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C. Gutierrez, K. Del Rio-Tsonis; Regulation of FGF-Induced Transdifferentiation by Shh Pathway. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5689.
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© ARVO (1962-2015); The Authors (2016-present)
: The embryonic chick is one of a handful of organisms that are capable of regenerating their entire retina. Regeneration occurs via two different modes, either by the activation of stem/progenitor cells located in the ciliary margin or by the transdifferentiation of the retina pigmented epithelium (RPE) in the presence of fibroblast growth factor (FGF). Transdifferentiation only takes place during a small window of development ending at embryonic day 4.5 (E4.5). We have previously shown that overexpressing Shh inhibits FGF-induced transdifferentiation and pERK activity in the RPE. Pax6 expression in RPE cells is required for transdifferentiation. This study examines how Shh blocks transdifferentiation and downregulates Pax6 in the presence of FGF. Examining the down stream effectors of the Shh pathway, the Glis, will aid in understanding how transdifferentiation is inhibited by active Shh signaling.
An RCAS viral system was used to over express Shh or GFP subretinally in embryonic day 2.5 (E2.5) chicks. At E4 retinectomies were performed and either heparin beads or heparin beads soaked with FGF were placed in the optic cup. Eyes were collected at different regenerative stages. In addition, E4 retinectomized eyes were electroporated with Gli constructs with the addition of FGF or heparin beads. Immunohistochemistry was performed to determine expression of Pax6, Mitf and BrdU incorporation.
When Shh is overexpressed, FGF-induced expression of Pax6 in the transdifferntiating RPE is inhibited. BrdU incorporation is also blocked. Mitf expression in the RPE is downregulated upon retina removal regardless of the presence or absence of FGF. The regulation of Mitf by Shh will be presented as well as the individual contribution of each of the Glis in the regulation of Pax6 and Mitf during the transdifferentiation of the RPE into neural retina.
During embryonic chick retina regeneration, FGF-induced transdifferentiation can be blocked by exogenous Shh signaling by inhibiting Pax-6 expression and while maintaining Mitf expression in the RPE.
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