H2A.Z reinforces maternal H3K4me3 formation and is essential for meiotic progression in mouse oocytes. H2A.Z reinforces maternal H3K4me3 formation and is essential for meiotic progression in mouse oocytes

Mammalian oocytes establish a unique landscape of histone modifications, some of which are inherited by early embryos. How histone variants shape the maternal histone landscape remains unknown. Here, we map histone H2A variants in mouse fully grown oocytes (FGOs) and find that H2A.Z forms broad domains across intergenic regions, along non-canonical H3K4me3 (ncH3K4me3). During oocyte growth, H2A.Z progressively transitions from an active promoter-rich, canonical distribution to a non-canonical broad distribution (ncH2A.Z). Depletion of H2A.Z in oocytes partially impairs ncH3K4me3 formation and causes severe defects in meiotic progression, which resemble Mll2-knockout oocytes. Conversely, depletion of ncH3K4me3 by Mll2 knockout also causes a reduction of ncH2A.Z in FGOs. Thus, our study suggests that ncH2A.Z and ncH3K4me3 reinforce each other to form functional oocytes. Overall design: CATCH-seq and CUT&RUN of canonical H2A and H2A variants, including H2A.Z and TH2A, in fully grown oocytes. CATCH-seq of H2A.Z in oocytes from 4 stages, including primary (5 days), secondary (10 days), preantral (15 days) stage of growing oocytes, and the fully grown stage of oocyte (28 days FGO) were conducted to profiling H2A.Z's landscape. Also, CATCH-seq of 10d growing oocytes with control and amanitin treated were performed. H2A.Z, H3K4me3, H3K27me3 and H2AK119ub1 CATCH-seq were performed in H2A.Z control and H2A.Z DKO FGO oocytes. H2A.Z and H3K4me3 CATCH-seq were performed in Mll2 wild type and Mll2 KO FGO oocytes.

哺乳动物卵母细胞可构建独特的组蛋白修饰（histone modifications）图谱，其中部分图谱可传递至早期胚胎（early embryos）。组蛋白变体（histone variants）如何塑造母源组蛋白图谱，目前仍不明确。本研究对小鼠完全成熟卵母细胞（fully grown oocytes, FGOs）中的组蛋白H2A变体进行了图谱绘制，发现H2A.Z可在基因间区域形成宽泛结构域，并伴随非经典H3K4me3（ncH3K4me3）分布。在卵母细胞生长过程中，H2A.Z会逐渐从富集于活性启动子的经典分布模式，转变为非经典的宽泛分布模式（ncH2A.Z）。卵母细胞中H2A.Z的缺失会部分损害ncH3K4me3的形成，并导致减数分裂进程（meiotic progression）出现严重缺陷，该表型与Mll2敲除（Mll2-knockout）的卵母细胞相似。反之，通过Mll2敲除消除ncH3K4me3，同样会导致完全成熟卵母细胞中ncH2A.Z水平降低。因此，本研究表明ncH2A.Z与ncH3K4me3可相互增强，共同促成功能性卵母细胞的形成。

整体实验设计：针对完全成熟卵母细胞中的经典H2A及组蛋白H2A变体（包括H2A.Z与TH2A），开展CATCH-seq与CUT&RUN实验。对4个发育阶段的卵母细胞进行H2A.Z的CATCH-seq分析，涵盖初级卵母细胞（5日龄）、次级卵母细胞（10日龄）、窦前生长期卵母细胞（15日龄）以及完全成熟卵母细胞（28日龄FGO），以解析H2A.Z的修饰图谱。此外，本研究还对对照组与鹅膏蕈碱（amanitin）处理的10日龄生长期卵母细胞开展了H2A.Z的CATCH-seq实验。在H2A.Z野生型及H2A.Z双敲除（double knockout, DKO）完全成熟卵母细胞中，分别开展H2A.Z、H3K4me3、H3K27me3及H2AK119ub1的CATCH-seq实验。在Mll2野生型与Mll2敲除的完全成熟卵母细胞中，开展H2A.Z与H3K4me3的CATCH-seq实验。