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S Chen, G Peng, X Wang, LY Li, S Xu, BL Sopher, AR La Spada; Poly-Q Mediated Interaction of Ataxin-7 and CRX Interferes with Photoreceptor Gene Expression: A Molecular Mechanism for Retinal Degeneration in SCA7 . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1376.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant poly-glutamine(Q) repeat disease characterized by a cone-rod dystrophy type of retinal degeneration. After developing a mouse model of SCA7, we demonstrated that photoreceptor degeneration of SCA7 results from the physical interaction of the poly-Q-expanded disease protein, ataxin-7, with the photoreceptor transcription factor CRX. This interaction interferes with CRX-dependent transcription activation of photoreceptor genes (Neuron, 31:913, 2001). The goal of the present study is to identify the domains of ataxin-7 and CRX that are important for their physical and functional interaction. Methods: Yeast two-hybrid and in vitro co-immunoprecipitation assays were employed to assess the effect of N- and C-terminal deletions of ataxin-7 and CRX upon their physical interaction. Transient co-transfection assays in HEK293T cells with a rhodopsin-luciferase reporter were used to gauge the ability of ataxin-7 deletions to repress CRX transactivation activity. Results: CRX deletions lacking the Q-rich region failed to interact with ataxin-7. Removing 7 out of 9 Q residues of CRX resulted in a CRX protein partially resistant to ataxin-7 mediated repression. Similarly, deleting the poly-Q repeat of ataxin-7 abolished the ataxin-7 - CRX interaction. Quantitative yeast two-hybrid assays demonstrated that the interaction strength of ataxin-7 and CRX is significantly enhanced when the length of the poly-Q tract of ataxin-7 increases from normal to disease-causing status. In addition, deleting the nuclear localization signal sequence from the poly-Q-expanded ataxin-7 reduced its potency to repress CRX. Conclusions: The physical and functional interaction of ataxin-7 with CRX depends upon the poly-Q or Q-rich region of each protein. The nuclear localization of ataxin-7 appears to be required for its role as a transcriptional repressor. Our results further support the view that antagonizing CRX function by expansion of the poly-Q tract in ataxin-7 is responsible for the cone-rod dystrophy phenotype of SCA7.
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