Graduate School of Frontier Biosciences, Osaka University

Japanese

Colloquium 232

Speaker Kensuke Sasaki (Postdoc (Cellular and Molecular Neurobiology Group ( Yamamoto Lab.)
Title Rho guanine nucleotide exchange factors regulate axon branching of cortical neurons
Speaker Yumi Miyasaka (Graduate student D5/D5 ( Cellular and Molecular Neurobiology Group ( Yamamoto Lab.))
Title Patterned neuronal firing regulates spatiotemporal gene expression in the developing cortex
Date Thu., Nov. 21, 2019, 12:15~13:00
Place 2F Seminar room, BioSystems Building
Host Name:Ryuichi Shirasaki       
Tel :06-6879-4635
E-mail:shirasaki@fbs.osaka-u.ac.jp
Language Japanese












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Title/Abstract

Rho guanine nucleotide exchange factors regulate axon branching of cortical neurons

Axon branching is a crucial process for neuronal circuit formation. However, how the cytoskeletal changes in axon branching are regulated is not fully understood. In the present study, we investigated the role of RhoA guanine nucleotide exchange factors (RhoA-GEFs) in branch formation of horizontally elongating axons (horizontal axons) in the mammalian cortex. In situ hybridization showed that more than half of all known RhoA-GEFs were expressed in the developing rat cortex. These RhoA-GEFs were mostly expressed in the macaque cortex as well. An overexpression study using organotypic cortical slice cultures demonstrated that several RhoA-GEFs strongly promoted horizontal axon branching. Moreover, branching patterns were different between overexpressed RhoA-GEFs. In particular, ARHGEF18 markedly increased terminal arbors of horizontal axons, whereas ABR increased short branches in both distal and proximal regions. Rho kinase inhibitor treatment completely suppressed the branch-promoting effect of ARHGEF18 overexpression, but partially affected that of ABR, suggesting that these RhoA-GEFs employ distinct downstream pathways. Furthermore, knockdown of either ARHGEF18 or ABR considerably suppressed axon branching. Taken together, the present study revealed that subsets of RhoA-GEFs promote axon branching of mammalian cortical neurons in different fashions.

Patterned neuronal firing regulates spatiotemporal gene expression in the developing cortex

Neuronal activity plays a crucial role in the formation of functional connections in the developing cortex. Previous studies have shown that neuronal activity induces expression of the effector molecules which regulate cortical circuit formation. An interesting question is how physiological neuronal activity modifies expression of these molecules within the cortex. To address this issue, we performed live imaging of gene expression in organotypically cultured cortical neurons, focusing on brain-derived neurotrophic factor (BDNF), one of the factors underlying cortical wiring. Then, the spatiotemporal changes of BDNF promoter activity which responds to pharmacological and electrical stimulation were investigated in individual cells. The result demonstrated that patterned stimuli with various frequency differentially increased the BDNF promoter activity in terms of the amplitudes and time courses. Interestingly, the increase levels were also varied among cells for the same patterned stimulation. Furthermore, cortical cells with similar increase levels were located closely. In summary, the present finding suggests that activity-dependent gene expression of BDNF in cortical neurons is regulated differentially by stimulation patterns whereas cortical cells with similar activity dependence are arranged structurally.


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