Single-cell transcriptome analysis reveals heterogeneity and a dynamic regenerative response of quiescent radial glia in adult zebrafish brain

Abstract

In zebrafish telencephalon, radial glial cells (RGs) show a remarkable ability to regenerate damaged neural tissue by re-initiating cell proliferation to produce neural precursors to rebuild the lost neural circuit. However, it is not fully understood how RGs respond to brain damage to initiate this regenerative response. Here we applied single-cell transcriptomics to RGs in adult zebrafish telencephalon and identified five RG subtypes, which are classified into four quiescent RGs (qRGs) and one proliferating RG (pRG). The four qRGs differentially express distinct subsets of qRG markers, suggesting heterogeneity of qRG in zebrafish adult brain. Interestingly, one qRG subtype shows high expression of ribosomal proteins, and its fraction increases in response to brain damage. Consistently, the mTOR pathway is activated in RGs near the injury site. It was reported that inflammatory responses of brain-resident immune cells, microglia, are required for inducing regenerative responses of RGs in zebrafish. Genetical elimination of microglia not only suppressed the damage-induced regenerative response of RGs, but also decreased the fraction of the ribosomal expression-enriched qRGs. Our pseudo-time analysis suggests that putative dormant RGs produce ribosomal expression-enriched qRGs through activation of ribosomal genesis, as well as suppression of cholesterol biogenesis, and pRGs through activation of the JAK/STAT pathway. Our findings reveal heterogeneity of qRGs in adult zebrafish brain and their dynamic regenerative response to brain damage.

Elevated glucocorticoid alters the developmental dynamics of hypothalamic neurogenesis

“…The initial GC-induced increase in cell proliferation observed here might be in part mediated by mechanisms akin to those observed during brain injury, whereby formerly quiescent radial glia enter the cell cycle in response to trauma 26,51 . In the published literature, there are very few previous studies of effects of GC on cell proliferation across development.…”

“…Indeed the concept of GC-inducible stem cells is not novel 47,48 , and there are many reports of a GC-induced increase in cell proliferation of various cell types including NSPCs 49,50,51,52 . The initial GC-induced increase in cell proliferation observed here might be in part mediated by mechanisms akin to those observed during brain injury, whereby formerly quiescent radial glia enter the cell cycle in response to trauma 28,53 . In the published literature, there are very few previous studies of effects of GC on cell proliferation across development.…”

“…Whilst rx3 appeared to be co-expressed with pcna in proliferating radial glia, we also analysed blbp (brain lipid binding protein, fabp7a) localisation, which is known to be expressed in predominantly quiescent radial glia in the zebrafish brain 28 . Consistent with this, we observed strong expression of blbp in cells lining the third ventricle in the pcna-negative rostral domains of the hypothalamus, whilst some blbp signal was also observed in pcna-positive cells of the lateral recess (Fig.2d).…”

Elevated glucocorticoid alters the developmental dynamics of hypothalamic neurogenesis in zebrafish

“…This aligns with the concept of GC-inducible stem cells 31,32 . Previous studies have demonstrated GC-induced proliferation in various contexts [33][34][35][36] , resembling mechanisms observed during brain injury, where quiescent radial glia enter the cell cycle in response to trauma 29,37 . Few studies have explored the developmental impact of GC on cell proliferation.…”

“…Whilst rx3 appeared to be co-expressed with Pcna in proliferating radial glia, we also analysed Blbp (brain lipid binding protein, fabp7a) localisation, which is known to be expressed in predominantly quiescent radial glia in the zebrafish brain 29 . Consistent with this, we observed strong expression of Blbp in cells lining the third ventricle in the Pcna-negative rostral domains of the hypothalamus, whilst some Blbp signal was also observed in Pcna-positive cells of the lateral recess (Fig.…”