Biology subjects

Watanabe, E.

Publications and source records attributed to Watanabe, E..

13 recordsLinked to original sources

bioRxiv2026

Aqp1aa and Aqp4a mediate collecting duct water permeability in a marine teleost

Regulation of water permeability in the collecting duct is important for osmoregulatory acclimation in teleost fish. In hyperosmotic environments such as seawater (SW), the teleost kidney functions as a site of divalent ion excretion. The collecting ducts reabsorb Na+, Cl-, and water, thereby reducing urine volume and producing small amounts of isotonic urine with high concentrations of divalent ions. In hypoosmotic environments such as freshwater (FW) or low-salinity brackish water (BW), the kidney produces large volumes of hypotonic urine and serves as a site of water excretion; under these conditions, the collecting ducts reabsorb Na+ and Cl- but not water. To identify aquaporins (Aqps) involved in regulating water permeability in the collecting ducts of teleosts, we analyzed renal Aqp expression in a euryhaline marine fish, the Japanese pufferfish (Takifugu rubripes), which possesses 16 Aqp genes in its genome, seven of which (Aqp1aa, 1ab, 3a, 4a, 7, 8bb, and 11a) are expressed in the kidney. Quantitative RT-PCR analysis showed that Aqp1aa and Aqp4a were highly expressed in collecting duct tissues, and that Aqp1aa expression was markedly reduced in fish acclimated to BW. Immunohistochemistry revealed apical localization of Aqp1aa and basolateral localization of Aqp4 in collecting duct cells, with apical Aqp1aa downregulated in BW. These results suggest that Aqp1aa and Aqp4 mediate water reabsorption in SW and that downregulation of Aqp1aa contributes to hypotonic urine production in BW. NEW & NOTEWORTHYRegulation of water permeability in the collecting duct is important for osmoregulation in teleost fish. Expression analyses of aquaporins (Aqps) in the marine pufferfish Takifugu rubripes showed that Aqp1aa and Aqp4a are highly expressed in the collecting duct and localized to the apical and basolateral membranes, respectively. Renal Aqp1aa expression was markedly reduced in fish acclimated to hypoosmotic brackish water. These results indicate that collecting duct water permeability is regulated by Aqp1aa expression.

physiology↗

bioRxiv2026

Controlling Integration and Segregation in Echo State Networks via Noradrenaline and Acetylcholine Neuromodulation

Biological brain networks flexibly reconfigure functional connectivity between integration and segregation through neuromodulatory systems--noradrenaline (NA) and acetylcholine (ACh)--without altering structural connectivity. Inspired by this mechanism, we propose a modular echo state network (ESN) with context-dependent NA and ACh gain modulation, where NA promotes inter-module integration via response gain and ACh promotes intra-module segregation via multiplicative gain. We evaluate the model on two context-dependent tasks: a segregation/integration task and a context-dependent decision task. Across both tasks, the modulated model consistently outperformed the baseline, with task-appropriate modulation profiles emerging naturally from optimization and functional connectivity analysis confirming context-appropriate dynamic reorganization. These results demonstrate that neuromodulatory gain control enables adaptive, context-sensitive computation in structurally fixed reservoir networks.

neuroscience↗

bioRxiv2025

Predictive Networks Generate Motion-Induced Color Illusions

Subjective color (SC) refers to chromatic perception induced by achromatic stimuli, as classically demonstrated using Benhams top. Despite nearly two centuries of investigation, the underlying neural mechanisms remain unclear. We developed artificial neural network (ANN) models trained on natural videos using predictive learning to investigate SC generation. These models successfully reproduced artificial subjective color (ASC) despite the absence of explicit color information in the training stimuli. Critically, ASC characteristics were systematically influenced by the colors of moving objects in the training videos. Using progressively simplified stimuli, ranging from natural scenes to 3D computer graphics to 2D animations, we demonstrated that the colors of moving objects are the primary determinant of ASC properties. We propose that predictive learning establishes color associations with motion patterns, causing the arcs on Benhams top to be perceived as moving objects with their corresponding colors. These findings suggest that cortical predictive mechanisms may complement retinal processes in generating subjective color phenomena.

