Biology subjects

Imaizumi, K.

Publications and source records attributed to Imaizumi, K..

9 recordsLinked to original sources

bioRxiv2026

Human organoid screen links transient translational modulation to progenitor progression in corticogenesis

Human pluripotent stem cell-derived models are increasingly used to recapitulate aspects of human corticogenesis, including the emergence of diverse cortical cell types and their progression through developmental states. These systems offer an opportunity to dissect the molecular mechanisms regulating transitions between cell states, but methods for perturbing them systematically at scale remain limited. Here, we developed a semi-automated culture and high-throughput arrayed screening platform for human cortical organoids. Using a library of 1,280 small molecules designed to systematically target major signaling and regulatory pathways, we screened for modulators of EOMES, which encodes for the transcription factor TBR2, and identified Emetine, an inhibitor of translation elongation, as the top hit. The effect of Emetine on cortical cell-state progression was reproduced across human pluripotent stem cell lines, non-human primate cortical organoids, and primary human cortical tissue but not broadly across translation inhibitors. Moreover, transient exposure resulted in a shift from dividing radial glia towards cortical glutamatergic neurons. Mechanistically, nascent-proteome profiling revealed an early and coordinated remodeling of newly translated proteins that preceded detectable transcriptional changes, placing translational regulation upstream of the ensuing cell-state transition. Together, these findings highlight a role for specific translational inhibitors in promoting cortical cell-state progression and establish a scalable platform for systematic perturbation and discovery in human neural organoids.

neuroscience↗

bioRxiv2026

Structure–activity relationship of antimycin A-like compounds as photosystem II inhibitors

Antimycin A (AA) is widely used as an inhibitor of the mitochondrial respiratory chain, targeting the Qi site of cytochrome bc1 (complex III). In photosynthetic organisms, AA is also well known to inhibit the photosynthetic PROTON GRADIENT REGULATION 5 (PGR5)-dependent cyclic electron flow around photosystem I (CEF-PSI). Although AA is frequently used as a specific inhibitor of PGR5-dependent CEF-PSI in photosynthetic reactions, we recently clarified that some of the major components of AA, which is typically a mixture of closely related compounds, also exert direct inhibitory effects on photosystem II (PSII). Nevertheless, the binding site and binding mode of AA in PSII remain largely unexplored. Structurally, AA consists of a salicylic acid moiety connected via an amide bond to a hydrophobic dilactone ring moiety. To identify important structural factors of AA for exhibiting inhibitory effects on PSII (assessed by QA- reoxidation measurements), we here investigated the relationship between structure and inhibitory potency using 38 AA-like compounds (AALCs), including commercial compounds and a series of synthetic AA analogs. Some AALCs exhibited substantially stronger impacts on PSII than natural AA. High acidity of the phenolic OH and the presence of a free amide NH of the salicylamide moiety were critical for the effects on PSII. In contrast, while the dilactone ring moiety also affected the inhibitory activity, this was replaceable with certain hydrophobic structures. Based on our results, together with the known structure-activity relationship and binding mode of AA in complex III, we propose tentative binding models for AA in PSII. HighlightsO_LIStructure-activity relationship of AA-like compounds on PSII is examined C_LIO_LISeveral AA-like compounds more potent than AA against PSII are identified C_LIO_LIPhenolic OH acidity and free amide NH of salicylamide moiety are key for AA effects C_LIO_LIThe dilactone ring moiety is replaceable with certain hydrophobic structures C_LIO_LITentative binding models for AA in PSII are proposed C_LI

Plant Biology↗

bioRxiv2026

PIFI Stabilizes Chloroplast NDH-PSI Supercomplex to Maintain Plastoquinone Redox Balance and PSII Efficiency

Photosynthetic electron transport is mediated by several protein supercomplexes that are spatially arranged in the thylakoid membranes of chloroplasts. The chloroplast NADH dehydrogenase-like (NDH) complex is part of the photosynthetic alternative electron transport (AET) chain, which reduces the plastoquinone (PQ) pool using reduced ferredoxin as a substrate. This NDH complex is associated with photosystem I (PSI) and mediates a portion of AET in stroma lamellae, whereas photosystem II (PSII) is concentrated in grana stacks. This study presents the findings regarding post-illumination chlorophyll fluorescence increase (PIFI), a protein crucial for regulating AET via the NDH pathway. A marked increase in NDH activity and a reduction in the PQ pool in the dark were observed in PIFI-deficient mutant strains (g-pifi) generated by genome editing. Blue native PAGE analysis indicated that PIFI was associated with the NDH-PSI supercomplex in the wild type, and the NDH complex was dissociated from PSI in the g-pifi mutants. Additionally, the g-pifi mutants exhibited a decrease in the maximum quantum yield of PSII (Fv/Fm). Notably, Fv/Fm was restored in a double mutant harboring both g-pifi and NDH-deficient pnsl1 mutations, demonstrating that deregulated NDH activity in g-pifi causes downregulation of PSII efficiency. However, the lower Fv/Fm was not observed in a mutant lacking thioredoxin m4 (trxm4), which showed deregulated NDH activity but maintained the NDH-PSI supercomplex. These data suggest that PIFI stabilizes the NDH-PSI supercomplex and maintains the spatial localization of PQ reduction via AET in thylakoid membranes, which is essential for the proper functioning of PSII.

