Maternal Dppa2 and Dppa4 are dispensable for zygotic genome activation but important for offspring survival

Zygotic Genome Activation (ZGA) represents the initiation of transcription following fertilization. Despite its importance in shifting developmental control from primarily maternal stores in the oocyte to the embryo proper, we know little of the molecular events that initiate ZGA in vivo. Recent in vitro studies in mouse embryonic stem cells (ESCs) have revealed Developmental Pluripotency Associated 2 and 4 (Dppa2/4) as key regulators of ZGA-associated transcription. However, their roles in initiating ZGA in vivo remain unexplored. We reveal Dppa2/4 proteins are present in the nucleus at all stages of preimplantation development and associate with mitotic chromatin. We generated single and double maternal knockout mouse models to deplete maternal stores of Dppa2/4. Importantly, while fertile, Dppa2/4 maternal knockout mice had reduced litter sizes, indicating decreased offspring survival. Immunofluorescence and transcriptome analyses of 2-cell embryos revealed while ZGA took place there were subtle defects in embryos lacking maternal Dppa2/4. Strikingly, heterozygous offspring that inherited the null allele maternally had higher preweaning lethality than those that inherited the null allele paternally. Together our results show that while Dppa2/4 are dispensable for ZGA transcription, maternal stores have an important role in offspring survival, potentially via epigenetic priming of developmental genes. Embryos were collected from 2x each mating (2x cKO x WT; 2x cKO x HET; 2x Ctrl x WT), denoted mating1 and mating2 in each file name; For the HET genotypes (included in each sample name) HET1= embryos from cKO x WT male mating (100% HET), and HET2= embryos from cKO x HET male mating (50% should be HET and 50% HOMs, according to the Mendelian ratio)合子基因组激活（Zygotic Genome Activation, ZGA）指受精后转录过程的启动。尽管其在将发育调控从卵母细胞内的母源储存物质转向胚胎自身这一核心过程中至关重要，但学界对体内启动ZGA的分子事件仍知之甚少。近期针对小鼠胚胎干细胞（embryonic stem cells, ESCs）的体外研究显示，发育多能性相关蛋白2与4（Developmental Pluripotency Associated 2 and 4, Dppa2/4）是ZGA相关转录的关键调控因子。然而，二者在体内启动ZGA过程中的具体作用仍未被探明。本研究发现，Dppa2/4蛋白在胚胎植入前发育的所有阶段均定位于细胞核，并与有丝分裂染色质相结合。我们构建了单基因及双基因母源敲除的小鼠模型，以清除卵母细胞内的Dppa2/4母源储存。值得注意的是，尽管Dppa2/4母源敲除小鼠仍可正常生育，但其产仔数显著减少，提示子代存活率下降。对2细胞胚胎开展的免疫荧光与转录组分析显示，尽管ZGA过程可正常发生，但缺失母源Dppa2/4的胚胎存在细微发育缺陷。尤为关键的是，母源遗传空等位基因的杂合子子代，其断奶前致死率高于父源遗传空等位基因的子代。综合上述结果，本研究表明：尽管Dppa2/4并非ZGA转录过程所必需，但母源储存的Dppa2/4对子代存活具有重要意义，这一作用可能通过对发育基因的表观遗传预激活实现。本研究从每组交配组合各收集2批胚胎：2批条件性敲除（conditional knockout, cKO）×野生型（wild type, WT）、2批cKO×杂合子（heterozygous, HET）、2批对照组×WT，每个文件名中均标注为mating1与mating2；对于样本名称中包含的HET基因型，HET1指来自cKO雄性×WT雌性交配的胚胎（全部为HET），HET2指来自cKO雄性×HET雌性交配的胚胎（根据孟德尔遗传比例，50%为HET，50%为纯合子）。