染色质开放程度的调节是诸多重要生物过程进行的基础。目前已有的基于核酸酶的敏感性检测方法由于对染色质的破坏性，仅能发现最开放的一小部分区域，无法在全基因组水平上清晰地区分不同染色质区域的开放或致密程度，亟需建立一套新的方法来研究哺乳动物染色质的开放程度。我们试图联合利用Dam甲基转移酶和针对甲基化位点的限制性内切酶的处理，通过高通量测序得到Dam修饰过的区域的信号强弱，从而得到所在染色质的开放程度。此技术（DamRE-seq）在保持染色质高级结构的同时，在较大的动态范围上测出了染色质开放程度，具备清晰区分更多染色质区域开放程度的能力。基于DamRE-seq，我们计划在细胞内验证致密染色质对PRC2活性的激活作用，这将提供高级染色质致密结构激活PRC2并导致基因沉默的细胞内证据。另外，我们也对RA诱导的ES细胞定向分化的不同阶段进行染色质开放程度的检测，以期发现分化过程中的染色质的动态变化。

Chromatin accessibility is critical for many fundamental biological processes. Because of invasive nature of nuclease, available methods measuring chromatin accessibility can only focus on the most open chromatin regions, therefore can not discriminate moderate open regions and the majority of dense chromatins. New methods are needed to overcome these limitations. In this project, in vitro treatment of nuclei with Dam methyltransferase followed by methylation-specific restriction enzyme are combined to establish a new technology named DamRE-seq, by which not only accessibility of open chromatins but dense chromatin could be measured in a genome-wide scale. Based on DamRE-seq, we plan to validate the stimulation of high-order dense chromatin to the activity of PRC2 at the genome wide level. By integrating our DamRE-seq data to existing epigenomic data, genome will be annotated by the accessibility and combination of epigenetic factors. In the end, dynamics of chromatin accessibility during RA-induced differentiation of ES cells will be measured to study the relationship between chromatin accessibility and cell fate transitions.