Biology subjects

Yoshida, T.

Publications and source records attributed to Yoshida, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Comparing the Influence of Habitat Configuration on Population Connectivity and Genetic Structure Using Congeneric Species Across Multiple Taxa

Abstract Habitat configuration influences population connectivity and, consequently, genetic structure. River networks provide heterogeneous, hierarchically arranged environments that shift drastically from upstream to downstream. We compared congeneric species across Ephemeroptera, Plecoptera, and Trichoptera, emphasizing longitudinal replacement (upstream to downstream) and the rarely studied wet rock (hygropetric) habitats. We surveyed six rivers on the Muroto Peninsula, Japan, qualitatively sampling aquatic insects at 63 sites. Cluster analysis based on the environmental data classified surveyed sites into four clusters. We analyzed a total of 10 species from four genera that exhibit longitudinal replacement patterns within genera. Genetic analyses based on the mitochondrial cytochrome c oxidase subunit I region revealed that upstream species showed higher genetic diversity than downstream species. In contrast, species adapted to hygropetric exhibited the lowest genetic differentiation among all habitat types. A novel contribution of this study is the inclusion of hygropetric species. The surprisingly low differentiation in hygropetric species suggests high connectivity, similar to lentic species. By comparing congeneric taxa across orders within environmentally similar rivers, we reduce phylogenetic and environmental confounds, strengthening inference that habitat configuration and dispersal traits jointly shape genetic structure. These findings provide a new perspective on riverine spatial ecology and underscore the importance of microhabitat-aware comparisons for evolutionary inference.

zoology↗

bioRxiv2026

Striatal dopamine dynamics across temporal scales in brain-specific Atp2a2 heterozygous knockout mice during reward conditioning

Dysregulated dopamine signaling is implicated in schizophrenia and mood disorders, yet how disease-associated genes alter dopamine dynamics during behavior remains poorly understood. ATP2A2 encodes sarco/endoplasmic reticulum Ca2+-ATPase 2 (SERCA2), a regulator of intracellular Ca2+ homeostasis, and has been associated with psychiatric vulnerability. Brain-specific Atp2a2 heterozygous conditional knockout (het-cKO) mice exhibit behavioral abnormalities and elevated extracellular dopamine in the nucleus accumbens (NAc) with microdialysis, but it lacks the temporal resolution to resolve rapid, context-dependent dopamine dynamics. Here, we used dual-site fiber photometry with the genetically encoded dopamine sensor dLight1.2 to monitor dopamine signals simultaneously in the NAc and tail of the striatum (TS) during classical reward conditioning. Control and het-cKO mice acquired task-related licking comparably. Nevertheless, het-cKO mice showed enhanced NAc reward-evoked dopamine responses in the pooled analysis, with indications of more frequent and longer-lasting spontaneous transients. Responses to unexpected reward omission were larger in het-cKO mice in both regions during the early phase, but they were not detected after further training. Notably, late-phase suppression of reward-predictive NAc dopamine responses by a preceding aversive outcome persisted in het-cKO mice, although evidence for genotype dependence was inconclusive. Regional dopamine transporter (DAT) protein expression showed no clear genotype differences. These findings identify context-dependent alterations in dopamine signaling across multiple temporal scales and striatal regions in brain-specific Atp2a2 haploinsufficiency, highlighting intracellular Ca2+ regulation and dopamine release as priorities for direct investigation. These results may help clarify the biological links between ATP2A2 haploinsufficiency and neuropsychiatric dysfunction.

neuroscience↗

bioRxiv2026

Ex vivo human tumor slices more accurately predict patient responses to an oncolytic virus than in vivo mouse models

