大野 伸彦

Structural observations are essential for the advancement of life science. Volume electron microscopy has recently realized remarkable progress in the three-dimensional analyses of biological specimens for elucidating complex ultrastructures in several fields of life science. The advancements in volume electron microscopy technologies have led to improvements, including higher resolution, more stability, and the ability to handle larger volumes. Although human applications of volume electron microscopy remain limited, the reported applications in various organs have already provided previously unrecognized features of human tissues and also novel insights of human diseases. Simultaneously, the application of volume electron microscopy to human studies faces challenges, including ethical and clinical hurdles, costs of data storage and analysis, and efficient and automated imaging methods for larger volume. Solutions including the use of residual clinical specimens and data analysis based on artificial intelligence would address those issues and establish the role of volume electron microscopy in human structural research. Future advancements in volume electron microscopy are anticipated to lead to transformative discoveries in basic research and clinical practice, deepening our understanding of human health and diseases for better diagnostic and therapeutic strategies.

Multiple sclerosis, neuromyelitis optica, Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are representative demyelinating diseases of the central and peripheral nervous system. Remyelination by myelin forming cells is important for functional recovery from the neurological deficits caused in the demyelinating diseases. Lysophosphatidylcholine-induced demyelination in mice is commonly used to identify and study the molecular pathways of demyelination and remyelination. However, detection of focally demyelinated lesions is difficult and usually requires sectioning of demyelinated lesions in tissues for microscopic analysis. In this review, we describe the development and application of a novel vital staining method for labeling demyelinated lesions using intraperitoneal injection of neutral red (NR) dye. NR labeling reduces the time and effort required to search for demyelinated lesions in tissues, and facilitates electron microscopic analysis of myelin structures. NR labeling also has the potential to contribute to the elucidation of pathologies in the central and peripheral nervous system and assist with identification of drug candidates that promote remyelination.

Myelin is an insulator that forms around axons that enhance the conduction velocity of nerve fibers. Oligodendrocytes dramatically change cell morphology to produce myelin throughout the central nervous system (CNS). Cytoskeletal alterations are critical for the morphogenesis of oligodendrocytes, and actin is involved in cell differentiation and myelin wrapping via polymerization and depolymerization, respectively. Various protein members of the myosin superfamily are known to be major binding partners of actin filaments and have been intensively researched because of their involvement in various cellular functions, including differentiation, cell movement, membrane trafficking, organelle transport, signal transduction, and morphogenesis. Some members of the myosin superfamily have been found to play important roles in the differentiation of oligodendrocytes and in CNS myelination. Interestingly, each member of the myosin superfamily expressed in oligodendrocyte lineage cells also shows specific spatial and temporal expression patterns and different distributions. In this review, we summarize previous findings related to the myosin superfamily and discuss how these molecules contribute to myelin formation and regeneration by oligodendrocytes.

The brain networks responsible for adaptive behavioral changes are based on the physical connections between neurons. Light and electron microscopy have long been used to study neural projections and the physical connections between neurons. Volume electron microscopy has recently expanded its scale of analysis due to methodological advances, resulting in complete wiring maps of neurites in a large volume of brain tissues and even entire nervous systems in a growing number of species. However, structural approaches frequently suffer from inherent limitations in which elements in images are identified solely by morphological criteria. Recently, an increasing number of tools and technologies have been developed to characterize cells and cellular components in the context of molecules and gene expression. These advancements include newly developed probes for visualization in electron microscopic images as well as correlative integration methods for the same elements across multiple microscopic modalities. Such approaches advance our understanding of interactions between specific neurons and circuits and may help to elucidate novel aspects of the basal ganglia network involving dopamine neurons. These advancements are expected to reveal mechanisms for processing adaptive changes in specific neural circuits that modulate brain functions.

In the injured brain, new neurons produced from endogenous neural stem cells form chains and migrate to injured areas and contribute to the regeneration of lost neurons. However, this endogenous regenerative capacity of the brain has not yet been leveraged for the treatment of brain injury. Here, we show that in healthy brain chains of migrating new neurons maintain unexpectedly large non-adherent areas between neighboring cells, allowing for efficient migration. In instances of brain injury, neuraminidase reduces polysialic acid levels, which negatively regulates adhesion, leading to increased cell-cell adhesion and reduced migration efficiency. The administration of zanamivir, a neuraminidase inhibitor used for influenza treatment, promotes neuronal migration toward damaged regions, fosters neuronal regeneration, and facilitates functional recovery. Together, these findings shed light on a new mechanism governing efficient neuronal migration in the adult brain under physiological conditions, pinpoint the disruption of this mechanism during brain injury, and propose a promising therapeutic avenue for brain injury through drug repositioning.

We previously clarified the histological characteristics of macrophages in the rat small intestine using serial block-face scanning electron microscopy (SBF-SEM). However, the regional differences in the characteristics of macrophages throughout the large intestine remain unknown. Here, we performed a pilot study to explore the regional differences in the ultrastructure of mucosal macrophages in the large intestine by using SBF-SEM analysis. SBF-SEM analysis conducted on the luminal side of the cecum and descending colon revealed macrophages as amorphous cells possessing abundant lysosomes and vacuoles. Macrophages in the cecum exhibited a higher abundance of lysosomes and a lower abundance of vacuoles than those in the descending colon. Macrophages with many intraepithelial cellular processes were observed beneath the intestinal superficial epithelium in the descending colon. Moreover, macrophages in contact with nerve fibers were more prevalent in the cecum than in the descending colon, and a subset of them surrounded a nerve bundle only in the cecum. In conclusion, the present pilot study suggested that the quantity of some organelles (lysosomes and vacuoles) in macrophages differed between the cecum and the descending colon and that there were some region-specific subsets of macrophages like nerve-associated macrophages in the cecum.

