The phenomenon of central nervous system (CNS) damage caused by spinal cord injury (SCI) or neurodegenerative diseases is widespread. Axon regeneration is a critical process in CNS injury repair and is important for restoring neural function and advancing treatment for neurological disorders. Axon regeneration within the mammalian CNS presents significant challenges. While the adult mammalian CNS exhibits limited regenerative capacity shortly after injury (Li et al., 2020), this capacity is insufficient to satisfy the criteria necessary for the functional recovery of axons. Successful axon regeneration is restricted by several factors, including scar tissue formation (Bradbury and Burnside, 2019; Zhao et al., 2022), energy requirements for regeneration (Zhou et al., 2016), and intrinsic molecular pathways (Mahar and Cavalli, 2018). Numerous studies have highlighted the crucial role of endogenous factors in axon regeneration (Curcio and Bradke, 2018; Mahar and Cavalli, 2018). Among these factors, several valuable molecules have been identified, including the phosphatase and tensin homolog PTEN, whose knockout significantly leads to the improvement in retinal ganglion cell (RGC) axon regeneration and promotes the survival of RGC neurons (Park et al., 2008). DLK-1 and SOCS3 also play unique roles in regulating axon regeneration (Smith et al., 2009; Yan et al., 2009). Growing evidence supports the influence of various endogenous elements on the profound modulation of axon regeneration capabilities. These explorations have further deepened our understanding of the intrinsic mechanisms that govern this complex process.

MicroRNAs (miRNAs), a class of small RNAs approximately 20–24 nucleotides in length, have been identified as endogenous factors that play important regulatory roles in various cellular processes. It is estimated that miRNAs regulate more than 60% of the protein-coding regions in the human genome (Ferragut Cardoso et al., 2021). MiRNAs have also been identified as participants in neural axon growth and regeneration (Ghibaudi et al., 2017). For instance, in the CNS of zebrafish, miR-133b has been shown to inhibit the regeneration of Mauthner cells (M-cells) (Huang et al., 2017), while overexpression of miR-21 in DRG neurons enhances neuronal regeneration (Strickland et al., 2011). miR-2184 was discovered through high-throughput sequencing and microarray analysis of small RNA libraries obtained from samples collected at different developmental stages of zebrafish (Soares et al., 2009). However, the biological function of miRNA-2184 remains largely unknown. In particular, its regulatory role in CNS axon regeneration is poorly understood. SYT3 is a high-affinity Ca2+ sensor primarily localized in synapses of neurons and is involved in the internalization of AMPA receptors (Awasthi et al., 2019). It can also accelerate vesicle replenishment and increase the size of the readily releasable pool (RRP) (Weingarten et al., 2022). However, its role in axon regeneration remains to be explored.

M-cells, a unique component of the zebrafish CNS, display characteristics distinct from mammalian neurons in axon regeneration capacity. They possess long axons extending along the spinal cord and facilitating detailed in vivo imaging and experimental investigation into regeneration (Chen et al., 2019). Recent studies into M-cell axon regeneration and axotomy models have revealed that modulation of neuronal activity and gene expression in vivo can significantly impact the CNS axonal regenerative capacity (Canty et al., 2013; Hu et al., 2018).

In the study, we revealed the regulatory role of miRNA-2184 in CNS axon regeneration. Gain-of-function and loss-of-function experiments indicated that miR-2184 promotes axon regeneration in injured M-cells. Direct binding of miR-2184 to its downstream target gene syt3 was confirmed by in vivo imaging. Furthermore, we investigated the impact of altering syt3 expression levels on axon regeneration and identified syt3 as a negative regulator. In vivo imaging following the expression of calcium-binding-deficient mutants of syt3 reveals that the regulation of axon regeneration by syt3 requires binding to Ca2+. Pharmacological manipulation notes that RRP has the potential to affect axon regeneration. In summary, our findings reveal the role of miR-2184 in promoting CNS axon regeneration by targeting syt3.