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Jie Zhu, Julia Zavada, Amy Burke, Katia Del Rio-Tsonis; Canonical Wnt Signaling Modulates Chick Retina Regeneration. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1120.
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© ARVO (1962-2015); The Authors (2016-present)
The embryonic chick is able to regenerate its retina after retinectomy when exposed to fibroblast growth factor (FGF). Regeneration occurs via the activation of stem/progenitor cells present in the ciliary margin (CM) of the eye and by transdifferentiation of Retina Pigmented Epithelium (RPE). Canonical Wnt signaling plays a critical role in the development of peripheral eye structures which house retina stem/progenitor cells and in RPE specification during eye development. Thus, we wanted to study the role of canonical Wnt signaling during retina regeneration from both cellular sources to better understand the molecular basis of retina regeneration.
Immunohistochemistry was used to determine the expression of molecules of the canonical Wnt pathway during retina regeneration. To examine the role of this pathway during retina regeneration, RCAS retroviruses were used to overexpress pathway activators or inhibitors. Eyes were collected at different stages of regeneration and processed for histology and immunohistochemistry.
Activation of canonical Wnt signaling assessed by nuclear b-catenin immunostaining was detected in the CM as well as in the RPE in embryonic day 4 (E4) chick eyes. At E5 and E6 when the RPE is unable to transdifferentiate and the CM has reduced regenerative ability, active b-catenin is absent in the RPE. After retina removal at E4, b-catenin activation is reduced in the CM and increased in the RPE cells to protect their phenotype. Intriguingly, Wnt signaling is completely absent in FGF-induced regeneration from the CM and RPE transdifferentiation. Over-expression of a negative lef1 construct (to inhibit canonical Wnt signaling) in chick eyes after retinectomy was sufficient to induce regeneration from both sources in the absence of FGF. Robust proliferation was observed in regenerating retina and no cell death was detected by 7 days post-retinectomy. The regenerated neuroepithelium differentiated into all major retina cell types with proper lamination.
Canonical Wnt signaling is downregulated in the CM after retinectomy to allow those cells to undergo regeneration; on the contrary, the canonical Wnt signaling is upregulated in RPE cells to protect their phenotype. Inhibition of canonical Wnt signaling is sufficient to induce retina regeneration via the activation of stem cells and by RPE transdifferentiation in the absence of FGF.
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