Changes in progenitor populations and ongoing neurogenesis in the regenerating chick spinal cord

The chick spinal cord can regenerate following injury until advanced developmental stages. It is conceivable that changes in stem/progenitor cell plasticity contribute to the loss of this capacity, which occurs around E13. We investigated the contribution of proliferation, phenotypic changes in radial glia progenitors, and neurogenesis to spinal cord regeneration. There was no early up-regulation of markers of gliogenic radial glia after injury either at E11 or E15. In contrast, increased proliferation in the grey matter and up-regulation of transitin expression following injury at E11, but not E15, suggested high levels of plasticity within the E11 spinal cord progenitor population that are lost by later stages. Changes in neural progenitors with development were also supported by a higher neurosphere forming ability at E11 than at E15. Co-labelling with doublecortin and neuron-specific markers and BrdU in spinal cord sections and dissociated cells showed that neurogenesis is an ongoing process in E11 chick spinal cords. This neurogenesis appeared to be complete by E15. Our findings demonstrate that the regeneration-competent chick spinal cord is less mature and more plastic than previously believed, which may contribute to its favourable response to injury, and suggest a role for neurogenesis in maintaining regenerative capacity.