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Ependymal Cells are a Heterogeneous Population in the Spinal Cord of the Leopard Gecko

The leopard gecko (Eublepharis macularius) is an emerging model for the study of spinal cord regeneration. As for many lizards, leopard geckos are able to self‐detach their tails (to escape predation) and then spontaneously regenerate a replacement. The regenerate tail is characterized by a centrally positioned spinal cord with a relatively simple morphology: a layer of ependymal cells surrounded by nerve tracts. We hypothesize that ependymal cells in the spinal cord are a heterogenous population. Prior to injury, virtually all ependymal cells of the original (uninjured) spinal cord express the neural stem/progenitor cell (NSPC) marker Sox2, and a subset of these cells also express the astrocyte marker glial fibrillary acid protein (GFAP). Neurons of the grey matter, but not ependymal cells, co‐express the neuronal markers HuCD and NeuN. During regeneration, ependymal cells remain Sox2+ and begin to express additional NSPC markers including Musashi‐1, βIII‐Tubulin and Sox9. Interestingly, a subset of ependymal cells in both the original tail stump and the newly formed regenerate spinal cord begin expressing HuCD, a protein otherwise characteristic of neuronal differentiation. These cells are negative for NeuN (a marker of neuronal nuclei) and are positionally restricted to locations bordering the central canal. A second subset of ependymal cells within the regenerating spinal cord begin to express GFAP and Vimentin but not HuCD. Our results suggest that there are at least three distinct populations of ependymal cells present during regeneration. The majority of ependymal cells are HuCD/GFAP− and display a dynamic NSPC profile following injury (Musashi‐1+/ βIII‐Tubulin+/ Sox9+). Two other populations are less widespread. HuCD+/GFAP−/NeuN− cells may represent a population of neuronal‐like central canal contacting cells, while HuCD−/GFAP+/Vimentin+ cells appear to be ependymo‐radial glia. This complex assemblage of cells may explain the remarkable regenerative abilities of the spinal cord in this species.