Biology subjects

Imamura, S.

Publications and source records attributed to Imamura, S..

7 recordsLinked to original sources

bioRxiv2026

Lhcf9 is a novel negative regulator of non-photochemical quenching in the diatom Chaetoceros gracilis

Photosynthetic organisms in aquatic environments experience rapid fluctuations in light intensity, light quality, and carbon availability, requiring tight regulation of photosynthetic energy conversion. In marine diatoms, non-photochemical quenching (NPQ), particularly energy-dependent quenching (qE), plays a central role in dissipating excess excitation energy as heat. However, excessive NPQ can reduce photosynthetic efficiency under light-limiting or carbon-rich conditions, and how this trade-off is regulated remains poorly understood. Here, we identify CgLhcf9, a previously uncharacterized light-harvesting complex (LHC) protein, as a negative regulator of qE-type NPQ in the centric diatom Chaetoceros gracilis. Expression of CgLhcf9 is induced under low red-light and high CO2 conditions and strongly suppressed by blue light, indicating regulation by both light quality and carbon availability. Functional analyses using CgLhcf9 knockout and overexpression lines reveal that CgLhcf9 suppresses qE: NPQ induction is enhanced in the absence of CgLhcf9, whereas its accumulation downregulates NPQ without affecting other established qE effectors, including Lhcx1 or xanthophyll cycle pigments. Notably, CgLhcf9 accumulation improves cellular growth under light-limiting conditions. These results identify CgLhcf9 as a novel LHC-type regulator that fine-tunes photosynthetic energy dissipation in response to environmental signals. Our findings establish a regulatory mechanism that balances photoprotection, electron transport, and carbon fixation, advancing our understanding of how marine diatoms optimize photosynthesis under fluctuating light and CO2 conditions. Significance statementPhotosynthetic microalgae must balance light-driven electron transport with carbon fixation to maximize growth under fluctuating light and CO2 conditions. While non-photochemical quenching (NPQ) protects photosystems from excess light, excessive NPQ can limit photosynthetic efficiency when light or carbon is limiting. Here, we identify the antenna protein CgLhcf9 as a negative regulator of energy-dependent NPQ in the marine diatom Chaetoceros gracilis. CgLhcf9 integrates light-quality and CO2 signals to suppress NPQ without altering canonical quenching effectors, thereby improving growth under light-limiting conditions. This study reveals a regulatory role for a light-harvesting complex protein in tuning the balance between photoprotection and photosynthetic efficiency, providing insight into how marine diatoms coordinate electron transport and carbon fixation in dynamic environments.

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↗

bioRxiv2022

Human blastoid from primed human embryonic stem cells

Artificial human blastoids are used to investigate early embryo development, pregnancy failures, and birth deficiencies, previously impossible without human embryos. Recent methods generating blastoids used human naive pluripotent stem cells, which are prone to genomic instability during in vitro culturing. Here, we introduce a simple, robust, and scalable method for generating human blastoids from more stable, primed human pluripotent stem cells (hPSC). Using a non-cell-adhesive hydrogel, hPSC aggregates formed an asymmetric blastoid structure with a cellular distribution similar to that of a human blastocyst, with in vitro implantation capability. Single-cell RNA-seq followed by cellular trajectory analysis revealed that hydrogel promoted differentiation to tri-lineage cells associated with a blastocyst. This model will allow studies on the underlying mechanisms of human pre- and postimplantation processes, consider elaborating on the potential implications of the model on assistive reproductive technology. One Sentence SummaryNo more than 125 characters and spaces.

bioengineering↗

bioRxiv2022

Gut-liver-axis microphysiological system for studying cellular fluidic shear stress and inter-tissue interaction

Gut-liver-axis (GLA) is a fundamental interaction between the gut and liver for maintaining human health. To clarify the physiological and pathological roles of GLA in the human body, a GLA microphysiological system (GLA-MPS) holds great potential. However, in current GLA-MPS, the importance of a physiologically relevant flow for gut and liver cells cultivation is not fully addressed. In addition, the integration of individual organ perfusion, circulation flow, and organ tissue functions in a single device has not been achieved. Here, we introduce a GLA-MPS by integrating two cell culture chambers with individually applied perfusion flows and a circulation channel with an on-chip pneumatic micropump under cell culture chambers via a porous membrane for interconnecting them. We analyzed the fluid shear stress (FSS) with computational fluid dynamics simulations and confirmed that the physiologically relevant FSS (i.e., 8 x 10-3 and 1.2 x 10-7 dyne cm-2) could be applied for the gut (Caco-2) and liver (HepG2) cells, respectively. Under physiologically relevant flow, the Caco-2 and HepG2 cells in the GLA-MPS maintained a cell survival rate of 95% and 92%, respectively; further, they enhanced the expression of functional proteins such as zonula occludens 1 (ZO-1) and albumin (ALB), respectively. Thus, the presented GLA-MPS can be adapted as an advanced in vitro model in a wide range of applications for disease modeling associated with inter-tissue interactions, such as fatty liver diseases.

