Neuraminidase inhibition promotes the collective migration of neurons and recovery of brain function.

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.

Identification of the growth cone as a probe and driver of neuronal migration in the injured brain.

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.

Corrigendum: PlexinD1 signaling controls domain-specific dendritic development in newborn neurons in the postnatal olfactory bulb.

[This corrects the article DOI: 10.3389/fnins.2023.1143130.].

PlexinD1 signaling controls domain-specific dendritic development in newborn neurons in the postnatal olfactory bulb.

Newborn neurons show immature bipolar morphology and continue to migrate toward their destinations. After the termination of migration, newborn neurons undergo spatially controlled dendrite formation and change into a complex morphology. The mechanisms of dendritic development of newborn neurons have not been fully understood. Here, we show that in the postnatal olfactory bulb (OB), the Sema3E-PlexinD1 signaling, which maintains bipolar morphology of newborn neurons, also regulates their dendritic development after the termination of migration in a dendritic domain-specific manner. Genetic ablation of Sema3E or PlexinD1 enhanced dendritic branching in the proximal domain of the apical dendrites of OB newborn granule cells, whereas PlexinD1 overexpression suppressed it in a Rho binding domain (RBD)-dependent manner. Furthermore, RhoJ, a small GTPase that directly binds to PlexinD1RBD in vascular endothelial cells, is expressed in migrating and differentiating newborn granule cells in the OB and is also involved in the suppression of proximal branching of their apical dendrites. These results suggest that the Sema3E-PlexinD1-RhoJ axis regulates domain-specific dendrite formation of newborn neurons in the postnatal OB.

Seg2Link: an efficient and versatile solution for semi-automatic cell segmentation in 3D image stacks.

Recent advances in microscopy techniques, especially in electron microscopy, are transforming biomedical studies by acquiring large quantities of high-precision 3D cell image stacks. To examine cell morphology and connectivity in organs such as the brain, scientists need to conduct cell segmentation, which extracts individual cell regions of different shapes and sizes from a 3D image. This is challenging due to the indistinct images often encountered in real biomedical research: in many cases, automatic segmentation methods inevitably contain numerous mistakes in the segmentation results, even when using advanced deep learning methods. To analyze 3D cell images effectively, a semi-automated software solution is needed that combines powerful deep learning techniques with the ability to perform post-processing, generate accurate segmentations, and incorporate manual corrections. To address this gap, we developed Seg2Link, which takes deep learning predictions as inputs and use watershed 2D + cross-slice linking to generate more accurate automatic segmentations than previous methods. Additionally, it provides various manual correction tools essential for correcting mistakes in 3D segmentation results. Moreover, our software has been optimized for efficiently processing large 3D images in diverse organisms. Thus, Seg2Link offers an practical solution for scientists to study cell morphology and connectivity in 3D image stacks.

An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia.

We present an optochemical O2 scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O2 by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560-590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O2 consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca2+ ) influx into HEK293T cells expressing the hypoxia-responsive Ca2+ channel TRPA1.

Habilitation Improves Mouse Gait Development Following Neonatal Brain Injury.

Objectives: Neonatal brain injury during gait development disrupts neural circuits and causes permanent gait dysfunction. Rehabilitation as an intervention to improve impaired gait function has been used in adults as a treatment for stroke and spinal cord injury. However, although neonates have greater neuroplasticity and regenerative capacity than adults, normal gait development and the effects of habilitation on gait function following neonatal brain injury are largely unknown. Methods: In this study, we generated cryogenic injury in mice at postnatal day 2 and subsequently performed habilitative training to promote autonomous limb movement for 4 weeks. We also quantitatively analyzed the gait acquisition process in developing mice using the Catwalk XT system. Results: Using quantitative gait analyses, we showed that during normal gait development in mice, stance phase function matures later than swing phase function. We also demonstrated that habilitation in which active limb movements were enhanced by suspending mice with a rubber band with no floor grounding promotes motor learning, including gait function, in mice with impaired acquisition of gait function resulting from neonatal brain injury. Conclusions: Our findings provide a basis for research on gait development in mice and suggest new habilitation strategies for patients with impaired gait development caused by perinatal brain diseases such as hypoxic-ischemic encephalopathy and periventricular leukomalacia.

Fluoride-free synthesis of high-silica CHA-type aluminosilicates by seed-assisted aging treatment for starting gel.

High-silica CHA-type aluminosilicates (Si/Al molar ratio >100) were synthesized hydrothermally in the absence of fluoride media, where the seed-assisted aging treatment played an important role on the crystallization. These aluminosilicates showed a long catalytic lifetime with high selectivity toward lower olefins in the methanol-to-olefins reaction.

Synaptic pruning of murine adult-born neurons by microglia depends on phosphatidylserine.

