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R. I. Martinez, H. M. El-Hodiri; Induction of Progenitor Cells During Retinal Regeneration in Pre-Metamorphic Xenopus Laevis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4063.
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Retinal progenitor cells (RPCs) are a population of multipotent cells present at the ciliary marginal zone (CMZ) in the developing retina of Xenopus laevis. Following partial resection, the retina of pre-metamorphic Xenopus laevis has the capacity to regenerate. The retinal homeobox (Rx) gene is essential for retinal development, suggesting it may also play a role in retinal regeneration. The purpose of this study is to characterize regeneration in the Xenopus retina after injury and investigate the role of Rx in RPCs of the regenerating retina.
A nasal-dorsal segment was removed from one retina of stage 44 tadpoles. The tadpoles were then followed for 30 days post-surgery. Histological staining, as well as Isl-1 and rhodopsin immunostaining of coronal eye sections, was performed to analyze the progress of regeneration. Expression of Rx and other RPC markers such as Pax6, Sox2 and Notch was examined by in situ hybridization. BrdU incorporation was also performed to analyze cellular proliferation in regenerating retinas.
We show that regeneration of the retina appears complete by 30 days post-surgery. Using hematoxylin and eosin staining we demonstrate that the retinal laminae are completely restored and contain continuous photoreceptor, inner nuclear and ganglion cell layers, as confirmed by Isl-1 and rhodopsin immunostaining. Interestingly, during the second week of regeneration we observed the appearance of cells morphologically similar to RPCs at the site of injury. By in situ hybridization we found that these putative RPCs express Rx, Sox2, Pax6 and Notch, all markers of the RPCs found at the CMZ. Moreover, these cells can incorporate BrdU, another characteristic of RPCs.
After resection, the retina of Xenopus laevis tadpoles appears completely regenerated by 30 days post-surgery. The spindle-like cells induced at the site injury have the capacity to proliferate, a characteristic typical of RPCs in a mature retina. In addition, these cells express Rx, Pax6, Sox2 and Notch, markers that define the identity of the endogenous RPCs at the CMZ. The appearance of RPCs at the site of injury suggests their direct contribution to regeneration. Moreover, since these injury-induced RPCs express Rx, these results suggest that Rx may be involved in regeneration.
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