Abstract Axonal growth cones mediate axonal guidance and growth regulation. We show that migrating neurons in mice possess a growth cone at the tip of their leading process, similar to that of axons, in terms of the cytoskeletal dynamics and functional responsivity through protein tyrosine phosphatase receptor type sigma (PTPσ). Migrating-neuron growth cones respond to chondroitin sulfate (CS) through PTPσ and collapse, which leads to inhibition of neuronal migration. In the presence of CS, the growth cones can revert to their extended morphology when their leading filopodia interact with heparan sulfate (HS), thus re-enabling neuronal migration. Implantation of an HS-containing biomaterial in the CS-rich injured cortex promotes the extension of the growth cone and improve the migration and regeneration of neurons, thereby enabling functional recovery. Thus, the growth cone of migrating neurons is responsive to extracellular environments and acts as a primary regulator of neuronal migration.

Although the role of aerobic glycolysis in activated T cells has been well characterized, whether and how fatty acids (FAs) contribute to donor T cell function in allogeneic hematopoietic stem cell transplantation is unclear. Using xenogeneic graft-versus-host disease (GVHD) models, this study demonstrated that exogenous FAs serve as a crucial source of mitochondrial respiration in donor T cells in humans. By comparing human T cells isolated from wild-type NOD/Shi-scid-IL2rγnull (NOG) mice with those from MHC class I/II-deficient NOG mice, we found that donor T cells increased extracellular FA uptake, the extent of which correlates with their proliferation, and continued to increase FA uptake during effector differentiation. Gene expression analysis showed the upregulation of a wide range of lipid metabolism-related genes, including lipid hydrolysis, mitochondrial FA transport, and FA oxidation. Extracellular flux analysis demonstrated that mitochondrial FA transport was required to fully achieve the mitochondrial maximal respiration rate and spare respiratory capacity, whereas the substantial disruption of glucose supply by either glucose deprivation or mitochondrial pyruvate transport blockade did not impair oxidative phosphorylation. Taken together, FA-driven mitochondrial respiration is a hallmark that differentiates TCR-dependent T cell activation from TCR-independent immune response after hematopoietic stem cell transplant.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system, characterized by remyelination failure and axonal dysfunction. Remyelination by oligodendrocytes is critical for improvement of neurological deficits associated with demyelination. Rodent models of demyelination are frequently used to develop and evaluate therapies for MS. However, a suitable mouse model for assessing remyelination-associated recovery of motor functions is currently unavailable. In this review, we describe the development of the mouse model of internal capsule (IC) demyelination by focal injection of lysolecithin into brain and its application in the evaluation of drugs for demyelinating diseases. This mouse model exhibits motor deficits and subsequent functional recovery accompanying IC remyelination. Notably, this model shows enhancement of functional recovery as well as tissue regeneration when treated with clemastine, a drug that promotes remyelination. The IC demyelination mouse model should contribute to the development of novel drugs that promote remyelination and ameliorate neurological deficits in demyelinating diseases.

The cranial muscle is a critical component in the vertebrate head for a predatory lifestyle. However, its evolutionary origin and possible segmental nature during embryogenesis have been controversial. In jawed vertebrates, the presence of pre-otic segments similar to trunk somites has been claimed based on developmental observations. However, evaluating such arguments has been hampered by the paucity of research on jawless vertebrates. Here, we discovered different cellular arrangements in the head mesoderm in lamprey embryos (Lethenteron camtschaticum) using serial block-face scanning electron and laser scanning microscopies. These cell populations were morphologically and molecularly different from somites. Furthermore, genetic comparison among deuterostomes revealed that mesodermal gene expression domains were segregated antero-posteriorly in vertebrates, whereas such segregation was not recognized in invertebrate deuterostome embryos. These findings indicate that the vertebrate head mesoderm evolved from the anteroposterior repatterning of an ancient mesoderm and developmentally diversified before the split of jawless and jawed vertebrates.

Dendritic outgrowth in immature neurons is enhanced by neuronal activity and is considered one of the mechanisms of neural circuit optimization. It is known that calcium signals affect transcriptional regulation and cytoskeletal remodeling necessary for dendritic outgrowth. Here we demonstrate that activity-dependent calcium signaling also controls mitochondrial homeostasis via AMP-activated protein kinase (AMPK) in growing dendrites of differentiating hippocampal neurons. We found that the inhibition of neuronal activity induces dendritic hypotrophy with abnormally elongated mitochondria. In growing dendrites, AMPK is activated by neuronal activity and dynamically oscillates in synchrony with calcium spikes, and this AMPK oscillation is inhibited by CaMKK2 knockdown. AMPK activation leads to phosphorylation of MFF and ULK1, which initiate mitochondrial fission and mitophagy, respectively. Dendritic mitochondria in AMPK-depleted neurons exhibit impaired fission and mitophagy and display multiple signs of dysfunction. Genetic inhibition of fission leads to dendritic hypoplasia reminiscent of AMPK deficient neurons. Thus, AMPK activity is finely tuned by the calcium-CaMKK2 pathway and regulates mitochondrial homeostasis by facilitating removal of damaged components of mitochondria in growing neurons during normal brain development.

Dyskinesia is involuntary movement caused by long-term medication with dopamine-related agents: the dopamine agonist 3,4-dihydroxy-L-phenylalanine (L-DOPA) to treat Parkinson's disease (L-DOPA-induced dyskinesia [LID]) or dopamine antagonists to treat schizophrenia (tardive dyskinesia [TD]). However, it remains unknown why distinct types of medications for distinct neuropsychiatric disorders induce similar involuntary movements. Here, we search for a shared structural footprint using magnetic resonance imaging-based macroscopic screening and super-resolution microscopy-based microscopic identification. We identify the enlarged axon terminals of striatal medium spiny neurons in LID and TD model mice. Striatal overexpression of the vesicular gamma-aminobutyric acid transporter (VGAT) is necessary and sufficient for modeling these structural changes; VGAT levels gate the functional and behavioral alterations in dyskinesia models. Our findings indicate that lowered type 2 dopamine receptor signaling with repetitive dopamine fluctuations is a common cause of VGAT overexpression and late-onset dyskinesia formation and that reducing dopamine fluctuation rescues dyskinesia pathology via VGAT downregulation.