plant biology↗

bioRxiv2025

Antimycin A, but not antimycin A3 or myxothiazol, directly suppresses photosystem II activity

Antimycin A (AA) is a widely used inhibitor to study photosynthesis and respiration. In photosynthesis, it is commonly used to inhibit a cyclic electron flow (CEF) pathway but has also been reported to affect photosystem II (PSII), which is not involved in CEF. Although concerns have been raised about AAs specificity, its impact on PSII activity remains unclear. AA3 was recently proposed as a more specific inhibitor of the same CEF pathway. In the mitochondrial respiratory chain, AA inhibits complex III, similar to myxothiazol. Here, we investigated the direct effects of AA, AA3, and myxothiazol on PSII activity and linear photosynthetic electron transport using isolated plant PSII and thylakoid membranes. AA, but neither AA3 nor myxothiazol, directly suppressed PSII activity and linear electron transport. Furthermore, the extent of AAs effects was batch-dependent. Thus, we propose using AA3 to inhibit CEF and myxothiazol to inhibit complex III, instead of AA. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=158 SRC="FIGDIR/small/675326v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@a61461org.highwire.dtl.DTLVardef@1841ac5org.highwire.dtl.DTLVardef@1f9a345org.highwire.dtl.DTLVardef@4e155c_HPS_FORMAT_FIGEXP M_FIG C_FIG Antimycin A inhibits at least three sites. Antimycin A3 has higher specificity for CEF-PSI, while myxothiazol is preferred to inhibit complex III.

plant biology↗

bioRxiv2025

Evolutionary origin and functional mechanism of Lhcx in the diatom photoprotection

Diatoms are red-lineage algae that utilize the light-harvesting complex (LHC) subfamily Lhcx for photoprotection via non-photochemical quenching (NPQ); however, its evolutionary origin and molecular mechanism remain poorly understood. Through molecular phylogenetic analysis, we show that diatom Lhcxs and green algal Lhcsrs evolved from a common ancestor, with green plants subsequently acquiring them via horizontal gene transfer. To investigate the functional role of Lhcx1, we generated knockout mutants of Chaetoceros gracilis, a diatom with low Lhcx redundancy. The lhcx1 mutants nearly abolished NPQ, and time-resolved fluorescence measurements revealed that Lhcx1-mediated quenching occurs in energetically detached antenna complexes. Clear-native PAGE with Amphipol further indicated that CgLhcx1 interacts with the FCP L-dimer, functioning as a peripheral antenna for the C2S2M2 PSII-FCPII supercomplex. Notably, under high-light acclimation, lhcx1 mutants exhibited higher PSII effective quantum yields than wild type, attributable to reduced antenna size and enhanced carbon fixation capacity. The absence of NPQ accelerated high-light acclimation and was accompanied by increased xanthophyll accumulation, indicating that compensatory mechanisms can enhance overall photosynthetic efficiency. Together, these findings reveal the evolutionary origin of Lhcx/Lhcsr proteins and define the molecular basis of Lhcx1-mediated photoprotection in diatoms, providing fundamental insights into LHC-based photoprotection across photosynthetic lineages.

plant biology↗

bioRxiv2024

Antimycin A induces light hypersensitivity of photosystem II in the presence of QB-site binding herbicides

