Establishment and maintenance of tissue-specific chromatin domains.

摘要

Chromatin structure is a critical component of eukaryotic transcriptional regulation. ATP-utilizing nucleosome remodeling enzyme complexes and histone modifying enzymes have emerged as major regulators of chromatin structure. However, the mechanism of how these enzymes establish and maintain broad chromatin domains is unclear. The murine beta-globin locus exhibits a developmentally dynamic histone acetylation and methylation patterns in adult erythroid cells. The histone modification profiles show hyperacetylation of H3 and H4 at the locus control region (LCR) and adult globin genes, whereas embryonic globin genes were embedded in a broad hypoacetylated region. Treatment of murine erythroleukemia cells with Histone deacetylase (HDAC) inhibitors induced H4 but not H3 acetylation. These results provide evidence for an active HDAC scanning model in which HDACs maintain histone H4 of the embryonic region is maintained in a hypoacetylated state. Histone H3 methylated at lysine 79 (H3-meK79), involved in telomere silencing in Saccharomyces cerevisiae , is the first histone modification enriched at the adult globin region but not at the LCR. H3-meK79 was further shown to be developmentally regulated and to associate with transcriptionally active genes. Thus, we proposed that Disruptor Of Telomere silencing 1 (DOT1) regulates beta-globin transcription at the murine beta-globin locus.; The erythroid-specific transcription factor, GATA-1 is critical for definitive erythropoiesis and megakaryopoeisis. By contrast, GATA-2 is important for hematopoietic stem cell proliferation and differentiation. Both GATA factors function through a well-defined GATA motif. However, the specificity of GATA factor occupancy in the context of chromatin is unknown. We find that estrogen receptor fusion of GATA-1 (ER-GATA-1) and GATA-2 occupy only a small number of the total GATA motifs. Kinetic analyses in GATA-1-null cells indicated that ER-GATA-1 preferentially occupied GATA motifs at the LCR, in which chromatin accessibility is largely GATA-1-independent. Subsequently, ER-GATA-1 increased promoter accessibility and occupied the downstream betamajor promoter. The increase in ER-GATA-1 occupancy at the adult beta-globin promoter correlated with increased chromatin accessibility at the promoter. Furthermore, ER-GATA-1 occupancy induced occupancy of Erythroid Kruppel-Like Factor (EKLF) and SWI/SNF chromatin remodeling complex to spatially restricted sites of the beta-globin locus. Based on these data, we propose a three-phase model for GATA-1-mediated activation of the adult beta-globin genes.