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Among physical stimulation modalities, magnetism has clear advantages, such as deep penetration and untethered interventions in biological subjects. However, some of the working principles and effectiveness of existing magnetic neurostimulation approaches have been challenged, leaving questions to be answered. Here we introduce m-Torquer, a magnetic toolkit that mimics magnetoreception in nature. It comprises a nanoscale magnetic torque actuator and a circular magnet array, which deliver piconewton-scale forces to cells over a working range of ~70 cm. With m-Torquer, stimulation of neurons expressing bona fide mechanosensitive ion channel Piezo1 enables consistent and reproducible neuromodulation in freely moving mice. With its long working distance and cellular targeting capability, m-Torquer provides versatility in its use, which can range from single cells to in vivo systems, with the potential application in large animals such as primates. A magnetic torque actuator has been developed and is capable of modulation of neurons expressing the mechanosensitive ion channel, Piezo1, resulting in long-distance control of locomotion of mice.

Adherens junctions (AJs) create spatially and mechanically discrete microdomains at the interfaces of cells. Using a mechanogenetic platform that generates artificial AJs with controlled protein localization, clustering, and mechanical loading, we report that AJs also organize proteolytic hotspots for γ-secretase with a spatially-regulated substrate selectivity that is critical in the processing of Notch and other transmembrane proteins. Membrane microdomains outside of AJs exclusively organize Notch ligand-receptor engagement (LRE-µdomain) to initialize receptor activation. Conversely, membrane microdomains within AJs exclusively serve to coordinate regulated intramembrane proteolysis (RIP-µdomain). They do so by concentrating γ-secretase and primed receptors while excluding full-length Notch. AJs induce these functionally distinct microdomains by means of cholesterol-dependent γ-secretase recruitment and size-dependent protein segregation. By excluding full-length Notch from RIP-µdomains, AJs prevents inappropriate enzyme-substrate interactions and suppresses spurious Notch activation. Ligand-induced ectodomain shedding eliminates size-dependent segregation, releasing Notch to translocate into AJs for processing by γ-secretase. This mechanism directs radial differentiative expansion of ventricular zone-neural progenitor cells in vivo and more broadly regulates the proteolysis of large cell-surface receptors like amyloid precursor protein. These findings suggest an unprecedented role of AJs in creating size-selective spatial switches that choreograph γ-secretase processing of multiple transmembrane proteins regulating development, homeostasis, and disease.

Adherens junctions (AJs) create spatially, chemically and mechanically discrete microdomains at cellular interfaces. Here, using a mechanogenetic platform that generates artificial AJs with controlled protein localization, clustering and mechanical loading, we find that AJs also organize proteolytic hotspots for γ-secretase with a spatially regulated substrate selectivity that is critical in the processing of Notch and other transmembrane proteins. Membrane microdomains outside of AJs exclusively organize Notch ligand-receptor engagement (LRE microdomains) to initiate receptor activation. Conversely, membrane microdomains within AJs exclusively serve to coordinate regulated intramembrane proteolysis (RIP microdomains). They do so by concentrating γ-secretase and primed receptors while excluding full-length Notch. AJs induce these functionally distinct microdomains by means of lipid-dependent γ-secretase recruitment and size-dependent protein segregation. By excluding full-length Notch from RIP microdomains, AJs prevent inappropriate enzyme-substrate interactions and suppress spurious Notch activation. Ligand-induced ectodomain shedding eliminates size-dependent segregation, releasing Notch to translocate into AJs for processing by γ-secretase. This mechanism directs radial differentiation of ventricular zone-neural progenitor cells in vivo and more broadly regulates the proteolysis of other large cell-surface receptors such as amyloid precursor protein. These findings suggest an unprecedented role of AJs in creating size-selective spatial switches that choreograph γ-secretase processing of multiple transmembrane proteins regulating development, homeostasis and disease.

Aberrant cleavage of Notch by γ-secretase is implicated in numerous diseases, but how cleavage is regulated in space and time is unclear. Here, we report that cadherin-based adherens junctions (cadAJs) are sites of high cell-surface γ-secretase activity, as well as sites of constrained physical space that excludes γ-secretase substrates having large extracellular domains (ECDs) like Notch. ECD shedding initiates drastic spatial relocalization of Notch to cadAJs, allowing enzyme-substrate interactions and downstream signaling. Spatial mutations by adjusting the ECD size or the physical constraint alter signaling. Dysregulation of this spatial switch promotes precocious differentiation of ventricular zone neural progenitor cells in vivo. We show the generality of this spatial switch for amyloid precursor protein proteolysis. Thus, cadAJs create spatially distinct biochemical compartments regulating cleavage events involving γ-secretase and preventing aberrant activation of receptors.

