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J.R. Spence, M.C. Madhavan, J. Ewing, D.K. Jones, K. Del Rio-Tsonis; Models for Neural Retina Regeneration: Transdifferentiation or Stem Cell Differentiation? . Invest. Ophthalmol. Vis. Sci. 2003;44(13):650.
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Purpose: The embryonic chick can regenerate the neural retina upon removal during its early stages of development (stages 22-24). When the retina of a chick eye is removed, and FGF-2 is introduced into the optic cup, the retina is replaced either by transdifferentiation of the retina pigment epithelial (RPE) cells in the posterior of the optic cup or from stem cells located in the ciliary margin. The purpose of this study is to compare the two methods of regeneration in a temporal manner, and also identify the participation of stem cells in the ciliary margin during this process. Because Sonic Hedgehog (Shh) is known to be a key molecule during normal development of the eye, its role is being elucidated during retina regeneration by carrying out functional studies. Methods: The chick retina is removed using microsurgical techniques, at which time an FGF-coated bead is placed into the optic cup. The retina is allowed to regenerate for either 1, 3, 5 or 7 days after the FGF is introduced. With the use of molecular/cell markers for the different retina layers, we use immunocytochemistry to track the timing of differentiation of the different retina cell types and to identify stem cells located in the ciliary margin using neural progenitor cell markers. For Shh inhibition experiments, a potent Shh pathway inhibitor, cyclopamine, is being introduced after retinectomy. Results: We have been able to track the regeneration of different cell layers as they differentiate, and have compared the two types of regeneration using cell markers. We have also identified active stem cells located in the ciliary margin of regenerating eyes. Inhibition of the hedgehog pathway is currently being carried out and will be discussed. Conclusions: The two regenerative processes, transdifferentiation and regeneration from the ciliary margin show the same pattern of regeneration. That is, the different layers of the regenerating retina show the presence of cell markers, and therefore presence of cell types, in a similar time frame. We also show that during regeneration stem cells are present and are proliferating in the ciliary margin.
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