Distinct dynamics and functions of H2AK119ub and H3K27me3 in mouse preimplantation embryos (RNA-Seq)

Polycomb repressive complexes 1 and 2 (PRC1/2) maintain transcriptional silencing of developmental genes largely by catalyzing mono-ubiquitination of histone H2A at lysine 119 (H2AK119ub1) and trimethylation of histone H3 at lysine 27 (H3K27me3), respectively. How Polycomb domains are reprogrammed during mammalian preimplantation development remains largely unclear. Here we show that, although H2AK119ub1 and H3K27me3 are highly colocalized in gametes, they undergo differential reprogramming dynamics following fertilization. H3K27me3 maintains thousands of maternally biased domains up to the blastocyst stage, whereas maternally biased H2AK119ub1 distribution in zygotes is largely equalized at the two-cell stage. Notably, while maternal PRC2 depletion has a limited effect on global H2AK119ub1 in early embryos, it disrupts allelic H2AK119ub1 at H3K27me3 imprinting loci including Xist. By contrast, acute H2AK119ub1 depletion in zygotes does not affect H3K27me3 imprinting maintenance, at least by the four-cell stage. Importantly, loss of H2AK119ub1, but not H3K27me3, causes premature activation of developmental genes during zygotic genome activation (ZGA) and subsequent embryonic arrest. Thus, our study reveals distinct dynamics and functions of H3K27me3 and H2AK119ub1 in mouse preimplantation embryos. RNA-seq was performed in H3K27me3 depleted 2-cell (2 rep for control and 2 rep for depletion) and H2Aub-depleted 2-cell (2 rep for control and 2 rep for depletion) and 4-cell embryos (2 rep for control and 2 rep for depletion) to determine how loss of H3K27me3 or H2Aub affects transcriptome. RNA-seq was performed in H3K27me3 depleted 4-cell (2 rep for control and 2 rep for depletion) and Eed maternal knockout 4-cell (2 rep for control and 2 rep for maternal KO). RNA-seq was also performed for MII oocyctes and 2-cell embryos (2 rep for each stage)多梳蛋白抑制复合体1和2（Polycomb repressive complexes 1 and 2, PRC1/2）主要通过分别催化组蛋白H2A赖氨酸119位点单泛素化（H2AK119ub1）与组蛋白H3赖氨酸27位点三甲基化（H3K27me3），来维持发育相关基因的转录沉默。哺乳动物着床前发育过程中，多梳结构域的重编程机制目前仍未完全阐明。本研究发现，尽管H2AK119ub1与H3K27me3在配子中高度共定位，但二者在受精后呈现出截然不同的重编程动态。H3K27me3可维持数千个母源偏向性结构域至囊胚阶段，而合子中母源偏向性的H2AK119ub1分布则在二细胞阶段基本趋于均等化。值得注意的是，尽管母源PRC2缺失对早期胚胎中整体H2AK119ub1水平影响有限，但它会破坏包括Xist在内的H3K27me3印记位点的等位基因H2AK119ub1修饰。与之相反，合子中急性H2AK119ub1缺失至少在四细胞阶段不会影响H3K27me3印记的维持。重要的是，H2AK119ub1的缺失而非H3K27me3的缺失，会在合子基因组激活（zygotic genome activation, ZGA）过程中导致发育基因提前激活，并引发后续的胚胎阻滞。综上，本研究揭示了H3K27me3与H2AK119ub1在小鼠着床前胚胎中截然不同的动态变化与功能。为探明H3K27me3或H2Aub缺失如何影响转录组，本研究对H3K27me3缺失的二细胞胚胎（对照组2个生物学重复，处理组2个生物学重复）、H2Aub缺失的二细胞胚胎（对照组2个生物学重复，处理组2个生物学重复）及四细胞胚胎（对照组2个生物学重复，处理组2个生物学重复）进行了RNA测序（RNA-seq）。同时，本研究还对H3K27me3缺失的四细胞胚胎（对照组2个生物学重复，处理组2个生物学重复）及Eed母源敲除的四细胞胚胎（对照组2个生物学重复，母源敲除组2个生物学重复）进行了RNA测序（RNA-seq）。此外，本研究还对MII期卵母细胞及二细胞胚胎（每个阶段2个生物学重复）进行了RNA测序（RNA-seq）。