Immunotherapies, including oncolytic viruses (OV), are promising therapies that can enhance anti-tumor immune responses. However, preclinical success of immunotherapies in mouse models has not always translated to clinical benefit in cancer patients. This study compared preclinical efficacy and mechanism of action for ASP9801, a vaccinia virus expressing IL-7 and IL-12, using mouse models of colorectal cancer (CRC) in vivo and in human organotypic tumor slice models ex vivo. The murine surrogate for ASP9801 significantly reduced tumor volumes in treated and abscopal tumors in two different CRC models in vivo (MC38 and RO100). Treatment efficacy was accentuated when combined with anti-PD1 treatment, and single-cell RNA sequencing analysis revealed depletion of tumor cells and increased T cell infiltration and activation in both treated and abscopal tumors. However, human tissue analysis ex vivo (E-slices) using PDX models and patient samples showed that ASP9801 is not effective in CRC, consistent with clinical trial results. On the other hand, ASP9801 was highly effective in GBM, indicating indication-specific efficacy of ASP9801, and how E-slice assays can be used to identify treatment-sensitive indications. This study demonstrates the superiority of E-slices over mouse models for predicting clinical response and its utility in planning clinical trials.

cancer biology↗

bioRxiv2026

Real-time near-infrared imaging distinguishes nasopharyngeal colonization from aspiration of Streptococcus pneumoniae and identifies aspiration as a trigger of severe disease

Streptococcus pneumoniae asymptomatically colonizes the nasopharynx but can invade the lower respiratory tract to cause life-threatening disease, particularly in older adults. However, whether the initial site of bacterial deposition following intranasal inoculation determines disease progression has not been directly examined. Here, we developed a near-infrared (NIR) fluorescence imaging approach using indocyanine green (ICG)-labeled S. pneumoniae TIGR4 to visualize early bacterial distribution in real time. ICG labeling by simple mixing, without genetic or chemical modification, neither impaired bacterial growth at 33 or 37{degrees}C, nor altered acid tolerance. Continuous video imaging during the first 10 min of infection resolved two distinct patterns: bacteria confined to the nasopharynx (colonization) and those aspirated into the lower respiratory tract (aspiration). Kaplan-Meier analysis revealed markedly higher mortality in the aspiration group in both young (hazard ratio = 7.9) and aged (hazard ratio = 8.4) mice, despite a 10-fold lower inoculum used for aged animals, with deaths beginning on day 3. Systemic profiling of blood at 24 h by RNA sequencing and plasma proteomics revealed that early aspiration in aged mice was associated with the activation of inflammatory and hematopoietic programs, enrichment of complement and coagulation cascades, and phagocytic pathways. Together, these findings establish aspiration into the lower respiratory tract as a trigger of severe pneumococcal disease and introduce real-time NIR imaging as a technique for linking early infection dynamics to systemic host responses.

microbiology↗

bioRxiv2026

Wide-Field Calcium and Flavoprotein Autofluorescence Imaging in Living Mice

Wide-field imaging (WFI) is a mesoscopic approach for monitoring cortex-wide activity with high temporal resolution and a broad field of view. Owing to its simple optical configuration and compatibility with chronic preparations, WFI has become an important tool in systems neuroscience and disease-model research. In this chapter, we describe practical protocols for chronic transcranial WFI in mice using two complementary optical signals: genetically encoded calcium indicators (GCaMP) and endogenous flavoprotein autofluorescence. Calcium imaging provides a robust readout of neuronal population activity, whereas flavoprotein imaging reflects mitochondrial redox dynamics and cellular metabolic demand. We detail procedures for animal preparation, skull clearing, headplate implantation, macroscope assembly, synchronized sensory stimulation, triggered image acquisition, and MATLAB-based data analysis. The analysis workflow includes {Delta}F/F normalization, reference-based signal correction, and artifact reduction, followed by trial averaging, atlas registration, and region-of-interest analysis. Because imaging is performed through the intact skull, the protocol enables repeated longitudinal measurements in the same animal over extended periods. This approach is reproducible, cost-effective, and adaptable to studies of cortical physiology and neurological disorders.

neuroscience↗

bioRxiv2026

Characterizing in vivo degradation of electrospun biodegradable nanofibers by size-exclusion chromatography

