Figure 9.

Summary of known events associated with motor neuron regeneration in adult zebrafish. Schematic cross-sections through the spinal cord are shown (the central canal is represented by a gray oval). Different ependymoradial glial cells in the unlesioned spinal cord express low levels (light shading) of different transcription factor combinations found in similar dorsoventral positions in the embryonic neural tube. After a lesion, the central canal widens close to the lesion site, concomitant with an increase in numbers of ependymoradial glial cells that also express higher levels of transcription factors (darker shading). A ventrodorsal hh signal, evidenced by a ventrodorsal patched1 (ptc1) mRNA expression gradient in ependymoradial glial cells, contributes to production of Hb9⁺/islet-1/-2⁺/ChAT⁺ motor neurons (MNs) from pMN-like ependymoradial glial cells (green) after a lesion. Increased expression of genes related to FGF and retinoic acid signaling suggests involvement of these signals in motor neuron regeneration.