公募シンポジウム９：神経細胞の発生と機能獲得のシンクロニティ
Symposium9 : The synchronicity of neuronal development and functional acquisition |
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| 2020/9/11 10:50～11:10 Zoom B
SY9-01
神経幹細胞における、転写因子のダイナミックな発現制御機構
Dynamic transcriptional regulation of neural stem cells by bHLH factors
*山田 真弓1
1. 京都大学大学院生命科学研究科
*Mayumi Yamada1
1. Graduate School of Biostudies, Kyoto University
The mammalian brain consists of a complex ensemble of neurons and glial cells. Their production during development and remodelling is tightly controlled by various regulatory mechanisms in neural stem cells (NSCs). Among such regulations, basic helix-loop-helix (bHLH) transcription factors have key functions in the self-renewal, multipotency, and fate determination of NSCs. Several bHLH transcription factors are co-expressed by NSCs and change its expression patterns uniquely during cell-fate determination. By time-lapse imaging, we found that these factors are expressed in an oscillatory manner by NSCs. Here, we focus on the importance of the expression dynamics of bHLH transcription factors. To analyze causal relationships between the dynamic gene expression changes of bHLH transcription factors and NSC regulations, it is essential to manipulate bHLH transcription factors expressions with the fine temporal and spatial resolution. Recently, we developed a novel photoactivatable gene expression system for precise temporal and spatial control of gene expression at single-cell resolution. This system had a large dynamic range of downstream gene expression, rapid activation, and deactivation kinetics. We are planning to adapt this optogenetic system to control the expression dynamics of bHLH transcription factors to understand their functional roles in cell proliferation, fate-determination, and differentiation of NSCs.
| | 2020/9/11 11:10～11:30 Zoom B
SY9-02
脳室面からの神経細胞離脱におけるDSCAMを介した制御
Regulation of Neuronal Delamination by DSCAM and its signaling molecules
*有村 奈利子1、田谷 真一郎1、星野 幹雄1
1. 国立精神・神経医療研究センター
*Nariko Arimura1, Shinichiro Taya1, Mikio Hoshino1
1. National Center of Neurology and Psychiatry
During brain development, most nascent neurons detach their apical endfeet from the ventricular surface and initiate migration towards their final positions from their site of production. The impairment of neuronal migration has been implicated in human brain disorders, such as periventricular nodular heterotopia and autism spectrum disorder. Thus, normal neuronal migration is fundamental to the architectural formation and functional wiring of the nervous system, and delamination of differentiating neurons from the proliferative zone must be precisely controlled; however, the regulatory mechanisms underlying cell attachment are poorly understood. Recently, we found that Down syndrome cell adhesion molecule (DSCAM) controls neuronal delamination by local suppression of the RapGEF2-Rap1-N-cadherin cascade at the apical endfeet in the dorsal midbrain. Dscam transcripts were expressed in differentiating neurons, and DSCAM protein accumulated at the distal part of the apical endfeet. Cre-loxP-based neuronal labelling revealed that Dscam knockdown impaired endfeet detachment from ventricles. DSCAM associated with RapGEF2 to inactivate Rap1, whose activity is required for membrane localization of N-cadherin. Correspondingly, Dscam knockdown increased N-cadherin localization and ventricular attachment area at the endfeet. Furthermore, excessive endfeet attachment by Dscam knockdown was restored by co-knockdown of RapGEF2 or N-cadherin. This study demonstrates the molecular mechanism by which DSCAM and its signaling molecules suppress cell adhesion molecules in a cell-autonomous manner, and it provides insight into various biological events that cell adhesion molecules may control for functional wiring of the nervous system.
| | 2020/9/11 11:30～11:50 Zoom B
SY9-03
サブプレートニューロンの神経活動による大脳新皮質構築のメカニズム
Mechanisms of neocortical organization by neuronal activity of subplate neurons
*丸山 千秋1
1. 公益財団法人東京都医学総合研究所
*Chiaki Ohtaka-Maruyama1
1. Tokyo Metropolitan Institute of Medical Science
In the mammalian neocortex, an enormous number of neurons are precisely arranged in an ordered 6-layered structure in an inside-out manner. This structure is formed by the sequential generation of neurons and their migration toward the brain surface, termed radial neuronal migration. We previously reported that subplate neurons (SpNs), which are one of the earliest born and matured types of neurons in the developing neocortex, play an important role in the regulation of radial migration. We revealed that SpNs exhibit spontaneous calcium oscillations at E15, and actively extend processes to contact newly born multipolar migrating neurons (MpNs). Electron microscopic observation demonstrated that synapse-like structures were formed at these contact sites. This synaptic communication leads to the switch from multipolar migration to locomotion. SpNs are the first cortical neurons to receive sensory input from thalamic axons. SpNs then project axons toward layer IV neurons to establish a temporal link between thalamic axons and their final target in layer IV. This initial wiring also depends on SpN activity, suggesting that they function as a conductor for mammalian neocortical formation by organizing multiple processes, such as migration, axon pathfinding and synaptogenesis, which progress simultaneously in the fetal period. SpNs consist of heterogeneous cell populations, suggesting that each subpopulation has distinct roles in neocortical formation and function. To elucidate the function of SpNs in more detail, we are now characterizing their subpopulations using a SpN-specific transgenic mouse lines.
| | 2020/9/11 11:50～12:10 Zoom B
SY9-04
大脳皮質領野固有の細胞構築様式表出に関わる細胞・分子機序
Cellular and molecular machinery to emerge area-specific cytoarchitecture in the cerebral cortex
*井上 高良1
1. 国立精神・神経医療研究センター 神経研究所
*Takayoshi Inoue1
1. National Institute of Neuroscience, NCNP
A mammal specific brain region, cerebral cortex (ctx) can be subdivided into tens of functional units, namely the neocortical areas in its tangential dimension. Here I dissect regulatory codes for mouse cadherin-6 (Cdh6) gene whose expression delineates cortical areal boundaries to elaborate the area specific cytoarchitecture at the postnatal stages. By generating stable transgenic mouse lines from reporter-modified bacterial artificial chromosomes (BACs) with differential and extensive coverage of the huge Cdh6 gene locus, I confirm that each discrete genomic segment that includes distinct sets of enhancers regulates Cdh6 expression only within a fraction of Cdh6 mRNA expressing domains in the mouse ctx. When mouse Cdh6 syntenic BAC clones from chicken (Gallus gallus), marmoset (Callithrix jacchus) and human (Homo sapiens) are reporter-modified and transferred into the mouse ctx, I find out that human and marmoset clones, but not chicken one, can fully recapitulate the layer-specificity comparable to the Cdh6::reporter expression profiles from the mouse clone. Additionally, I reveal that the areal specificity yielded by specific sets of enhancers varies among mouse, marmoset and human clones, implicating its rapid evolutionary incorporation into the genome. I further demonstrate that the layer VI specific Cdh6::reporter expression is developmentally and evolutionarily under the control of Tbr1 and these layer VI Cdh6::reporter positive cells are selectively sorted in the in vitro aggregation assay in a manner dependent of Ca2+. These results provide evidence that cooption of divisible genetic elements with Cdh6 adhesive function may direct development and/or evolution of cytoarchitecture exclusive to each neocortical area and/or layer in mammals.
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