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.

Postnatal neuronal migration in health and disease.

Postnatal neuronal migration modulates neuronal circuit formation and function throughout life and is conserved among species. Pathological conditions activate the generation of neuroblasts in the ventricular-subventricular zone (V-SVZ) and promote their migration towards a lesion. However, the neuroblasts generally terminate their migration before reaching the lesion site unless their intrinsic capacity is modified or the environment is improved. It is important to understand which factors impede neuronal migration for functional recovery of the brain. We highlight similarities and differences in the mechanisms of neuroblast migration under physiological and pathological conditions to provide novel insights into endogenous neuronal regeneration.

In vitro Time-lapse Imaging of Primary Cilium in Migrating Neuroblasts.

Neuronal migration is a critical step for the development of neuronal circuits in the brain. Immature new neurons (neuroblasts) generated in the postnatal ventricular-subventricular zone (V-SVZ) show a remarkable potential to migrate for a long distance at a high speed in the postnatal mammalian brain, and are thus a powerful model to analyze the molecular and cellular mechanisms of neuronal migration. Here we describe a methodology for in vitro time-lapse imaging of the primary cilium and its related structures in migrating V-SVZ-derived neuroblasts using confocal or superresolution laser-scanning microscopy. The V-SVZ tissues are dissected from postnatal day 0-1 (P0-1) mouse brains and dissociated into single cells by trypsinization and gentle pipetting. These cells are then transduced with a plasmid(s) encoding a gene(s) of interest, aggregated by centrifugation, and cultured for 2 days in Matrigel. Time-lapse images of migratory behaviors of cultured neuroblasts and their ciliary structures, including the ciliary membrane and basal body, are acquired by confocal or superresolution laser-scanning microscopy. This method provides information about the spatiotemporal dynamics of neuroblasts' morphology and ciliary structures, and is widely applicable to various types of migrating neuronal and nonneuronal cells in various species.

Dynamic Changes in Ultrastructure of the Primary Cilium in Migrating Neuroblasts in the Postnatal Brain.

New neurons, referred to as neuroblasts, are continuously generated in the ventricular-subventricular zone of the brain throughout an animal's life. These neuroblasts are characterized by their unique potential for proliferation, formation of chain-like cell aggregates, and long-distance and high-speed migration through the rostral migratory stream (RMS) toward the olfactory bulb (OB), where they decelerate and differentiate into mature interneurons. The dynamic changes of ultrastructural features in postnatal-born neuroblasts during migration are not yet fully understood. Here we report the presence of a primary cilium, and its ultrastructural morphology and spatiotemporal dynamics, in migrating neuroblasts in the postnatal RMS and OB. The primary cilium was observed in migrating neuroblasts in the postnatal RMS and OB in male and female mice and zebrafish, and a male rhesus monkey. Inhibition of intraflagellar transport molecules in migrating neuroblasts impaired their ciliogenesis and rostral migration toward the OB. Serial section transmission electron microscopy revealed that each migrating neuroblast possesses either a pair of centrioles or a basal body with an immature or mature primary cilium. Using immunohistochemistry, live imaging, and serial block-face scanning electron microscopy, we demonstrate that the localization and orientation of the primary cilium are altered depending on the mitotic state, saltatory migration, and deceleration of neuroblasts. Together, our results highlight a close mutual relationship between spatiotemporal regulation of the primary cilium and efficient chain migration of neuroblasts in the postnatal brain.SIGNIFICANCE STATEMENT Immature neurons (neuroblasts) generated in the postnatal brain have a mitotic potential and migrate in chain-like cell aggregates toward the olfactory bulb. Here we report that migrating neuroblasts possess a tiny cellular protrusion called a primary cilium. Immunohistochemical studies with zebrafish, mouse, and monkey brains suggest that the presence of the primary cilium in migrating neuroblasts is evolutionarily conserved. Ciliogenesis in migrating neuroblasts in the rostral migratory stream is suppressed during mitosis and promoted after cell cycle exit. Moreover, live imaging and 3D electron microscopy revealed that ciliary localization and orientation change during saltatory movement of neuroblasts. Our results reveal highly organized dynamics in maturation and positioning of the primary cilium during neuroblast migration that underlie saltatory movement of postnatal-born neuroblasts.

Heterogeneous distribution of doublecortin-expressing cells surrounding the rostral migratory stream in the juvenile mouse.

