Biology subjects

Mikoshiba, K.

Publications and source records attributed to Mikoshiba, K..

5 recordsLinked to original sources

bioRxiv2026

Large-scale dimensional behavioral profiling dissociates fear memory from locomotor confounds in mice: The necessity of baseline-normalized metrics

Fear conditioning is widely used to assess associative memory in mice, yet percent freezing conflates memory with baseline locomotor and anxiety-related traits. A systematic survey of recent studies (2020-2025) found that fewer than 1% statistically integrate locomotor activity into freezing analyses. Here, we address this gap using a large-scale dataset of >10,000 mice across >160 comparisons, including genetic mutations, pharmacological interventions and aging, tested in 15 standardized behavioral paradigms. Conventional freezing scores covaried strongly with general locomotor activity, obscuring memory-related phenotypes. Multiple factor analysis identified two principal behavioral dimensions, locomotor activity and learning/memory: conventional freezing aligned with the locomotor dimension, whereas freezing subtraction and the activity suppression ratio mapped onto the memory dimension and improved detection of synaptic plasticity phenotypes. These analyses show that baseline locomotor normalization is essential for interpreting fear conditioning as a memory assay and provide an open framework for selecting and reporting locomotor-normalized metrics.

neuroscience↗

bioRxiv2024

ER-mitochondria distance is a critical parameter for efficient mitochondrial Ca2+ uptake and oxidative metabolism.

IP3 receptor (IP3R)-mediated Ca2+ transfer at the mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) drives mitochondrial Ca2+ uptake and oxidative metabolism and is linked to different pathologies, including Parkinsons disease (PD). The dependence of Ca2+ transfer efficiency on the ER-mitochondria distance remains unexplored. Employing molecular rulers that stabilize ER-mitochondrial distances at 5 nm resolution, and using genetically-encoded Ca2+ indicators targeting the ER lumen and the sub-mitochondrial compartments, we now show that a distance of [~]20 nm is optimal for Ca2+ transfer and mitochondrial oxidative metabolism due to enrichment of IP3R at MERCS. In human iPSC-derived astrocytes from PD patients, 20 nm MERCS were specifically reduced which correlated with a reduction of mitochondrial Ca2+ uptake. Our work determines with precision the optimal distance for Ca2+ flux between ER and mitochondria and suggests a new paradigm for fine control over mitochondrial function.

cell biology↗

bioRxiv2024

Epilepsy protein myoclonin1 interacts with inositol 1,4,5-trisphosphate (IP3) receptor and reduces Ca2+ store in endoplasmic reticulum

Mutations of EFHC1 gene have been identified in patients with epilepsies including juvenile myoclonic epilepsy (JME), and mice with Efhc1 deficiency exhibit epileptic phenotypes. Myoclonin1 protein encoded by EFHC1 is not expressed in neurons but in cells with motile cilia including those of choroid plexus and ependymal cells which form an epithelial layer lining brain ventricles. Detailed molecular basis of epilepsies caused by EFHC1 mutations, however, remain unclear. Here we report that myoclonin1 is well co-expressed with inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) at choroid plexus and ependymal cells and these two proteins bind each other. Endoplasmic reticulum (ER) of Efhc1-deficient mouse (Efhc1-/-) cells contains larger levels of calcium ions (Ca2+) than that of wild-type (WT) mice, and IP3-induced Ca2+ release (IICR) from ER is higher in Efhc1-/- cells than that of WT. Furthermore, myoclonin1 revealed to interact with PRKCSH, also known as a protein kinase C substrate 80K-H which interacts with IP3R1. Myoclonin1 further binds to IP3R2 and IP3R3. Thus, our results indicate that myoclonin1 modulates ER-Ca2+ homeostasis through interactions with IP3Rs and PRKCSH, and suggest that myoclonin1 dysfunctions cause impaired intracellular Ca2+ mobilization. Its relevance to the epileptic phenotypes of patients with EFHC1 mutations is now of interest.

physiology↗

bioRxiv2019

Reactive astrocyte-driven epileptogenesis is induced by microglia initially activated following status epilepticus

Extensive activation of glial cells during a latent period has been well documented in various animal models of epilepsy; however, it remains unknown whether such glial activation is capable of promoting epileptogenesis. Here, we show that temporally distinct activation profiles of microglia and astrocytes collaboratively contribute to epileptogenesis in a drug-induced status epilepticus model. We found that reactive microglia appear first, followed by reactive astrocytes and increased susceptibility to seizures. Pharmacological intervention against microglial activation reduces astrogliosis, aberrant astrocyte Ca2+ signaling, and seizure susceptibility. Reactive astrocytes exhibit larger Ca2+ signals mediated by IP3R2, whereas deletion of this type of Ca2+ signaling reduces seizure susceptibility after status epilepticus. Together, our findings indicate that the sequential activation of glial cells constitutes a cause of epileptogenesis after status epilepticus.

neuroscience↗

bioRxiv2018

Calcium nanodomains in spindles

The role of calcium signaling in specific events of animal cell meiosis or mitosis (M-phase) is a subject of enduring controversy. Early efforts suggested that increases in intracellular free calcium ([Ca2+]i) promote spindle disassembly 1, 2 while subsequent work suggested that global [Ca2+]i increases trigger nuclear envelope breakdown, spindle assembly, the metaphase-anaphase transition, and cytokinesis 3-6. However, further studies led to the conclusion that elevation of [Ca2+]i either has no role in these events, plays a permissive role in these events, or functions as an auxiliary signaling pathway that supplements other mechanisms 7. One potential explanation of the controversy is that specific M-phase events might depend on highly localized increases in [Ca2+]i, variously referred to as microdomains 8 or nanodomains 9, as proposed recently 10. Such domains are hypothesized to arise from rapid shuttling of calcium between closely positioned sources and sinks, rendering them potentially difficult to detect with traditional dyes and largely insensitive to slow chelators such as EGTA 9. Here a novel microtubule-binding calcium sensor--TubeCamp--was used to test the hypothesis 10 that spindles are associated with calcium nanodomains. TubeCamp imaging revealed that spindles in Xenopus eggs, Xenopus embryos, and HeLa cells were all associated with calcium nanodomains at the spindle poles. Calcium nanodomains also formed in spindles assembled in cell extracts and at the center of monopolar spindles, suggesting that they are a basic feature of spindle self-assembly. Disruption of calcium nanodomains via perturbation of inositol-1,4,5-trisphosphate signaling or rapid chelation of [Ca2+]i resulted in spindle disassembly in vivo and vitro. The results demonstrate the existence of spindle-associated calcium nanodomains and indicate that such domains are an essential and common feature of spindles in vertebrates.

cell biology↗