Abstract
Xenopus laevis are able to regenerate the spinal cord during larvae stages through the activation of neural stem progenitor cells (NSPCs). Here we use high-resolution expression profiling to characterize the early transcriptome changes induced after spinal cord injury, aiming to identify the signals that trigger NSPC proliferation. The analysis delineates a pathway that starts with a rapid and transitory activation of immediate early genes, followed by migration processes and immune response genes, the pervasive increase of NSPC-specific ribosome biogenesis factors, and genes involved in stem cell proliferation. Western blot and immunofluorescence analysis showed that mTORC1 is rapidly and transiently activated after SCI, and its pharmacological inhibition impairs spinal cord regeneration and proliferation of NSPC through the downregulation of genes involved in the G1/S transition of cell cycle, with a strong effect on PCNA. We propose that the mTOR signaling pathway is a key player in the activation of NPSCs during the early steps of spinal cord regeneration.
Highlights
Mammals can regenerate some tissues like the skin, muscle, bones, and liver, they are unable to efficiently regenerate the central nervous system (CNS)
We found that a large group of genes related to G1/S transition of mitotic cell cycle and DNA replication initiation were downregulated at 1 days post-transection (dpT) in animals treated with Torin[1] (Fig. 7p), which is consistent with the results observed for proliferating cell nuclear antigen (PCNA) and EdU+/Sox2+ (Fig. 7a–o)
We performed a high-resolution expression profiling analysis of the first 21 h after spinal cord transection, which led to the identification of the transcriptome changes deployed during this early response, allowing the delineation of the regenerative program deployed after spinal cord transection, those steps involved in the activation of neural stem progenitor cells (NSPCs) (Fig. 8), and the identification of the mTORC1 pathway as a key component in the activation of this process
Summary
Mammals can regenerate some tissues like the skin, muscle, bones, and liver, they are unable to efficiently regenerate the central nervous system (CNS). At 2 and 4 dpT, an enrichment of genes (upregulated or downregulated) associated with the immune response and other biological processes was observed, suggesting that an early inhibition of mTORC1 could have a prolonged effect in many process involved in spinal cord regeneration (see Supplementary Information Fig. S5f–i). All together, these results show that an early and transitory inhibition of mTORC1 have a negative effect on NSPC proliferation. This analysis suggests an early regulation of cell death and immune response by mTORC1 that could contribute to the effects on spinal cord regeneration
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