The present study aimed to histologically clarify the regional specificity of the mucosal enteric glial cells (mEGCs) in the rat intestine with serial block-face scanning electron microscopy (SBF-SEM). SBF-SEM analysis with the ileum, the cecum and the descending colon revealed that mEGC nuclei were more abundant in the data stacks from the apical portion of the villus and the lateral portion of the crypt of the ileum. mEGCs exhibited a high rate of coverage over the nerve bundle around the lateral portion of the ileal crypt, but showed an extremely low level of coverage in the luminal portion of the cecum. These findings evidenced regional differences in the localization of mEGCs and in their sheath structure in the rat intestine.

BACKGROUND AND AIMS: During an analysis of plant male meiocytes coming from destroyed meiocyte columns - united multicellular structures formed by male meiocytes in each anther locule - a considerable amount of information becomes unavailable. Therefore, in this study, intact meiocyte columns were studied by volume microscopy in wild-type rye for the most relevant presentation of 3D structure of rye meiocytes throughout meiosis. METHODS: We used two types of volume light microscopy: confocal laser scanning microscopy and non-confocal brightfield scanning microscopy combined with alcohol and aldehyde fixation as well as serial block-face scanning electron microscopy. KEY RESULTS: Unusual structures called nuclear protuberances were detected. At certain meiotic stages, nuclei formed protuberances that crossed the cell wall through intercellular channels and extended into the cytoplasm of neighbouring cells, while all other aspects of cell structure appeared to be normal. This phenomenon of intercellular nuclear migration (INM) was detected in most meiocytes at leptotene/zygotene. No cases of micronuclei formation or appearance of binucleated meiocytes were noticed. There were instances of direct contact between two nuclei during INM. No influence of fixation or of mechanical impact on the induction of INM was detected. CONCLUSIONS: INM in rye may be a programmed process (a normal part of rye male meiosis) or a tricky artefact that cannot be avoided in any way no matter which approach to meiocyte imaging is used. In both cases, INM seems to be an obligatory phenomenon that has previously been hidden by limitations of common microscopic techniques and by two-dimensional perception of plant male meiocytes. INM cannot be ignored in any studies involving manipulations of rye anthers.

Nuclear morphology of carcinoma cells is critical for the pathological diagnosis of papillary thyroid carcinoma (PTC). However, three-dimensional architecture of PTC nuclei is still elusive. In this study, we analyzed the three-dimensional ultrastructure of PTC nuclei using serial block-face scanning electron microscopy which takes advantage of the high-throughput acquisition of serial electron microscopic images and three-dimensional reconstruction of subcellular structures. En bloc-stained and resin-embedded specimens were prepared from surgically removed PTCs and normal thyroid tissues. We acquired two-dimensional images from serial block-face scanning electron microscopy and reconstructed three-dimensional nuclear structures. Quantitative comparisons showed that the nuclei of carcinoma cells were larger and more complex than those of normal follicular cells. The three-dimensional reconstruction of carcinoma nuclei divided intranuclear cytoplasmic inclusions into "open intranuclear cytoplasmic inclusions" connecting to cytoplasm outside the nucleus and "closed intranuclear cytoplasmic inclusions" without that connection. Cytoplasm with abundant organelles was observed in open inclusions, but closed inclusions contained fewer organelles with or without degeneration. Granules with a dense core were only observed in closed inclusions. Our observations suggested that open inclusions originate from nuclear invaginations, and disconnection from cytoplasm leads to closed inclusions.

Cross-modal plasticity is the repurposing of brain regions associated with deprived sensory inputs to improve the capacity of other sensory modalities. The functional mechanisms of cross-modal plasticity can indicate how the brain recovers from various forms of injury and how different sensory modalities are integrated. Here, we demonstrate that rewiring of the microglia-mediated local circuit synapse is crucial for cross-modal plasticity induced by visual deprivation (monocular deprivation [MD]). MD relieves the usual inhibition of functional connectivity between the somatosensory cortex and secondary lateral visual cortex (V2L). This results in enhanced excitatory responses in V2L neurons during whisker stimulation and a greater capacity for vibrissae sensory discrimination. The enhanced cross-modal response is mediated by selective removal of inhibitory synapse terminals on pyramidal neurons by the microglia in the V2L via matrix metalloproteinase 9 signaling. Our results provide insights into how cortical circuits integrate different inputs to functionally compensate for neuronal damage.

Cerebrospinal fluid-contacting neurons (CSF-cNs) are enigmatic mechano- or chemosensory cells lying along the central canal of the spinal cord. Recent studies in zebrafish larvae and lampreys have shown that CSF-cNs control postures and movements via spinal connections. However, the structures, connectivity, and functions in mammals remain largely unknown. Here we developed a method to genetically target mouse CSF-cNs that highlighted structural connections and functions. We first found that intracerebroventricular injection of adeno-associated virus with a neuron-specific promoter and Pkd2l1-Cre mice specifically labeled CSF-cNs. Single-cell labeling of 71 CSF-cNs revealed rostral axon extensions of over 1800 μm in unmyelinated bundles in the ventral funiculus and terminated on CSF-cNs to form a recurrent circuitry, which was further determined by serial electron microscopy and electrophysiology. CSF-cNs were also found to connect with axial motor neurons and premotor interneurons around the central canal and within the axon bundles. Chemogenetic CSF-cNs inactivation reduced speed and step frequency during treadmill locomotion. Our data revealed the basic structures and connections of mouse CSF-cNs to control spinal motor circuits for proper locomotion. The versatile methods developed in this study will contribute to further understanding of CSF-cN functions in mammals.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system characterized by remyelination failure, axonal degeneration, and progressive worsening of motor functions. Animal models of demyelination are frequently used to develop and evaluate therapies for MS. We recently reported that focal internal capsule (IC) demyelination in mice with lysophosphatidylcholine injection induced acute motor deficits followed by recovery through remyelination. However, it remains unknown whether the IC demyelination mouse model can be used to evaluate changes in motor functions caused by pharmacological treatments that promote remyelination using behavioral testing and histological analysis. In this study, we examined the effect of clemastine, an anti-muscarinic drug that promotes remyelination, in the mouse IC demyelination model. Clemastine administration improved motor function and changed forepaw preference in the IC demyelinated mice. Moreover, clemastine-treated mice showed increased mature oligodendrocyte density, reduced axonal injury, an increased number of myelinated axons and thicker myelin in the IC lesions compared with control (PBS-treated) mice. These results suggest that the lysophosphatidylcholine-induced IC demyelination model is useful for evaluating changes in motor functions following pharmacological treatments that promote remyelination.

