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V. Canto Soler, H. Huang, R. Adler; The Transcription Factors CTCF and Pax6 Show Mutually Exclusive Expression Domains During Retinal Cell Differentiation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4195.
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Pax6 blocks the differentiation of progenitor cells as photoreceptors, while promoting their differentiation into non–photoreceptor neurons (Toy et al, 2002). On the other hand, Pax6 expression can be repressed by CTCF, a conserved 11 zinc–finger transcription factor (Li et al, 2004). We have therefore hypothesized that CTCF may also influence retinal cell differentiation by controlling Pax6 expression. The purpose of this study is to investigate whether, as predicted by this hypothesis, CTCF and Pax6 expression patterns are mutually exclusive in differentiating retinal cells.
Chick embryo retinas from ED3 to ED18 were analyzed. RT PCR and Real Time PCR were used to detect expression in: i) retinal extracts; ii) cDNA from separate retinal inner nuclear layer (INL) and outer nuclear layer (ONL) samples isolated by laser capture microdissection (LCM); and iii) cDNA from individual rod and cone photoreceptors. In situ hybridization (ISH) was used to investigate CTCF and Pax6 expression patterns in retinal sections.
CTCF was detectable in the chick embryo retina at all the stages studied, with a relative decrease in its expression level during development. PCR analysis of LCM–isolated ONL and of isolated single photoreceptors demonstrated that rods and cones are devoid of Pax6 but are CTCF (+). Both CTCF and Pax6 could be detected by PCR in cDNA samples from the INL. ISH analysis showed reciprocally exclusive expression domains for CTCF and Pax6 throughout retinal development. Their expression gradients were periphery–low to fundus–high for CTCF and periphery–high to fundus–low for Pax6. CTCF and Pax6 showed diffuse distribution at ED 3–4 but, as Pax6 became gradually restricted to ganglion, amacrine and horizontal cells, CTCF became restricted to the ONL and bipolar/Müller region of the INL.
Given that Pax6 can regulate retinal cell differentiation and that CTCF can regulate Pax6 expression, their reciprocal expression patterns are consistent with the hypothesis that CTCF may influence retinal cell differentiation through the downregulation of Pax6.
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