Proliferation together with an influx of ependymal cells are crucial during spinal cord regeneration: an approach of quantitative biology

CHARA OSVALDO

Sitges

Workshop; EMBO Workshop "Development and regeneration of the spinal cord"; 2014

EMBO (European Molecular Biology Organization)

Unlike mammals and most other vertebrates, axolotl, the Mexican salamander (A. mexicanum) can regenerate the spinal cord after amputation constituting an excellent model for exploring regenerative mechanisms of the central nervous system of vertebrates. The number of proliferative ependymal cells (co-expressing PCNA and SOX2) and their mitotic events were quantified along the anteroposterior axis in the axolotl spinal cord during the first 8 days of regeneration. These data together with the analysis of cumulative BrdU labeling experiments allowed us to determine the time course of the cell cycle length of ependymal cells. To gain mechanistic understanding of the axolotl spinal cord regenerative process we developed a data-driven mathematical model  of ependymal proliferation. The model incorporating the experimental time course of cell cycle length fails to explain the experimentally observed proliferative ependymal cell numbers. In contrast, an alternative model involving both, proliferation and an influx of cells into the regenerating zone does reproduce the experimental data. Fitting this extended model to the experimental data allows us to predict the velocity that ependymal cells would have  then entering into the regenerating zone. Cell tracking of ependymal cells during axolotl spinal cord regeneration allows us to test the mathematical model. By performing cell tracking after electroporating axolotl larvae with fluorescent reporter plasmids, the velocity of the ependymal cells during the process of regeneration was measured and found to be in agreement with the model prediction. It is concluded that proliferation of ependymal cells as well as an influx of them towards the regenerative zone would be sufficient to explain axolotl spinal cord regeneration.