Biodegradable electrospun nanofiber (NF) scaffolds have emerged as promising materials for tissue engineering applications, including vascular grafts, because their mechanical properties and degradability can be tuned. However, their in vivo degradation behavior remains poorly understood. In this study, we characterized the in vivo degradation profiles of representative biodegradable NF materials widely used in small-caliber vascular graft research, namely polycaprolactone (PCL), poly(D,L-lactide) (PLA), polyglycolic acid (PGA), and a PCL/PLA blend, by monitoring molecular weight changes in subcutaneous and vascular environments. Electrospun NF sheets were implanted subcutaneously in mice, and tubular NF grafts were implanted into the abdominal aorta of rats. Samples were harvested for up to 48 weeks after implantation and analyzed primarily by size-exclusion chromatography (SEC) to assess time-dependent changes in molecular weight. Scanning electron microscopy (SEM) and solid-state 13C nuclear magnetic resonance (NMR) were additionally performed to evaluate ultrastructural and chemical changes associated with degradation. SEC analysis revealed distinct material-specific degradation patterns. PCL showed the slowest degradation and retained a relatively high weight-average molecular weight (Mw) in both environments. PLA exhibited marked environment dependence, with near-complete degradation in the subcutaneous environment by 48 weeks, whereas scaffold structure was maintained in the vascular environment. The PCL/PLA blend showed earlier reduction in the high-molecular-weight fraction than PCL, indicating faster scaffold breakdown. PGA degraded most rapidly and could not be evaluated beyond 2 weeks in the subcutaneous model or in the vascular model because of early graft rupture. SEM analysis further demonstrated that progressive loss of fibrous ultrastructure over time was a common feature across all materials. In addition, NF scaffolds became resistant to organic solvent after implantation in vivo, and solid-state 13C NMR analysis of the solvent-insoluble fractions detected polymer-derived signals together with additional signals consistent with biological constituents. These findings indicate that in vivo degradation of biodegradable NF scaffolds is material dependent, environment dependent, and more complex than simple hydrolytic chain cleavage alone. This study provides a quantitative framework for evaluating NF degradability and offers new insight into the design of biodegradable vascular grafts. HighlightsO_LISEC quantified long-term in vivo degradation of PCL, PLA, PGA, and PCL/PLA. C_LIO_LIDegradation was both material dependent and implantation environment dependent. C_LIO_LIIn vivo nanofiber degradation involved structural and chemical changes beyond hydrolysis. C_LI

bioengineering↗

bioRxiv2026

The strictly conserved GGG-tracts in the 5' and 3' long terminal repeat of HIV-1 are critical to control multiple steps of HIV-1 replication to prevent acquisition of unwanted mutations in the region

Three consecutive deoxyguanosine residues (the GGG-tract) in the U3/R junction of the 5 long terminal repeat (LTR) are strictly conserved among all HIV-1 subtypes. Each deoxyguanosine within the tract has been reported to function as transcription initiation site for HIV-1 RNA. Furthermore, RNAs whose transcription initiates from the third deoxyguanosine in the tract (1G form RNAs) are predominant in virus particles and serve as the primary templates for reverse-transcription. In this study, we generated mutant HIV-1s by replacing the tracts in both the 5 and 3 LTR with other nucleotides to elucidate their functional significance. We identified several proviral sequences containing unexpected mutations near the 5 tract after infection with the mutant, but not the wild-type virus. Five-prime rapid amplification of cDNA end (5 RACE) analyses of RNAs purified from mutant virus particles revealed multiple RNA variants with 5 terminal sequences differing from the plasmid used for producing the particles. Some of the unexpected proviral sequences likely arise directly from these variants during reverse-transcription. We also found that replacing all three nucleotides in the 3 tract with deoxyadenosines decreased the proportion of the 1G form RNAs in particles to 32.6%. Nevertheless, up to 88% of provirus was likely generated with the 1G form RNAs, although they were no longer absolutely predominant in particles. Our results demonstrate that the GGG-tracts in the 5 and 3 LTR are conserved to maintain the integrity of reverse-transcription for LTR sequence generation by controlling multiple steps of HIV-1 replication, including transcription, RNA packaging and reverse-transcription. ImportanceHIV-1 is highly mutable, yet certain conserved sequences remain consistent across most strains. These sequences are thought to be maintained because mutations in these regions typically impair viral fitness, leading to the elimination of such variants through natural selections. This study suggests that HIV-1 has a unique mechanism to autonomously prevent acquisition of mutations in certain regions. Specifically, the GGG-tracts in the 5 and 3 LTR ensure accurate transcription of HIV-1 RNAs, selective packaging of the 1G form RNAs, and preferential use of these 1G forms as a template for reverse-transcription. GGG preservation minimizes unwanted mutations in this region, allowing progeny virus to inherit intact LTR sequences. Interestingly, the preferential usage of 1G form RNAs as template for reverse-transcription is not due to their predominance in virus particles. This suggests that genome packaging independently contributes to reverse-transcription as preparatory stage by concentrating the most suitable RNAs for reverse-transcription in particles.