Considering the effects of circadian misalignment on human pathophysiology and behavior, it is important to be able to detect an individual’s endogenous circadian time. We developed an endogenous Clock Estimation Model (eCEM) based on a machine learning process using the expression of 10 circadian genes. Hair follicle cells were collected from 18 healthy subjects at 08:00, 11:00, 15:00, 19:00, and 23:00 h for two consecutive days, and the expression patterns of 10 circadian genes were obtained. The eCEM was designed using the inverse form of the circadian gene rhythm function (i.e., Circadian Time = F(gene)), and the accuracy of eCEM was evaluated by leave-one-out cross-validation (LOOCV). As a result, six genes (PER1, PER3, CLOCK, CRY2, NPAS2, and NR1D2) were selected as the best model, and the error range between actual and predicted time was 3.24 h. The eCEM is simple and applicable in that a single time-point sampling of hair follicle cells at any time of the day is sufficient to estimate the endogenous circadian time.

Neural stem cells are found in adult mammalian brain regions including the subgranular zone (SGZ) of the dentate gyrus (DG) and the subventricular zone (SVZ). In addition to these two regions, other neurogenic regions are often reported in many species. Recently, the subcallosal zone (SCZ) has been identified as a novel neurogenic region where new neuroblasts are spontaneously generated and then, by Bax-dependent apoptosis, eliminated. However, the development of SCZ in the postnatal brain is not yet fully explored. The present study investigated the precise location and amount of neuroblasts in the developing brain. To estimate the importance of programmed cell death (PCD) for SCZ histogenesis, SCZ development in the Bax-knockout (KO) mouse was examined. Interestingly, an accumulation of extra neurons with synaptic fibers in the SCZ of Bax-KO mice was observed. Indeed, Bax-KO mice exhibited enhanced startle response to loud acoustic stimuli and reduced anxiety level. Considering the prevention of PCD in the SCZ leads to sensory-motor gating dysfunction in the Bax-KO mice, active elimination of SCZ neuroblasts may promote optimal brain function.

Throughout life, new neurons are continuously generated from subventricular zone and added to the olfactory bulb (OB). Because a subset of mature OB neurons undergoes spontaneous cell death, adult OB neurogenesis serves for the replacement of this cell loss. Spontaneous cell turnover should alter the neuronal circuits, but the significance of cell turnover on olfactory learning is yet poorly understood. In this study, we explored the olfactory learning behaviors of model mice showing (1) absence of cell death and cell addition (aged Bax-KO mice); (2) absence of cell death but presence of cell addition (young Bax-KO mice); or (3) presence cell death but absence of cell addition (surgical lesion of rostral migratory stream of neuroblasts). Interestingly, aged Bax-KO mice with no cell replacement acquired the ability to discriminate odor differences faster than WT littermates, whereas other model mice exhibited virtually normal learning ability. These results suggest that the cell replacement is necessary for the normal olfactory learning behavior, and the chronic perturbation of cell replacement may result in the imbalance of neural circuits driving unexpected enhancement of olfactory learning ability.

LIM domain-binding protein 1 (Ldb1) is a nuclear cofactor that interacts with LIM homeodomain proteins to form multiprotein complexes that are important for transcription regulation. Ldb1 has been shown to play essential roles in various processes during mouse embryogenesis. To determine the role of Ldb1 in mid- and hindbrain development, we have generated a conditional mutant with a specific deletion of the Ldb1 in the Engrailed-1-expressing region of the developing mid- and hindbrain. Our study showed that the deletion impaired the expression of signaling molecules, such as fibroblast growth factor 8 (FGF8) and Wnt1, in the isthmic organizer and the expression of Shh in the ventral midbrain. The midbrain and the cerebellum were severely reduced in size, and the midbrain dopaminergic (mDA) neurons were missing in the mutant. These defects are identical to the phenotype that has been observed previously in mice with a deletion of the LIM homeodomain gene Lmx1b. Our results thus provide genetic evidence supporting that Ldb1 and Lmx1b function cooperatively to regulate mid- and hindbrain development. In addition, we found that mouse embryonic stem cells lacking Ldb1 failed to generate several types of differentiated neurons, including the mDA neurons, serotonergic neurons, cholinergic neurons, and olfactory bulb neurons, indicating an essential cell-autonomous role for Ldb1 in the development of these neurons.

