Abstract: Zebrafish are an effective vertebrate model to study the mechanisms underlying recovery after spinal cord injury. The subacute phase after spinal cord injury is critical to the recovery of neurological function, which involves tissue bridging and axon regeneration. In this study, we found that zebrafish spontaneously recovered 44% of their swimming ability within the subacute phase (2 weeks) after spinal cord injury. During this period, we identified 7762 differentially expressed genes in spinal cord tissue: 2950 were up-regulated and 4812 were down-regulated. These differentially expressed genes were primarily concentrated in the biological processes of the respiratory chain, axon regeneration, and cell-component morphogenesis. The genes were also mostly involved in the regulation of metabolic pathways, the cell cycle, and gene-regulation pathways. We verified the gene expression of two differentially expressed genes, clasp2 up-regulation and h1m down-regulation, in zebrafish spinal cord tissue in vitro. Pathway enrichment analysis revealed that up-regulated clasp2 functions similarly to microtubule-associated protein, which is responsible for axon extension regulated by microtubules. Down-regulated h1m controls endogenous stem cell differentiation after spinal cord injury. This study provides new candidate genes, clasp2 and h1m, as potential therapeutic intervention targets for spinal cord injury repair by neuroregeneration. All experimental procedures and protocols were approved by the Animal Ethics Committee of Tianjin Institute of Medical & Pharmaceutical Sciences (approval No. IMPS-EAEP-Q-2019-02) on September 24, 2019. 

Key words: axon regeneration, clasp2, endogenous neural stem cells, h1m, microtubule, nanog, neural regeneration, neurogenesis, spinal cord injury, subacute phase