Biology subjects

Miyasaka, T.

Publications and source records attributed to Miyasaka, T..

7 recordsLinked to original sources

bioRxiv2026

Oribatid Mites Supply Tetrodotoxin to Poisonous Newts

Tetrodotoxin (TTX) is a potent neurotoxin widely distributed among marine and terrestrial animals, yet how terrestrial vertebrates acquire this toxin has been debated for decades. Here, we identify oribatid mites as the primary dietary sources of TTX for the Japanese fire-bellied newt, Cynops pyrrhogaster. We detect TTX and its analogs in the mites Scheloribates processus and Galumna sp. KM1, which are preferentially consumed by terrestrial newts. In a controlled toxification experiment, juvenile newts accumulated TTX after consuming TTX-bearing mites, directly demonstrating dietary sequestration. Our results demonstrate that the early terrestrial stage is critical for lifelong TTX acquisition in newts. Notably, we also detect pumiliotoxin, a poison-frog alkaloid, in S. processus, suggesting that newts and poison frogs have convergently evolved to exploit toxin-bearing microarthropods for chemical defense. We propose a "terrestrial toxic web" hypothesis in which oribatid mites act as a shared environmental reservoir linking putative microbial toxin production to vertebrate chemical defense, highlighting microarthropods as key mediators in terrestrial toxin flow.

ecology↗

bioRxiv2025

Graded regulation of microtubule-binding of Tau by the phosphorylation state of the proline-rich region in living neurons

Tau protein is a microtubule-associated protein that plays a crucial role in maintaining neuronal morphology and axonal transport. While phosphorylation is known to regulate Tau-microtubule interactions, the contribution of specific phosphorylation patterns in situ remains poorly understood due to the complexity of the intracellular environment. In this study, we combined fluorescence recovery after photobleaching (FRAP) in primary cultured rat hippocampal neurons with dephosphorylation-mimetic mutations and computational modeling to analyze the effects of phosphorylation on Tau-microtubule interaction. We particularly focused on the proline-rich region, of which phosphorylation has been studied in physiological and pathological perspectives, and generated a dephosphorylation-mimetic Tau mutant by substituting key phosphorylation sites with alanine residues and compared its microtubule-binding dynamics to those of WT-Tau in FRAP experiments. Experimental data, together with simulation-based parameter exploration, revealed that the overall number of phosphorylated sites plays a more dominant role than their specific locations in modulating Tau-microtubule affinity. These findings provide new insights into the post-translational regulation of Tau and establish a computational-experimental framework for interrogating intracellular protein dynamics.

neuroscience↗

bioRxiv2023

Active Transport by Cytoplasmic Dynein Maintains the Localization of MAP-2 in Developing Neurons

MAP2 has been widely used as a marker of neuronal dendrites because of its extensive restriction in the somatodendritic region of neurons. Despite that, how the precise localization of such a soluble protein is established and maintained against thermal forces and diffusion has been elusive and long remained a mystery in neuroscience. In this study, we aimed to uncover the mechanism behind how MAP2 is retained in the somatodendritic region. Using GFP-tagged MAP2 expressed in cultured hippocampal neurons, we discovered a crucial protein region responsible for the localization of MAP2, the serine/proline-rich (S/P) region. Our pulse-chase live-cell imaging revealed the slow but steady migration of MAP2 toward distal dendrites, which was not observed in a MAP2 mutant lacking the S/P region, indicating that S/P-dependent transport is vital for the proper localization of MAP2. Furthermore, our experiments using an inhibitor of cytoplasmic Dynein, ciliobrevin D, as well as Dynein knockdown, showed that cytoplasmic Dynein is involved in the transport of MAP2 in dendrites. We also found that Dynein complex binds to MAP2 through the S/P region in heterologous cells. Using mathematical modeling based on experimental data, we confirmed that an intermittent active transport mechanism is essential. Thus, we propose that the cytoplasmic Dynein recruits and transports free MAP2 toward distal dendrites, thereby maintaining the precise dendritic localization of MAP2 in neurons. Our findings shed light on the previously unknown mechanism behind MAP2 localization and provide a new direction for soluble protein trafficking research in the field of cell biology of neurons.

neuroscience↗

bioRxiv2022

Safety margin evaluations for transtympanic laser stimulation of the cochlea from the outer ear in Mongolian gerbils (Meriones unguiculatus)

Infrared laser cochlear stimulation has been suggested as an alternative to traditional auditory prostheses. Previous research has mainly examined the short-term effects of laser stimulation, but to effectively use this technique, it is necessary to study whether prolonged laser exposure can safely and sustainably induce cochlear responses. This study assessed the effect of laser-induced cochlear damage using classically-conditioned Mongolian gerbils. The white noise was presented as a conditioned stimulus, and reward licking was recorded as a conditioned response. After training, the subjects cochlea was exposed to a continuous pulsed laser for 15 h. The licking rate drastically decreased after the exposure of 26.4 W/cm2, while it did not change after 6.6 W/cm2 or weaker. These findings showed, for the first time, that the safety margin of long-term, at least several hours, cochlear laser stimulation exists and will contribute to the safe and effective delimitation of laser parameters in future research.

bioengineering↗

bioRxiv2021

Microtubule assembly by soluble tau impairs vesicle endocytosis and excitatory neurotransmission via dynamin sequestration in Alzheimer's disease synapse model

