Biology subjects

Murai, K. K.

Publications and source records attributed to Murai, K. K..

6 recordsLinked to original sources

bioRxiv2024

Human-specific features of cerebellar astrocytes and Purkinje cells: an anatomical comparison with mice and macaques

Little is known about the morphological diversity and distribution of cerebellar astrocytes in the human brain and how or if these features differ from those of cerebellar astrocytes in species used to model human illnesses. To address this, we performed a comparative post-mortem examination of cerebellar astrocytes and Purkinje cells (PCs) in healthy humans, macaques, and mice using microscopy-based techniques. Visualizing with canonical astrocyte markers glial fibrillary acidic protein (GFAP) and aldehyde dehydrogenase-1 family member L1 (ALDH1L1), we mapped astrocytes within a complete cerebellar hemisphere. Astrocytes were observed to be differentially distributed across the cerebellar layers, displayed overall increases in area coverages with evolution, and showed features uniquely hominoid. Stereological quantifications in 3 functionally distinct cerebellar lobules demonstrated opposing trends for the canonical astrocyte markers across species with ALDH1L1+ astrocytes increasing with evolution and GFAP+ astrocytes decreasing. PC analyses revealed that while humans have the lowest PC densities, their cell body sizes were the largest with more ALDH1L1 immunoreactive astrocytes surrounding. Notably, the cognitive lobule crus I displayed the highest ratio of Bergmann glia to PC in all species. These findings align with the growing literature for astrocyte and PC heterogeneity and suggest cerebellar astrocyte and PC divergence both within and across species, possibly indicative of a role for these cells in higher-order cerebellar processing.

neuroscience↗

bioRxiv2023

Rapid TetOn-mediated gene expression in neuronsacross the lifespan using uTTOP

Conditional expression of genes of interest is essential for interrogation of cellular development and function. Although tools exist for conditional gene expression, techniques for rapid-onset, temporally precise expression are lacking. The doxycyclineinducible TetOn expression system allows for this in numerous organ systems, however, transgenic TetOn expression cassettes become silenced in the nervous system during postnatal development. Here, we circumvent this silencing with uTTOP: in utero electroporation of Transposable TetOn Plasmids. When electroporated as transposable elements that integrate into the genome, the TetOn system allowed for robust DOX-dependent induction of expression across the postnatal lifespan of the mouse. We demonstrated induction in neurons of sensorimotor and retrospleninal cortex, hippocampus and the olfactory bulb. Latency to peak induction was [≤]12 hours, a several fold increase in induction kinetics over existing methodology for in vivo conditional expression. To demonstrate the utility of uTTOP, we induced ectopic expression of Sonic hedgehog in adult mouse layer 2/3 cortical neurons, demonstrating that its expression can diversify expression of Kir4.1 in surrounding astrocytes. The rapid induction kinetics of uTTOP allowed us to show that Kir4.1 upregulation significantly lags onset of Shh expression by [~]2 days, a difference in expression time course that is likely not resolvable with current methods. Together, these data demonstrate that uTTOP is a powerful and flexible system for conditional gene expression in multiple brain areas across the mouse lifespan.

neuroscience↗

bioRxiv2021

Organizing Principles of Astrocytic Nanoarchitecture in the Mouse Cerebral Cortex

Astrocytes have complex roles in central nervous system (CNS) health and disease. Underlying these roles is an elaborate architecture based on frequent, extremely fine, but seemingly haphazard branches, as well as prominent features including tripartite synaptic complexes and perivascular endfeet. While broad categories of structures in astrocytes are known, the fundamental building blocks that compose them and their organizing principles have yet to be adequately defined. This is largely due to the absence of high-resolution datasets that can reveal nanoscopic features of astrocytes (i.e. 10-20nm diameter in x, y, and z) and a lack of computational approaches that can effectively interrogate astrocyte shape, organization, and nanoarchitecture. Here, we produced and analyzed multiple, high-resolution datasets of layer 2/3 mouse somatosensory cortex using focused ion beam scanning electron microscopy (8nm intervals) and computer vision approaches to provide a principled, quantitative analysis of astrocytic nanoarchitecture. A decomposition of astrocytes into fundamental parts led to the discovery of unique structural components, recurring structural motifs, and assembly of parts into an organized hierarchy. New relationships were also discerned between astrocytic processes and other CNS microanatomy including mitochondria, tripartite synapses, and cerebrovasculature. By deploying computational resources to quantitatively understand the organizing principles and nanoarchitecture of astrocytes, this study reveals the specialized anatomical adaptations of these complex cells within the CNS. One Sentence SummaryUsing high-resolution serial electron microscopy datasets and computer vision, this study provides a systematic analysis of astrocytic nanoarchitecture from multiple samples of layer 2/3 of adult mouse neocortex, and presents quantitative evidence that astrocytes organize their morphology into purposeful, classifiable assemblies with unique structural and subcellular organelle adaptations related to their physiological functions.