Surface micropatterns have been widely used as chemical cues to control the microenvironment of cultured neurons, particularly for neurobiological assays and neurochip designs. However, the cell-type dependency on the interactions between neurons and underlying micropatterns has been rarely investigated despite the inherent differences in the morphology of neuronal types. In this study, we used surface-printed microdot arrays to investigate the effect of the same micropatterns on the growth of mouse spinal interneuron, mouse hippocampal neurons, and rat hippocampal neurons. While mouse hippocampal neurons showed no significantly different growth on control and patterned substrates, we found the microdot arrays had different effects on early neuronal growth depending on the cell type; spinal interneurons tended to grow faster in length, whereas hippocampal neurons tended to form more axon collateral branches in response to the microdot arrays. Although there was a similar trend in the neurite length and branch number of both neurons changed across the microdot arrays with the expanded range of size and spacing, the dominant responses of each neuron, neurite elongation of mouse spinal interneurons and branching augmentation of rat hippocampal neurons were still preserved. Therefore, our results demonstrate that the same design of micropatterns could cause different neuronal growth results, raising an intriguing issue of considering cell types in neural interface designs.

Adult-born neurons are continuously generated and incorporated into the circuitry of the hippocampus throughout life in mammals. Cumulative evidence supports a physiological role for adult-born neurons, yet it not clear whether this subset of dentate granule cells makes a unique contribution to hippocampal function. Perturbation or ablation of adult hippocampal neurogenesis leads to deficits in the acquisition of learned associations or memory recall, whereas an increase in adult hippocampal neurogenesis enhances some forms of learning and memory. The observed effects thus far appear to be task-dependent, species-specific, and sensitive to the timing of manipulations. Here, we review the recent evidence correlating adult-born dentate granule cells (DGCs) with hippocampal-dependent behavior and focus on the dynamic properties of this neuronal population that may underlie its function. We further discuss a framework for future investigations of how newly integrated neurons may contribute to hippocampal processing using advanced genetic techniques with enhanced temporal resolution.

Human embryonic stem cells (hESCs) hold enormous promise for regenerative medicine. Typically, hESC-based applications would require their in vitro differentiation into a desirable homogenous cell population. A major challenge of the current hESC differentiation paradigm is the inability to effectively capture and, in the long-term, stably expand primitive lineage-specific stem/precursor cells that retain broad differentiation potential and, more importantly, developmental stage-specific differentiation propensity. Here, we report synergistic inhibition of glycogen synthase kinase 3 (GSK3), transforming growth factor β (TGF-β), and Notch signaling pathways by small molecules can efficiently convert monolayer cultured hESCs into homogenous primitive neuroepithelium within 1 wk under chemically defined condition. These primitive neuroepithelia can stably self-renew in the presence of leukemia inhibitory factor, GSK3 inhibitor (CHIR99021), and TGF-β receptor inhibitor (SB431542); retain high neurogenic potential and responsiveness to instructive neural patterning cues toward midbrain and hindbrain neuronal subtypes; and exhibit in vivo integration. Our work uniformly captures and maintains primitive neural stem cells from hESCs.

During development, elimination of excess cells through programmed cell death (PCD) is essential for the establishment and maintenance of the nervous system. In many brain regions, development and major histogenesis continue beyond postnatal stages, and therefore, signs of neurogenesis and PCD are frequently observed in these postnatal brain regions. Furthermore, some brain regions maintain neurogenic potential throughout life, and continuous genesis and PCD play critical roles in sculpting these adult neural circuits. Although similar regulatory mechanisms that control PCD during development appear to also control PCD in the adult brain, adult-generated neurons must integrate into mature neural circuits for their survival. This novel requirement appears to result in unique features of PCD in the adult brain. In this article, we summarize recent findings related to PCD in the early postnatal and adult brain in rodents.

