Zebrafish Müller glia-derived progenitors are multipotent, exhibit proliferative biases and regenerate excess neurons

Abstract

Unlike mammals, zebrafish can regenerate a damaged retina. Key to this regenerative response are Müller glia (MG) that respond to injury by reprogramming and adopting retinal stem cell properties. These reprogrammed MG divide to produce a proliferating population of retinal progenitors that migrate to areas of retinal damage and regenerate lost neurons. Previous studies have suggested that MG-derived progenitors may be biased to produce that are lost with injury. Here we investigated MG multipotency using injury paradigms that target different retinal nuclear layers for cell ablation. Our data indicate that regardless of which nuclear layer was damaged, MG respond by generating multipotent progenitors that migrate to all nuclear layers and differentiate into layer-specific cell types, suggesting that MG-derived progenitors in the injured retina are intrinsically multipotent. However, our analysis of progenitor proliferation reveals a proliferative advantage in nuclear layers where neurons were ablated. This suggests that feedback inhibition from surviving neurons may skew neuronal regeneration towards ablated cell types.

Opposing Actions of Fgf8a on Notch Signaling Distinguish Two Muller Glial Cell Populations that Contribute to Retina Growth and Regeneration

“…ascl1a , a transcript known to be induced in MG-derived progenitors (Fausett et al, 2008; Ramachandran et al, 2010a), served as a positive control for their purification by FACS (Figure 1C). Furthermore, fgf8a suppression was not unique to the needle poke injury model as destruction of neurons in the INL and ganglion cell layer (GCL) using NMDA, or the photoreceptor layer using metronidazole in zop:nsfb-EGFP transgenic fish also caused fgf8a suppression (Figure S1F-S1I) (Montgomery et al, 2010; Powell et al, 2016). …”

“…Animals were anesthetized and retinas were injured with a needle poke injury once to each quadrant, intravitreal injection of NMDA, or via transgenic expression of nitroreductase in the presence of metronidazole as previously described (Fausett and Goldman, 2006; Montgomery et al, 2010; Powell et al, 2016). For gene expression assays retinas received a needle poke injury twice in each retinal quadrant.…”

“…Following retinal injury, zebrafish MG reprogram their genome so they express genes that endow them with stem cell properties (Powell et al, 2013; Ramachandran et al, 2010a). These reprogrammed MG exhibit a transient gliotic response, divide and generate a proliferating population of progenitors that regenerate all major retinal cell types regardless of which neurons are lost (Fausett and Goldman, 2006; Nagashima et al, 2013; Powell et al, 2016; Ramachandran, 2010; Thomas et al, 2016). …”

Retina regeneration in zebrafish

“…Other studies suggest progenitors in the injured retina may retain a multipotent character regardless of the type of neuron ablated since ectopic neurons appear outside the injury site and are also found in uninjured retinas treated with a variety of growth factors and cytokines 20–22,24 . Recent studies suggest Müller glia are intrinsically multipotent regardless of the type of neuron ablated and that ectopic or excess neurons are generated 45 . Thus, it is important to determine if these additional neurons persist in the retina and contribute to retina structure and function.…”

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

“…Proliferative cells show a bias towards generating ablated cell fates, but also generate non-ablated cells [33, 35, 36]. This shows their intrinsic multipotency and may reflect recapitulation of intrinsic molecular processes that control temporal cell fate decision as observed in development.…”