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August 16-17, 2018 | Copenhagen, Denmark
Dementia and Alzheimer ’s Disease
10
th
World congress on
Journal of Neurology and Neurorehabilitation Research | Volume: 3
Electric axon guidance in embryonic retina: Involvement of integrins
Masayuki Yamashita
Center for Medical Science, Japan
T
he axons of embryonic brain, spinal cord, and retina extend
along the extracellular voltage gradient towards the cathode
in a process known as galvanotropism. In embryonic nervous
tissues, positive direct current (DC) potentials are generated by
neuroepithelial cell’s sodium transport1, of which disruption
results in erroneous axon path-finding4, suggesting that electric
fields play a pivotal role in orienting newborn axons. However,
the experimental evidence was lacking for the cell surface
molecule that is activated asymmetrically in an electric field.
Here I show that integrin activation mediates electric axon
guidance. Retinal strips of chick embryos were embedded
in Matrigel®, and cultured in the electric field of the same
strength as that in vivo (15 mV/mm)4. Matrigel® contained the
same extracellular matrix proteins as in the embryonic retina,
laminin and collagen, to which integrins bind. Retinal ganglion
cell axons extended towards the cathode2. A monoclonal anti-
chicken integrin antibody (TASC), which enhances integrin-
ligand binding, accelerated the cathodal growth. A reduction
in the extracellular free Ca2+ with EGTA also enhanced the
cathodal growth, which suggested that millimolar Ca2+ inhibits
axon growth, and also that the influx of Ca2+ was unlikely to
be essential for cathodal steering. In the presence of Mn2+,
which non-specifically activates integrin-ligand binding, the
axons formed local meshes. These results suggested that the
inhibition of integrins by the extracellular Ca2+ underlies
electric axon guidance.
Recent Publications:
1. Yamashita M (2016) Epithelial sodium channels (ENaC)
produce extracellular positive DC potentials in the retinal
neuroepithelium. Data in Brief, 6: 253-256.
2. Yamashita M (2015) Weak electric fields serve as
guidance cues that direct retinal ganglion cell axons in vitro.
Biochemistry and Biophysics Reports, 4: 83-88.
3. Yamashita M (2015) Electrophysiological recordings from
neuroepithelial stem cells. Stem Cell Renewal and Cell-Cell
Communication (Ed. Turksen K), Methods in Molecular
Biology, Springer Protocols, 1212: 195-200.
4. Yamashita M (2013) Electric axon guidance in embryonic
retina: Galvanotropism revisited. Biochem Biophys Res
Commun, 431: 280-283.
5. Yamashita M (2013) From neuroepithelial cells to neurons:
Changes in the physiological properties of neuroepithelial
stem cells. Arch Biochem Biophys, 534: 64-70.
6. Yamashita M (2012) Ion channel activities in neural stem
cells of the neuroepithelium. Stem Cells International, 2012:
doi: org/10.1155/2012/247670.
Speaker Biography
Masayuki Yamashita is a professor of physiology at International University of
Health and Welfare. He received his PhD at the Department of Neurophysiology,
Institute of Brain Research, School of Medicine, University of Tokyo in 1986. He
moved to National Institute for Physiological Sciences (Okazaki, Japan) as a JSPS
fellow and a research associate. In 1989, he started physiological studies of retina
at the Department of Neuroanatomy, Max-Planck-Institute for Brain Research
(Frankfurt/M). After the reunification of Germany, he moved to the Department
of Physiology, Osaka University Medical School. He studied the calcium signaling
systems in embryonic chick retina. Then, he moved to the Department of Physiology,
Nara Medical University as a professor (1999-2014). He has been interested in the
electrophysiological properties of neuroepithelial cells and newborn neurons. The
retina is a nice model for studying the early development of central nervous systems.
e:
my57@iuhw.ac.jp