In the last 10 years, many studies have reported that neural stem ⁄progenitor cells spontaneously produce new neurons in a subset of adult brain regions, including the hippocampus, olfactory bulb (OB), cerebral cortex, substantia nigra, hypothalamus, white matter and amygdala in several mammalian species. Although adult neurogenesis in the hippocampus and OB has been clearly documented, its occurrence in other brain regions is controversial. In the present study, we identified a marked accumulation of new neurons in the subcallosal zone (SCZ) of Bax-knockout mice in which programmed cell death (PCD) of adultgenerated hippocampal and OB neurons has been shown to be completely prevented. By contrast, in the SCZ of wild-type (WT) mice, only a few immature (but no mature) newly generated neurons were observed, suggesting that virtually all postnatally generated immature neurons in the SCZ were eliminated by Bax-dependent PCD. Treatment of 2-month-old WT mice with a caspase inhibitor, or with the neurotrophic factor brain-derived neurotrophic factor, promoted the survival of adult-generated neurons, suggesting that it is the absence of sufficient neurotrophic signaling in WT SCZ that triggers the Bax-dependent, apoptotic PCD of newly generated SCZ neurons. Furthermore, following focal traumatic brain injury to the posterior brain, SCZ neurogenesis in WT mice was increased, and a subset of these newly generated neurons migrated toward the injury site. These data indicate that the adult SCZ maintains a neurogenic potential that could contribute to recovery in the brain in response to the injury-induced upregulation of neurotrophic signaling.

Humans and animals form internal representations of external space based on their own body movement (dead reckoning) as well as external landmarks. It is poorly understood, however, how different types of information are integrated to form a unified representation of external space. To examine the role of dentate gyrus (DG) in this process, we conducted physiological and behavioral experiments using Bax knockout (Bax-KO) mice in which newly generated granule cells continue to accumulate disrupting neural circuitry specifically in the DG. Unlike in wild-type (WT) littermates, spatial firing of hippocampal neurons was completely dissociated from a distinct visual cue and instead, tended to stay constant relative to the recording room in Bax-KO mice. Behaviorally, whereas spatial learning was intact in conventional spatial reference memory tasks, Bax-KO mice were impaired in finding a target location based on visual landmarks when target locations predicted by dead reckoning and visual landmarks were made incongruent. These results provide converging evidence for the role of DG in binding animal's internal spatial map with the sensory information on external landmarks in building a distinct spatial representation for each environment.

Rats and mice exhibit neurogenesis of olfactory bulb (OB) interneurons throughout adulthood. To homeostatically maintain stable neuron numbers, it is necessary to continuously remove a subset of OB neurons by programmed cell death (PCD). Here we demonstrate that Bax is critical for the elimination of OB neurons by showing that Bax-KO mice exhibit greatly reduced PCD in the OB. Despite the reduction of PCD, however, proliferation of progenitors and the size of the OB were virtually unaffected in Bax-knock-out (KO) mice. However, reducing PCD by Bax deletion affected the migration of a subset of adult-produced neurons by the disruption of glial tube formation as well as by premature detachment of neuroblasts from the migratory chain. Rescued cells aberrantly remained in the subventricular zone (SVZ)-rostral migratory stream (RMS), in which they differentiated into calretinin+or GABA-expressing interneurons. Because of the migratory deficit, OB cell homeostasis involving new cell entry and PCD (neuronal turnover) was virtually absent in adult Bax-KO mice. Despite this, Bax-KO mice exhibited normal olfactory behaviors such as odor discrimination and olfactory memory which are thought to be influenced by adult neurogenesis. These results demonstrate that PCD is involved in the regulation of RMS migration and differentiation after OB neurogenesis, but that animals maintain normal olfactory function in the absence of PCD.

Auditory fear memory is thought to be maintained by fear conditioning-induced potentiation of synaptic efficacy, which involves enhanced expression of surface AMPA receptor (AMPAR) at excitatory synapses in the lateral amygdala (LA). Depotentiation, reversal of conditioning-induced potentiation, has been proposed as a cellular mechanism for fear extinction; however, a direct link between depotentiation and extinction has not yet been tested. To address this issue, we applied both ex vivo and in vivo approaches to rats in which fear memory had been consolidated. A unique form of depotentiation reversed conditioning-induced potentiation at thalamic input synapses onto the LA (T-LA synapses) ex vivo . Extinction returned the enhanced T-LA synaptic efficacy observed in conditioned rats to baseline and occluded the depotentiation. Consistently, extinction reversed conditioning-induced enhancement of surface expression of AMPAR subunits in LA synaptosomal preparations. A GluR2-derived peptide that blocks regulated AMPAR endocytosis inhibited depotentiation, and microinjection of a cell-permeable form of the peptide into the LA attenuated extinction. Our results are consistent with the use of depotentiation to weaken potentiated synaptic inputs onto the LA during extinction and provide strong evidence that AMPAR removal at excitatory synapses in the LA underlies extinction.

