Transcription factors CTCF and Pax6 are segregated to different cell types during retinal cell differentiation.

We have hypothesized that the transcription factor CTCF may influence retinal cell differentiation by controlling Pax6 expression, because (1) CTCF has been shown to repress Pax6 expression in some tissues, and (2) Pax6 blocks the differentiation of retinal progenitor cells as photoreceptors and promotes their differentiation as nonphotoreceptor neurons. Our results show that, as predicted by this hypothesis, CTCF and Pax6 become segregated to different retinal cell types. The factors are initially coexpressed in the undifferentiated neuroepithelium, but already at that time they show complementary periphery-to-fundus gradients of distribution. As the retina laminates, Pax6 becomes restricted to ganglion and amacrine cells, and CTCF to the bipolar/Muller cell layer and the outer nuclear layer. Polymerase chain reaction analysis of laser capture microdissection samples and dissociated cells showed that both immature and differentiated photoreceptors are CTCF (+)/ Pax6 (-). Functional studies are now under way to further analyze the role of CTCF in retinal cell differentiation.

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