| 藤本 聡志（ふじもと さとし） | データ更新日：2024.04.10 |
助教 ／
医学研究院
基礎医学部門
生体情報科学
| 1. | Tetsushi Niiyama, Satoshi Fujimoto, Takeshi Imai, Microglia are dispensable for developmental dendrite pruning of mitral cells in mice, eNeuro, 10.1523/ENEURO.0323-23.2023, 2023.10, During early development, neurons in the brain often form excess synaptic connections. Later, they strengthen some connections while eliminating others to build functional neuronal circuits. In the olfactory bulb, a mitral cell initially extends multiple dendrites to multiple glomeruli but eventually forms a single primary dendrite through the activity-dependent dendrite pruning process. Recent studies have reported that microglia facilitate synapse pruning during the circuit remodeling in some systems. It has remained unclear whether microglia are involved in the activity-dependent dendrite pruning in the developing brains. Here, we examined whether microglia are required for the developmental dendrite pruning of mitral cells in mice. To deplete microglia in the fetal brain, we treated mice with a CSF1R inhibitor, PLX5622, from pregnancy. Microglia were reduced by >90% in mice treated with PLX5622. However, dendrite pruning of mitral cells was not significantly affected. Moreover, we found no significant differences in the number, density, and size of excitatory synapses formed in mitral cell dendrites. We also found no evidence for the role of microglia in the activity-dependent dendrite remodeling of layer 4 neurons in the barrel cortex. In contrast, the density of excitatory synapses (dendritic spines) in granule cells in the olfactory bulb was significantly increased in mice treated with PLX5622 at P6, suggesting a role for the regulation of dendritic spines. Our results indicate that microglia do not play a critical role in activity-dependent dendrite pruning at the neurite level during early postnatal development in mice.Significance StatementSynapse elimination is essential for activity-dependent circuit remodeling in the developing brains of mammals. Recent studies suggested that microglia play a critical role in the synapse elimination. This study found that microglia are dispensable for the activity-dependent dendrite pruning in developing mitral cells and layer 4 neurons in the barrel cortex. Thus, microglia are not critical for activity-dependent dendrite pruning at the neurite level during normal developmental process.. |
| 2. | Marcus N Leiwe, Satoshi Fujimoto, Takeshi Imai, Effective Hand Rearing of Neonatal Mice for Developmental Studies, Bio-protocol, 10.21769/BioProtoc.4755, 2023.06, [URL]. |
| 3. | Satoshi Fujimoto, Marcus N. Leiwe, Shuhei Aihara, Richi Sakaguchi, Yuko Muroyama, Reiko Kobayakawa, Ko Kobayakawa, Tetsuichiro Saito, Takeshi Imai , Activity-dependent local protection and lateral inhibition control synaptic competition in developing mitral cells in mice, Developmental Cell, 10.1016/j.devcel.2023.05.004, 2023.06, In developing brains, activity-dependent remodeling facilitates the formation of precise neuronal connectivity. Synaptic competition is known to facilitate synapse elimination; however, it has remained unknown how different synapses compete with one another within a post-synaptic cell. Here, we investigate how a mitral cell in the mouse olfactory bulb prunes all but one primary dendrite during the developmental remodeling process. We find that spontaneous activity generated within the olfactory bulb is essential. We show that strong glutamatergic inputs to one dendrite trigger branch-specific changes in RhoA activity to facilitate the pruning of the remaining dendrites: NMDAR-dependent local signals suppress RhoA to protect it from pruning; however, the subsequent neuronal depolarization induces neuron-wide activation of RhoA to prune non-protected dendrites. NMDAR-RhoA signals are also essential for the synaptic competition in the mouse barrel cortex. Our results demonstrate a general principle whereby activity-dependent lateral inhibition across synapses establishes a discrete receptive field of a neuron.. |
| 4. | Marcus N Leiwe, Satoshi Fujimoto, Takeshi Imai, Post hoc Correction of Chromatic Aberrations in Large-Scale Volumetric Images in Confocal Microscopy, FRONTIERS IN NEUROANATOMY, 10.3389/fnana.2021.760063, 15, 2021.12. |
| 5. | Aihara Shuhei, Fujimoto Satoshi, Sakaguchi Richi, Imai Takeshi, BMPR-2 gates activity-dependent stabilization of primary dendrites during mitral cell remodeling, CELL REPORTS, 10.1016/j.celrep.2021.109276, 35, 12, 2021.06. |
