Kantor Boris, Makedonski Kirill, Shemer Ruth, Razin Aharon
Department of Cellular Biochemistry and Human Genetics, The Hebrew University-Hadassah Medical School, 91120, Jerusalem, Israel.
Gene Expr Patterns. 2003 Dec;3(6):697-702. doi: 10.1016/j.modgep.2003.07.003.
DNA methylation had been implicated in the assembly of multiprotein repressory complexes that affect chromatin architecture thereby rendering genes inactive. Proteins containing methyl binding domains (MBDs) are major components of these complexes. MBD3 is a component of the HDAC associated chromatin remodeling complex Mi2/NuRD. The addition of MBD2 to the Mi2/NuRD complex creates MeCP1, a complex that is known to inactivate methylated promoters. The undermethylated state of the mouse preimplantation embryo prompted us to investigate the known repressory complexes at this developmental stage. We found individual components of Mi2/NuRD: MBD3, Mi2, HDAC1 and HDAC2 to be expressed from a very early stage of embryo development and to localize in close proximity with each other and with constitutive heterochromatin by the blastula stage. Expression of MBD2, a component of MeCP1, starts in the blastula stage. Then it is also found to be in proximity with heterochromatin (based on DAPI staining) and with MBD3, Mi2 and HDAC1. In contrast, expression of MeCP2, an MBD containing component of a third repressory complex (MeCP2/Sin3A), is not seen in the preimplantation embryo. Our results suggest that both Mi2/NuRD and MeCP1 complexes are already present at the very early stages of embryo development, while a MeCP2 complex is added to the arsenal of repressory complexes post-implantation at a stage when DNA methylation takes place.
DNA甲基化与多蛋白抑制复合物的组装有关，这些复合物会影响染色质结构，从而使基因失活。含有甲基结合域（MBD）的蛋白质是这些复合物的主要成分。MBD3是与HDAC相关的染色质重塑复合物Mi2/NuRD的一个成分。向Mi2/NuRD复合物中添加MBD2会产生MeCP1，这是一种已知能使甲基化启动子失活的复合物。小鼠植入前胚胎的低甲基化状态促使我们研究这个发育阶段已知的抑制复合物。我们发现Mi2/NuRD的各个成分：MBD3、Mi2、HDAC1和HDAC2从胚胎发育的早期阶段就开始表达，并在囊胚期彼此紧密定位，且与组成型异染色质紧密相邻。MeCP1的一个成分MBD2的表达始于囊胚期。然后还发现它与异染色质（基于DAPI染色）以及MBD3、Mi2和HDAC1相邻。相比之下，第三种抑制复合物（MeCP2/Sin3A）的一个含MBD成分MeCP2在植入前胚胎中未检测到表达。我们的结果表明，Mi2/NuRD和MeCP1复合物在胚胎发育的早期阶段就已存在，而MeCP2复合物是在植入后DNA甲基化发生的阶段添加到抑制复合物库中的。