Calcium phosphate forms particles under excessive urinary excretion of phosphate in the kidney. While the formation of calcium phosphate particles (CaPs) has been implicated in the damage to renal tubular cells and renal dysfunction, clarifying the ultrastructural information and the elemental composition of the small CaPs in the wide areas of kidney tissue has been technically difficult. This study introduces correlative and sequential light as well as electron microscopic CaP observation in the kidney tissue by combining fluorescent staining for CaPs and energy-dispersive X-ray spectroscopy (EDS) in scanning electron microscopy (SEM) on resin sections prepared using high-pressure freezing and freeze substitution. CaPs formed in mouse kidneys under long-term feeding of a high-phosphate diet were clearly visualized on resin sections by fluorescence-conjugated alendronate derivatives and toluidine blue metachromasia. These CaPs were verified by correlative observation with EDS. Furthermore, small CaPs formed in the kidney under short-term feeding were detected using fluorescent probes. The elemental composition of the particles, including calcium and magnesium, was identified following EDS analyses. These results suggest that the correlative microscopy approach is helpful for observing in situ distribution and elemental composition of CaPs in the kidney and contributing to studies regarding CaP formation-associated pathophysiology.

Recent advances of volume electron microscopy (volume EM) have been driving our thorough understanding of the brain architecture. Volume EM becomes increasingly powerful when cells and their subcellular structures that are imaged in light microscopy are correlated to those in ultramicrographs obtained with EM. This correlative approach, called correlative light and volume electron microscopy (vCLEM), is used to link three-dimensional ultrastructural information with physiological data such as intracellular Ca2+ dynamics. Genetic tools to express fluorescent proteins and/or an engineered form of a soybean ascorbate peroxidase (APEX) allow us to perform vCLEM using natural landmarks including blood vessels without immunohistochemical staining. This immunostaining-free vCLEM has been successfully employed in two-photon Ca2+ imaging in vivo as well as in studying complex synaptic connections in thalamic neurons that receive variety of specialised inputs from the cerebral cortex. In this mini-review, we overview how volume EM and vCLEM have contributed to studying developmental processes of the brain. We also discuss potential applications of genetic manipulation of target cells using clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (Cas9) and subsequent volume EM to analysis of protein localisation as well as to loss of function studies of genes regulating brain development. We give examples for the combinatorial usage of genetic tools with vCLEM that will further enhance our understanding of regulatory mechanisms underlying brain development.

A long-term high-fat diet (HFD) causes obesity and changes in renal lipid metabolism and lysosomal dysfunction in mice, causing renal damage. Sodium-glucose co-transporter inhibitors, including phlorizin, exert nephroprotective effects in patients with chronic kidney disease, but the underlying mechanism remains unclear. A HFD or standard diet was fed to adult C57BL/6J male mice, and phlorizin was administered. Lamellar body components of the proximal tubular epithelial cells (PTECs) were investigated. After phlorizin administration in HFD-fed mice, sphingomyelin and ceramide in urine and tissues were assessed and label-free quantitative proteomics was performed using kidney tissue samples. Mitochondrial elongation by fusion was effective in the PTECs of HFD-fed obese mice under phlorizin administration, and many lamellar bodies were found in the apical portion of the S2 segment of the proximal tubule. Phlorizin functioned as a diuretic, releasing lamellar bodies from the apical membrane of PTECs and clearing the obstruction in nephrons. The main component of the lamellar bodies was sphingomyelin. On the first day of phlorizin administration in HFD-fed obese mice, the diuretic effect was increased, and more sphingomyelin was excreted through urine than in vehicle-treated mice. The expressions of three peroxisomal β-oxidation proteins involved in fatty acid metabolism were downregulated after phlorizin administration in the kidneys of HFD-fed mice. Fatty acid elongation protein levels increased with phlorizin administration, indicating an increase in long-chain fatty acids. Lamellar bodies accumulated in the proximal renal tubule of the S2 segment of the HFD-fed mice, indicating that the urinary excretion of lamellar bodies has nephroprotective effects.

Our previous studies and others have revealed detailed characteristics of the mucosal nerve network in the small intestine, but much remains unknown about the corresponding network in the large intestine. We herein investigated regional differences in the expression of neurochemical markers, the nerve network structure, and the cells in contact with nerve fibers by histological analysis using both immunohistochemistry and serial block-face scanning electron microscopy (SBF-SEM). Immunohistochemistry revealed that immunopositive structures for protein gene product 9.5, vasoactive intestinal peptide (VIP), calretinin and vesicular acetylcholine transporter were more prevalent in the lamina propria of the ascending colon than the cecum and descending colon (DC). There was no significant difference in the frequency of most neurochemical markers between the cecum and DC, but the frequencies of VIP+ structures were higher in the cecum than in the DC. SBF-SEM analysis showed that the nerve network structure was more developed on the luminal side of the DC than the cecum. The cells that nerve fibers abundantly contacted were subepithelial and lamina propria fibroblast-like cells and macrophages. In addition, nerve fibers in the cecum were in more frequent contact with immune cells such as macrophages and plasma cells than nerve fibers in the DC. Thus, the present histological analysis suggested that the mucosal nerve network in the large intestine possessed both regional universality and various specificities, and revealed the intimate relationship between the nerve network and immune cells, especially in the cecum.

