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AP-1cFos/JunB/miR-200a regulate the pro-regenerative glial cell response during axolotl spinal cord regeneration

ABSTRACT: Salamanders have the remarkable ability to functionally regenerate after spinal cord transection. In response to injury, GFAP+ glial cells in the axolotl spinal cord proliferate and migrate to replace the missing neural tube and create a permissive environment for axon regeneration. Molecular pathways that regulate the pro-regenerative axolotl glial cell response are poorly understood. Here we show axolotl glial cells up-regulate AP-1cFos/JunB after injury, which promotes a pro-regenerative glial cell response. Axolotl glial cells directly repress c-Jun expression via up-regulation of miR-200a. Inhibition of miR-200a during regeneration causes defects in axonal regrowth and transcriptomic analysis revealed that miR-200a inhibition leads to differential regulation of genes involved with reactive gliosis, the glial scar, ECM remodeling and axon guidance. This work identifies a novel role for miR-200a in inhibiting reactive gliosis in glial cell in axolotl during spinal cord regeneration

ORGANISM(S): Ambystoma mexicanum

PROVIDER: GSE122939 | GEO | 2019/03/19

REPOSITORIES: GEO

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Project description:Salamanders, such as the Mexican axolotl, are some of the few vertebrates fortunate in their ability to regenerate diverse structures after injury. Unlike mammals they are able to regenerate a fully functional spinal cord after injury. However, the early signals required to initiate a pro-regenerative response after spinal cord injury is not well understood. To address this question we developed a spinal cord injury model in axolotls and used in vivo imaging of ion sensitive dyes and determined that spinal cord injury induces a rapid and dynamic change in the resting membrane potential of ependymoglial cells. Prolonged depolarization of ependymoglial cells after injury inhibits glial cell proliferation and subsequent axon regeneration. Using transcriptional profiling we identified c-Fos as a key voltage sensitive early response gene that is expressed specifically in the ependymoglial cells after injury. This data establishes that dynamic changes in the membrane potential after injury are essential for regulating the specific spatiotemporal expression of c-Fos that is critical for promoting faithful spinal cord regeneration in axolotl. All axolotls used in these experiments were bred in the axolotl facility at the University of Minnesota under the IACUC protocol #1201A08381. Axolotls of 2â3 cm were used for all in vivo experiments, and animals were kept in separate containers and fed daily with artemia; water was changed daily. Animals were anesthetized in 0.01% p-amino benzocaine (Sigma) before microinjection was performed. Experimental Design: Ivermectin injection Ivermectin or vehicle only (water) was pressure injected into the central canal of the spinal cord, and this was visualized by the addition of Fast Green into the solution. Directly after injection, a portion of the spinal cord was surgically removed and the animals were placed back into water in individual containers. One day post injury (1dpi) animals were anesthetized again and the area of the injury was removed. Tissue from 10 animals were pooled for each microarray replicate.

Project description:Background: The efficient regenerative abilities at larvae stages followed by a non-regenerative response after metamorphosis in froglets makes Xenopus an ideal model organism to understand the cellular responses leading to spinal cord regeneration. Methods: We compared the cellular response to spinal cord injury between the regenerative and non-regenerative stages of Xenopus laevis. For this analysis, we used electron microscopy, immunofluorescence and histological staining of the extracellular matrix. We generated two transgenic lines: i) the reporter line with the zebrafish GFAP regulatory regions driving the expression of EGFP, and ii) a cell specific inducible ablation line with the same GFAP regulatory regions. In addition, we used FACS to isolate EGFP + cells for RNAseq analysis. Results: In regenerative stage animals, spinal cord regeneration triggers a rapid sealing of the injured stumps, followed by proliferation of cells lining the central canal, and formation of rosette-like structures in the ablation gap. In addition, the central canal is filled by cells with similar morphology to the cells lining the central canal, neurons, axons, and even synaptic structures. Regeneration is almost completed after 20 days post injury. In non-regenerative stage animals, mostly damaged tissue was observed, without clear closure of the stumps. The ablation gap was filled with fibroblast-like cells, and deposition of extracellular matrix components. No reconstruction of the spinal cord was observed even after 40 days post injury. Cellular markers analysis confirmed these histological differences, a transient increase of vimentin, fibronectin and collagen was detected in regenerative stages, contrary to a sustained accumulation of most of these markers, including chondroitin sulfate proteoglycans in the NR-stage. The zebrafish GFAP transgenic line was validated, and we have demonstrated that is a very reliable and new tool to study the role of neural stem progenitor cells (NSPCs). RNASeq of GFAP::EGFP cells has allowed us to clearly demonstrate that indeed these cells are NSPCs. On the contrary, the GFAP::EGFP transgene is mainly expressed in astrocytes in non-regenerative stages. During regenerative stages, spinal cord injury activates proliferation of NSPCs, and we found that are mainly fated to form neurons and glial cells. Specific ablation of these cells abolished proper regeneration, confirming that NSPCs cells are necessary for functional regeneration of the spinal cord. Conclusions: The cellular response to spinal cord injury in regenerative and non-regenerative stages is profoundly different between both stages. A key hallmark of the regenerative response is the activation of NSPCs, which massively proliferate to reconstitute the spinal cord, and are differentiated into neurons. Also very notably, no glial scar formation is observed in regenerative stages, but a transient, glial scar-like structure is formed in non-regenerative stage animals.

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AP-1cFos/JunB/miR-200a regulate the pro-regenerative glial cell response during axolotl spinal cord regeneration

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