Precise and quantitative control of extracellular signalling cues using surface-engineered chips has facilitated various neurobiological assays in vitro. Although the formation of axon collateral branches is important for the establishment and refinement of the neuronal connections during the development and regeneration, surface designs for controlling branch phenotypes have been rarely proposed. In this work, we fabricated a surface-printed microdot array for controlling axon branch formation. Following the culture of hippocampal neurons on a 5 μm dot array patterned by micro-contact printing of poly-D-lysine, we found that most axon collateral branches were initiated from axonal regions on a microdot and terminated on neighboring dots. In addition, the length of branches increased as the spacing between dots increased. Surprisingly, other morphological features were not significantly different from the neurons cultured on a conventional unpatterned surface. Further investigation of this phenomenon indicated that the branch-forming machineries, such as actin patches, were focused on the dot. According to these investigations, we concluded that discontinuous adhesion spots given by dot arrays arranged the branching formation on the expectable location and direction. Therefore, microdot arrays will be applicable as the surface design parameter of bio-chip platforms to reduce branching complexity and quantize branching formation for the simple and easy assay in neurobiological studies.

Traditional methods of immunohistochemistry (IHC) following tissue fixation allow visualization of various cell types. These typically proceed with the application of antibodies to bind antigens and identify cells with characteristics that are a function of the inherent biology and development. Adult hippocampal neurogenesis is a sequential process wherein a quiescent neural stem cell can become activated and proceed through stages of proliferation, differentiation, maturation and functional integration. Each phase is distinct with a characteristic morphology and upregulation of genes. Identification of these phases is important to understand the regulatory mechanisms at play and any alterations in this process that underlie the pathophysiology of debilitating disorders. Our heat-induced antigen retrieval approach improves the intensity of the signal that is detected and allows correct identification of the progenitor cell type. As discussed in this paper, it especially allows us to circumvent current problems in detection of certain progenitor cell types.

Background Huntington’s Disease (HD) is a devastating neurodegenerative disorder that clinically manifests as motor dysfunction, cognitive impairment and psychiatric symptoms. There is currently no cure for this progressive and fatal disorder. The causative mutation of this hereditary disease is a trinucleotide repeat expansion (CAG) in the Huntingtin gene that results in an expanded polyglutamine tract. Multiple mechanisms have been proposed to explain the preferential striatal and cortical degeneration that occurs with HD, including non-cell-autonomous contribution from astrocytes. Although numerous cell culture and animal models exist, there is a great need for experimental systems that can more accurately replicate the human disease. Human induced pluripotent stem cells (iPSCs) are a remarkable new tool to study neurological disorders because this cell type can be derived from patients as a renewable, genetically tractable source for unlimited cells that are difficult to acquire, such as neurons and astrocytes. The development of experimental systems based on iPSC technology could aid in the identification of molecular lesions and therapeutic treatments. Results We derived iPSCs from a father with adult onset HD and 50 CAG repeats (F-HD-iPSC) and his daughter with juvenile HD and 109 CAG repeats (D-HD-iPSC). These disease-specific iPSC lines were characterized by standard assays to assess the quality of iPSC lines and to demonstrate their pluripotency. HD-iPSCs were capable of producing phenotypically normal, functional neurons in vitro and were able to survive and differentiate into neurons in the adult mouse brain in vivo after transplantation. Surprisingly, when HD-iPSCs were directed to differentiate into an astrocytic lineage, we observed the presence of cytoplasmic, electron clear vacuoles in astrocytes from both F-HD-iPSCs and D-HD-iPSCs, which were significantly more pronounced in D-HD-astrocytes. Remarkably, the vacuolation in diseased astrocytes was observed under basal culture conditions without additional stressors and increased over time. Importantly, similar vacuolation phenotype has also been observed in peripheral blood lymphocytes from individuals with HD. Together, these data suggest that vacuolation may be a phenotype associated with HD. Conclusions We have generated a unique in vitro system to study HD pathogenesis using patient-specific iPSCs. The astrocytes derived from patient-specific iPSCs exhibit a vacuolation phenotype, a phenomenon previously documented in primary lymphocytes from HD patients. Our studies pave the way for future mechanistic investigations using human iPSCs to model HD and for high-throughput therapeutic screens.