CCCTC-binding factor (CTCF) has a key role in higher-order chromatin architecture that is important for establishing and maintaining cell identity by controlling gene expression. In the mature cerebellum, CTCF is highly expressed in Purkinje cells (PCs) as compared with other cerebellar neurons. The cerebellum plays an important role in motor function by regulating PCs, which are the sole output neurons, and defects in PCs cause motor dysfunction. However, the role of CTCF in PCs has not yet been explored. Here we found that the absence of CTCF in mouse PCs led to progressive motor dysfunction and abnormal dendritic morphology in those cells, which included dendritic self-avoidance defects and a proximal shift in the climbing fibre innervation territory on PC dendrites. Furthermore, we found the peculiar lamellar structures known as "giant lamellar bodies" (GLBs), which have been reported in PCs of patients with Werdnig-Hoffman disease, 13q deletion syndrome, and Krabbe disease. GLBs are localized to PC dendrites and are assumed to be associated with neurodegeneration. They have been noted, however, only in case reports following autopsy, and reports of their existence have been very limited. Here we show that GLBs were reproducibly formed in PC dendrites of a mouse model in which CTCF was deleted. GLBs were not noted in PC dendrites at infancy but instead developed over time. In conjunction with GLB development in PC dendrites, the endoplasmic reticulum was almost absent around the nuclei, the mitochondria were markedly swollen and their cristae had decreased drastically, and almost all PCs eventually disappeared as severe motor deficits manifested. Our results revealed the important role of CTCF during normal development and in maintaining PCs and provide new insights into the molecular mechanism of GLB formation during neurodegenerative disease.

Astrocyte abnormalities have received great attention for their association with various diseases in the brain but not so much in the eye. Recent independent genome-wide association studies of glaucoma, optic neuropathy characterized by retinal ganglion cell (RGC) degeneration, and vision loss found that single-nucleotide polymorphisms near the ABCA1 locus were common risk factors. Here, we show that Abca1 loss in retinal astrocytes causes glaucoma-like optic neuropathy in aged mice. ABCA1 was highly expressed in retinal astrocytes in mice. Thus, we generated macroglia-specific Abca1-deficient mice (Glia-KO) and found that aged Glia-KO mice had RGC degeneration and ocular dysfunction without affected intraocular pressure, a conventional risk factor for glaucoma. Single-cell RNA sequencing revealed that Abca1 deficiency in aged Glia-KO mice caused astrocyte-triggered inflammation and increased the susceptibility of certain RGC clusters to excitotoxicity. Together, astrocytes play a pivotal role in eye diseases, and loss of ABCA1 in astrocytes causes glaucoma-like neuropathy.

Synaptic pruning is a fundamental process of neuronal circuit refinement in learning and memory. Accumulating evidence suggests that glia participates in sculpting the neuronal circuits through synapse engulfment. However, whether glial involvement in synaptic pruning has a role in memory formation remains elusive. Using newly developed phagocytosis reporter mice and three-dimensional ultrastructural characterization, we found that synaptic engulfment by cerebellar Bergmann glia (BG) frequently occurred upon cerebellum-dependent motor learning in mice. We observed increases in pre- and postsynaptic nibbling by BG along with a reduction in spine volume after learning. Pharmacological blockade of engulfment with Annexin V inhibited both the spine volume reduction and overnight improvement of motor adaptation. These results indicate that BG contribute to the refinement of the mature cerebellar cortical circuit through synaptic engulfment during motor learning.

INTRODUCTION: Improved long-term patency of the no-touch (NT) saphenous vein graft has been reported to result from the preservation of a healthy vascular microstructure, especially endothelial cells. However, the precise morphology of endothelial cells and their organelles in NT saphenous vein graft has not been fully investigated. In this study, we assessed the ultrastructure of preserved endothelial cells in saphenous vein graft using transmission electron microscopy. METHODS: Intact control (IC) vein, NT saphenous vein graft, and conventional (CT) saphenous vein graft were harvested from a patient. After observation by light microscopy, the nuclei and mitochondria in the preserved endothelial cells were compared among IC, NT, and CT using transmission electron microscopy, and the endothelial organelles were assessed quantitatively. RESULTS: Light microscopy showed that the preservation of endothelial cells was comparable in IC, NT, and CT. Subsequent transmission electron microscopy observation showed that the nuclei in preserved endothelial cells appeared more swollen in CT than that in NT. Quantitative analysis revealed that nuclear size and circularity of preserved endothelial cells in NT and IC were similar, but those in CT were larger and higher, respectively, than those in IC and NT. In addition, the mitochondrial size in preserved endothelial cells in CT was larger than that in IC and NT. CONCLUSION: Necrotic changes in endothelial organelles characterized by swelling of nuclei and mitochondria were prominent in CT saphenous vein graft. The normally maintained ultrastructure of preserved endothelial cells in NT saphenous vein graft could contribute to long-term patency.

