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A. Cvekl, Y. Yang, M. Pirity, W. Wang, B. Chauhan; Integrated Analysis of Transcriptional Regulation During Lens Development . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1514.
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Lens development requires a coordinated expression of thousands of genes encoding essential regulatory and structural proteins. Genetic studies have determined that DNA–binding transcription factors including Pax6, c–Maf, FoxE3, Prox1 and Sox1 have important roles in this process. Specific genes poised for transcription undergo a complex process of chromatin remodeling of their promoters and enhancers that includes covalent modifications and exchanges of core histones and generation of nucleosome–free regions. We seek to show how chromatin remodeling is involved in lens lineage formation and differentiation.
Chromatin immunoprecipitations were performed and analyzed by quantitative PCR and on high density tiled oligonucleotide arrays (ChIP on chip). Localization of Pax6, c–Maf, Brg1 and Snf2h (two ATP–dependent catalytical subunits of SWI/SNF and ISWI chromatin remodeling complexes) was observed in a critical 16 kb region of the mouse aA–crystallin locus. To further probe the function of Brg1 in lens development, transgenic mice were generated to express a dominant negative form of Brg1 in lens fiber cells. Finally, lens–specific conditional inactivation of Brg1 was performed and analyzed.
Both SWI/SNF and ISWI complexes are recruited to the aA–crystallin locus. In lens epithelial cells with moderate levels of aA–crystallin expression, Snf2h was found only in the promoter. In contrast, low abundance of Brg1 was found in multiple sites of the locus. In mouse lens with high levels of aA–crystallin expression, both Brg1 and Snf2h were present in the entire 16 kb locus. Both transgenic models showed abnormal ocular development and lens fiber cell differentiation. Molecular interaction studies showed complex formation between Brg1 and Pax6, and Snf2h and c–Maf.
Our data demonstrate the importance of chromatin remodeling for lens fiber cell differentiation and crystallin gene expression. These findings in turn helped to identify novel roles of Pax6 and c–Maf in the recruitment of SWI/SNF and ISWI chromatin remodeling complexes, respectively.
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