Epigenetic regulation of active chromatin’

果蝇对X染色体单体的补偿为活性染色质的表观遗传调控提供了一个有指导意义的例子。果蝇的剂量补偿通过大约2倍的激活来调节雄性单个X染色体的转录，以匹配两个雌性X染色体的组合输出。这种调节的核心是剂量补偿复合物（DCC），它由5个男性特异性致死蛋白亚基和非编码roX RNA组成。根据流行的模型，X染色体上基因的独占激活涉及遗传和表观遗传原理。首先，DCC选择性地与x上大约300个DNA序列定义的“高亲和力位点”（HAS）结合，从那里它“接触”到表观遗传标记的靶基因，通过组蛋白乙酰化促进它们的转录。该建议解决了关于表观遗传染色质修饰的本质和DCC的“读取器”和“写入器”功能的未解决的问题，这些功能允许它选择性地乙酰化活性染色质。目前的模型表明，结合到HAS的DCC使用MSL3亚基的染色体结构域作为“读卡头”，在染色体邻域搜索转录的染色质。该结构域可以结合以赖氨酸36 （H3K36me3）组蛋白H3甲基化为标志的核小体，这是一种共转录修饰。MSL3通过支架蛋白MSL1与乙酰转移酶MOF连接。因此，msl3 -核小体相互作用将MOF招募到活性染色质上，使H4K16乙酰化。这种乙酰化被认为通过染色质展开促进转录。我们希望批判性地评估这个模型，并探索允许染色体中区域H4K16乙酰化的原理。我们的生化方法旨在破译分子机制。强化反馈回路以抑制染色质结构的维持而闻名，如本构性和兼性异染色质。我们的研究解决了一个不寻常的情况，其中活性染色质的特征触发额外的激活。DCC（一种甲基赖氨酸结合物）中的表观遗传读取器和写入酶（一种组蛋白乙酰转移酶）是广泛使用的进化保守调节分子的例子。从我们的研究中获得的知识将具有广泛的意义，超出了果蝇性染色体调节的具体情况。

The compensation for X chromosome monosomy in Drosophila serves as an instructive example for epigenetic regulation of active chromatin. Dosage compensation in flies adjusts the transcription of the single X chromosome in males by roughly 2-fold activation to match the combined output of the two female X’s. Central to this regulation is the Dosage Compensation Complex (DCC), which consists of 5 male-specific-lethal protein subunits and non-coding roX RNA.According to the prevalent model, the exclusive activation of genes on the X chromosome involves genetic and epigenetic principles. First, the DCC selectively binds to some 300 DNA sequence-defined ‘High Affinity Sites’ (HAS) on the X. From there it ‘reaches out’ to epigenetically marked target genes to boost their transcription through histone acetylation. This proposal addresses unsolved questions about the nature of the epigenetic chromatin modification and the ‘reader’ and ‘writer’ functions of the DCC that allows it to selectively acetylate active chromatin. The current model states that DCC bound to a HAS searches the chromosomal neighborhood for transcribed chromatin, using the chromodomain of the MSL3 subunit as a ‘reader head’. This domain can bind nucleosomes marked by methylation of histone H3 at lysine 36 (H3K36me3), a modification that is placed co-transcriptionally. MSL3 is connected to the acetyltransferase MOF through the scaffold protein MSL1. Accordingly, the MSL3-nucleosome interaction recruits MOF to active chromatin, where it acetylates H4K16. This acetylation is thought to facilitate transcription through chromatin unfolding. We wish to critically evaluate this model and explore the principles that allow regional H4K16 acetylation in the chromosome. Our biochemical approach is aimed at deciphering molecular mechanism.Reinforcing feedback loops are better known for the maintenance of repressive chromatin structures, such as constitutive and facultative heterochromatin. Our study addresses an unusual case, where features of active chromatin trigger additional activation. The epigenetic reader in the DCC (a methyllysine binder) and the writer enzyme (a histone acetyltransferase) exemplify widely used, evolutionary conserved regulatory molecules. Knowledge gained from our study will have wide implications beyond the specific case of sex chromosome regulation in flies.