Our previous studies using immunohistochemistry and serial block-face scanning electron microscopy (SBF-SEM) clarified that fibroblast-like cells (FBLCs) in the rat ileal mucosa are classifiable into several subtypes, but their characteristics throughout the large intestine remain unknown. In this study, we investigated the region-specific characteristics of FBLCs in the rat large intestine using histological analysis including SBF-SEM. Immunohistochemistry revealed that CD34+CD31- FBLCs were localized in the lamina propria beneath the crypt bases throughout the large intestine and were more abundant in the descending colon than in the other regions. In addition, platelet-derived growth factor receptor α (PDGFRα)+ FBLCs were ubiquitously present just below the epithelium throughout the large intestine, and those at the crypt base were slightly more abundant in the descending colon than in the other regions. SBF-SEM analysis revealed that there were two types of FBLCs around the crypt base in both the cecum and the descending colon: sub-epithelial FBLCs localizing just beneath the epithelium in the manner of PDGFRα+ FBLCs, and lamina propria FBLCs localizing farther away from the epithelium than sub-epithelial FBLCs in the manner of CD34+CD31- FBLCs. The lamina propria FBLCs were closely apposed to various immune cells in the lamina propria, and their endoplasmic reticulum in the descending colon exhibited various dilatation levels, unlike that in the cecum. These findings indicate that FBLCs, especially around the crypt base, differed in each region of the large intestine with respect to localization, abundance, and ultrastructure, which could lead to the region-specific microenvironment around the crypt base.

An appropriate sensory experience during the early developmental period is important for brain maturation. Dark rearing during the visual critical period delays the maturation of neuronal circuits in the visual cortex. Although the formation and structural plasticity of the myelin sheaths on retinal ganglion cell axons modulate the visual function, the effects of dark rearing during the visual critical period on the structure of the retinal ganglion cell axons and their myelin sheaths are still unclear. To address this question, mice were reared in a dark box during the visual critical period and then normally reared to adulthood. We found that myelin sheaths on the retinal ganglion cell axons of dark-reared mice were thicker than those of normally reared mice in both the optic chiasm and optic nerve. Furthermore, whole-mount immunostaining with fluorescent axonal labeling and tissue clearing revealed that the myelin internodal length in dark-reared mice was shorter than that in normally reared mice in both the optic chiasm and optic nerve. These findings demonstrate that dark rearing during the visual critical period affects the morphology of myelin sheaths, shortens and thickens myelin sheaths in the visual pathway, despite the mice being reared in normal light/dark conditions after the dark rearing.

Diabetic peripheral neuropathy (DPN) includes symptoms of thermosensory impairment, which are reported to involve changes in the expression or function, or both, of nociceptive TRPV1 and TRPA1 channels in rodents. In the present study, we did not find changes in the expression or function of TRPV1 or TRPA1 in DPN mice caused by STZ, although thermal hypoalgesia was observed in a murine model of DPN or TRPV1-/- mice with a Plantar test, which specifically detects temperature avoidance. With a Thermal Gradient Ring in which mice can move freely in a temperature gradient, temperature preference can be analyzed, and we clearly discriminated the temperature-dependent phenotype between DPN and TRPV1-/- mice. Accordingly, we propose approaches with multiple behavioral methods to analyze the progression of DPN by response to thermal stimuli. Attention to both thermal avoidance and preference may provide insight into the symptoms of DPN.

The Golgi apparatus, which plays a role in various biosynthetic pathways, is usually identified in electron microscopy by the morphological criteria of lamellae. A 3-dimensional analyses with SBF-SEM, a volume-SEM proficient in obtaining large volumes of data at the whole-cell level, could be a promising technique for understanding the precise distribution and complex ultrastructure of Golgi apparatus, although optimal methods for such analyses remain unclear since the observation can be hampered with sample charging and low image contrast, and manual segmentation often requires significant manpower. The present study attempted the whole-cell observation and semi-automatic classification and segmentation of the Golgi apparatus in rat hepatocytes for the first time by SBF-SEM via ZIO staining, a classical osmium impregnation. The staining electron-densely visualized individual Golgi lamellae and their ultrastructure could stably be observed without any noticeable charging. The simple thresholding of the serial images enabled the efficient reconstruction of the labeled Golgi apparatus, which revealed plural Golgi apparatus in one hepatocyte. The combination of the heavy metal-based histochemistry of ZIO staining and SBF-SEM was useful in the 3-dimensional observation of the Golgi apparatus at the whole-cell level because of two technical advantages: 1) visualization of the Golgi apparatus without any heavy metal staining and efficient acquisition of the block-face images without additional conductive staining or any devices for eliminating charging; 2) easy identification of the staining and hassle-free, semi-automatic classification and segmentation by simple thresholding of the images. This novel approach could elucidate the topographic characteristics of the Golgi apparatus in hepatocytes.

New neurons, continuously added in the adult olfactory bulb (OB) and hippocampus, are involved in information processing in neural circuits. Here, we show that synaptic pruning of adult-born neurons by microglia depends on phosphatidylserine (PS), whose exposure on dendritic spines is inversely correlated with their input activity. To study the role of PS in spine pruning by microglia in vivo, we developed an inducible transgenic mouse line, in which the exposed PS is masked by a dominant-negative form of milk fat globule-EGF-factor 8 (MFG-E8), MFG-E8D89E. In this transgenic mouse, the spine pruning of adult-born neurons by microglia is impaired in the OB and hippocampus. Furthermore, the electrophysiological properties of these adult-born neurons are altered in MFG-E8D89E mice. These data suggest that PS is involved in the microglial spine pruning and the functional maturation of adult-born neurons. The MFG-E8D89E-based genetic approach shown in this study has broad applications for understanding the biology of PS-mediated phagocytosis in vivo.

Oligodendrocyte precursor cells (OPC) arise from restricted regions of the central nervous system (CNS) and differentiate into myelin-forming cells after migration, but their ultrastructural characteristics have not been fully elucidated. This study examined the three-dimensional ultrastructure of OPCs in comparison with other glial cells in the early postnatal optic nerve by serial block-face scanning electron microscopy. We examined 70 putative OPCs (pOPC) that were distinct from other glial cells according to established morphological criteria. The pOPCs were unipolar in shape with relatively few processes, and their Golgi apparatus were localized in the perinuclear region with a single cisterna. Astrocytes abundant in the optic nerve were distinct from pOPCs and had a greater number of processes and more complicated Golgi apparatus morphology. All pOPCs and astrocytes contained a pair of centrioles (basal bodies). Among them, 45% of pOPCs extended a short cilium, and 20% of pOPCs had centrioles accompanied by vesicles, whereas all astrocytes with basal bodies had cilia with invaginated ciliary pockets. These results suggest that the fine structures of pOPCs during the developing and immature stages may account for their distinct behavior. Additionally, the vesicular transport of the centrioles, along with a short cilium length, suggests active ciliogenesis in pOPCs.

