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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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Schematic representation of the pLL neuromast innervation patterns before and after nerve regeneration. (A) The specific innervation of neuromasts (L1 to L5 or the terminal neuromasts, (LT) by single labeled pLL ganglion neurons was recorded before neurectomy and after nerve regeneration (48 hpn). Each neuron belongs to a different larva and is represented by a unique color in the diagram. The larger circles represent the innervated primary neuromasts whereas the small ovals represent secondary neuromasts. (B) The number of neuromasts innervated by single labeled neurons was recorded before (1 hbi) and 48 hpn. The average number of neuromasts innervated is not significantly different between both samples (P <0.05). (C) The pattern of pLL neuromast innervation before neurectomy and after regeneration was compared by calculating the ‘mean sensory field’ of individual neurons in both conditions (calculated from data shown in panel A; see Methods). A perfect fit (reinnervation of the exact same targets after regeneration) is shown as a dashed red line, and the actual data is the solid black line (significance of fit: P = 0.009). Statistically (P = 0.0618), both slopes are equal.
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Figure 2: Schematic representation of the pLL neuromast innervation patterns before and after nerve regeneration. (A) The specific innervation of neuromasts (L1 to L5 or the terminal neuromasts, (LT) by single labeled pLL ganglion neurons was recorded before neurectomy and after nerve regeneration (48 hpn). Each neuron belongs to a different larva and is represented by a unique color in the diagram. The larger circles represent the innervated primary neuromasts whereas the small ovals represent secondary neuromasts. (B) The number of neuromasts innervated by single labeled neurons was recorded before (1 hbi) and 48 hpn. The average number of neuromasts innervated is not significantly different between both samples (P <0.05). (C) The pattern of pLL neuromast innervation before neurectomy and after regeneration was compared by calculating the ‘mean sensory field’ of individual neurons in both conditions (calculated from data shown in panel A; see Methods). A perfect fit (reinnervation of the exact same targets after regeneration) is shown as a dashed red line, and the actual data is the solid black line (significance of fit: P = 0.009). Statistically (P = 0.0618), both slopes are equal.

Mentions: Using the strategy described above, we examined individual axons in DNA injected larvae and recorded which neuromasts were innervated pre vs. post neurectomy (Figure 2). We considered only afferent neurons whose peripheral projections were recognizable continuously throughout the experiment in order to ensure that we were always evaluating the behavior of the same neuron (see Additional file1).


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)

Schematic representation of the pLL neuromast innervation patterns before and after nerve regeneration. (A) The specific innervation of neuromasts (L1 to L5 or the terminal neuromasts, (LT) by single labeled pLL ganglion neurons was recorded before neurectomy and after nerve regeneration (48 hpn). Each neuron belongs to a different larva and is represented by a unique color in the diagram. The larger circles represent the innervated primary neuromasts whereas the small ovals represent secondary neuromasts. (B) The number of neuromasts innervated by single labeled neurons was recorded before (1 hbi) and 48 hpn. The average number of neuromasts innervated is not significantly different between both samples (P <0.05). (C) The pattern of pLL neuromast innervation before neurectomy and after regeneration was compared by calculating the ‘mean sensory field’ of individual neurons in both conditions (calculated from data shown in panel A; see Methods). A perfect fit (reinnervation of the exact same targets after regeneration) is shown as a dashed red line, and the actual data is the solid black line (significance of fit: P = 0.009). Statistically (P = 0.0618), both slopes are equal.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Schematic representation of the pLL neuromast innervation patterns before and after nerve regeneration. (A) The specific innervation of neuromasts (L1 to L5 or the terminal neuromasts, (LT) by single labeled pLL ganglion neurons was recorded before neurectomy and after nerve regeneration (48 hpn). Each neuron belongs to a different larva and is represented by a unique color in the diagram. The larger circles represent the innervated primary neuromasts whereas the small ovals represent secondary neuromasts. (B) The number of neuromasts innervated by single labeled neurons was recorded before (1 hbi) and 48 hpn. The average number of neuromasts innervated is not significantly different between both samples (P <0.05). (C) The pattern of pLL neuromast innervation before neurectomy and after regeneration was compared by calculating the ‘mean sensory field’ of individual neurons in both conditions (calculated from data shown in panel A; see Methods). A perfect fit (reinnervation of the exact same targets after regeneration) is shown as a dashed red line, and the actual data is the solid black line (significance of fit: P = 0.009). Statistically (P = 0.0618), both slopes are equal.
Mentions: Using the strategy described above, we examined individual axons in DNA injected larvae and recorded which neuromasts were innervated pre vs. post neurectomy (Figure 2). We considered only afferent neurons whose peripheral projections were recognizable continuously throughout the experiment in order to ensure that we were always evaluating the behavior of the same neuron (see Additional file1).

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