Fate bias during neural regeneration adjusts dynamically without recapitulating developmental fate progression

Abstract

BackgroundRegeneration of neurons in the central nervous system is poor in humans. In other vertebrates neural regeneration does occur efficiently and involves reactivation of developmental processes. Within the neural retina of zebrafish, Müller glia are the main stem cell source and are capable of generating progenitors to replace lost neurons after injury. However, it remains largely unknown to what extent Müller glia and neuron differentiation mirror development.MethodsFollowing neural ablation in the zebrafish retina, dividing cells were tracked using a prolonged labelling technique. We investigated to what extent extrinsic feedback influences fate choices in two injury models, and whether fate specification follows the histogenic order observed in development.ResultsBy comparing two injury paradigms that affect different subpopulations of neurons, we found a dynamic adaptability of fate choices during regeneration. Both injuries followed a similar time course of cell death, and activated Müller glia proliferation. However, these newly generated cells were initially biased towards replacing specifically the ablated cell types, and subsequently generating all cell types as the appropriate neuron proportions became re-established. This dynamic behaviour has implications for shaping regenerative processes and ensuring restoration of appropriate proportions of neuron types regardless of injury or cell type lost.ConclusionsOur findings suggest that regenerative fate processes are more flexible than development processes. Compared to development fate specification we observed a disruption in stereotypical birth order of neurons during regeneration Understanding such feedback systems can allow us to direct regenerative fate specification in injury and diseases to regenerate specific neuron types in vivo.

Transcriptomic comparison of two selective retinal cell ablation paradigms in zebrafish reveals shared and cell-specific regenerative responses

“…It is likely that novel pathways were easier to associate with bipolar cell regeneration due to the fact that this paradigm has been comparatively understudied compared to rod photoreceptor regeneration. These findings expand upon previous studies demonstrating that selective retinal cell loss can trigger a fate biased regenerative responses (8)(9)(10)(11), and provide potential insights useful for developing selective cell regeneration therapies. Collectively, these findings emphasize that regeneration need not always "recapitulate development", particularly for paradigms that mimic the selective cell loss attending most neurodegenerative diseases.…”

“…In contrast, the responsiveness and regenerative properties of stem cells following the discrete loss of retinal cell subtypes remain less well undefined. Intriguingly, recent studies suggest that selective retinal cell loss in zebrafish elicits a fate-biased regenerative response; i.e., selective cell replacement (8)(9)(10)(11). To increase understanding of fate-biased regenerative responses at the transcriptomic level, we used time-resolved gene expression profiling to compare two cell-specific ablation paradigms in the zebrafish retina involving the targeted loss of 1) bipolar cells, versus, 2) rod photoreceptors.…”

“…Coexpression of a fluorescent reporter in NTR-targeted cells allows the regenerative process to be characterized in detail using in vivo time-lapse imaging (32,35) or quantified using highthroughput methods (36,37). Using this approach, recent studies have shown that selective retinal cell loss does not trigger a developmental response but rather a fate-biased regenerative process (8)(9)(10)(11). These data suggest differential regulation of selective and non-selective cellular regeneration.…”

Correspondence Between Behavioral, Physiological, and Anatomical Measurements of Visual Function in Inhibitory Neuron–Ablated Zebrafish

“…The model of inhibitory neuron ablation was adapted from previous studies. 33,34 In Tg(ptf1a:Gal4/UAS:nfsb-mCherry) larvae, Gal4 expression is driven by the Ptf1a promotor to bind the activating sequence UAS, leading to the production of the nitroreductase enzyme and the red fluorescent reporter mCherry. Expression is restricted to inhibitory neurons, as Ptf1a determines inhibitory fate in the developing vertebrate CNS.…”

“…Here, we used a transgenic zebrafish line Tg(ptf1a:Gal4/ UAS:nfsb-mCherry) with nitroreductase-mediated cell ablation to selectively ablate inhibitory neurons, 33 based on the spatiotemporal expression of the pancreas-specific transcription factor 1a (Ptf1a). 34 Ptf1a is a basic helix-loop-helix (bHLH) transcriptional gene that determines inhibitory neuron fate in many regions of the CNS including the retina, and is transiently expressed in developing zebrafish. [35][36][37][38] We measured ERG and OMR for inhibitory neuron-ablated larvae to analyze visual behavior and function.…”