| 6. | Aya Murai, Ryo Iwata, Satoshi Fujimoto, Shuhei Aihara, Akio Tsuboi, Yuko Muroyama, Tetsuichiro Saito, Kazunori Nishizaki, Takeshi Imai, Distorted Coarse Axon Targeting and Reduced Dendrite Connectivity Underlie Dysosmia after Olfactory Axon Injury, eNeuro, 10.1523/ENEURO.0242-16.2016, 3, 5, 2016.10, [URL], The glomerular map in the olfactory bulb (OB) is the basis for odor recognition. Once established during development, the glomerular map is stably maintained throughout the life of an animal despite the continuous turnover of olfactory sensory neurons (OSNs). However, traumatic damage to OSN axons in the adult often leads to dysosmia, a qualitative and quantitative change in olfaction in humans. A mouse model of dysosmia has previously indicated that there is an altered glomerular map in the OB after the OSN axon injury; however, the underlying mechanisms that cause the map distortion remain unknown. In this study, we examined how the glomerular map is disturbed and how the odor information processing in the OB is affected in the dysosmia model mice. We found that the anterior-posterior coarse targeting of OSN axons is disrupted after OSN axon injury, while the local axon sorting mechanisms remained. We also found that the connectivity of mitral/tufted cell dendrites is reduced after injury, leading to attenuated odor responses in mitral/tufted cells. These results suggest that existing OSN axons are an essential scaffold for maintaining the integrity of the olfactory circuit, both OSN axons and mitral/tufted cell dendrites, in the adult.. |
| 7. | Meng Tsen Ke, Yasuhiro Nakai, Satoshi Fujimoto, Rie Takayama, Shuhei Yoshida, Tomoya S. Kitajima, Makoto Sato, Takeshi Imai, Super-Resolution Mapping of Neuronal Circuitry With an Index-Optimized Clearing Agent, Cell Reports, 10.1016/j.celrep.2016.02.057, 14, 11, 2718-2732, 2016.03, [URL], Super-resolution imaging deep inside tissues has been challenging, as it is extremely sensitive to light scattering and spherical aberrations. Here, we report an optimized optical clearing agent for high-resolution fluorescence imaging (SeeDB2). SeeDB2 matches the refractive indices of fixed tissues to that of immersion oil (1.518), thus minimizing both light scattering and spherical aberrations. During the clearing process, fine morphology and fluorescent proteins were highly preserved. SeeDB2 enabled super-resolution microscopy of various tissue samples up to a depth of >100 μm, an order of magnitude deeper than previously possible under standard mounting conditions. Using this approach, we demonstrate accumulation of inhibitory synapses on spine heads in NMDA-receptor-deficient neurons. In the fly medulla, we found unexpected heterogeneity in axon bouton orientations among Mi1 neurons, a part of the motion detection circuitry. Thus, volumetric super-resolution microscopy of cleared tissues is a powerful strategy in connectomic studies at synaptic levels.. |
| 8. | Meng-Tsen Ke, Satoshi Fujimoto, Takeshi Imai, Optical Clearing Using SeeDB, Bio-protocol, 10.21769/BioProtoc.1042, 2014.02, [URL]. |
| 9. | Meng Tsen Ke, Satoshi Fujimoto, Takeshi Imai, SeeDB A simple and morphology-preserving optical clearing agent for neuronal circuit reconstruction, Nature Neuroscience, 10.1038/nn.3447, 16, 8, 1154-1161, 2013.08, [URL], We report a water-based optical clearing agent, SeeDB, which clears fixed brain samples in a few days without quenching many types of fluorescent dyes, including fluorescent proteins and lipophilic neuronal tracers. Our method maintained a constant sample volume during the clearing procedure, an important factor for keeping cellular morphology intact, and facilitated the quantitative reconstruction of neuronal circuits. Combined with two-photon microscopy and an optimized objective lens, we were able to image the mouse brain from the dorsal to the ventral side. We used SeeDB to describe the near-complete wiring diagram of sister mitral cells associated with a common glomerulus in the mouse olfactory bulb. We found the diversity of dendrite wiring patterns among sister mitral cells, and our results provide an anatomical basis for non-redundant odor coding by these neurons. Our simple and efficient method is useful for imaging intact morphological architecture at large scales in both the adult and developing brains.. |
| 10. | Nao Hiramoto-Yamaki, Shingo Takeuchi, Shuhei Ueda, Kohei Harada, Satoshi Fujimoto, Manabu Negishi, Hironori Katoh, Ephexin4 and EphA2 mediate cell migration through a RhoG-dependent mechanism, Journal of Cell Biology, 10.1083/jcb.201005141, 190, 3, 461-477, 2010.08, [URL], EphA2, a member of the Eph receptor family, is frequently overexpressed in a variety of human cancers, including breast cancers, and promotes cancer cell motility and invasion independently of its ligand ephrin stimulation. In this study, we identify Ephexin4 as a guanine nucleotide exchange factor (GEF) for RhoG that interacts with EphA2 in breast cancer cells, and knockdown and rescue experiments show that Ephexin4 acts downstream of EphA2 to promote ligand-independent breast cancer cell migration and invasion toward epidermal growth factor through activation of RhoG. The activation of RhoG recruits its effector ELMO2 and a Rac GEF Dock4 to form a complex with EphA2 at the tips of cortactinrich protrusions in migrating breast cancer cells. In addition, the Dock4-mediated Rac activation is required for breast cancer cell migration. Our findings reveal a novel link between EphA2 and Rac activation that contributes to the cell motility and invasiveness of breast cancer cells.. |