bioengineering↗

bioRxiv2020

Cyclo olefin polymer-based solvent-free mass-productive microphysiological systems

A microphysiological system (MPS) holds a great promise for drug screening and toxicological testing as an alternative to animal models. However, this platform has several issues in terms of the materials used (e.g., polydimethylsiloxane), such as the absorbance of tested drug candidates and fluorescent dyes by the material, as well as the effect on cultured cellular status, thus misleading the results obtained from cell assays and fabrication processes. Hence, to eliminate the issues mentioned above, we developed a cyclo olefin polymer (COP)-based MPS via photobonding process using vacuum ultraviolet (VUV), named COP-VUV-MPS. COP-VUV-MPS showed better chemical resistance and avoided molecule absorption. COP-VUV-MPS could maintain the stemness of environmentally sensitive human-induced pluripotent stem cells without causing undesired cellular phenotypes and gene expression. These results suggested that COP-VUV-MPS might be broadly used for the advancement of MPS and applications in drug development and in vitro toxicological testing.Competing Interest StatementM.Y. is an employee of Ushio Inc. The part of this project was financially supported by Ushio Inc. Kyoto University (K.K.) and Ushio INC. (M.Y.) filed a Japanese patent application based on the research presented herein. The remaining authors declare no competing interests.View Full Text

bioengineering↗

bioRxiv2020

39°C-in vitro culture facilitates hepatic functions of hepatocyte-like cells derived from human embryonic stem cells

Hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) offer an alternative to primary hepatocytes commonly used for drug screenings and toxicological tests. Although tremendous efforts have been made to facilitate hepatic functions of hPSC-HLCs using growth factors and chemicals, these cells have not yet reached hepatic functions comparable to hepatocytes in vivo. Therefore, there exists a critical need to use an alternative trigger to facilitate hepatic functions in hPSC-HLCs. We noted that human liver temperature (around 39{degrees}C) is higher than normal human body temperature (around 36.5{degrees}C), yet hepatocytes are generally cultured at 37{degrees}C in-vitro. Here we showed that hepatic functions of hPSC-HLCs would be facilitated under physiological liver temperatures. We identified the optimal temperature by treating HLCs derived from H9 human embryonic stem cells (hESC-HLCs) at 39{degrees}C and 42{degrees}C. 42{degrees}C-treatment caused significantly greater cell death compared to 39{degrees}C. We also confirmed the increases of hepatic functions, such as secretion of albumin, cytochrome P450 3A4 (CYP3A4) activities, and collagen productions, without severe cell damages. To elucidate the underlying mechanisms of heat-induced hepatic functions, RNA-seq was to identify gene expression signatures due to 39{degrees}C-treated hESC-HLCs. This study also showed the possible mechanisms of heat-induced hepatic function via glucocorticoid receptor pathway and molecular chaperons. In combination with existing hepatic differentiation protocols, the method proposed here may further improve hepatic functions for hPSCs, and lead to the realization of drug discovery efforts and drug toxicological tests. Significance statementHepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) offer an alternative to primary hepatocytes commonly used for drug screenings and toxicological tests. We noted that human liver temperature (around 39{degrees}C) is higher than normal human body temperature (around 36.5{degrees}C), affecting the in-vitro hepatic functions of hPSC-HLCs, such as metabolic activities. Here we showed that hepatic functions of hPSC-HLCs, albumin secretion, CYP3A4 activities, and collagen production would be facilitated under physiological liver temperatures at 39{degrees}C, without severe cell damages. RNA-seq was used to elucidate the underlying mechanisms of heat-induced hepatic functions. This study also showed the possible mechanisms of heat-induced hepatic function via glucocorticoid receptor pathway and molecular chaperons.

bioengineering↗

bioRxiv2019

Evaluation of host effects on ectomycorrhizal fungal community compositions in a forest landscape in northern Japan

Community compositions of ectomycorrhizal (ECM) fungi are similar within the same host taxa. However, careful interpretation is required to determine whether the combination of ECM fungi and plants is explained by the host preference of ECM fungi or by the influence of neighboring conspecific and/or heterospecific hosts. In the present study, we aimed to evaluate the effects of host species on the ECM community compositions in a forest landscape (~ 10 km) where monodominant forest stands of six ECM host species belonging to three families were patchily distributed. The ECM communities were identified with DNA metabarcoding. A total of 180 ECM operational taxonomic units (OTUs) were detected. The ECM community compositions were primarily structured by host species and families, regardless of the soil environments and spatial arrangements of the sampling plots. In addition, 38 ECM OTUs were detected from particular host tree species. Furthermore, the neighboring plots harbored similar fungal compositions, although the host species were different. The relative effect of the spatial factors on the ECM compositions was weaker than that of host species. Our results suggest that the host preference of ECM fungi is a primary determinant of ECM fungal compositions in the forest landscape.

ecology↗