abundance, accompanied by the loss of ribosome-binding sites on rough endoplasmic reticulum and impaired translation. These defects are linked to decreased levels of nucleolar ribosomal RNA. Notably, NudC knockdown also triggered a homeostatic response, characterized by increased transcription and translation of both ribosome biogenesis factors (RBFs) and ribosomal proteins. This response parallels that seen in RBF-deficient cells, suggesting that NudC and RBFs cooperate to maintain RiBi homeostasis. Meanwhile, NudC-deficient cells exhibited chromosome abnormalities, activated JNK signaling, and underwent autophagy, closely resembling the defects observed upon loss of RBFs. Finally, our findings suggest that the role of NudC in RiBi is independent of its established function in dynein regulation, indicating the moonlighting role in RiBi played by this gene. Together, these results uncover a new, fundamental function for NudC in maintaining RiBi and homeostasis in polyploid cells, with broader implications for understanding conserved mechanisms of NudC function and RiBi across species.

cell biology↗

bioRxiv2025

Blaming Luck, Claiming Skill: Self-Attribution Bias in Error Assignment

Mistakes are valuable learning opportunities, yet in uncertain environments, whether a lack of reward is due to poor performance or bad luck can be hard to tell. To investigate how humans address this issue, we developed a visuomotor task where rewards depended on either skill or chance. Participants consistently displayed a self-attribution bias, crediting successes to their own ability while blaming failures on randomness, an effect that influenced their subsequent decisions. Computational modelling revealed two underlying mechanisms--a distorted perception of ability and a positivity bias in the skill condition. Notably, while distorted self-perception shaped behaviour, it did not affect confidence; instead, self-attribution bias led to overconfidence in external blame. These findings suggest a more complex picture in which self-attribution biases arise from both perceptual distortions and post-decision evaluations, highlighting the need for an interplay between experimental design and computational modelling to understand behavioural biases.

animal behavior and cognition↗

bioRxiv2024

The seminal vesicle is a juvenile hormone-responsive tissue in adult male Drosophila melanogaster

Juvenile hormone (JH) is one of the most essential hormones controlling insect metamorphosis and physiology. While it is well known that JH affects many tissues throughout the insects life cycle, the difference in JH responsiveness and the repertoire of JH-inducible genes among different tissues has not been fully investigated. In this study, we monitored JH responsiveness in vivo using transgenic Drosophila melanogaster flies carrying a JH response element-GFP (JHRE-GFP) construct. Our data highlight the high responsiveness of the epithelial cells within the seminal vesicle, a component of the male reproductive tract, to JH. Specifically, we observe an elevation in the JHRE-GFP signal within the seminal vesicle epithelium upon JH analog administration, while suppression occurs upon knockdown of genes encoding the intracellular JH receptors, Methoprene-tolerant and germ cell-expressed. Starting from published transcriptomic and proteomics datasets, we next identified Lactate dehydrogenase as a JH-response gene expressed in the seminal vesicle epithelium, suggesting insect seminal vesicles undergo metabolic regulation by JH. Together, this study sheds new light on biology of the insect reproductive regulatory system.

physiology↗

bioRxiv2023

Atypical cell death in the growth plate chondrocytes of Tric-b-knockout mice

TRIC-A and TRIC-B proteins form homotrimeric cation-permeable channels in the sarco/endoplasmic reticulum (SR/ER) and nuclear membranes and are thought to contribute to counterionic flux coupled with store Ca2+ release in various cell types. Serious mutations in the TRIC-B locus cause autosomal recessive osteogenesis imperfecta (OI), which is characterized by insufficient bone mineralization. We have reported that Tric-b-knockout mice can be used as an OI model. Here we report irregular cell death in proliferating growth plate chondrocytes in developing Tric-b-knockout bones. In the knockout chondrocytes, excess pro-collagen fibers were occasionally accumulated in severely dilated ER elements. Of the major ER stress pathways, the PERK pathway was preferentially hyperactivated in the knockout chondrocytes, and most likely altered gene expression to induce apoptosis-related proteins including CHOP and caspase 12. In Ca2+ imaging experiments, the knockout chondrocytes exhibited aberrant Ca2+ handling; ER Ca2+ release was impaired, and intracellular Ca2+ concentration was elevated. Our data suggest that Tric-b deficiency directs growth plate chondrocytes to pro-apoptotic stages by compromising cellular Ca2+-handling and exacerbating ER stress, leading to atypical apoptotic cell death.