Photosynthetic electron transport consists of linear electron flow and two cyclic electron flow (CEF) pathways around photosystem I (PSI). PGR5-dependent CEF-PSI is thought to be the major CEF-PSI pathway and an important regulator of photosynthetic electron transfer. Antimycin A (AA) is commonly recognized as an inhibitor of PGR5-dependent CEF-PSI in photosynthesis. Although previous findings imply that AA may also affect photosystem II (PSII), which does not participate in CEF-PSI, these "secondary effects" tend to be neglected, and AA is often used for inhibition of PGR5-dependent CEF-PSI as if it were a specific inhibitor. Here, we investigated the direct effects of AA on PSII using isolated spinach PSII membranes, and spinach and Chlamydomonas thylakoid membranes. Measurements of QA- reoxidation kinetics showed that AA affects the acceptor side of PSII and inhibits electron transport within PSII. Furthermore, repetitive Fv/Fm measurements revealed that, in the presence of QB-site binding inhibitors, AA treatment results in severe photoinhibition even from a single-turnover flash. The direct effects of AA on PSII are non-negligible and caution is required when using AA as an inhibitor of PGR5-dependent CEF-PSI. Meanwhile, we found that the commercially available compound AA3, which is a component of the AA complex, inhibits PGR5-dependent CEF-PSI without having notable effects on PSII. Thus, we propose that AA3 should be used for the physiological study of the PGR5-dependent CEF-PSI.

plant biology↗

bioRxiv2024

Human assembloid model of the ascending neural sensory pathway

The ascending somatosensory pathways convey crucial information about pain, touch, itch, and body part movement from peripheral organs to the central nervous system. Despite a significant need for effective therapeutics modulating pain and other somatosensory modalities, clinical translation remains challenging, which is likely related to species-specific features and the lack of in vitro models to directly probe and manipulate this polysynaptic pathway. Here, we established human ascending somatosensory assembloids (hASA)- a four-part assembloid completely generated from human pluripotent stem cells that integrates somatosensory, spinal, diencephalic, and cortical organoids to model the human ascending spinothalamic pathway. Transcriptomic profiling confirmed the presence of key cell types in this circuit. Rabies tracing and calcium imaging showed that sensory neurons connected with dorsal spinal cord projection neurons, which ascending axons further connected to thalamic neurons. Following noxious chemical stimulation, single neuron calcium imaging of intact hASA demonstrated coordinated response, while four-part concomitant extracellular recordings and calcium imaging revealed synchronized activity across the assembloid. Loss of the sodium channel SCN9A, which causes pain insensitivity in humans, disrupted synchrony across the four-part hASA. Taken together, these experiments demonstrate the ability to functionally assemble the essential components of the human sensory pathway. These findings could both accelerate our understanding of human sensory circuits and facilitate therapeutic development.

neuroscience↗

bioRxiv2021

Novel System to Monitor In Vivo Neural Graft Activity After Spinal Cord Injury

Expectations for neural stem/progenitor cell (NS/PC) transplantation as a treatment for spinal cord injury (SCI) are increasing. However, whether and how grafted cells are incorporated into the host neural circuit and contribute to motor function recovery remain unknown. The aim of this project was to establish a novel non-invasive in vivo imaging system to visualize the activity of neural grafts by which we can simultaneously demonstrate the circuit-level integration between the graft and host, and the contribution of graft neuronal activity to host behaviour. We introduced Akaluc, a newly engineered luciferase, under control of a potent neuronal activity-dependent synthetic promoter, E-SARE, into NS/PCs and engrafted the cells into SCI model mice. Through the use of this system, we reveal that the activity of grafted cells was integrated with host behaviour and driven by host neural circuit inputs. This non-invasive system is expected to help elucidate the therapeutic mechanism of cell transplantation treatment for SCI and determine better therapy techniques that maximize the function of cells in the host circuit.

neuroscience↗

bioRxiv2019

Decreased Activity of the Ghrhr and Gh Promoters Causes Dominantly Inherited GH Deficiency

Isolated growth hormone deficiency type II (IGHD2) is mainly caused by heterozygous splice-site mutations in intron 3 of the GH1 gene. A dominant negative effect of the mutant growth hormone (GH) lacking exon 3 on wild-type GH secretion has been proposed; however, the molecular mechanisms involved are elusive. To uncover the molecular systems underlying GH deficiency in IGHD2, we established IGHD2 model mice, which carry both wild-type and mutant copies of the human GH1 gene, replacing each of the endogenous mouse Gh loci. Our IGHD2 model mice exhibited growth retardation associated with intact cellular architecture and mildly activated ER stress in the pituitary gland, caused by decreases in the growth hormone releasing hormone receptor (Ghrhr) and Gh gene promoter activities. Decreases in Ghrhr and Gh promoter activities were likely caused by reduced levels of nuclear CREB3L2, which was demonstrated to stimulate the activity of the Ghrhr and Gh promoters. This is the first in vivo study revealing a novel molecular mechanism of GH deficiency in IGHD2, representing a new paradigm, differing from widely accepted models.

genetics↗