microbiology↗

bioRxiv2026

A senescent iCAF-like fibroblast state governs therapy resistance in rheumatoid arthritis

ObjectivesRheumatoid arthritis (RA) synovitis frequently persists despite cytokine-targeted therapies, suggesting the existence of pathogenic stromal programs that sustain chronic inflammation independently of canonical immune pathways. Although synovial fibroblasts (SF) are increasingly implicated in treatment resistance, the pathogenic fibroblast states driving refractory disease and their therapeutic vulnerabilities remain poorly defined. MethodsWe integrated multimodal single-cell and spatial profiling of synovial tissue from 54 patients with RA with prospective treatment-response data and functional studies in human fibroblasts and experimental arthritis models. ResultsWe identified a C-X-C motif chemokine 12 (CXCL12)hi Apolipoprotein C1 (APOC1)+ fibroblast population selectively enriched in treatment-refractory synovitis. Spatial analyses demonstrated that these fibroblasts establish CXCL12-dependent plasmablast niches within inflamed synovium, resembling inflammatory cancer-associated fibroblasts (iCAF) that orchestrate immune cell recruitment in the tumor microenvironment. CXCL12hi APOC1+ fibroblasts exhibited a senescence-associated iCAF-like transcriptional program characterized by STAT3-C/EBP activation and APOC1 expression and were associated with poor response to TNF and IL-6 pathway inhibition. Mechanistically, APOC1 knockdown in RA-SF attenuated invasive mesenchymal behavior and disrupted senescence-associated inflammatory programs, identifying APOC1 as a central regulator of pathogenic fibroblast reprogramming. Importantly, genetic or pharmacological elimination of senescent cells ameliorated experimental arthritis and enhanced the efficacy of TNF blockade. ConclusionsThese findings implicate iCAF-like fibroblasts with senescent properties as a mechanistic driver of refractory RA synovitis and highlight stromal senescence programs as preclinically actionable therapeutic targets beyond cytokine inhibition.

immunology↗

bioRxiv2026

Ecological Role of the Heterotrophic Protist Aurantiochytrium (Labyrinthulomycetes) as a Key Consumer of Viral-Induced Dissolved Organic Matter Following the Lysis of the Red Tide-forming Microalga Heterosigma akashiwo

Marine algal blooms play a vital role in oceanic carbon cycling, yet the ecological consequences of algal organic matter released following their collapse via viral infection are poorly understood. Recent studies have shown that viral infection dramatically alters the hosts intracellular metabolite composition, and the subsequent viral lysate selectively promotes the growth of specific prokaryotic populations. This study aimed to elucidate the effect of organic matter derived from healthy and virus-infected cells of the bloom-forming alga Heterosigma akashiwo on the growth of heterotrophic eukaryotes, specifically Labyrinthulomycetes. These marine protists are primarily saprotrophic or predatory and contribute to dissolved organic matter (DOM) decomposition and nutrient cycling. Our field monitoring in Osaka Bay over 12 months revealed that while the overall Labyrinthulomycetes community showed no clear seasonality, specific populations of the protists co-occurred with Heterosigma akashiwo. To mechanistically investigate the potential trophic linkage suggested by these field observations, a co-culture system comprising H. akashiwo, its specific virus (HaV53), and Aurantiochytrium sp. NBRC102614, used here as a model Labyrinthulomycete, was established. In the co-culture experiments, viral lysis of H. akashiwo led to a significant increase in the cell density of Aurantiochytrium sp., demonstrating that Aurantiochytrium can thrive on substrates derived from the virus-infected alga, such as viral-induced dissolved organic matter (vDOM). These findings highlight that heterotrophic Labyrinthulomycetes are one of key consumers of virus-modified organic matter, playing a pivotal role in carbon cycling following the collapse of harmful algal blooms and influencing carbon transfer in coastal microbial food webs. IMPORTANCEMarine ecosystems are tightly regulated by the interplay between microalgae, viruses, and heterotrophic eukaryotes, yet their roles within this network have long been underestimated. Accordingly, this study aimed to provide an overview of the dynamics of environmental microalgae and heterotrophic eukaryotes, namely Heterosigma species and Labyrinthulomycetes, and to elucidate the impact of virus-infected Heterosigma akashiwo on the growth and proliferation of Aurantiochytrium species within heterotrophic Labyrinthulomycetes. This study revealed the dynamics of several Labyrinthulomycetes species associated with Heterosigma populations in coastal marine environments and demonstrated that Aurantiochytrium species have the capacity to redistribute carbon, such as by utilizing vDOM released during the termination of Heterosigma blooms via viral infection, thereby repositioning Aurantiochytrium from a passive component of Heterosigma viral infection toward an active ecological agent that facilitates energy transfer and contributes to the maintenance of microalgal community dynamics. Overall, this work provides new insights into the fate of virus-infected Heterosigma in coastal marine systems mediated by heterotrophic Labyrinthulomycetes, particularly Aurantiochytrium species, thereby filling an important knowledge gap in microbial ecology.