developmental biology↗

bioRxiv2023

DNA methylation signature in NSD2 loss-of-function variants appeared similar to that in Wolf-Hirschhorn syndrome

PurposeWolf-Hirschhorn syndrome (WHS), a contiguous gene syndrome caused by the hemizygous deletion of the distal short arm of chromosome 4 where NSD2 is, reportedly exhibits specific DNA methylation signatures in peripheral blood cells. However, responsible genomic loci for signatures are unreported. The objective of the study is to define the loci of WHS-related DNA methylation signatures and to explore the role of NSD2 for the signatures. MethodsWe conducted genome-wide methylation analysis of individuals with WHS or NSD2 variants using array. We studied genome-edited knock in mice or induced pluripotent stem cells to explore the function of NSD2 variants which are observed in congenital anomaly cases. ResultsThree undiagnosed cases with NSD2 variants showed WHS-related DNA methylation signatures. These variants were validated to be NSD2 loss-of-function in induced pluripotent stem cells or genome-edited knock-in mice. p.Pro905Leu variant decreased Nsd2 protein levels, and changed Histone H3-Lysine 36 demethylation levels in similar way in the same genomic regions as Nsd2 knock out mice regulated. Nsd2 knock out mice exhibited common DNA methylation changes. ConclusionThese results revealed that WHS-related DNA methylation signatures are dependent on NSD2 dysfunction and are useful in diagnosing NSD2 variants of unknown significance.

genetics↗

bioRxiv2022

Comparing Deep Learning Models for Age Prediction Based on the Resting State fMRI Dataset from the "Brain Dock" Service in Japan

In Japan, many hospitals provide the unequaled service of medical check-up called the "Brain Dock"; however, there is a paucity of studies aimed at leveraging functional magnetic resonance imaging (fMRI) in hospitals. We obtained the resting-state fMRI (rs-fMRI) scans of about 695 patients who accessed this service for preventive medicine against Alzheimers Disease. In this study, we created deep learning models for age prediction with the ultimate aim of arriving at standard protocols for introducing rs-fMRI into clinical settings, particularly in Brain Docks. With that view, an assemblage of modeling conditions was attempted, changing multiple parameter values, features based on data extraction methods (region of interest-wise mean blood-oxygen-level-dependent lump-sum time series models or dynamic functional connectivity models), deep learning algorithms (Transformer, Multi-task Transformer, and unidirectional or bidirectional long short-term memory models), and different atlas-dependent brain region segmentation methods (including the Automated Anatomical Labeling and Harvard-Oxford atlases). As a result, a robust and highly significant correlation was obtained between actual and predicted ages from all types of methodologies. In addition, we determined that some conditions had a relatively large impact on prediction performance based on extended comparisons. The accuracy decreased, particularly according to the choice of atlases but with the same modeling conditions. Notwithstanding, we found that atlases based on intrinsic functional connectivity provided significant prediction accuracy even with a small number of regions to a similar extent as networks lowered spatial granularity. Moreover, we found that multi-task learning with other phenotype data (related to gender differences) was possible, but did not improve the prediction accuracy as much as expected. Despite these limitations, our results could provide a hopeful prospect of introducing fMRI into the field of neuro-clinical practice. HighlightsO_LIAge prediction modeling was performed using the rs-fMRI data of a Japanese "Brain Dock" service targeting mainly elderly people, which made prediction more challenging. C_LIO_LIA robust and highly significant correlation was obtained from all types of methodologies changing data extraction methods, deep learning algorithms, and brain atlases. C_LIO_LIAge prediction was successful even with a very small number of regions exclusively based on intrinsic functional connectivity networks, although there was a difference in the achievement of modeling. C_LI

neuroscience↗

bioRxiv2022

Virucidal activity and mechanism of action of cetylpyridinium chloride against SARS-CoV-2

ObjectiveSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the pathogen causing the coronavirus disease 2019 (COVID-19) global pandemic. Recent studies have shown the importance of the throat and salivary glands as sites of virus replication and transmission. The viral host receptor, angiotensin-converting enzyme 2 (ACE2), is broadly enriched in epithelial cells of the salivary glands and oral mucosae. Oral care products containing cetylpyridinium chloride (CPC) as a bactericidal ingredient are known to exhibit antiviral activity against SARS-CoV-2 in vitro. However, the exact mechanism of action remains unknown. MethodsThis study examined the antiviral activity of CPC against SARS-CoV-2 and its inhibitory effect on the interaction between the viral spike (S) protein and ACE2 using an enzyme-linked immunosorbent assay. ResultsCPC (0.05%, 0.1% and 0.3%) effectively inactivated SARS-CoV-2 within the contact times (20 and 60 s) in directions for use of oral care products in vitro. The binding ability of both the S protein and ACE2 were reduced by CPC. ConclusionsOur results suggest that CPC inhibits the interaction between S protein and ACE2, and thus, reduces infectivity of SARS-CoV-2 and suppresses viral adsorption.

microbiology↗

bioRxiv2021

C-type natriuretic peptide facilitates autonomic Ca2+ entry in growth plate chondrocytes for stimulating bone growth

The growth plates are cartilage tissues found at both ends of developing bones, and vital proliferation and differentiation of growth plate chondrocytes are primarily responsible for bone growth. C-type natriuretic peptide (CNP) stimulates bone growth by activating natriuretic peptide receptor 2 (NPR2) which is equipped with guanylate cyclase on the cytoplasmic side, but its signaling pathway is unclear in growth plate chondrocytes. We previously reported that transient receptor potential melastatin-like 7 (TRPM7) channels mediate intermissive Ca2+ influx in growth plate chondrocytes, leading to activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) for promoting bone growth. In this report, we provide experimental evidence indicating a functional link between CNP and TRPM7 channels. Our pharmacological data suggest that CNP-evoked NPR2 activation elevates cellular cGMP content and stimulates big-conductance Ca2+-dependent K+ (BK) channels as a substrate for cGMP-dependent protein kinase (PKG). BK channel-induced hyperpolarization likely enhances the driving force of TRPM7-mediated Ca2+ entry and seems to accordingly activate CaMKII. Indeed, ex vivo organ culture analysis indicates that CNP-facilitated bone growth is abolished by chondrocyte-specific Trpm7 gene ablation. The defined CNP signaling pathway, the NPR2-PKG-BK channel-TRPM7 channel-CaMKII axis, likely pinpoints promising target proteins for developing new therapeutic treatments for divergent growth disorders.

cell biology↗

bioRxiv2021

Essential functions of mosquito ecdysone importers in development and reproduction

The primary insect steroid hormone ecdysone requires a membrane transporter to enter its target cells. Although an organic anion-transporting polypeptide (OATP) named Ecdysone Importer (EcI) serves this role in the fruit fly Drosophila melanogaster and most likely in other arthropod species, this highly conserved transporter is apparently missing in mosquitoes. Here we report three additional OATPs that facilitate cellular incorporation of ecdysone in Drosophila and the yellow fever mosquito Aedes aegypti. These additional ecdysone importers (EcI-2, 3, and 4) are dispensable for development and reproduction in Drosophila, consistent with the predominant role of EcI. In contrast, in Aedes, EcI-2 is indispensable for ecdysone-mediated development, whereas EcI-4 is critical for vitellogenesis induced by ecdysone in adult females. Altogether, our results indicate unique and essential functions of these additional ecdysone importers in mosquito development and reproduction, making them attractive molecular targets for species- and stage-specific control of ecdysone signaling in mosquitoes.

developmental biology↗

bioRxiv2018

Phylogeny, evidence for a cryptic plastid, and distribution of Chytriodinium parasites (Dinophyceae) infecting copepods

Spores of the dinoflagellate Chytriodinium are known to infest copepod eggs causing their lethality. Despite the potential to control the population of such an ecologically important host, knowledge about Chytriodinium parasites is limited: we know little about phylogeny, parasitism, abundance, or geographical distribution. We carried out genome sequence surveys on four manually isolated sporocytes from the same sporangium to analyse the phylogenetic position of Chytriodinium based on SSU and concatenated SSU/LSU rRNA gene sequences, and also characterize two genes related to the plastidial heme pathway, hemL and hemY. The results suggest the presence of a cryptic plastid in Chytriodinium and a photosynthetic ancestral state of the parasitic Chytriodinium/Dissodinium clade. Finally, by mapping Tara Oceans V9 SSU amplicon data to the recovered SSU rRNA gene sequences from the sporocytes, we show that globally, Chytriodinium parasites are most abundant within the pico/nano- and mesoplankton of the surface ocean and almost absent within microplankton, a distribution indicating that they generally exist either as free-living spores or host-associated sporangia.

microbiology↗