Abstract
Mitochondrial transport is essential for neuronal function, but the evidence of connections between mitochondrial transport and axon regeneration in the central nervous system (CNS) of living vertebrates remains limited. Here, we developed a novel model to explore mitochondrial transport in a single Mauthner axon (M axon) of zebrafish with non-invasive in vivo imaging. To confirm the feasibility of using this model, we treated labeled zebrafish with nocodazole and demonstrated that it could disrupt mitochondrial transport. We also used two-photon laser axotomy to precisely axotomize M axons and simultaneously recorded their regeneration and the process of mitochondrial transport in living zebrafish larvae. The findings showed that the injured axons with stronger regenerative capability maintain greater mitochondrial motility. Furthermore, to stimulate axon regeneration, treatment with dibutyryl cyclic adenosine monophosphate (db-cAMP) could also augment mitochondrial motility. Taken together, our results provide new evidence that mitochondrial motility is positively correlated with axon regeneration in the living vertebrate CNS. This promising model will be useful for further studies on the interaction between axon regeneration and mitochondrial dynamics, using various genetic and pharmacological techniques.
Highlights
We could simultaneously label Mauthner cells (M cells) and their mitochondria because of the co-expression of upstream activating sequence (UAS)-mito-EGFP and UAS-DsRed2 using the CMV promoter to drive the expression of Gal4-vp16
The labeled single M cells could be detected 48 h later (Figure 1A), and the labeled mitochondria in the Mauthner axon (M axon) of living zebrafish larvae could be non-invasively imaged with a confocal microscope (Figures 1C,D)
We developed a novel model to clarify the relationship between axon regenerative capacity and inner mitochondrial transport in the vertebrate central nervous system (CNS) using non-invasive in vivo imaging at the single-axon level
Summary
Mitochondria are dynamic organelles (Misgeld et al, 2007; Saxton and Hollenbeck, 2012; Schwarz, 2013; Sheng, 2014) that play an essential role under different physiological conditions in neurons, such as synaptic plasticity (Li et al, 2004), axon degeneration (Court and Coleman, 2012; O’Donnell et al, 2013), and growth cone guidance (Steketee et al, 2012; Lathrop and Steketee, 2013). When it comes to zebrafish, previous studies were mainly focused on the peripheral nervous system (PNS) (Plucinska et al, 2012; O’Donnell et al, 2013) or particular types of neurons in CNS transgenic lines they labeled (Bergamin et al, 2016; Dukes et al, 2016) Despite these advances, non-invasive in vivo imaging of axonal transport of mitochondria in vertebrate CNS at a single-cell level remains limited. Non-invasive in vivo observation of axon regeneration in the vertebrate CNS at the single-axon levels remains to be established
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