2013 Fiscal Year Annual Research Report
マウス体性感覚野を用いた皮質カラム構造の発達メカニズムの解明
| Project/Area Number |
13J05789
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| Research Institution | The Graduate University for Advanced Studies |
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Principal Investigator |
羅 ブンジュウ 総合研究大学院大学, 生命科学研究科, 特別研究員(DC2)
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| Keywords | 皮質カラム / 神経回路形成 / バレル / 体性感覚野 / Gap結合 / コネキシン / NMDA受容体 / 樹状突起伸展 |
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| Research Abstract |
The cortex of mammalian brain is composed of distinct functional areas, which are believed to be further formed by "cortical columns". Cortical columns refer to a vertical cluster of cells with the same tuning for given receptive field. Thus, they are regarded as the fundamental unit of cortical information processing. However, how cortical column forms remains unclear. To address this issue, we utilized "barrels" as a model system. In layer 4 (L4) of mouse somatosensory cortex, spiny stellate neurons (barrel cells) extend their dendrites toward barrel center to make synapses with thalamocortical axon terminals. This dendritic asymmetry, which is established during early postnatal stage in an activity-dependent manner, enables each barrel cell to process sensory information from one whisker.
We supposed that gap junction-mediated interactions between L4 cortical neurons may play important roles in dendritic formation of barrel cells. In immature neocortex, gap junction-mediated neural c
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oupling between cortical neurons and the expression of the neuron-specific gap junction protein, connexin 36 (Cx36), increase during first two weeks of postnatal development, and then decline during the following two weeks, at a time just before the numbers of chemical synapse increase most rapidly. To address whether and how gap junction participates in dendritic refinement of barrel cells, we blocked endogenous Cx36 function by transfecting dominant negative form of Cx36 (mutant Cx36) into most or sparse L4 neurons using in utero electroporation. Morphological analysis under both conditions showed that Cx36 functions cell-autonomously to regulate dendritic refinement of barrel cells by enhancing their dendritic orientation through extending their inside dendrites. Moreover, we also over-expressed mutant Cx36 into most L4 neurons from 2nd postnatal week, after barrel cells dendrites acquired orientation bias. Histological analysis revealed that Cx36 may functions from 2nd postnatal week to regulate barrel cell dendrites refinement. Less
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We developed a novel system to express various types of proteins in a sparse population of neurons (Mizuno H., Luo W., et al. 2014) and successfully characterized the cell-autonomous function of Cx36 in dendritic. refinement of barrel cells. These results may provide valuable information for characterizing the role of synaptic and/or gap junction-mediated interactions in barrel formation, thus further elucidating the mechanisms of development of cortical neural circuit underlying pattern of columnar architecture.
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| Strategy for Future Research Activity |
Further analysis will be performed to characterize the molecular and cellular mechanisms of to Cx36-dependent dendritic refinement of barrel cells. (1) To exam whether Cx36 expression is activity-dependent or not, we will block the neural activity by over-expressing kir2.1 into most of L4 cortical neurons and quantify Cx36 protein expression. (2) To characterize whether electrical coupling between cortical neurons are decreased when mutant Cx36 is over-expressed in most L4 neurons or not, we will quantify the coupling frequency between L4 neurons under normal and mutant Cx36 over-expressing condition whole cell patch clamp recording.
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Research Products
(3 results)