In the postnatal mammalian brain, neural stem cells of the ventricular-subventricular zone continue to generate doublecortin (Dcx)-expressing immature neurons. Throughout life, these immature neurons migrate to the olfactory bulb through the rostral migratory stream (RMS). In this study, we investigated the distribution of these putative immature neurons using enhanced green fluorescent protein (EGFP) expression in the area surrounding the RMS of the juvenile Dcx-EGFP mice. Through the combined use of an optical clearing reagent (a 2,2'-thiodiethanol solution) and two-photon microscopy, we visualized three-dimensionally the EGFP-positive cells in the entire RMS and its surroundings. The resulting wide-field and high-definition images along with computational image processing methods developed in this study were used to comprehensively determine the position of the EGFP-positive cells. Our findings revealed that the EGFP-positive cells were heterogeneously distributed in the area surrounding the RMS. In addition, the orientation patterns of the leading process of these cells, which displayed the morphology of migrating immature neurons, differed depending on their location. These novel results provide highly precise morphological information for immature neurons and suggest that a portion of immature neurons may be detached from the RMS and migrate in various directions.

Detachment of Chain-Forming Neuroblasts by Fyn-Mediated Control of cell-cell Adhesion in the Postnatal Brain.

In the rodent olfactory system, neuroblasts produced in the ventricular-subventricular zone of the postnatal brain migrate tangentially in chain-like cell aggregates toward the olfactory bulb (OB) through the rostral migratory stream (RMS). After reaching the OB, the chains are dissociated and the neuroblasts migrate individually and radially toward their final destination. The cellular and molecular mechanisms controlling cell-cell adhesion during this detachment remain unclear. Here we report that Fyn, a nonreceptor tyrosine kinase, regulates the detachment of neuroblasts from chains in the male and female mouse OB. By performing chemical screening and in vivo loss-of-function and gain-of-function experiments, we found that Fyn promotes somal disengagement from the chains and is involved in neuronal migration from the RMS into the granule cell layer of the OB. Fyn knockdown or Dab1 (disabled-1) deficiency caused p120-catenin to accumulate and adherens junction-like structures to be sustained at the contact sites between neuroblasts. Moreover, a Fyn and N-cadherin double-knockdown experiment indicated that Fyn regulates the N-cadherin-mediated cell adhesion between neuroblasts. These results suggest that the Fyn-mediated control of cell-cell adhesion is critical for the detachment of chain-forming neuroblasts in the postnatal OB.SIGNIFICANCE STATEMENT In the postnatal brain, newly born neurons (neuroblasts) migrate in chain-like cell aggregates toward their destination, where they are dissociated into individual cells and mature. The cellular and molecular mechanisms controlling the detachment of neuroblasts from chains are not understood. Here we show that Fyn, a nonreceptor tyrosine kinase, promotes the somal detachment of neuroblasts from chains, and that this regulation is critical for the efficient migration of neuroblasts to their destination. We further show that Fyn and Dab1 (disabled-1) decrease the cell-cell adhesion between chain-forming neuroblasts, which involves adherens junction-like structures. Our results suggest that Fyn-mediated regulation of the cell-cell adhesion of neuroblasts is critical for their detachment from chains in the postnatal brain.

PlexinD1 signaling controls morphological changes and migration termination in newborn neurons.

Newborn neurons maintain a very simple, bipolar shape, while they migrate from their birthplace toward their destinations in the brain, where they differentiate into mature neurons with complex dendritic morphologies. Here, we report a mechanism by which the termination of neuronal migration is maintained in the postnatal olfactory bulb (OB). During neuronal deceleration in the OB, newborn neurons transiently extend a protrusion from the proximal part of their leading process in the resting phase, which we refer to as a filopodium-like lateral protrusion (FLP). The FLP formation is induced by PlexinD1 downregulation and local Rac1 activation, which coincide with microtubule reorganization and the pausing of somal translocation. The somal translocation of resting neurons is suppressed by microtubule polymerization within the FLP The timing of neuronal migration termination, controlled by Sema3E-PlexinD1-Rac1 signaling, influences the final positioning, dendritic patterns, and functions of the neurons in the OB These results suggest that PlexinD1 signaling controls FLP formation and the termination of neuronal migration through a precise control of microtubule dynamics.

Radial Glial Fibers Promote Neuronal Migration and Functional Recovery after Neonatal Brain Injury.

Radial glia (RG) are embryonic neural stem cells (NSCs) that produce neuroblasts and provide fibers that act as a scaffold for neuroblast migration during embryonic development. Although they normally disappear soon after birth, here we found that RG fibers can persist in injured neonatal mouse brains and act as a scaffold for postnatal ventricular-subventricular zone (V-SVZ)-derived neuroblasts that migrate to the lesion site. This injury-induced maintenance of RG fibers has a limited time window during post-natal development and promotes directional saltatory movement of neuroblasts via N-cadherin-mediated cell-cell contacts that promote RhoA activation. Transplanting an N-cadherin-containing scaffold into injured neonatal brains likewise promotes migration and maturation of V-SVZ-derived neuroblasts, leading to functional improvements in impaired gait behaviors. Together these results suggest that RG fibers enable postnatal V-SVZ-derived neuroblasts to migrate toward sites of injury, thereby enhancing neuronal regeneration and functional recovery from neonatal brain injuries.

