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T.L. Belecky–Adams, M. Shook, C. Scott; Ectopic expression of paired homeobox transcription factor PAX2 in the developing chick optic cup. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):700.
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Purpose: PAX2, a member of the paired homeobox transcription factor family, is expressed in the early optic cup, optic stalk, otic vesicle, neural tube, and urogenital system. While studies from other labs have indicated that PAX2 may be involved in proliferation and/or survival in kidney cells (Dressler et al., 1993), the only evidence to support such a role for PAX2 in the nervous system are observations by Favor et al., (1996) and Green et al (1997), in which it was noted that a loss of PAX2 leads to retinal and neural tube hypoplasia. This study addresses the hypothesis that PAX2 is critical for ventral optic cup precursors to remain undifferentiated to aid in the proliferation and migration of cells that give rise to the ventral optic cup. Methods: A bicistronic vector that expresses either green fluorescent (GFP) alone or in addition to PAX2 was electroporated in ovo into optic cup precursors during early optic cup development at Hamburger and Hamilton stage 18–20 (E3). Sections and wholemounts expressing control and PAX2 were analyzed using morphometry, immunocytochemistry and in situ hybridization on E4, E6, and E8. Proliferation was studied by studies using tritiated thymidine and/or BrDU uptake. Identification of proliferating cells was analyzed using a BrDU–specific antibody and/or autoradiography on cytospun samples from labeled retinae. Results: Control embryos electroporated with GFP alone appeared to be completely normal on the electroporated and control sides, whereas embryos that were electroporated with PAX2 showed phenotypes that appeared to vary with the region of retina that was electroporated. Preliminary evidence indicates those that were electroporated near the dorsal margin of the optic cup developed a small globe of neuroepithelial cells resembling a secondary neural retina, while expression of PAX2 in the ventral portion of the optic cup led to formation of colobomas and larger than normal optic stalks. There did not appear to be an increase in proliferation or a change in survival of cells in regions expressing PAX2. Conclusions: The effects of ectopic PAX2 expression in the developing optic cup were hemi–retina–dependent. None of the effects appeared to be dependent upon increased proliferation and/or survival in the nervous system.
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