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R.–T. Yan, W. Xie, S.–Z. Wang; Homeobox genes and RPE transdifferentiation towards retinal neurons . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5347.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine whether homeobox genes known to play important roles in eye and/or retinal development would be sufficient to specify retina neural identity and guide cultured embryonic chick RPE cells to transdifferentiate towards retinal neurons. Methods: Replication–competent retrovirus, RCAS, was used to ectopically express several homeobox genes in cultured RPE cells derived from day 6 chick embryos. Homeobox genes tested include chick Rax, RaxL, Six3, Six6, Msx1, and mouse Msx2. Recombinant retrovirus was added to primary cultures of E6 RPE cells. Around 8 days after the administration of the virus, cells from the cultures were fixed and analyzed using immunocytochemistry with markers that label various types of retinal neurons. Morphological changes from RPE to neuron were also considered in judging whether neural transdifferentiation had occurred. Results: A total of 6 homeobox genes have been assayed for their ability to induce cultured RPE cells to transdifferentiate into molecularly and morphologically recognizable neurons. The criteria for RPE transdifferentiation were the same as those used in revealing and characterizing the proneural activities of bHLH genes neurogenin2, neuroD, cath5, and cNSCL1. Among the homeobox genes tested, Six6 was found to be able to induce the expression of Visinin, a photoreceptor marker, RA4, a retinal ganglion cell marker, and MAP2, a general neural marker. Morphologically, transdifferentiating cells exhibited neuron–like morphologies. The other homeobox genes did not induce detectable transdifferentiation. Conclusions: The majority of the homeobox genes examined lacked the ability to induce RPE transdifferentiation into retinal neurons under the conditions in which ngn2, neuroD, and cath5 can readily do so. Only one (Six6) of the 6 homeobox genes induced the expression of markers that identify photoreceptor and retinal ganglion cells. The data suggest that Six6 is sufficient to specify retina neural identity in the context of an RPE cell, whereas Rax, RaxL, Six3, Msx1, or Msx2 is not.
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