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Axon-Schwann cell interactions during peripheral nerve regeneration in zebrafish larvae.

Ceci ML, Mardones-Krsulovic C, Sánchez M, Valdivia LE, Allende ML - Neural Dev (2014)

Bottom Line: Furthermore, Schwann cells are required for directional extension and fasciculation of the regenerating nerve.We provide evidence that these cells and regrowing axons are mutually dependant during early stages of nerve regeneration in the pLL.The accessibility of the pLL nerve and the availability of transgenic lines that label this structure and their synaptic targets provides an outstanding in vivo model to study the different events associated with axonal extension, target reinnervation, and the complex cellular interactions between glial cells and injured axons during nerve regeneration.

View Article: PubMed Central - HTML - PubMed

Affiliation: FONDAP Center for Genome Regulation, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile. allende@uchile.cl.

ABSTRACT

Background: Peripheral nerve injuries can severely affect the way that animals perceive signals from the surrounding environment. While damage to peripheral axons generally has a better outcome than injuries to central nervous system axons, it is currently unknown how neurons re-establish their target innervations to recover function after injury, and how accessory cells contribute to this task. Here we use a simple technique to create reproducible and localized injury in the posterior lateral line (pLL) nerve of zebrafish and follow the fate of both neurons and Schwann cells.

Results: Using pLL single axon labeling by transient transgene expression, as well as transplantation of glial precursor cells in zebrafish larvae, we individualize different components in this system and characterize their cellular behaviors during the regenerative process. Neurectomy is followed by loss of Schwann cell differentiation markers that is reverted after nerve regrowth. We show that reinnervation of lateral line hair cells in neuromasts during pLL nerve regeneration is a highly dynamic process with promiscuous yet non-random target recognition. Furthermore, Schwann cells are required for directional extension and fasciculation of the regenerating nerve. We provide evidence that these cells and regrowing axons are mutually dependant during early stages of nerve regeneration in the pLL. The role of ErbB signaling in this context is also explored.

Conclusion: The accessibility of the pLL nerve and the availability of transgenic lines that label this structure and their synaptic targets provides an outstanding in vivo model to study the different events associated with axonal extension, target reinnervation, and the complex cellular interactions between glial cells and injured axons during nerve regeneration.

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pLL nerve regeneration in sdf1 mutant larvae. (A) A 3 dpf sdf1 mutant larva (also transgenic for neuroD:EGFP) shows a severely altered pLL due to failures in primordium migration during early development. The nerve is located over the yolk rather than along the horizontal myoseptum. (B) The larva was imaged immediately after neurectomy; the point of neurectomy is indicated by an arrow. Arrowhead points to an aberrant branch of the nerve that migrated towards the ventral yolk. (C) A few hours after neurectomy, the distal nerve has degenerated. (D) Twenty-four hours post neurectomy, the nerve has regenerated and follows exactly the same route as that of the original nerve, including the aberrant branch indicated in B (arrowhead). Scale: A-D: 100 μm.
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Figure 9: pLL nerve regeneration in sdf1 mutant larvae. (A) A 3 dpf sdf1 mutant larva (also transgenic for neuroD:EGFP) shows a severely altered pLL due to failures in primordium migration during early development. The nerve is located over the yolk rather than along the horizontal myoseptum. (B) The larva was imaged immediately after neurectomy; the point of neurectomy is indicated by an arrow. Arrowhead points to an aberrant branch of the nerve that migrated towards the ventral yolk. (C) A few hours after neurectomy, the distal nerve has degenerated. (D) Twenty-four hours post neurectomy, the nerve has regenerated and follows exactly the same route as that of the original nerve, including the aberrant branch indicated in B (arrowhead). Scale: A-D: 100 μm.

Mentions: We wished to provide further confirmation of this interdependence between Schwann cells and regrowing axons by carrying out regeneration experiments in the sdf1a mutant, in which the pLL primordium migrates aberrantly during development along the ventral body or yolk sac, misguiding the axons of the pLL nerve (C. Mardones, unpublished results). In the mutants, glial cells co-migrate with the ectopically growing nerve and are present in all the nerve branches that defasciculate to innervate nearby neuromasts (not shown). In order to neurectomize the nerve in mutant animals, we crossed the sdf1au766 mutants into the tg(neuroD:EGFP) background, which labels the pLL axons[30,54]. At 3 dpf, sdf1a mutant nerves are observed to follow different pathways originating at the ganglion (Figure 9). After 24 hpn in mutant fish, the regrowing axons strictly follow the aberrant route established during development, maintaining close contact with the chain of glial cells that lie along the way and reproducing the exact pattern of nerve branching observed after initial development of the tract (Figure 9B and D, arrowhead).