microbiology↗

bioRxiv2026

Studies of mice with a large deletion of the ARPKD-associated Pkhd1 locus likely explain its GWAS association with glaucoma in humans

PKHD1, the gene primarily mutated in human autosomal recessive polycystic kidney disease, is one of the top 20 genes associated with primary open angle glaucoma (POAG) and associated endophenotypes in Genome-Wide Association Studies. Here, we show that Pkhd1del3-67/del3-67 mutant mice develop congenital glaucoma due to anterior segment dysgenesis. Using a combination of genetic, epigenetic, bioinformatics and mouse developmental biology approaches, we show that Pkhd1del3-67/del3-67 mice lack Tfap2b and AP-2{beta} expression in a subset of periocular mesenchymal cells at E13.5 and its derivatives. Our data suggest that the Pkhd1del3-67 deletion disrupts features of the Pkhd1-Tfap2b genomic architecture essential for Tfap2b cell-specific activities. Consistent with this model, Pkhd1del3-67/+;Tfap2bko/+trans-heterozygotes lack Tfap2b and AP-2{beta} in relevant cell-types and have similar eye abnormalities as neural crest cell-specific Tfap2bko mutants. These findings provide a likely causal explanation for how SNPs associated with PKHD1 are functionally linked to POAG and add insight into understanding the complexity of disease-causing SNP associations and gene regulatory mechanisms.

genetics↗

bioRxiv2026

Rapid diversification of a natural Heterosigma akashiwo virus population during a host bloom

Despite the ecological importance of viruses, our understanding of their evolutionary dynamics in natural environments remains limited. This gap is particularly pronounced for giant dsDNA viruses of the phyla Nucleocytoviricota and Mirusviricota. Most knowledge on their population genetic dynamics is derived from a small number of laboratory-based experiments, whereas patterns in nature are rarely observed. To overcome this limitation, we traced genetic structure and transcription status of Heterosigma akashiwo virus (HaV) using high-frequency, time-resolved sampling during a host bloom in a coastal area of Japan, by integrating cell counting, metabarcoding, metagenomic and metatranscriptomic sequencing. Our study revealed that HaV dominated the giant virus community in most samples, with the relative abundances of up to 56%. Despite the high abundances, the HaV population exhibited a relatively low level of microdiversity but with a high pN/pS ratio compared to other giant viruses in the study site. Microdiversity increased during the early sampling period, reached a maximum at mid-sampling, and decreased during the later period, consistent with rapid diversification during viral expansion, possibly driven by both in situ mutations and the succession of pre-existing minor variants. Several accessory genes, including a glycosyltransferase and an endonuclease, were highly expressed, providing functional evidence consistent with host interaction-driven selective pressure during the bloom. Together, these results indicate that HaV population dynamics during algal blooms are shaped by host-driven selection acting on standing genetic variation.

ecology↗

bioRxiv2026

Single-cell RNA sequencing reveals collagen interactions between detached osteoclasts and activated fibroblasts in granulation tissue surrounding sequestra in medication-related osteonecrosis of the jaw