neuroscience↗

bioRxiv2025

A New Look at Medaka: Surprising Deep Diving Behavior Uncovered in the Lab

Medaka (Oryzias latipes and O. sakaizumii) are small freshwater fish native to East Asia, commonly found in shallow waters. However, their presence and behavior in deeper habitats remain poorly understood due to observational challenges. Here, we introduce a novel experimental system--a 9-meter-tall cylindrical tank made from vertically connected transparent PVC pipes--that enables direct observation of medaka diving behavior. Our results demonstrate that medaka voluntarily dive to depths of up to 9 meters and remain at the bottom for extended periods, a behavior contrasting with that of zebrafish (Danio rerio), which rarely reached such depths. Moreover, when fish were introduced from the bottom of the tank, zebrafish exhibited repeated vertical movements, ascending and descending but rarely reaching the water surface, whereas medaka consistently remained at the bottom. While primarily descriptive, these findings represent a significant and previously unrecognized aspect of medaka ecology, challenging the traditional view of them as purely surface-dwelling fish. This study provides a unique tool and foundational insight that opens new avenues for ecological and physiological investigations of fish depth preferences.

animal behavior and cognition↗

bioRxiv2025

Enhancing role of nitrogen fixation in biogeochemical cycles of the Pacific Arctic

The Arctic Ocean is warming rapidly, prompting increased attention to the ecosystems response to sea-ice loss and the influx of organisms from lower latitudes. Here we found that nitrogen fixation in the Pacific Arctic region was significantly elevated when sea ice in the Chukchi shelf region retreated earlier. UCYN-A2 was determined to be the dominant diazotroph, with numerical simulation and water mass analyses implying its origin to be in the Bering Sea. UCYN-A2 abundance was positively correlated with temperature, and it extended into the Arctic off-shelf region, which is undergoing oligotrophication as a result of sea-ice loss. In this region, nitrogen fixation contributed significantly to new production (4.6- 100%, average: 34%), underscoring its impact on the biogeochemical cycles. This study highlights the increasing importance of nitrogen fixation in the Pacific Arctic region, driven by warming, sea-ice loss, and borealization.

microbiology↗

bioRxiv2025

Efficient Production of Pseudopregnant Female Mice Using Non-Estrous Individuals and the Whitten Effect

Pseudopregnant recipient females are essential for transplanting early mouse embryos during individualization. Traditionally, pseudopregnancy is induced through mating stimulation with vasectomized males, targeting females in proestrus or estrus. However, group housing of females in animal facilities often leads to fewer females entering estrus due to the Lee-Boot effect. This study focused on utilizing non-estrous females and the Whitten effect to produce pseudopregnant females. Females exhibiting characteristics of non-estrous states were visually selected and paired monogamously with vasectomized males for three consecutive days. This approach resulted in a high copulation success rate of 72.1% (CLEA Japan, Inc.) and 77.0% (Japan SLC, Inc.) on the expected third day. Subsequent embryo transfer using successfully copulated females resulted in offspring from 93.5% of ICR females from CLEA Japan, Inc. and 89.6% of ICR females from Japan SLC, Inc. Additionally, the suitability for embryo transfer could be determined by observing the condition of the ampulla of the oviduct. While this method requires a three-day preparation period compared to conventional approaches, it offers an effective alternative for creating pseudopregnant females for embryo transfer, potentially reducing animal use and associated costs.

bioengineering↗

bioRxiv2024

Model-based analysis on the generation of the circadian rhythm of the bioluminescence reporter activities in duckweed

Bioluminescence monitoring techniques are widely used to study the gene expression dynamics in living plants. Monitoring the bioluminescence from a luciferase gene under the control of a circadian promoter is indispensable for examining plant circadian systems. The bioluminescence monitoring technique was successfully applied to physiological studies of circadian rhythms in duckweed plants. It has been reported that a luciferase gene under a constitutive promoter also exhibits a bioluminescent circadian rhythm in duckweed. However, the mechanisms underlying rhythm generation remain unknown. In this study, we performed a model-based analysis to evaluate the machinery that generates the bioluminescence rhythm. We hypothesized the rhythmic factor of three aspects regarding the bioluminescence intensities of luciferase in cells: luminescence efficiency, production rate, and degradation rate. Theoretically, if the latter two are involved in rhythm generation, the difference in luciferase stability affects the amplitude and phase relations of the bioluminescence rhythm. Luciferase stability is irrelevant to these rhythm properties if only the luminescence efficiency is involved. First, we simulated the bioluminescence rhythms of two luciferases with different stabilities associated with each of three rhythmic factors. Luciferase stability was set based on the reported values for Emerald-luciferase and Emerald-luciferase-PEST. We then experimentally examined the bioluminescence rhythms of reporters of these luciferases driven by the CAULIFLOWER MOSAIC VIRUS 35S promoter in the duckweed Lemna japonica. Their circadian properties matched those obtained from the simulation of the luminescence efficiency. This supports the view that cells in duckweed show circadian changes in physiological conditions associated with the luciferase enzyme reaction.

plant biology↗

bioRxiv2022

Lifelong temporal dynamics of the gut microbiome associated with longevity in mice

