Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant cerebellar ataxia caused by the expansion of polyglutamine (polyQ) within the TATA box-binding protein (TBP). Previous studies have shown that polyQ-expanded TBP forms neurotoxic aggregates and alters downstream genes. However, how expanded polyQ tracts affect the function of TBP and the link between dysfunctional TBP and SCA17 is not clearly understood. In this study, we generated novel Drosophila models for SCA17 that recapitulate pathological features such as aggregate formation, mobility defects and premature death. In addition to forming neurotoxic aggregates, we determined that polyQ-expanded TBP reduces its own intrinsic DNA-binding and transcription abilities. Dysfunctional TBP also disrupts normal TBP function. Furthermore, heterozygous dTbp amorph mutant flies exhibited SCA17-like phenotypes and flies expressing polyQ-expanded TBP exhibited enhanced retinal degeneration, suggesting that loss of TBP function may contribute to SCA17 pathogenesis. We further determined that the downregulation of TBP activity enhances retinal degeneration in SCA3 and Huntington's disease fly models, indicating that the deactivation of TBP is likely to play a common role in polyQ-induced neurodegeneration.
Background: A previous screening of Arabidopsis thaliana for mutants exhibiting dysfunctional chloroplast protein transport identified the chloroplast import apparatus (cia) gene. The cia2 mutant has a pale green phenotype and reduced rate of protein import into chloroplasts, but leaf shape and size are similar to wild-type plants of the same developmental stage. Microarray analysis showed that nuclear CIA2 protein enhances expression of the Toc75, Toc33, CPN10 and cpRPs genes, thereby up-regulating protein import and synthesis efficiency in chloroplasts. CIA2-like (CIL) shares 65% sequence identity to CIA2, suggesting that CIL and CIA2 are homologous proteins in Arabidopsis. Here, we further assess the protein interactions and sequence features of CIA2 and CIL. Results: Subcellular localizations of truncated CIA2 protein fragments in our onion transient assay demonstrate that CIA2 contains two nuclear localization signals (NLS) located at amino acids (aa) 62-65 and 291-308, whereas CIL has only one NLS at aa 47-50. We screened a yeast two-hybrid (Y2H) Arabidopsis cDNA library to search for putative CIA2interacting proteins and identified 12 nuclear proteins, including itself, CIL, and flowering-control proteins (such as CO, NF-YB1, NF-YC1, NF-YC9 and ABI3). Additional Y2H experiments demonstrate that CIA2 and CIL mainly interact with flowering-control proteins via their N-termini, but preferentially form homo-or hetero-dimers through their C-termini. Moreover, sequence alignment showed that the N-terminal sequences of CIA2, CIL and NF-YA are highly conserved. Therefore, NF-YA in the NF-Y complex could be substituted by CIA2 or CIL. Conclusions: We show that Arabidopsis CIA2 and CIL can interact with CO and NF-Y complex, so not only may they contribute to regulate chloroplast function but also to modulate flower development.
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