Circadian clocka regulates the zebrafish central neuronal Mauthner-cell axon regeneration via phosphodiesterase family pde4a.

Axon regeneration is the key to repairing spinal cord injury. Circadian rhythm plays regulatory roles in axonal regeneration. The endogenous molecular clock serves as the molecular basis for the generation and precise maintenance of circadian rhythms. CLOCK is one of the most core transcription factors in the endogenous molecular clock. However, the role of CLOCK in axon regeneration has so far remained elusive. Therefore, this study explored how the circadian gene clocka regulates the zebrafish central neuronal Mauthner cells (M-cells) axon regeneration. Using the M-cell axonal regeneration model, we found that M-cell axons exhibited circadian-phase-dependent regeneration after two-photon laser ablation, while in the clocka mutant, the circadian-phase-dependent regeneration of M-cells was deprived and their regenerative ability was inhibited. Subsequently, a combination of single-cell electroporation, single-cell capture, transcriptome sequencing, and Rolipram treatment demonstrated that clocka is required for M-cell axonal regeneration and regulates axonal regeneration through phosphodiesterase pde4a-cAMP axis. Together, these findings demonstrate that endogenous molecular clock gene clocka regulates zebrafish central M-cell axonal regeneration via pde4a-cAMP pathway and provide new insights into rhythmic regulation for central nerve repair.