Reorganization of the ependyma during axolotl spinal cord regeneration: Changes in intermediate filament and fibronectin expression

Abstract

Changes in intermediate fiiament content and extracellular matrix material showed that the injury response of ependymal cells in lesioned axolotl spinal cord involves an epithelial-to-mesenchymal transformation, and that fibrous astrocytes are excluded from the remodeling lesion site. Antibody localization was used to visualize cytokeratin-, vimentin-, and glial fibrillary acidic protein-(GFAP-) containing intermediate filaments, as well as the adhesive glycoprotein fibronectin. In normal axolotl spinal cord cytokeratins were found near the apical surface of the ependymal cells. Transmission electron microscopic examination suggested that these cytokeratins were in tonofilaments. Cytokeratin expression was lost and vimentin production was initiated in ependymal cells 23 weeks following spinal cord injury. There was a period of approximately 1-2 weeks when cytokeratins and vimentin were co-expressed in vivo. This co-expression was maintained in vitro by culture on a fibronectin-coated substratum. As the central canal reformed, vimentin expression was lost. Ependymal cells lacked GFAP intermediate filaments, but GFAP was present in fibrous astrocytes of the neuropil and white matter. Following injury, GFAP localization showed that fibrous astrocytes disappeared from the remodeling lesion site and reappeared only after the ependymal epithelium reformed and newly myelinated axons were found. Fibronectin expression closely followed the expression of vimentin during mesenchymal ependymal cell outgrowth. These results suggest that the ependymal cell outgrowth requires changes in cell shape followed by changes in production of extracellular matrix.

Cellular response after crush injury in adult zebrafish spinal cord

“…Observation by others confirms a similar nature of expression of GFAP where they showed initial loss after injury followed by an increased level of expression at later time points in urodele cord (O'Hara et al, 1992;Chernoff et al, 2003).…”

“…Ependymal sealing can be seen in both crush and transection injury (data not shown) in zebrafish. A similar mechanism of migration and accumulation of cells here may also involve epithelial to mesenchymal transition as observed by O'Hara et al (1992) and Chernoff (1996) in urodele. Sealing of ependyma during spinal cord regeneration was also confirmed in other regeneration-competent species in both adult and larval stages , Chernoff et al, 2003.…”

A clonal analysis of neural progenitors during axolotl spinal cord regeneration reveals evidence for both spatially restricted and multipotent progenitors

“…The terminal vesicle has in fact long been characterized as a region where an epithelial to mesenchymal transition occurs, and where cells are proposed to delaminate from the ependymal tube to join the surrounding blastema tissue (Benraiss et al, 1997;Egar and Singer, 1972;O'Hara et al, 1992). Our eGFP + spinal cord transplantation and the eGFP + embryonic neural tube grafting experiments allowed us to confirm that cells escape the regenerating spinal cord from this region, as we observe trails of cells emanating from the posterior-dorsal wall of the terminal vesicle.…”

“…Histological characterization of the urodele spinal cord indicates that the animals retain cells with radial glial characteristics throughout life (Holder et al, 1990;O'Hara et al, 1992). Upon amputation and lesioning of the spinal cord, the terminal radial glial cells polarize toward the tail tip and apparently undergo an epithelial to mesenchymal transition to migrate toward the cut surface (O'Hara et al, 1992). These cells then form a single-cell-layered tube of neuroepithelial cells called the ependymal tube that extends posteriorly in concert with overall tail regeneration.…”

“…A fundamental question in this system is how the resident spinal cord cells are activated to produce the regenerating spinal cord and how they come to form the full spectrum of neuronal cell types. Histological characterization of the urodele spinal cord indicates that the animals retain cells with radial glial characteristics throughout life (Holder et al, 1990;O'Hara et al, 1992). Upon amputation and lesioning of the spinal cord, the terminal radial glial cells polarize toward the tail tip and apparently undergo an epithelial to mesenchymal transition to migrate toward the cut surface (O'Hara et al, 1992).…”