ObjectivesMedication-related osteonecrosis of the jaw (MRONJ) is a rare but serious complication of anti-resorptive agents used for osteoporosis and bone metastasis. As the global population ages, the number of patients with MRONJ continues to rise. Resorptive osteoclasts firmly attached to bone surfaces cannot be detected using single-cell RNA-Seq (scRNA-Seq); however, we hypothesized that multinucleated giant and detached osteoclasts (DetOCs) can be detected by this method. This study aimed to characterize DetOCs with scRNA-seq. Materials and MethodsscRNA-Seq and immunohistochemistry staining was performed on granulation tissues surrounding sequestra from four patients with MRONJ and radicular cysts, a common odontogenic infectious disease with normal bone metabolism. ResultsscRNA-Seq and immunohistochemistry staining revealed that DetOCs were detected exclusively in the granulation tissues of MRONJ. These DetOCs expressed well-known osteoclast markers as well as COL27A1. Subcluster analysis revealed that SPP1+ TREM2+ macrophages differentiated into DetOCs and expressed several types of collagens. Immunostaining confirmed the expression of COL27A1 not only in DetOCs in MRONJ but also in osteoclasts in mandibular cancer. CellChat analysis revealed interactions mediated by collagen signaling pathways between DetOCs, myeloid cells, and activated fibroblasts. ConclusionsWe successfully characterized DetOCs and identified a distinctive microenvironment involving DetOCs and activated fibroblasts in the granulation tissues surrounding sequestra in MRONJ. Clinical RelevanceIdentification of DetOCs and their unique interaction with activated fibroblasts in MRONJ lesions provides novel insight into the pathophysiology of sequestrum formation, suggesting potential therapeutic targets to ameliorate MRONJ.

immunology↗

bioRxiv2025

LARP6 Promotes Features of Plaque Stability and Smooth Muscle Cell Survival in Atherosclerosis

IntroductionAcute plaque rupture or erosion followed by luminal thrombosis is a major cause of myocardial infarction and sudden cardiac death. Vulnerable plaques are characterized by a thin fibrous cap and reduced numbers of smooth muscle cells (SMCs). SMCs are essential for plaque stability, as they synthesize collagen and support fibrous cap structure. Our previous work demonstrated that insulin-like growth factor-1(IGF-1) enhances plaque stability and upregulates La ribonucleoprotein domain family member 6 (Larp6), a collagen mRNA-binding protein in SMCs. However, the specific role of Larp6 in atherosclerotic plaque stability remains undefined. MethodsIn vitro, human aortic SMCs (hAoSMCs) were used to investigate the molecular mechanism underlying IGF-1 regulation of LARP6. Using the Myh11 promotor we generated SMC specific Larp6 overexpression mice on an ApoE-/- background (SMC-Larp6) to assess effects on plaque stability. Bulk RNA sequencing data from human atherosclerotic plaques (GSE120521) were analyzed to compare stable and vulnerable plaques. ResultsIGF-1 regulates LARP6 through phosphorylation and downregulation of microRNAs. Plaques from SMC-Larp6 mice exhibited a significantly higher collagen content, accompanied by a thicker fibrous cap and a smaller necrotic core, increased presence of SMCs, without changes in overall plaque burden compared to controls. LARP6 overexpression in hAoSMCs significantly increased cell proliferation and survival under oxidative stress and promoted collagen accumulation by enhancing collagen synthesis. RNA sequencing analysis of human atherosclerotic plaques revealed reduced expression of LARP6 and downregulation of extracellular matrix-related pathways in unstable plaques, underscoring the clinical relevance of these findings. ConclusionsLarp6 overexpression promotes SMC survival, collagen synthesis and features of plaque stability under atherosclerotic conditions. These findings suggest that Larp6 is a potential therapeutic target for stabilization of atherosclerotic plaques.

pathology↗

bioRxiv2025

Structural basis of stereochemical promiscuity by an umami taste receptor ortholog, Tas1r1/Tas1r3 from pufferfish

