Hassan-Zadeh Vahideh, Rugg-Gunn Peter, Bazett-Jones David P
Department of Cell and Molecular Biology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran.
Epigenetics Programme, The Babraham Institute, Babraham Research Campus, Cambridge, UK.
Chromosoma. 2017 Oct;126(5):605-614. doi: 10.1007/s00412-017-0625-x. Epub 2017 Jan 13.
Epiblast stem cells (EpiSCs), which are pluripotent cells isolated from early post-implantation mouse embryos (E5.5), show both similarities and differences compared to mouse embryonic stem cells (mESCs), isolated earlier from the inner cell mass (ICM) of the E3.5 embryo. Previously, we have observed that while chromatin is very dispersed in E3.5 ICM, compact chromatin domains and chromocentres appear in E5.5 epiblasts after embryo implantation. Given that the observed chromatin re-organization in E5.5 epiblasts coincides with an increase in DNA methylation, in this study, we aimed to examine the role of DNA methylation in chromatin re-organization during the in vitro conversion of ESCs to EpiSCs. The requirement for DNA methylation was determined by converting both wild-type and DNA methylation-deficient ESCs to EpiSCs, followed by structural analysis with electron spectroscopic imaging (ESI). We show that the chromatin re-organization which occurs in vivo can be re-capitulated in vitro during the ESC to EpiSC conversion. Indeed, after 7 days in EpiSC media, compact chromatin domains begin to appear throughout the nuclear volume, creating a chromatin organization similar to E5 epiblasts and embryo-derived EpiSCs. Our data demonstrate that DNA methylation is dispensable for this global chromatin re-organization but required for the compaction of pericentromeric chromatin into chromocentres.
上胚层干细胞（EpiSCs）是从植入后早期小鼠胚胎（E5.5）中分离出来的多能细胞，与早期从E3.5胚胎的内细胞团（ICM）中分离出来的小鼠胚胎干细胞（mESCs）相比，既有相似之处，也有不同之处。此前，我们观察到，虽然染色质在E3.5的ICM中非常分散，但在胚胎植入后的E5.5上胚层中会出现紧密的染色质结构域和染色中心。鉴于在E5.5上胚层中观察到的染色质重组与DNA甲基化的增加同时发生，在本研究中，我们旨在研究DNA甲基化在ESC体外转化为EpiSC过程中染色质重组中的作用。通过将野生型和DNA甲基化缺陷型ESC都转化为EpiSC，然后用电子光谱成像（ESI）进行结构分析，来确定对DNA甲基化的需求。我们表明，体内发生的染色质重组在ESC向EpiSC转化的体外过程中可以重现。事实上，在EpiSC培养基中培养7天后，紧密的染色质结构域开始在整个核体积中出现，形成了一种类似于E5上胚层和胚胎来源的EpiSCs的染色质组织。我们的数据表明，DNA甲基化对于这种整体染色质重组是可有可无的，但对于着丝粒周围染色质压缩形成染色中心是必需的。