Elevation of soluble wild-type (WT) tau occurs in synaptic compartments in Alzheimers disease. We addressed whether tau elevation affects synaptic transmission at the calyx of Held in brainstem slices. Whole-cell loading of WT human tau (h-tau) in presynaptic terminals at 10-20 {micro}M caused microtubule (MT) assembly and activity-dependent rundown of excitatory neurotransmission. Capacitance measurements revealed that the primary target of WT h-tau is vesicle endocytosis. Blocking MT assembly using nocodazole prevented tau-induced impairments of endocytosis and neurotransmission. Immunofluorescence imaging analyses revealed that MT assembly by WT h-tau loading was associated with an increased bound fraction of the endocytic protein dynamin. A synthetic dodecapeptide corresponding to dynamin-1-pleckstrin-homology domain inhibited MT-dynamin interaction and rescued tau-induced impairments of endocytosis and neurotransmission. We conclude that elevation of presynaptic WT tau induces de novo assembly of MTs, thereby sequestering free dynamins. As a result, endocytosis and subsequent vesicle replenishment are impaired, causing activity-dependent rundown of neurotransmission. Significance StatementWild-type human recombinant tau loaded in rodent presynaptic terminals inhibited vesicle endocytosis, thereby causing activity-dependent rundown of excitatory transmission. This endocytic block is caused by a sequestration of dynamin by excess microtubules newly assembled by tau and can be rescued by a peptide inhibiting the microtubules-dynamin interaction, or by the microtubule disassembler nocodazole. Thus, synaptic dysfunction can be induced by pathological increase of endogenous soluble tau in Alzheimer disease slice model.

neuroscience↗

bioRxiv2018

Ectopic expression induces abnormal somatodendritic distribution of tau in the mouse brain

Tau is a microtubule-associated protein that is localized to the axon. In Alzheimers disease, the distribution of tau undergoes a remarkable alteration, leading to the formation of tau inclusions in the somatodendritic compartment. To investigate how this mis-localization occurs, we recently developed immunohistochemical techniques that can separately detect endogenous mouse and exogenous human tau with high sensitivity, which allows us to visualize not only the pathological but pre-aggregated tau in mouse brain tissues of both sex. In tau transgenic mouse brains, exogenous human tau was abundant in dendrites and somata even in the presymptomatic period, whereas the axonal localization of endogenous mouse tau was unaffected. In stark contrast, exogenous tau was properly localized to the axon in human tau knock-in mice. We tracked this difference to the temporal expression patterns of tau. Tau mRNA was continuously expressed in the transgenic mice, whereas endogenous tau and exogenous tau in the knock-in mice exhibited high expression levels during the neonatal period and strong suppression into the adulthood. These results indicated the uncontrolled expression of exogenous tau beyond the developmental period as a cause of mis-localization in the transgenic mice. Super-resolution microscopic and biochemical analyses also indicated that the interaction between microtubules and exogenous tau was indeed impaired in the tau transgenic mice. Thus, the ectopic expression of tau may be critical for its somatodendritic mis-localization, a key step of the tauopathy.\n\nSignificance StatementSomatodendritic localization of tau may be an early step leading to the neuronal degeneration in tauopathies. However, the mechanisms of the normal axonal distribution of tau and the mis-localization of pathological tau remain obscure. Our immunohistochemical and biochemical analyses demonstrated that the endogenous mouse tau is transiently expressed in neonatal brains, that exogenous human tau expressed corresponding to such tau expression profile can distribute into the axon, and that the constitutive expression of tau into adulthood (ex. human tau in Tg mice) results in abnormal somatodendritic localization. Thus, the expression profile of tau is tightly associated with the localization of tau, and the ectopic expression of tau in matured neurons may be involved in the pathogenesis of tauopathy.

neuroscience↗

bioRxiv2018

Regulatory mechanisms for the axonal localization of tau in neurons

Tau is a microtubule (MT)-associated protein, which precisely localizes to the axon of a mature neuron. Although it has been widely used as an axonal marker, the mechanisms for its axonal localization have been elusive. This might be largely due to the lack of an experimental system, as exogenously expressed tau, such as GFP-tau, mis-localizes to the soma and dendrites. In this study, we found that the expression of endogenous tau and its axonal localization in cultured rat hippocampal neurons mainly occur during early neuronal development and are coupled. By mimicking this early expression, we demonstrate that exogenously expressed human tau can be properly localized to the axon, thereby providing the first experimental model to study the mechanisms of tau localization. Using this model, we obtained surprising findings that the axonal localization of tau did not require the MT-binding domain nor correlate with the MT-binding ability. Instead, we identified a transport mechanism mediated by the proline-rich region 2 (PRR2), which contains a number of important phosphorylation sites. Mimicking phosphorylation and dephosphorylation in PRR2 disrupts the axonal localization, suggesting that it is regulated by the phosphorylation state of PRR2. These results shed new lights on the mechanism for the axonal localization of tau and indicate a link between the hyperphosphorylation and mis-localization of tau observed in tauopathies.\n\nSignificance statementIn this paper, we present a first experimental system, in which expressed tau is properly localized to the axon, and which can therefore be used to study the mechanisms of tau localization and mis-localization. Using this system, we provide evidence that the microtubule binding domain of tau nor stable binding of tau to microtubules is not necessary for its axonal localization. Instead, we identified the proline-rich region and its phosphorylation-state dictate the localization of tau in neurons. These results provide a novel foundation to consider how axonal tau mis-localize to the soma and dendrites during early pathogenesis of Alzheimers disease.

neuroscience↗