Taste receptor type 1 (TAS1R), which consists of sweet and umami receptors in humans, senses nutrients (such as sugars and amino acids) with substrate specificity that is often broad and varies among animals and subtypes. However, the structural basis for achieving diverse specificities remains largely elusive. Here, we present the crystal structure of the ligand-binding domain (LBD) of Tas1r1/Tas1r3 heterodimer from pufferfish, an ortholog of the human umami taste receptor. The overall structure of Tas1r1/Tas1r3LBD resembles previously reported TAS1R structures, indicating a conserved core architecture within the family. Nevertheless, pufferfish Tas1r1/Tas1r3 was found to bind and respond to both L- and D-amino acids, even though TAS1Rs are considered to respond to either enantiomer. Structural and mutational analyses revealed that this non-rigorous stereochemical recognition is attributed to inter- subdomain interactions that latch the cleft containing the amino acid-binding site. These interactions prevent the cleft from fully opening, thereby stabilizing the active conformation, even if the ligand shares a different chirality. These results suggest that different substrate specificities in TAS1Rs can be acquired not only by the gain or loss of direct interactions with the substrate but also by the gain of intramolecular interactions, which alter the conformational equilibrium of the receptor.

biochemistry↗

bioRxiv2025

Phylo-MIP: Phylogeny-based Molecular Identification Pipeline for DNA metabarcoding, and assessment of insect communities in subalpine river ecosystems

AbstractEnvironmental DNA metabarcoding is a powerful tool for biodiversity assessment; however, species identification often relies on sequence similarity searches (BLAST), which are limited by incomplete reference databases and result in frequent misidentifications or unclassified taxa. To overcome these challenges, we designed a novel analytical pipeline, Phylo-MIP, which integrates phylogenetic analysis and species delimitation. Phylo-MIP combines sequence alignment, haplotype thinning, phylogenetic tree construction, and multiple species delimitation methods (bPTP, bPTP-ML, mPTP) to objectively identify Molecular Operational Taxonomic Units (MOTUs) without relying on reference databases. As a validation, we applied Phylo-MIP to previously published eDNA data from river in Kanagawa Prefecture, detecting approximately 28% more species than only BLAST-based methods. We also conducted a eDNA survey in the subalpine zone of Kamikochi, Nagano Prefecture, Japan, where Phylo-MIP revealed distinct community structures associated with specific aquatic environments. Phylo-MIP enables non- invasive and efficient biodiversity monitoring, even in protected areas, and offers a reproducible framework for ecological research. This approach has the potential to become a new standard method in river ecology, taxonomy, conservation biology, and ecosystem management.

molecular biology↗

bioRxiv2025

Carbon monoxide-driven proton respiration enables facultative anaerobes to survive electron acceptor limitation

Diverse microorganisms couple the oxidation of carbon monoxide gas (CO) to the reduction of protons, producing hydrogen gas (H2). This energy-conserving process is mediated by the nickel-containing CO dehydrogenase/energy-converting hydrogenase (Ni-CODH/ECH). Yielding only a small supply of energy, the physiological role of this process at environmentally relevant CO levels remains unresolved. Here, we show that Ni-CODH/ECH enables metabolically flexible facultative anaerobes within the Anoxybacillaceae to survive electron acceptor limitation. Analysis of 387 Anoxybacillaceae genomes revealed that Ni-CODH/ECH had a patchy distribution and, with one exception, was mutually exclusive with the aerobic molybdenum-containing CODH. Culture experiments using the three isolates (Parageobacillus sp. G301, P. thermoglucosidasius NBRC 107763, and Thermolongibacillus altinsuensis B1-1) demonstrated that CO-dependent proton respiration is activated during stationary phase when exogenous electron acceptors are limiting, enhancing cell density 1.2-to 1.5-fold under 25% CO, whereas no effect was observed in a Ni-CODH knockout ({Delta}cooCSF) strain. RNA-seq analysis of strain G301 under twelve conditions revealed that Ni-CODH genes reached 2,000-12,500 TPM (top 0.2-1.9% of all genes) during stationary phase, independent of CO presence, under the predicted control of the redox-dependent transcriptional repressor Rex. {Delta}cooCSF cultures accumulated more trace CO than the wild-type, suggesting trace CO uptake by the wild-type. Thus, Ni-CODH/ECH is a redox-regulated auxiliary energy-conservation system that supports adaptation to electron acceptor limitation. Given the continual environmental supply of the two substrates for this enzyme, we propose CO-dependent proton respiration is a dependable way for metabolically flexible microorganisms to stay energized in spatiotemporally variable environments. Significance statementMicroorganisms are frequently challenged to survive in environments where both energy sources and electron acceptors are limited. We reveal that facultative anaerobes activate a respiratory process that utilizes carbon monoxide (CO) and protons to survive under electron acceptor limitation. This hydrogenogenic CO-oxidizing reaction, termed CO-dependent proton respiration, is catalyzed by an ancient and minimal complex, the nickel-containing CO dehydrogenase/energy-converting hydrogenase. Although the reaction yields barely enough energy to translocate protons, this complex provides a reliable lifeline by extracting energy from trace CO and protons that are ubiquitous in nature, even when other electron acceptors are depleted. The widespread distribution of this complex across bacteria and archaea suggests that it provides a universal adaptive advantage for life under energy-limited conditions.

