A satellite DNA array barcodes chromosome 7 and regulates totipotency via ZFP819

Mammalian genomes are a battleground for genetic conflict between repetitive elements (REs) and KRAB-zinc finger proteins (KZFPs). We explored whether KZFPs can regulate cell fate by employing Zfp819, which targets a satellite DNA array, ZP3AR. ZP3AR coats a megabase region of chromosome 7 that encompasses genes encoding ZSCAN4, a master transcription factor of totipotency. Depleting Zfp819 in mouse embryonic stem cells (mESCs) causes them to transition to a 2-cell (2C)-like state, whereby the ZP3AR array switches from a poised to an active enhancer state. This is accompanied by a global eviction of heterochromatin roadblocks, which we link to decreased SETDB1 stability. These events result in transcription of active LINE-1 elements and a block in differentiation. In sum, ZFP819 and TRIM28 partner up to close chromatin across Zscan4, allowing exit from totipotency. We propose that satellite DNAs may control developmental fate transitions through the barcoding and switching off of master transcription factor genes. Overall design: Identification of how ZFP819 and its co-opted satellite repeat, ZP3AR, influence cell fate transitions through chromatin and gene expression changes.

哺乳动物基因组是重复元件（repetitive elements, REs）与KRAB型锌指蛋白（KRAB-zinc finger proteins, KZFPs）之间遗传冲突的战场。本研究以靶向卫星DNA阵列ZP3AR的Zfp819为模型，探究KRAB型锌指蛋白是否能够调控细胞命运。ZP3AR覆盖7号染色体上一段兆碱基大小的区域，该区域包含编码全能性主转录因子ZSCAN4的基因。在小鼠胚胎干细胞（mouse embryonic stem cells, mESCs）中敲低Zfp819，可使其转变为2细胞样（2-cell-like, 2C）状态，此时ZP3AR阵列从预激活增强子状态切换为活性增强子状态。这一过程伴随全局异染色质屏障的清除，我们将其与SETDB1稳定性降低关联起来。上述事件会引发活性LINE-1元件的转录，并阻断细胞分化进程。综上，ZFP819与TRIM28协同作用，在Zscan4所在区域关闭染色质，使细胞脱离全能性状态。我们提出，卫星DNA可通过对主转录因子基因进行条形码标记并使其沉默，来调控发育命运的转变。
实验整体设计：阐明ZFP819及其靶向的卫星重复序列ZP3AR如何通过染色质与基因表达变化，调控细胞命运的转变。