IMR Press / JIN / Volume 18 / Issue 4 / DOI: 10.31083/j.jin.2019.04.1191
Retraction published on 30 September 2020, see Journal of Integrative Neuroscience 2020, 19(3)
Open Access Original Research
Real time large scale in vivo observations reveal intrinsic synchrony, plasticity and growth cone dynamics of midline crossing axons at the ventral floor plate of the zebrafish spinal cord
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1 SciLifeLab BioVis Facility, Uppsala University, Dag Hammarskjölds väg 14 B, S-751 85 Uppsala, Sweden
2 Department of Neuroscience, Biomedical Center (BMC), Uppsala University, Husargatan 3, Box 593, S-751 24 Uppsala, Sweden
3 SciLifeLab Zebrafish Technology Facility, Evolutionary Biology Center (EBC), Uppsala University, Norbyvägen 18A, S-752 36 Uppsala, Sweden
*Correspondence: (Søren S. L. Andersen)
J. Integr. Neurosci. 2019, 18(4), 351–368;
Submitted: 19 September 2019 | Accepted: 18 November 2019 | Published: 30 December 2019
Copyright: © 2019 Andersen Published by IMR Press.
This is an open access article under the CC BY-NC 4.0 license

How axons are wiring the vertebrate spinal cord has in particular been studied at the ventral floor plate using fixed samples or looking at single growing axons with various microscopy techniques. Thereby may remain hidden important live organismal scale information concerning dynamics and concurrent timing of the many axons simultaneously crossing the floor plate. Here then, applying light-sheet microscopy, axonal growth and guidance at the floor plate are followed in vivo in real time at high resolution along several hundred micrometers of the zebrafish spinal cord by using an interneuron expressing GFP as a model axon. The commissural axons are observed crossing the ventral floor plate midline perpendicularly at about 20 microns/h and in a manner dependent on the Robo3 receptor. Commissural growth rate reaches a minimum at the midline, confirming previous observations. Ipsilateral axons extend concurrently, at three to six times higher growth rates. At guidance points, commissural axons are seen to decrease their growth rate and growth cones increase in size. Commissural filopodia appear to interact with the nascent neural network, and thereby trigger immediate plastic and reversible sinusoidal-shaped bending movements of neighboring commissural shafts. A simple protocol isolating single neuronal cells from the spinal cord is developed to facilitate further molecular characterization. The recordings show the strikingly stereotyped spatio-temporal control that governs midline crossing. The live observations give renewed perspective on the mechanisms of axonal guidance in the spinal cord that provide for a discussion of the current distinction between diffusible long-range versus substrate-bound short-range guidance cues.

Light sheet
model axon
extracellular matrix
real time
Figure 1.
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