Reactive astrocytes greatly influence the wound healing and neuronal regeneration processes following brain injury. However, the origin and fate of reactive astrocytes appear to be different depending on the type, severity and duration of brain injury. Using the cryogenic traumatic brain injury model, here we comprehensively addressed the regional differences of reactive astrocytes in the injured cortex. In the proximal region of injury site, NG2-expressing and cytoplasmic Olig2-labeled cells were densely localized 3 days after the injury. Next to this proximal layer, most of reactive astrocytes did not express NG2 but exhibited radial glia-like shape with elongated processes. Accordingly, they expressed the progenitor or radial glial markers, such as vimentin, brain lipid binding protein (BLBP) and the green fluorescent protein (GFP) under the control of the human GFAP (hGFAP) promoter. However, only few glial fibrillary acidic protein (GFAP) expressing astrocytes were found in this layer. Distal to the injury site, most of astrocytes strongly expressed GFAP with hypertonic morphology. At day 15 after injury, all layers expressing GFAP and other marker expressions disappeared, indicating the termination of reactive astrogliosis. Taken together, our data suggest that reactive astrogliosis occurs in a regionally segregated manner in the early phase of brain injury.

During development, elimination of excess cells through programmed cell death (PCD) is essential for the establishment and maintenance of the nervous system. In many brain regions, development and major histogenesis continue beyond postnatal stages, and therefore, signs of neurogenesis and PCD are frequently observed in these postnatal brain regions. Furthermore, some brain regions maintain neurogenic potential throughout life, and continuous genesis and PCD play critical roles in sculpting these adult neural circuits. Although similar regulatory mechanisms that control PCD during development appear to also control PCD in the adult brain, adult-generated neurons must integrate into mature neural circuits for their survival. This novel requirement appears to result in unique features of PCD in the adult brain. In this article, we summarize recent findings related to PCD in the early postnatal and adult brain in rodents.

In the last 10 years, many studies have reported that neural stem/progenitor cells spontaneously produce new neurons in a subset of adult brain regions, including the hippocampus, olfactory bulb (OB), cerebral cortex, substantia nigra, hypothalamus, white matter and amygdala in several mammalian species. Although adult neurogenesis in the hippocampus and OB has been clearly documented, its occurrence in other brain regions is controversial. In the present study, we identified a marked accumulation of new neurons in the subcallosal zone (SCZ) of Bax-knockout mice in which programmed cell death (PCD) of adult-generated hippocampal and OB neurons has been shown to be completely prevented. By contrast, in the SCZ of wild-type (WT) mice, only a few immature (but no mature) newly generated neurons were observed, suggesting that virtually all postnatally generated immature neurons in the SCZ were eliminated by Bax-dependent PCD. Treatment of 2-month-old WT mice with a caspase inhibitor, or with the neurotrophic factor brain-derived neurotrophic factor, promoted the survival of adult-generated neurons, suggesting that it is the absence of sufficient neurotrophic signaling in WT SCZ that triggers the Bax-dependent, apoptotic PCD of newly generated SCZ neurons. Furthermore, following focal traumatic brain injury to the posterior brain, SCZ neurogenesis in WT mice was increased, and a subset of these newly generated neurons migrated toward the injury site. These data indicate that the adult SCZ maintains a neurogenic potential that could contribute to recovery in the brain in response to the injury-induced upregulation of neurotrophic signaling.

The cAMP cascade and vascular endothelial growth factor (VEGF) are critical modulators of depression. Here we have tested whether the antidepressive effect of the cAMP cascade is mediated by VEGF in the adult hippocampus. We used a conditional genetic system in which the Aplysia octopamine receptor (Ap oa(1)), a G(s)-coupled receptor, is transgenically expressed in the forebrain neurons of mice. Chronic activation of the heterologous Ap oa(1) by its natural ligand evoked antidepressant-like behaviors, accompanied by enhanced phosphorylation of cAMP response element-binding protein and transcription of VEGF in hippocampal dentate gyrus (DG) neurons. Selective knockdown of VEGF in these cells during the period of cAMP elevation inhibited the antidepressant-like behaviors. These findings reveal a molecular interaction between the cAMP cascade and VEGF expression, and the pronounced behavioral consequences of this interaction shed light on the mechanism underlying neuronal VEGF functions in antidepression.