Daple Coordinates Planar Polarized Microtubule Dynamics in Ependymal Cells and Contributes to Hydrocephalus.

Motile cilia in ependymal cells, which line the cerebral ventricles, exhibit a coordinated beating motion that drives directional cerebrospinal fluid (CSF) flow and guides neuroblast migration. At the apical cortex of these multi-ciliated cells, asymmetric localization of planar cell polarity (PCP) proteins is required for the planar polarization of microtubule dynamics, which coordinates cilia orientation. Daple is a disheveled-associating protein that controls the non-canonical Wnt signaling pathway and cell motility. Here, we show that Daple-deficient mice present hydrocephalus and their ependymal cilia lack coordinated orientation. Daple regulates microtubule dynamics at the anterior side of ependymal cells, which in turn orients the cilial basal bodies required for the directional cerebrospinal fluid flow. These results demonstrate an important role for Daple in planar polarity in motile cilia and provide a framework for understanding the mechanisms and functions of planar polarization in the ependymal cells.

Mechanisms of neuronal migration in the adult brain.

Adult neurogenesis was first observed nearly 60 years ago, and it has since grown into an important neurochemistry research field. Much recent research has focused on the treatment of brain diseases through neuronal regeneration with endogenously generated neurons. In the adult brain, immature neurons called neuroblasts are continuously generated in the ventricular-subventricular zone (V-SVZ). These neuroblasts migrate rapidly through the rostral migratory stream to the olfactory bulb, where they mature and are integrated into the neuronal circuitry. After brain insult, some of the neuroblasts in the V-SVZ migrate toward the lesion to repopulate the injured tissue. This notable migratory capacity of V-SVZ-derived neuroblasts is important for efficiently regenerating neurons in remote areas of the brain. As these neurons migrate for long distances through adult brain tissue, they are supported by various guidance cues and structures that act as scaffolds. Some of these mechanisms are unique to neuroblast migration in the adult brain, and are not involved in migration in the developing brain. Here, we review the latest findings on the mechanisms of neuroblast migration in the adult brain under physiological and pathological conditions, and discuss various issues that still need to be resolved. This article is part of the mini review series "60th Anniversary of the Japanese Society for Neurochemistry".

[Do envious people show better performance?: Focusing on the function of benign envy as personality trait].

This study focused on the differences between two, subtypes of envy known as "benign envy" and "malicious envy" as personality traits, and examined the effects of these traits on academic achievement. Two hundred fifty-one university students participated in the study. Both benign envy and malicious envy were found to be independent as also found in a previous study by Lange & Crusius (2015), and a high criterion-related validity was revealed by an association with characteristic variables such as dispositional envy and self-esteem. The students with higher levels of benign envy were found to set goals higher, and as a result achieved higher levels of academic performance. In contrast, no such effect was found for malicious envy. The importance of focusing more attention on the positive aspects of the emotion of envy is discussed.

Subchronic inhalation exposure to 2-ethyl-1-hexanol impairs the mouse olfactory bulb via injury and subsequent repair of the nasal olfactory epithelium.

The olfactory system can be a toxicological target of volatile organic compounds present in indoor air. Recently, 2-ethyl-1-hexanol (2E1H) emitted from adhesives and carpeting materials has been postulated to cause "sick building syndrome." Patients' symptoms are associated with an increased sense of smell. This investigation aimed to characterize the histopathological changes of the olfactory epithelium (OE) of the nasal cavity and the olfactory bulb (OB) in the brain, due to subchronic exposure to 2E1H. Male ICR mice were exposed to 0, 20, 60, or 150 ppm 2E1H for 8 h every day for 1 week, or 5 days per week for 1 or 3 months. After a 1-week exposure, the OE showed inflammation and degeneration, with a significant concentration-dependent reduction in the staining of olfactory receptor neurons and in the numbers of globose basal cells at ≥20 ppm. Regeneration occurred at 1 month along with an increase in the basal cells, but lymphocytic infiltration, expanded Bowman's glands, and a decrease in the olfactory receptor neurons were observed at 3 months. Intriguingly, the OB at 3 months showed a reduction in the diameters of the glomeruli and in the number of olfactory nerves and tyrosine hydroxylase-positive neurons, but an increased number of ionized calcium-binding adaptor molecule 1-positive microglia in glomeruli. Accordingly, 2E1H inhalation induced degeneration of the OE with the lowest-observed-adverse-effect level of 20 ppm. The altered number of functional cell components in the OB suggests that effects on olfactory sensation persist after subchronic exposure to 2E1H.