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K.P. Mitton, G.–H. Peng, S. Chen, W. Hoerauf; Spatial and Temporal Expression Patterns of Fiz1, Implicating its Role in the Control of Photoreceptor Gene Expression in vivo . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4189.
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Fiz1 is a zinc–finger (Zf) protein that interacts with NRL and attenuates its ability to activate the rhodopsin promoter. We hypothesize that Fiz1 is an integral part of repressor pathways that contribute to the precise control of photoreceptor–specific genes. (i.e. rhodopsin in photoreceptors). We examined the expression pattern of Fiz1 in postnatal mouse retina and tested for association of Fiz1 with retinal–specific gene promoters in vivo.
Expression of Fiz1 protein in the mouse neural retina was examined at several stages of postnatal development using immunohistochemistry and immunoblotting. Expression of the Fiz1 and Rhodopsin genes was monitored by quantitative real–time PCR. Association of the Fiz1 protein with opsin promoters was examined using chromatin immunoprecipitation (ChIP) assays.
Fiz1 protein was not detectable in tissue sections of P0 retina. Low levels of Fiz1 protein were detected in photoreceptors and the ganglion cell layer by P7. Mature mouse retina displayed intense staining for Fiz1. Quantitative immunoblot analysis confirmed that the amount of Fiz1 increases more than ten–fold during photoreceptor maturation. Real–time PCR analysis revealed a synchronized increase in Fiz1 and rhodopsin gene expression. ChIP analysis demonstrated that Fiz1 is part of the molecular complex on rod– and cone–opsin promoters.
Fiz1 protein concentration increases considerably during photoreceptor maturation, coinciding with photoreceptor–specific gene expression (i.e. rhodopsin). Fiz1 protein associates with rod– and cone–opsin promoters in vivo. Thus, Fiz1 is expressed in the right place, at the correct time, to contribute to the precise control of photoreceptor–specific gene expression during maturation of retinal neurons.
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