The temporal changes of the gut microbiome are thought to be critical for understanding its interactions with host aging, but lifelong dynamics within the same individual remain largely unknown. Here we firstly report the high temporal resolution dynamics of gut microbiomes in mice sharing the same genetic background and environment from their birth to natural death, spanning >1,000 days. The 16S rRNA sequencing analysis revealed 9 patterns of OTU temporal dynamics and 38 common "life-core" bacterial species/operational taxonomic units (OTUs) in [≥]80% of all samples across the lifespan of individual mice. The life-core OTUs are largely represented by the phylum Bacteroidota, whereas the transient bacterial group predominantly includes the phylum Firmicutes (Bacillota). Despite the shared genetic background and dietary habits, the gut microbiome structure significantly diversified with age and among individuals. A positive correlation existed between longevity and the microbiome -diversity in middle age (200-500 days) followed by a negative correlation in old age (>700 days), likely influenced by the increase in diversity during the last days of life. The abundance of several "life-core" species also exhibited non-static correlation trends with lifespan. Overall, this research characterized the gut microbiomes based on its persistence over hosts lifetime and suggested a non-static host-microbiome relationship within individual mice.

microbiology↗

bioRxiv2022

No circadian clock-gene circuit in the generation of cellular bioluminescence rhythm of CaMV35S::PtRLUC in duckweed

Physiological circadian rhythms are coordinated in the plant body in an orderly manner. The coordination of time information has been studied from the aspects of cell-cell local coupling and long-distance communication between tissues. These studies were based on the idea that the behavior of the clock gene circuit represents the physiological rhythms. Here we report the cellular circadian rhythm of a bioluminescence reporter which is not governed by the clock gene circuit in the expressing cells. Using a dual-color bioluminescence monitoring system in Lemna minor transfected with the AtCCA1::LUC+ and CaMV35S::PtRLUC reporters, cellular bioluminescence rhythms with different free-running periods (FRPs) were detected in the same cells. Co-transfection experiments with the two reporters and a clock gene overexpressing effector revealed that the circadian properties of the AtCCA1::LUC+ rhythm, but not those of the CaMV35S::PtRLUC rhythm, were altered in the cells with a dysfunctional clock gene circuit. This indicates that the AtCCA1::LUC+ rhythm is a direct output of the cellular circadian clock while the CaMV35S::PtRLUC rhythm is not. After plasmolysis, the CaMV35S::PtRLUC rhythm disappeared while the AtCCA1::LUC+ rhythm persisted. The plant circadian system consists of both cell-autonomous rhythms and non-cell-autonomous rhythms that are unaffected by the cellular clock.

plant biology↗

bioRxiv2021

Placental mammals acquired the functional region and domain in NRK for regulating the CK2-PTEN-AKT pathway and placental cell proliferation

The molecular evolution processes underlying the acquisition of the placenta in eutherian ancestors are not fully understood. Mouse NCK-interacting kinase (NIK)-related kinase (NRK) is expressed highly in the placenta and plays a role in preventing placental hyperplasia. Here, we show the molecular evolution of NRK, which confers its function for inhibiting placental cell proliferation. Comparative genome analysis identified NRK orthologues across vertebrates, which share the kinase and citron homology (CNH) domains. Evolutionary analysis revealed that NRK underwent extensive amino acid substitutions in the ancestor of placental mammals and has been since conserved. Biochemical analysis of mouse NRK revealed that the CNH domain binds to phospholipids, and a region in NRK binds to and inhibits casein kinase-2 (CK2), which we named the CK2-inhibitory region (CIR). Cell culture experiments suggest the following: (1) mouse NRK is localised at the plasma membrane via the CNH domain, where the CIR inhibits CK2. (2) This mitigates CK2-dependent phosphorylation and inhibition of PTEN, and (3) leads to the inhibition of AKT signalling and cell proliferation. Nrk deficiency increased phosphorylation levels of PTEN and AKT in mouse placenta, supporting our hypothesis. Unlike mouse NRK, chicken NRK did not bind to phospholipids and CK2, decrease phosphorylation of AKT, or inhibit cell proliferation. Both the CNH domain and CIR have evolved under purifying selection in placental mammals. Taken together, our study suggests that placental mammals acquired the phospholipid-binding CNH domain and CIR in NRK for regulating the CK2-PTEN-AKT pathway and placental cell proliferation.

