Heterogeneity in quiescent Müller glia in the uninjured zebrafish retina drive differential responses following photoreceptor ablation

Abstract

IntroductionLoss of neurons in the neural retina is a leading cause of vision loss. While humans do not possess the capacity for retinal regeneration, zebrafish can achieve this through activation of resident Müller glia. Remarkably, despite the presence of Müller glia in humans and other mammalian vertebrates, these cells lack an intrinsic ability to contribute to regeneration. Upon activation, zebrafish Müller glia can adopt a stem cell-like state, undergo proliferation and generate new neurons. However, the underlying molecular mechanisms of this activation subsequent retinal regeneration remains unclear.Methods/ResultsTo address this, we performed single-cell RNA sequencing (scRNA-seq) and report remarkable heterogeneity in gene expression within quiescent Müller glia across distinct dorsal, central and ventral retina pools of such cells. Next, we utilized a genetically driven, chemically inducible nitroreductase approach to study Müller glia activation following selective ablation of three distinct photoreceptor subtypes: long wavelength sensitive cones, short wavelength sensitive cones, and rods. There, our data revealed that a region-specific bias in activation of Müller glia exists in the zebrafish retina, and this is independent of the distribution of the ablated cell type across retinal regions. Notably, gene ontology analysis revealed that injury-responsive dorsal and central Müller glia express genes related to dorsal/ventral pattern formation, growth factor activity, and regulation of developmental process. Through scRNA-seq analysis, we identify a shared genetic program underlying initial Müller glia activation and cell cycle entry, followed by differences that drive the fate of regenerating neurons. We observed an initial expression of AP-1 and injury-responsive transcription factors, followed by genes involved in Notch signaling, ribosome biogenesis and gliogenesis, and finally expression of cell cycle, chromatin remodeling and microtubule-associated genes.DiscussionTaken together, our findings document the regional specificity of gene expression within quiescent Müller glia and demonstrate unique Müller glia activation and regeneration features following neural ablation. These findings will improve our understanding of the molecular pathways relevant to neural regeneration in the retina.

Adult Neurogenesis of Teleost Fish Determines High Neuronal Plasticity and Regeneration

“…The impressive capacity of juvenile salmon to regenerate brain suggests that most NSPCs are likely multipotent, as they are capable of replacing virtually all cell lineages lost during injury, including neuroepithelial cells (NEC), radial glia (RGC), oligodendrocytes, and neurons [14,15]. To date, this hypothesis appears to be supported largely by studies of the quiescent Müller glia in the adult human retina [16] and results from studies conducted on zebrafish [17,18]. However, the unique regenerative profile of individual cell phenotypes in the diverse niches of brain stem cells remains unclear.…”

“…Zebrafish has a high neurogenic and regenerative potential and is thus a well-established experimental model of choice for studying neural stem cells and neurodegenerative diseases [1,2,11,17,20,21]. Therefore, we review the cellular and molecular aspects of the neurogenic potential of zebrafish radial glia, and then compare them with those of mammalian radial and astroglia.…”

Intercellular contact and cargo transfer between Müller glia and to microglia precede apoptotic cell clearance in the developing retina

“…Further, MG-microglia interactions appear to influence such regenerative potential ( Fischer et al, 2014 ; Fogerty et al, 2022 ; Todd et al, 2020 ; White et al, 2017 ). Phagocytosis, or engulfment of dying neurons by retinal MG, has been described in several studies through static visualization of dying cell markers within Müller cells ( Bailey et al, 2010 ; Egensperger et al, 1996 ; Krylov et al, 2023 ; Lew et al, 2022 ; Morris et al, 2005 ; Nomura-Komoike et al, 2020 ; Sakami et al, 2019 ; Thiel et al, 2022b ). In some cases, these reports appear to contrast with evidence that microglia dominate clearance of dying cells during retinal development ( Blume et al, 2020 ; Francisco-Morcillo et al, 2014 ; Thiel et al, 2022b ) or following induced retinal damage ( Mitchell et al, 2018 ; White et al, 2017 ).…”