neuroscience↗

bioRxiv2020

The McGill-Mouse-Marmoset Platform: A Standardized Approach for High-throughput Imaging of Neuronal Dynamics During Behavior

Understanding the rules that govern neuronal dynamics throughout the brain to subserve behavior and cognition remain one of the biggest challenges in neuroscience research. Recent technical advances enable the recording of increasingly larger neuronal populations to produce increasingly more sophisticated datasets. Despite bold and important open-science and data-sharing policies, these datasets tend to include unique data acquisition methods, behavior, and file structures. Discrepancies between experimental protocols present several key challenges including the analysis of the data itself, comparison of data collected between laboratories, and for the comparison of dynamics between brain regions and species. Here, we discuss our recent efforts to create a standardized and high-throughput research platform to address these issues. The McGill-Mouse-Marmoset (M3) platform combines miniscope calcium imaging recording in both mice and marmosets with standardized touchscreen-based behavioral testing. The goal is to curate an open-source and standardized framework for acquiring, analyzing, and accessing high-quality data of the neuronal dynamics that underly cognition throughout the brain in mice, marmosets, and models of disease. We end with a discussion of future developments and a call for users to adopt this standardized approach.

neuroscience↗

bioRxiv2019

Depolarizing GABA Transmission Restrains Activity-Dependent Glutamatergic Synapse Formation in the Developing Hippocampal Circuit

GABA is the main inhibitory neurotransmitter in the mature brain but has the paradoxical property of depolarizing neurons during early development. Depolarization provided by GABAA transmission during this early phase regulates neural stem cell proliferation, neural migration, neurite outgrowth, synapse formation, and circuit refinement, making GABA a key factor in neural circuit development. Importantly, depending on the context, depolarizing GABAA transmission can either drive neural activity, or inhibit it through shunting inhibition. The varying roles of depolarizing GABAA transmission during development, and its ability to both drive and inhibit neural activity, makes it a difficult developmental cue to study. This is particularly true in the later stages of development, when the majority of synapses form and GABAA transmission switches from depolarizing to hyperpolarizing. Here we addressed the importance of depolarizing but inhibitory (or shunting) GABAA transmission in glutamatergic synapse formation in hippocampal CA1 pyramidal neurons. We first showed that the developmental depolarizing-to-hyperpolarizing switch in GABAA transmission is recapitulated in organotypic hippocampal slice cultures. Based on the expression profile of K+-Cl- co-transporter 2 (KCC2) and changes in the GABA reversal potential, we pinpointed the timing of the switch from depolarizing to hyperpolarizing GABAA transmission in CA1 neurons. We found that blocking depolarizing but shunting GABAA transmission increased excitatory synapse number and strength, indicating that depolarizing GABAA transmission can restrain glutamatergic synapse formation. The increase in glutamatergic synapses was activity-dependent, but independent of BDNF signalling. Importantly, the elevated number of synapses was stable for more than a week after GABAA inhibitors were washed out. Together these findings point to the ability of immature GABAergic transmission to restrain glutamatergic synapse formation and suggest an unexpected role for depolarizing GABAA transmission in shaping excitatory connectivity during neural circuit development.

neuroscience↗

bioRxiv2018

MIC-MAC: High-throughput analysis of three-dimensional microglia morphology in mammalian brains

Microglia, the resident immune cells of the brain, exhibit complex and diverse phenotypes depending on their physiological context including brain regions and disease states. While single-cell RNA-sequencing has recently resolved this heterogeneity, it does not capture tissue and intercellular mechanisms. Our complementary imaging-based approach enables automatic 3D-morphology characterization and classification of thousands of individual microglia in situ and revealed species- and disease-specific morphological phenotypes in mouse and human brain samples.

neuroscience↗