In contrast to most vertebrates Xenopus tropicalis tadpoles have the ability to regenerate their central nervous system. I investigated spinal cord regeneration by focusing both on the molecular mechanism driving regeneration as well as characterizing the changes in structure and gene expression of the regenerate. To investigate the molecular mechanisms of regeneration, I used a bio- informatic approach to uncover genes upregulated in the spinal cord during regeneration. This led to the identification of foxm1, a transcription factor, which is upregulated in the outgrowing spinal cord. To characterise its role I have used knockdown and knockout approaches. I have shown that in the regenerating spinal cord Foxm1 promotes cyclinb3 and cdc25b expression leading to an increased rate of proliferation that drives neural progenitors towards differentiation. I have also investigated the signals controlling the dynamic expression of foxm1 using chemical inhibitors of signalling pathways acting early during regeneration and identified that elevated Reactive Oxygen Species (ROS) levels are required for foxm1 expression. Using these approaches allowed me to identify of a novel role for Foxm1 during spinal cord regeneration, and to better understand the mechanisms controlling the balance of cell proliferation and differentiation upon amputation. I next investigated the principles of spinal cord regeneration. I have shown that the spinal cord is required for tail regeneration and that its structure differs from its original. Comparison of the structure as well as gene expression changes revealed that there is a shift in balance towards an increase in progenitor pool at the expense of differentiating neurons, which coincides with an increase of proliferation in the regenerate. I further explored the regenerative behaviour of specific neuronal subtype, the motor neurons. I show that these regenerate and find no evidence for the contribution of dedifferentiation of mature motor neurons towards the regeneration of the spinal cord. In combination these two approaches help to better understand the mechanism underlying spinal cord regeneration in Xenopus tadpoles.
Spinal Cord Regeneration in Xenopus tropicalis: General Principles and the Role of Foxm1
Pelzer, D. (Author). 1 Aug 2018
Student thesis: Phd