| 11. | Satoshi Fujimoto, Manabu Negishi, Hironori Katoh, RhoG promotes neural progenitor cell proliferation in mouse cerebral cortex, Molecular Biology of the Cell, 10.1091/mbc.E09-03-0200, 20, 23, 4941-4950, 2009.12, [URL], In early cortical development, neural progenitor cells (NPCs) expand their population in the ventricular zone (VZ), and produce neurons. Although a series of studies have revealed the process of neurogenesis, the molecular mechanisms regulating NPC proliferation are still largely unknown. Here we found that RhoG, a member of Rho family GTPases, was expressed in the VZ at early stages of cortical development. Expression of constitutively active RhoG promoted NPC proliferation and incorporation of bromodeoxyuridine (BrdU) in vitro, and the proportion of Ki67-positive cells in vivo. In contrast, knockdown of RhoG by RNA interference suppressed the proliferation, BrdU incorporation, and the proportion of Ki67-positive cells in NPCs. However, knockdown of RhoG did not affect differentiation and survival of NPC. The RhoG-induced promotion of BrdU incorporation required phosphatidylinositol 3-kinase (PI3K) activity but not the interaction with ELMO. Taken together, these results indicate that RhoG promotes NPC proliferation through PI3K in cortical development.. |
| 12. | Yasuhiro Saito, Izumi Oinuma, Satoshi Fujimoto, Manabu Negishi, Plexin-B1 is a GTPase activating protein for M-Ras, remodelling dendrite morphology, EMBO Reports, 10.1038/embor.2009.63, 10, 6, 614-621, 2009.06, [URL], Plexins are receptors for axonal guidance molecules known as semaphorins. We recently reported that the semaphorin 4D (Sema4D) receptor, Plexin-B1, induces axonal growth cone collapse by functioning as an R-Ras GTPase activating protein (GAP). Here, we report that Plexin-B1 shows GAP activity for M-Ras, another member of the Ras family of GTPases. In cortical neurons, the expression of M-Ras was upregulated during dendritic development. Knockdown of endogenous M-Ras-but not R-Ras-reduced dendritic outgrowth and branching, whereas overexpression of constitutively active M-Ras, M-Ras(Q71L), enhanced dendritic outgrowth and branching. Sema4D suppressed M-Ras activity and reduced dendritic outgrowth and branching, but this reduction was blocked by M-Ras(Q71L). M-Ras(Q71L) stimulated extracellular signal-regulated kinase (ERK) activation, inducing dendrite growth, whereas Sema4D suppressed ERK activity and down-regulation of ERK was required for a Sema4D-induced reduction of dendrite growth. Thus, we conclude that Plexin-B1 is a dual functional GAP for R-Ras and M-Ras, remodelling axon and dendrite morphology, respectively.. |
| 13. | Shuhei Ueda, Satoshi Fujimoto, Kiyo Hiramoto, Manabu Negishi, Hironori Katoh, Dock4 regulates dendritic development in hippocampal neurons, Journal of Neuroscience Research, 10.1002/jnr.21763, 86, 14, 3052-3061, 2008.11, [URL], Dendrite development is required for establishing proper neuronal connectivity. Rho-family small GTPases have been reported to play important roles in the regulation of dendritic growth and morphology. However, the molecular mechanisms that control the activities of Rho GTPases in developing dendrites are not well understood. In the present study we found Dock4, an activator of the small GTPase Rac, to have a role in regulating dendritic growth and branching in rat hippocampal neurons. Dock4 is highly expressed in the developing rat brain, predominantly in hippocampal neurons. In dissociated cultured hippocampal neurons, the expression of Dock4 protein is up-regulated after between 3 and 8 days in culture, when dendrites begin to grow. Knockdown of endogenous Dock4 results in reduced dendritic growth and branching. Conversely, overexpression of Dock4 with its binding partner ELMO2 enhances the numbers of dendrites and dendritic branches. These morphological effects elicited by Dock4 and ELMO2 require Rac activation and the C-terminal Crk-binding region of Dock4. Indeed, Dock4 forms a complex with ELMO2 and CrkII in hippocampal neurons. These findings demonstrate a new function of the Rac activator Dock4 in dendritic morphogenesis in hippocampal neurons.. |
| 14. | Hironori Katoh, Satoshi Fujimoto, Chisaki Ishida, Yukio Ishikawa, Manabu Negishi, Differential distribution of ELMO1 and ELMO2 mRNAs in the developing mouse brain, Brain Research, 10.1016/j.brainres.2005.12.085, 1073-1074, 1, 103-108, 2006.02, [URL], ELMO is an upstream regulator of the Rho family small GTPase Rac. We investigated the distributions of mRNAs of two subtypes of ELMO, ELMO1 and ELMO2, in the developing mouse brain. Both ELMO1 and ELMO2 mRNAs are widely distributed in the developing mouse brain, but they were expressed in different neuronal populations in the cerebral cortex, thalamus, and cerebellum. Thus, ELMO1 and ELMO2 may play different roles during brain development.. |
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