Oligodendrocytes form multiple myelin sheaths in the central nervous system (CNS), which increase nerve conduction velocity and are necessary for basic and higher brain functions such as sensory function, motor control, and learning. Structures of the myelin sheath such as myelin internodal length and myelin thickness regulate nerve conduction. Various parts of the central nervous system exhibit different myelin structures and oligodendrocyte morphologies. Recent studies supported that oligodendrocytes are a heterogenous population of cells and myelin sheaths formed by some oligodendrocytes can be biased to particular groups of axons, and myelin structures are dynamically modulated in certain classes of neurons by specific experiences. Structures of oligodendrocyte/myelin are also affected in pathological conditions such as demyelinating and neuropsychiatric disorders. This review summarizes our understanding of heterogeneity and regulation of oligodendrocyte morphology concerning central nervous system regions, neuronal classes, experiences, diseases, and how oligodendrocytes are optimized to execute central nervous system functions.

Plasmodium falciparum gametocytes have unique morphology, metabolism, and protein expression profiles in their asexual stages of development. In addition to the striking changes in their appearance, a wide variety of "exo-membrane structures" are newly formed in the gametocyte stage. Little is known about their function, localization, or three-dimensional structural information, and only some structural data, typically two-dimensional, have been reported using conventional electron microscopy or fluorescence microscopy. For better visualization of intracellular organelle and exo-membrane structures, we previously established an unroofing technique to directly observe Maurer's clefts (MCs) in asexual parasitized erythrocytes by removing the top part of the cell's membrane followed by transmission electron microscopy. We found that MCs have numerous tethers connecting themselves to the host erythrocyte membrane skeletons. In this study, we investigated the intracellular structures of gametocytes using unroofing-TEM, Serial Block Face scanning electron microscopy, and fluorescence microscopy to unveil the exo-membrane structures in gametocytes. Our data showed "balloon/pouch"-like objects budding from the parasitophorous vacuole membrane (PVM) in gametocytes, and some balloons included multiple layers of other balloons. Furthermore, numerous bubbles appeared on the inner surface of the erythrocyte membrane or PVM; these were similar to MC-like membranes but were smaller than asexual MCs. Our study demonstrated P. falciparum reforms exo-membranes in erythrocytes to meet stage-specific biological activities during their sexual development.

Germ cells develop into eggs and sperms and represent a lineage that survives through multiple generations. Germ cell specification during embryogenesis proceeds through one of two basic modes: either the cell-autonomous mode or the inductive mode. In the cell-autonomous mode, specification of germ cell fate involves asymmetric partitioning of the specialized maternal cytoplasm, known as the germplasm. Oikopleura dioica is a larvacean (class Appendicularia) and a chordate. It is regarded as a promising animal model for studying chordate development because of its short life cycle (5 days) and small genome size (∼60 ​Mb). We show that their embryos possess germplasm, as observed in ascidians (class Ascidiacea). The vegetal cytoplasm shifted towards the future posterior pole before the first cleavage occurred. A bilateral pair of primordial germ cells (PGC, B11 ​cells) was formed at the posterior pole at the 32-cell stage through two rounds of unequal cleavage. These B11 ​cells did not undergo further division before hatching of the tadpole-shaped larvae. The centrosome-attracting body (CAB) is a subcellular structure that contains the germplasm and plays crucial roles in germ cell development in ascidians. The presence of CAB with germplasm was observed in the germline lineage cells of larvaceans via electron microscopy and using extracted embryos. The CAB appeared at the 8-cell stage and persisted until the middle stage of embryogenesis. The antigen for the phosphorylated histone 3 antibody was localized to the CAB and persisted in the PGC until hatching after the CAB disappeared. Maternal snail mRNA, which encodes a transcription factor, was co-localized with the antigen for the H3S28p antibody. Furthermore, we found a novel PGC-specific subcellular structure that we call the germ body (GB). This study thus highlights the conserved and non-conserved features of germline development between ascidians and larvaceans. The rapid development and short life cycle (five days) of O. dioica would open the way to genetically analyze germ cell development in the future.

In this study, intercellular nuclear migration (INM), also known as cytomixis, was documented in cryofixed plant meiocytes for the first time. Intact tobacco inflorescences and flower buds as well as dissected individual anthers were cryofixed in liquid nitrogen by plunge freezing. Cryosubstituted and cryosectioned male meiocytes were analyzed by light microscopy. For cryosubstitution, the frozen material was kept in acetic alcohol at - 70 °C for 1 week. For cryosectioning, the frozen material was sectioned at - 20 °C, and fixed with precooled acetic alcohol. Fixation of the intact tobacco inflorescences in Carnoy's solution was used as a control. Microscopy revealed good preservation of cell structure in the cryofixed anthers, flower buds, and inflorescences. INM was detectable in all the studied cryofixed and chemically fixed samples. The cytological picture of INM observed in the cryofixed meiocytes did not noticeably differ from the picture obtained with the chemically fixed cells. These results indicate that INM is observable irrespective of whether a physical or chemical fixation method is employed, with minimal damage from handling. Our results contradict the notion that INM is a phenomenon caused by mechanical, osmotic, or chemical artifacts during sample preparation.

Typical skeletal muscles are composed of mixed muscle fiber types, which are classified as slow-twitch (type I) and fast-twitch (type II) fibers, whereas pectoralis major muscles (PMs) in broiler chickens are 100% composed of type IIb fast-twitch fibers. Since metabolic properties differ among muscle fiber types, the combination of muscle fiber types is involved in physiological functions and pathological conditions in skeletal muscles. In this study, using serial block-face scanning electron microscopy, we compared three-dimensional (3D) mitochondrial properties in type IIb fibers in broiler PMs and those in type I fibers of broiler gastrocnemius muscles (GMs) heterogeneously composed of slow- and fast-twitch muscle fibers. In type I fibers in the GMs, elongated mitochondria with numerous interconnections to form a substantial network among myofibrils were observed. Along with lipid droplets sandwiched by mitochondria, these features are an adaptation to effective oxidative respiration and constant oxidative damage in slow-twitch muscle fibers. In contrast, type IIb fibers in the PMs showed small and ellipsoid-shaped mitochondria with few interconnections and no lipid droplets, forming a sparse network. The mitochondrial spatial network comprises of active mitochondrial dynamics to reduce mitochondrial damage; therefore, type IIb fibers possess physiologically low capacity to maintain mitochondrial wellness due to static mitochondrial dynamics. Based on 3D mitochondrial properties, we discussed the contrasting physiological functions between type I and IIb fibers and proposed a high contractile power and low stress resistance as unique physiological properties of broiler PMs.

Galanin, one of the most inducible neuropeptides, is widely present in developing brains, and its expression is altered by pathological events (such as epilepsy, ischemia and axotomy). The roles of galanin in brain development under both normal and pathological conditions have been hypothesized, but the question of how galanin is involved in fetal and early postnatal brain development remains largely unanswered. In this study, using granule cell migration in the cerebellum of early postnatal mice (both sexes) as a model system, we examined the role of galanin in neuronal cell migration during normal development and after brain injury. Here we show that during normal development, endogenous galanin participates in accelerating granule cell migration via altering the Ca2+ and cAMP signaling pathways. Upon brain injury induced by the application of cold insults, galanin levels decrease at the lesion sites, but increase in the surroundings of lesion sites. Granule cells exhibit corresponding changes in migration; (1) slowing down migration at the lesion sites, and (2) accelerating migration in the surroundings of lesion sites. Experimental manipulations of galanin signaling reduce the lesion-site specific changes in granule cell migration, indicating that galanin plays a role in such deficits in neuronal cell migration. The present study suggests that manipulating galanin signaling may be a potential therapeutic target for acutely injured brains during development.SIGNIFICANCE STATEMENT:Deficits in neuronal cell migration caused by brain injury result in abnormal development of cortical layers, but the underlying mechanisms remain to be determined. Here, we report that upon brain injury, endogenous levels of galanin, a neuropeptide, are altered in a lesion-site specific manner; decreasing at the lesion sites, but increasing in the surroundings of lesion sites. The changes in galanin levels positively correlate with the migration rate of immature neurons. Manipulations of galanin signaling ameliorate the effects of injury on neuronal migration and cortical layer development. These results shed a light on galanin as a potential therapeutic target for acutely injured brains during development.

Lysophosphatidylcholine (LPC)-induced demyelination is a versatile animal model that is frequently used to identify and examine molecular pathways of demyelination and remyelination in the central (CNS) and peripheral nervous system (PNS). However, identification of focally demyelinated lesion had been difficult and usually required tissue fixation, sectioning and histological analysis. Recently, a method for labeling and identification of demyelinated lesions in the CNS by intraperitoneal injection of neutral red (NR) dye was developed. However, it remained unknown whether NR can be used to label demyelinated lesions in PNS. In this study, we generated LPC-induced demyelination in sciatic nerve of mice, and demonstrated that the demyelinated lesions at the site of LPC injection were readily detectable at 7 days postlesion (dpl) by macroscopic observation of NR labeling. Moreover, NR staining gradually decreased from 7 to 21 dpl over the course of remyelination. Electron microscopy analysis of NR-labeled sciatic nerves at 7 dpl confirmed demyelination and myelin debris in lesions. Furthermore, fluorescence microscopy showed NR co-labeling with activated macrophages and Schwann cells in the PNS lesions. Together, NR labeling is a straightforward method that allows the macroscopic detection of demyelinated lesions in sciatic nerves after LPC injection.

BACKGROUND AND PURPOSE: Glaucoma, the leading cause of blindness, damages the retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is a high-risk factor for glaucoma, so topical hypotensive drugs are usually used for treatment. However, not all patients adequately respond to current treatments, so there is a need to identify a new molecular target to reduce IOP. This study was aimed to determine whether the P2Y1 receptors reduce IOP. EXPERIMENTAL APPROACH: P2Y1 receptor agonist was instilled on the eyes of mice, and the IOP changes were measured by a rebound-type tonometer. Expression of P2Y1 receptors was estimated by immunohistochemistry. The ocular function was measured by a multifocal electroretinogram. KEY RESULTS: Single-dose of the P2Y1 receptor agonist transiently reduced IOP. The hypotensive effect was disappeared in P2Y1 receptor-deficient (P2Y1 KO) mice. The P2Y1 receptor was functionally expressed in the ciliary body, trabecular meshwork, and Schlemm's canal. We found that P2Y1 receptor negatively regulated aquaporin 4 (AQP4) whereas positively regulated endothelial nitric oxide synthase (eNOS). P2Y1 KO mice showed chronic ocular hypertension regardless of their ages. The P2Y1 KO mice at 3 months old showed no RGC damage, whereas 12-month-old mice showed a significant loss of RGCs and impairment of ocular functions. The RGC damages were attenuated by chronic administration of an IOP-reducing agent. CONCLUSIONS AND IMPLICATIONS: P2Y1 receptor activation reduces IOP via dual pathways including AQP4 and eNOS. Dysregulated P2Y1 receptors results in glaucomatous optic neuropathy, suggesting that P2Y1 receptor might be an attractive target for the treatment of glaucoma.