Abstract
Zebrafish are able to regenerate the spinal cord and recover motor and sensory functions upon severe injury, through the activation of cells located at the ependymal canal. Here, we show that cells surrounding the ependymal canal in the adult zebrafish spinal cord express Foxj1a. We demonstrate that ependymal cells express Foxj1a from their birth in the embryonic neural tube and that Foxj1a activity is required for the final positioning of the ependymal canal. We also show that in response to spinal cord injury, Foxj1a ependymal cells actively proliferate and contribute to the restoration of the spinal cord structure. Finally, this study reveals that Foxj1a expression in the injured spinal cord is regulated by regulatory elements activated during regeneration. These data establish Foxj1a as a pan-ependymal marker in development, homeostasis and regeneration and may help identify the signals that enable this progenitor population to replace lost cells after spinal cord injury.
Highlights
The spinal cord develops from the embryonic neural tube, an initially homogeneous neuroepithelium
To determine if Foxj1a is expressed in the adult zebrafish spinal cord, we used the reporter transgenic line Tg(0.6foxj1a:GFP), in which a small enhancer sequence drives the expression of the fluorescent protein GFP [18]
We confirmed by fluorescent in situ RNA hybridization (FISH) on transgenic sections that the distribution of the foxj1a:GFP reporter is similar to the endogenous foxj1a gene, which is detected in the cells surrounding the central canal
Summary
The spinal cord develops from the embryonic neural tube, an initially homogeneous neuroepithelium. Progenitor cells in the neural tube acquire different identities depending on their position along the dorsoventral axis. The roof plate on the dorsal side (via BMPs and Wnts) and the floor plate on the ventral side (via Shh) provide positional information that assigns cells to distinct progenitor domains [1,2]. Each progenitor domain can give rise to several cell fates that emerge sequentially. After the differentiation and migration of neurons and glial cells from the neuroepithelium, the remaining cells lining the central canal give rise to an additional cell fate—ependymal cells. Ependymal cells (i.e. all the cells that contact the central canal) descend predominantly from the ventral progenitor domains p2 and pMN [4,5] and the floor plate [6], and require the ventral signal Shh for their correct specification [7]
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