molecular biology↗

bioRxiv2021

Laterally biased diffusion of males of the water flea Daphnia magna

The water flea Daphnia magna is a representative example of zooplankton living in freshwater environments. They primarily propagate via asexual reproduction under normal and healthy environmental conditions. Environmental stimuli that signal a shift to disadvantageous conditions induce D. magna to change their mode of reproduction from asexual to sexual reproduction. During the sexual reproduction phase, they produce special tough eggs (resting eggs), which can survive severe environmental conditions. Despite our increased understanding of their mating behaviours, the sex-specific characteristics of swimming behaviours among daphnid species are poorly understood. In this study, we analysed the swimming patterns and dynamics of female and male adult D. magna. First, we found laterally biased diffusion of males in contrast to the homogeneous, nondirectional diffusion of females. Second, computer modelling analysis using a discrete-time Markov chain simulation, in which the frequencies of turning behaviour were evaluated as probability distributions, explained the greater diffusion of males in the horizontal direction. Under the presumption that high diffusion in the horizontal direction increases the probability of encountering a distant mate, these findings led us to hypothesise that male D. magna increase genotype heterogeneity by effectively selecting the probability distributions of certain motion parameters. Summary statementsWe analysed the swimming behaviours of adult water flea Daphnia magna, and found apparent sexual differences: laterally biased diffusion of males in contrast to the nondirectional diffusion of females.

animal behavior and cognition↗

bioRxiv2020

Detection of uncoupled circadian rhythms in individual cells of Lemna minor by using a dual-color bioluminescence monitoring system

The plant circadian oscillation system is based on the circadian clock of individual cells and coordinates the circadian behavior of the plant body. To observe the cellular circadian behavior of both the oscillator and its output in plants, we developed the dual-color bioluminescence monitoring system that automatically measured the luminescence of two luciferase reporters simultaneously at a single-cell level. We selected a yellow-green-emitting firefly luciferase (LUC+) and a red-emitting luciferase (PtRLUC) that is a mutant form of Brazilian click beetle ELUC. We used AtCCA1::LUC+ and CaMV35S::PtRLUC to observe the cellular behavior of the oscillator and output, respectively. These bioluminescent reporters were introduced into the cells of a duckweed, Lemna minor, by particle bombardment. Time series of the bioluminescence of individual cells in a frond were obtained using a dual-color bioluminescence monitoring system with a green-pass- and red-pass filter. Luminescence intensities from the LUC+ and PtRLUC of each cell were calculated from the filtered luminescence intensities. We succeeded in reconstructing the bioluminescence behaviors of AtCCA1::LUC+ and CaMV35S::PtRLUC in the same cells. Under prolonged constant light conditions, AtCCA1::LUC+ showed a robust circadian rhythm in individual cells in an asynchronous state in the frond, as previously reported in studies using other plants. In contrast, CaMV35S::PtRLUC stochastically showed circadian rhythms in a synchronous state. Thus, we clearly demonstrated the uncoupling between the oscillator and output in individual cells. This dual-color bioluminescence monitoring system is a powerful tool to analyze various stochastic phenomena accompanying large cell-to-cell variation in gene expression. Significance statementWe succeeded in establishing the worlds first dual-color bioluminescence monitoring system at a single-cell level that enables simultaneous measurement of the luminescence activities of two reporter genes in plants. This system is a strong tool to analyze stochastic phenomena, and we clearly demonstrated the uncoupling of rhythmic behavior between two bioluminescent reporters in individual cells that stochastically occurred in the same plant.

plant biology↗

bioRxiv2019

Plagiarism in Brazil: A perspective of 25,000 PhD holders across the sciences

When it comes to ownership of ideas in science, Robert K. Merton (1957) observed in Priorities in Scientific Discovery: A Chapter in the Sociology of Science that "what is true of physics, chemistry, astronomy, medicine and mathematics is true also of all the other scientific disciplines, not excluding the social and psychological sciences". However, consensus over related issues, such as what constitutes plagiarism in these fields cannot be taken for granted. We conducted a comprehensive study on plagiarism views among PhD holders registered in the database of the Brazilian National Council for Scientific and Technological Development (CNPq). We collected 25,157 valid responses encompassing views and attitudes toward plagiarism from a probability sample of PhD holders across the fields, including biologists, physicists, mathematicians, and engineers as well as linguists, philosophers and anthropologists. The results suggest that core principles about plagiarism are shared among this multidisciplinary community and that they corroborate Mertons observations. Before this study, we could only speculate that this is the case. With these data from a probability sample of Brazilian academia (PhD holders), this study offers insight into the way plagiarism is perceived across the sciences, including the literature and arts, and sheds light on the problem in the context of international collaborative research networks. The data focus on a young research system in Latin America, but, given the cultural similarities that bind most Latin-American nations, these results may be relevant to other PhD populations in the region and should provide a comparison with studies from other emerging, non-Anglophone regions.

scientific communication and education↗