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Reyna Martinez-De Luna, René Y. Choi, Christine M. Ly, Andrea Sophia Viczian, Michael Zuber; Rapid entry of RPE and Müller glia cells into the cell cycle following rod-specific ablation in Xenopus laevis. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5396.
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© ARVO (1962-2015); The Authors (2016-present)
The retinal pigment epithelium (RPE) and the ciliary marginal zone (CMZ) are established sources of regenerated retina in amphibians following retinectomy. However, mechanical removal of the retina to initiate regeneration may have concealed other potential sources of new retinal cells. We previously demonstrated rod photoreceptors regenerate following rod-specific ablation. Here we determine which retinal cell types enter the cell cycle following rod loss and if only rods are generated as part of the regenerative response to rod-specific ablation.
Rod photoreceptors were specifically ablated by metronidazole (Mtz) treatment of XOPNTR transgenic tadpoles, which were then allowed to recover for up to 30 days. Cycling cells were labeled with EdU or BrdU. The number and identity of EdU+ or BrdU+ retinal cells was determined by immunolabeling retinal sections at different time points during regeneration with RPE65 (RPE cells); R5 (Müller glia); XAP2/transducin (rods); calbindin (cones); calretinin (Bipolar, subsets of Amacrine and RGCs); Pax6 (retinal progenitors); PCNA (S-phase).
We identified cycling Müller glia (R5+/BrdU+) and RPE (RPE65+/BrdU+) cells in the central retina 7 days after rod ablation. Cycling RPE cells were sometimes still pigmented, while cycling Müller cells were often clustered with BrdU+ cells not expressing the Müller glial marker R5. Müller glia and RPE cells also expressed the cell cycle marker PCNA, and the retinal progenitor marker Pax6. After 30 days recovery, BrdU+ rods and cones were detected in the ONL, while regenerated bipolar cells (Calretinin+/BrdU+) were detected in the central INL. BrdU+ mature cell types were never detected in the central retina of Mtz-treated wild-type or untreated XOPNTR animals. In the CMZ, rod ablation resulted in the production of twice as many BrdU+ cells relative to controls. Interestingly, we did not observe a significant increase in the proportion of rods generated from the CMZ.
We demonstrate for the first time that, following rod-specific ablation, Müller glia and RPE enter the cell cycle and become Pax6+ in the X. laevis retina. We show rod death is sufficient to activate a proliferative response from the retinal progenitors of the CMZ. Furthermore, newborn cells are not restricted to a rod fate, since other retinal cell types were also generated in the central and peripheral retina.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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