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M.E. Zuber, A.S. Viczian, E.C. Solessio, N. Schmidt; Generation of Retinal Stem/Progenitor Cells From Primitive Ectoderm . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5766.
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Retinal stem and progenitor cells provide an important opportunity for treating retinal injuries and degenerations. For their successful use in cell replacement therapies, a plentiful source of these cells is necessary. One approach is to convert non–retinal cell types into retinal stem/progenitor cells. Ectopic eyes can be induced in Xenopus laevis by the coordinated expression of seven transcription factors normally present in the eye primordia (eye field) and required for normal eye formation. In this study, we test the ability of these eye field transcription factors (EFTFs) to reprogram plentiful ectoderm into retinal stem/progenitor cells.
We coinjected RNA for the transcription factors Otx2, Pax6, Six3, Lhx2, Rx, ET, and Optx2 (Six6) into Xenopus embryos at the two–cell stage. The primitive ectoderm from pre–gastrula donor (EFTF–injected) embryos was removed and cultured overnight. One of the two eye fields of stage–matched host embryos was removed and the donor tissue transplanted in its place. Immunocytochemistry and in situ hybridization were used to identify the retinal cell types that formed. Electroretinograms were used to test for retinal function. BrdU incorporation was also used to test for the presence of adult retinal stem cells in the induced eyes.
EFTF–expressing primitive ectoderm formed eyes that were anatomically, molecularly and functionally normal. This is in striking contrast to control transplants, which never formed eyes. Induced eyes had a lens, RPE, and retina. Retinal structures were normal, consisting of photoreceptor, inner nuclear and ganglion cell layers separated by inner and outer plexiform layers. ERGs recorded from induced eyes were also normal and identical to those recorded from control, stage–matched embryos. Finally, induced retinas contained a ciliary marginal zone. In Xenopus, the CMZ is located at the peripheral edge of the retina, and is composed of self–renewing adult retinal stem cells.
These results demonstrate that non–retinal cell types can be converted to retinal cell types using the appropriate combination of gene products.
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