microbiology↗

bioRxiv2025

Environmental exosomes: Evidence of extracellular RNA release by aquatic organisms

Aquatic organisms continuously interact with surrounding water, yet whether they release extracellular vesicles remains unknown. We hypothesized that pearl oysters (Pinctada fucata) release exosomes/small extracellular vesicles (sEVs) into the aquatic environment. To this end, we collected exosomes/sEV-sized components by ultrafiltration from tank water and open-sea culture areas. Microscopy revealed abundant vesicles consistent with exosome/sEV size, and RNA sequencing identified oyster-specific piRNAs that matched sequences previously detected in hemolymph exosomes. These findings demonstrated that pearl oysters actively released exosomes containing species-specific nucleic acids into surrounding water. We propose referring to these vesicles as environmental exosomes/environmental sEVs (eExosomes/esEVs). This finding suggests that aquatic exosomes serve as carriers of RNA and may contribute to inter-organismal communication networks. Beyond their functional role, eExosomes/esEVs also hold promise as novel targets for environmental DNA/RNA (eDNA/eRNA) analysis, offering new opportunities for ecological monitoring and biodiversity research.

ecology↗

bioRxiv2025

Molecular unbalances between striosome and matrix compartments characterize the pathogenesis of Huntington's disease model mouse

The pathogenesis of Huntingtons disease is still incompletely understood, despite the remarkable advances in identifying the molecular effects of the Htt mutation in this disease. When we focus on movement disorders, clinical studies offer us some hints about this issue. Human studies employing positron emission tomography have identified a reduction in phosphodiesterase 10A (PDE10A) as the earliest event in the brain of patients with Huntingtons disease, which occurs about 25 years before symptom onset. A PDE10A mutation is also known to cause childhood-onset chorea. GNAL encodes the olfactory type G-protein subunit (Golf), strongly expressed in the striatum, and its mutation causes familial dystonia. PDE10A and Golf are both critical regulators of cyclic AMP and are abundant in striatal spiny projection neurons. These findings suggest that maintaining cyclic AMP levels in the striatum might be an essential target for the pathogenesis of movement disorders such as chorea and dystonia. Why and how these changes in the striatum cause movement disorder are still a mystery. Here we suggest that a key might be evaluating these messenger systems in light of the circuit-level compartmental organization of the striatum, in which there is particular vulnerability of the striosome compartment. We developed machine learning algorithms to define with high precision and reproducibility the borders of striosomes in the brains of q175 Huntingtons disease model mice from 3-12 months of age. We demonstrate that multiple molecules including Golf, PDE10A, dopamine D1 and D2 receptors, adenosine 2A receptors, and mu-opioid receptors differentially change their expression patterns in striosomes across ages by comparison with their expression patterns in the matrix compartment. An early and pronounced differential vulnerability of striosomes has been demonstrated in studies of post-mortem Huntingtons brains. Our findings here, mapping the molecular distributions across age in a widely studied mouse model of Huntingtons disease, may help to pinpoint the pathogenic mechanisms of Huntingtons disease by demonstrating the differential molecular changes in the striosome compartment.

neuroscience↗