The adult mammalian brain continuously generates new neurons in the olfactory bulb and hippocampus throughout life. Adult neurogenesis, a highly dynamic process, has been shown to be exquisitely modulated by neuronal circuit activity at different stages, from proliferation of adult neural progenitors, to differentiation, maturation, integration, and survival of newborn neurons in the adult brain. Strategic activity-dependent addition of new neurons into the existing neuronal circuitry represents a prominent form of structural plasticity and may contribute to specific brain functions, such as learning, memory, and mood modulation. Here we review extrinsic mechanisms through which adult neurogenesis is regulated by environmental cues, physiological learning-related stimuli, and neuronal activities.

A considerable number of new neurons are generated daily in the dentate gyrus (DG) of the adult hippocampus, but only a subset of these survive, as many adult-generated neurons undergo programmed cell death (PCD). However, the significance of PCD in the adult brain for the functionality of DG circuits is not known. Here, we examined the electrophysiological and behavioral characteristics of Bax-knockout (Bax-KO) mice in which PCD of post-mitotic neurons is prevented. The continuous increase in DG cell numbers in Bax-KO mice resulted in the readjustment of afferent and efferent synaptic connections, represented by age-dependent reductions in the dendritic arborization of DG neurons and in the synaptic contact ratio of mossy fibers with CA3 dendritic spines. These neuroanatomical changes were associated with reductions in synaptic transmission and reduced performance in a contextual fear memory task in 6-month-old Bax-KO mice. These results suggest that the elimination of excess DG neurons via Bax-dependent PCD in the adult brain is required for the normal organization and function of the hippocampus.

Mitochondrial functions are essential for the survival and function of neurons. Recently, it has been demonstrated that mitochondrial functions are highly associated with mitochondrial morphology, which is dynamically changed by the balance between fusion and fission. Mitochondrial morphology is primarily controlled by the activation of dynamin-related proteins including dynamin-related protein 1 (Drp1), which promotes mitochondrial fission. Drp1 activity is regulated by several post-translational modifications, thereby modifying mitochondrial morphology. Here, we found that phosphorylation of Drp1 at serine 616 (S616) is mediated by cyclin-dependent kinase 5 (CDK5) in post-mitotic rat neurons. Perturbation of CDK5 activity modified the level of Drp1S616 phosphorylation and mitochondrial morphology in neurons. In addition, phosphorylated Drp1S616 preferentially localized as a cytosolic monomer compared with total Drp1. Furthermore, roscovitine, a chemical inhibitor of CDKs, increased oligomerization and mitochondrial translocation of Drp1, suggesting that CDK5-dependent phosphorylation of Drp1 serves to reduce Drp1's fission-promoting activity. Taken together, we propose that CDK5 has a significant role in the regulation of mitochondrial morphology via inhibitory phosphorylation of Drp1S616 in post-mitotic neurons.

BACKGROUND: Adult neural stem cells have the potential for self-renewal and differentiation into multiple cell lineages via symmetric or asymmetric cell division. Preso1 is a recently identified protein involved in the formation of dendritic spines and the promotion of axonal growth in developing neurons. Preso1 can also bind to cell polarity proteins, suggesting a potential role for Preso1 in asymmetric cell division. METHODS: To investigate the distribution of Preso1, we performed immunohistochemistry with adult mouse brain slice. Also, polarized distribution of Preso1 was assessed by immunocytochemistry in cultured neural stem cells. RESULTS: Immunoreactivity for Preso1 (Preso1-IR) was strong in the rostral migratory stream and subventricular zone, where proliferating transit-amplifying cells and neuroblasts are prevalent. In cultured neural stem cells, Preso1-IR was unequally distributed in the cell cytosol. We also observed the distribution of Preso1 in the subgranular zone of the hippocampal dentate gyrus, another neurogenic region in the adult brain. Interestingly, Preso1-IR was transiently observed in the nuclei of doublecortin-expressing neuroblasts immediately after asymmetric cell division. CONCLUSION: Our study demonstrated that Preso1 is asymmetrically distributed in the cytosol and nuclei of neural stem/progenitor cells in the adult brain, and may play a significant role in cell differentiation via association with cell polarity machinery.