Axon-Schwann cell interactions during peripheral nerve regeneration in zebrafish larvae.

Ceci ML, Mardones-Krsulovic C, Sánchez M, Valdivia LE, Allende ML - Neural Dev (2014)

pLL nerve regeneration in sdf1 mutant larvae. (A) A 3 dpf sdf1 mutant larva (also transgenic for neuroD:EGFP) shows a severely altered pLL due to failures in primordium migration during early development. The nerve is located over the yolk rather than along the horizontal myoseptum. (B) The larva was imaged immediately after neurectomy; the point of neurectomy is indicated by an arrow. Arrowhead points to an aberrant branch of the nerve that migrated towards the ventral yolk. (C) A few hours after neurectomy, the distal nerve has degenerated. (D) Twenty-four hours post neurectomy, the nerve has regenerated and follows exactly the same route as that of the original nerve, including the aberrant branch indicated in B (arrowhead). Scale: A-D: 100 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4214607&req=5

Figure 9: pLL nerve regeneration in sdf1 mutant larvae. (A) A 3 dpf sdf1 mutant larva (also transgenic for neuroD:EGFP) shows a severely altered pLL due to failures in primordium migration during early development. The nerve is located over the yolk rather than along the horizontal myoseptum. (B) The larva was imaged immediately after neurectomy; the point of neurectomy is indicated by an arrow. Arrowhead points to an aberrant branch of the nerve that migrated towards the ventral yolk. (C) A few hours after neurectomy, the distal nerve has degenerated. (D) Twenty-four hours post neurectomy, the nerve has regenerated and follows exactly the same route as that of the original nerve, including the aberrant branch indicated in B (arrowhead). Scale: A-D: 100 μm.
Mentions: We wished to provide further confirmation of this interdependence between Schwann cells and regrowing axons by carrying out regeneration experiments in the sdf1a mutant, in which the pLL primordium migrates aberrantly during development along the ventral body or yolk sac, misguiding the axons of the pLL nerve (C. Mardones, unpublished results). In the mutants, glial cells co-migrate with the ectopically growing nerve and are present in all the nerve branches that defasciculate to innervate nearby neuromasts (not shown). In order to neurectomize the nerve in mutant animals, we crossed the sdf1au766 mutants into the tg(neuroD:EGFP) background, which labels the pLL axons[30,54]. At 3 dpf, sdf1a mutant nerves are observed to follow different pathways originating at the ganglion (Figure 9). After 24 hpn in mutant fish, the regrowing axons strictly follow the aberrant route established during development, maintaining close contact with the chain of glial cells that lie along the way and reproducing the exact pattern of nerve branching observed after initial development of the tract (Figure 9B and D, arrowhead).

Bottom Line: Furthermore, Schwann cells are required for directional extension and fasciculation of the regenerating nerve.We provide evidence that these cells and regrowing axons are mutually dependant during early stages of nerve regeneration in the pLL.The accessibility of the pLL nerve and the availability of transgenic lines that label this structure and their synaptic targets provides an outstanding in vivo model to study the different events associated with axonal extension, target reinnervation, and the complex cellular interactions between glial cells and injured axons during nerve regeneration.

View Article: PubMed Central - HTML - PubMed

Affiliation: FONDAP Center for Genome Regulation, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile. allende@uchile.cl.

ABSTRACT

Background: Peripheral nerve injuries can severely affect the way that animals perceive signals from the surrounding environment. While damage to peripheral axons generally has a better outcome than injuries to central nervous system axons, it is currently unknown how neurons re-establish their target innervations to recover function after injury, and how accessory cells contribute to this task. Here we use a simple technique to create reproducible and localized injury in the posterior lateral line (pLL) nerve of zebrafish and follow the fate of both neurons and Schwann cells.

Results: Using pLL single axon labeling by transient transgene expression, as well as transplantation of glial precursor cells in zebrafish larvae, we individualize different components in this system and characterize their cellular behaviors during the regenerative process. Neurectomy is followed by loss of Schwann cell differentiation markers that is reverted after nerve regrowth. We show that reinnervation of lateral line hair cells in neuromasts during pLL nerve regeneration is a highly dynamic process with promiscuous yet non-random target recognition. Furthermore, Schwann cells are required for directional extension and fasciculation of the regenerating nerve. We provide evidence that these cells and regrowing axons are mutually dependant during early stages of nerve regeneration in the pLL. The role of ErbB signaling in this context is also explored.

Conclusion: The accessibility of the pLL nerve and the availability of transgenic lines that label this structure and their synaptic targets provides an outstanding in vivo model to study the different events associated with axonal extension, target reinnervation, and the complex cellular interactions between glial cells and injured axons during nerve regeneration.

Show MeSH
Related in: MedlinePlus