Cellular Dynamics during Spinal Cord Regeneration in Larval Zebrafish.

The study of spinal cord regeneration using diverse animal models, which range from null to robust regenerative capabilities, is imperative for understanding how regeneration evolved and, eventually, to treat spinal cord injury and paralysis in humans. In this study, we used electroablation to fully transect the spinal cord of zebrafish larvae (3 days postfertilization) and examined regeneration of the tissue over time. We used transgenic lines to follow immune cells, oligodendrocytes, and neurons in vivo during the entire regenerative process. We observed that immune cells are recruited to the injury site, oligodendrocytes progenitor cells (olig2-expressing cells) invade, and axons cross the gap generated upon damage from anterior to reinnervate caudal structures. Together with the recovery of cell types and structures, a complete reversal of paralysis was observed in the lesioned larvae indicating functional regeneration. Finally, using transplantation to obtain mosaic larvae with single-labeled neurons, we show that severed spinal axons exhibited varying regenerative capabilities and plasticity depending on their original dorsoventral position in the spinal cord.