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Jin Wan, Daniel J. Goldman; HB-EGF is a Master Regulator of Müller Glia Dedifferentiation and Retina Regeneration. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5927.
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© ARVO (1962-2015); The Authors (2016-present)
Müller glia (MG) dedifferentiation into a cycling population of multipotent progenitors is crucial to zebrafish retina regeneration. The mechanisms underlying MG dedifferentiation are unknown. Here we tested the hypothesis that heparin binding epidermal-like growth factor (HB-EGF) is a secreted MG-derived factor that stimulates MG dedifferentiation and retina regeneration.
Eye lesions were performed by needle poke. Dividing cells were labeled with BrdU. Growth factors were delivered into the uninjured eyes' vitreous through the cornea. RT-PCR was combined with in situ hybridization and immunohistochemistry to identify the expression of regeneration-associated genes and regenerated cell types. The function of proteins induced during regeneration was explored by knocking down their expression with morpholino-modified antisense oligonucleotides introduced into the retina by electroporation.
Within 1 hr post retinal injury, HB-EGF was induced in MG residing at the injury site. Morpholino-mediated HB-EGF knockdown suppressed injury-dependent retina regeneration. Metalloproteinase inhibition suggested proHB-EGF ectodomain shedding was necessary for HB-EGF’s action in the injured retina. Remarkably, HB-EGF stimulated the formation of multipotent MG-derived progenitors in the uninjured retina. HB-EGF mediated its effects via an EGFR/MAPK signal transduction cascade that regulated the expression of regeneration-associated genes, like ascl1a and pax6b. We uncovered an HB-EGF/Ascl1a/Notch/hb-egfa signaling loop that helps define the zone of injury-responsive MG. Finally, we show that HB-EGF acts upstream of the Wnt/b-catenin signaling cascade that controls progenitor proliferation.
These results suggest that HB-EGF may be master regulators of MG dedifferentiation following retinal injury and MG themselves influence their regenerative capacity. This study provides the first link between extracellular signaling and regeneration-associated gene expression in the injured retina and suggests strategies for stimulating retina regeneration in mammals.
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