Cell-cell interactions during the migration of an identified commissural growth cone in the embryonic grasshopper

Abstract

One of the fascicles of the posterior commissure of the embryonic grasshopper is pioneered by an individually identifiable neuron named Q1. Q1 initially grows along a longitudinal pathway established by another pioneer neuron, MP1, and then crosses to the midline, where it meets and fasciculates with the axon of the contralateral Q1. The Q1 growth cone follows the contralateral Q1 axon to the contralateral longitudinal pathway, where it then fasciculates with axons of the MP1/dMP2 fascicle. In this work, we have identified a small set of early neurons that Q1 could use as guidance cues while negotiating its way along a specific and stereotyped pathway to the midline. Furthermore, we have observed characteristic morphological changes in the Q1 growth cone that could indicate responses to changing adhesivity in the substrates it contacts. We have also quantified the pattern of dye coupling between neurons in this system. Most of the neurons to which Q1 becomes coupled retain a strong, consistent pattern of dye coupling that shows no recognizable variation at times when growth cones are making pathway decisions. However, we have found one clear instance of transient, site-specific dye coupling between the Q1 growth cone and the ipsilateral MP1 soma. The timing and pattern of dye coupling in this system suggest that dye coupling may play a role in synchronizing the initiation of axon outgrowth among a small population of neurons. Although dye coupling may not play a direct role in neuronal pathfinding, it may exert a profound indirect influence on neuronal interactions by regulating the timing of axon outgrowth.

Commissural axonal corridors instruct neuronal migration in the mouse spinal cord

“…This idea is supported further by the finding that the cell bodies of Robo3-negative ipsilaterally projecting neurons migrate aberrantly through loss of the commissural neuron-specific receptor Robo3. There is good evidence to support the idea that in some contexts pioneer axons provide a growth substrate for newly migrating axons and cell bodies [10][11][12] . In addition, there are a number of reports of neuronal cell bodies that have the morphological appearance of migrating along axonal tracts 13,14,29,43,44 .…”

“…A small number of studies have shown that the position of cell bodies influence the guidance of axons by the production of chemotactic cues [7][8][9] . Conversely, there is also evidence to support the idea that pioneer axons provide a growth substrate for newly migrating axons and cell bodies [10][11][12] . In addition, during a form of tangential migration, photographic evidence suggests that the migrating neuronal cell bodies appear as if they are using axons as migration scaffolds 5,6,[13][14][15] .…”

Synergistic Effects of Physical and Chemical Guidance Cues on Neurite Alignment and Outgrowth on Biodegradable Polymer Substrates

“…Developing axons use adhesive cell contacts between the growth cone and cell adhesion molecules mediating interactions between the cell surface and extracellular matrix molecules. 20 Laminin acts as a cell adhesion molecule and also provides chemotropism by binding chemical factors such as nerve growth factor to the substrate surface, orienting neurite outgrowth. By combining laminin as a chemical cue with the patterned substrates for physical guidance, disruption in alignment due to interactions between cells on microgrooved substrates presenting only physical cues were found to be overcome to a great extent.…”

Cellular Strategies of Axonal Pathfinding

“…Fasciculation of axons enables the younger axons of a given population within the same trajectory to add onto the tracts laid down by pioneer and older axons. During midline crossing in the fly CNS, homotypic axons from opposite sides of the neuraxis meet and grow along each other's surfaces, an interaction that is required for midline crossing (Myers and Bastiani 1993). Reordering of axon subpopulations can occur along pathways through changes in fasciculation, such as when retinal ganglion cell axons from nasotemporal and dorso-ventral retinal quadrants shift their relative positions as they the extend through the optic chiasm (Chan and Chung 1999) and when bundles of retinal axons shift positions as they extend in the optic tract (Walsh and Guillery 1985).…”