Abstract
In contrast to the mammalian retina, the zebrafish retina exhibits the potential for lifelong retinal neurogenesis and regeneration even after severe damage. Previous studies have shown that the transforming growth factor beta (TGFβ) signaling pathway is activated during the regeneration of different tissues in the zebrafish and is needed for regeneration in the heart and the fin. In this study, we have investigated the role of the TGFβ pathway in the N-methyl-N-nitrosourea (MNU)-induced chemical model of rod photoreceptor de- and regeneration in adult zebrafish. Immunohistochemical staining for phosphorylated Smad3 was elevated during retinal regeneration, and phosphorylated Smad3 co-localized with proliferating cell nuclear antigen and glutamine synthetase, indicating TGFβ pathway activation in proliferating Müller glia. Inhibiting the TGFβ signaling pathway using a small molecule inhibitor (SB431542) resulted in accelerated recovery from retinal degeneration. Accordingly, we observed increased cell proliferation in the outer nuclear layer at days 3 to 8 after MNU treatment. In contrast to the observations in the heart and the fin, the inhibition of the TGFβ signaling pathway resulted in increased proliferation after the induction of retinal degeneration. A better understanding of the underlying pathways with the possibility to boost retinal regeneration in adult zebrafish may potentially help to stimulate such proliferation also in other species.
Highlights
Zebrafish (Danio rerio) is an important model system in visual research, amongst others, as its retina shows the typical structure of vertebrates and is rich in cone photoreceptors [1,2,3,4,5,6]
Immunohistochemical staining for phosphorylated Smad3 was elevated during retinal regeneration, and phosphorylated Smad3 co-localized with proliferating cell nuclear antigen and glutamine synthetase, indicating TGFβ pathway activation in proliferating Muller glia
After inducing retinal degeneration using 150 mg/l MNU, maximal activation of the TGFβ pathway occurred between days 3 and 8 as demonstrated by immunohistochemistry for phosphorylated Smad3 (P-Smad3) (Fig 1; representative immunohistochemistry for day 5 is shown)
Summary
Zebrafish (Danio rerio) is an important model system in visual research, amongst others, as its retina shows the typical structure of vertebrates and is rich in cone photoreceptors [1,2,3,4,5,6]. The zebrafish retina regenerates even after severe damage [13,14,15,16]. Thereby, proliferating de-differentiated Muller glia exhibit the ability to replace all types of neurons to reconstitute the damaged retina, forming rod progenitors that regenerate photoreceptor cells [7,15,17,18,19,20].
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