Oct4 regulates the embryonic axis and coordinates exit from pluripotency and germ layer specification in the mouse embryo

Lineage segregation in the mouse embryo is a finely controlled process dependent upon coordination of signalling pathways and transcriptional responses. We employed conditional deletion of Oct4 to investigate consequences of interference with embryonic patterning and lineage specification. Nanog becomes upregulated in the first epiblast cells to lose Oct4, leading to an expanded Nanog-positive domain. The primitive streak forms in the presumptive proximal posterior region, but epithelial to mesenchymal transition is impeded by dramatic increase of E-cadherin, leading to complete disorganisation and failure to generate germ layers. Formerly, expression domains of lineage markers were disrupted. Specifically, definitive endoderm expanded, the boundaries between presumptive anterior and posterior domains blurred and an ectopic posterior-like region appeared anteriorly, suggesting a role for Oct4 in maintaining the embryonic axis. Despite intermixing of lineage marker domains in mutants, cells co-expressing distinct lineage genes were not observed, suggesting that Oct4 deletion does not alter the connectivity of the transcription networks which underlie cell fate decisions in vivo. Molecular profiling corroborated genome-wide posteriorisation of mutants and disrupted expression of genes involved in gastrulation. Lastly, we confirmed a requirement for Oct4 in self-renewal of post-implantation epiblast ex vivo mRNA profiling of OCT4- and OCT4+ mouse in post implantation stage小鼠胚胎中的谱系分离是一项受精细调控的过程，依赖于信号通路与转录应答的协同调控。我们通过对八聚体结合转录因子4（Oct4）进行条件性敲除，探究了胚胎模式建成与谱系特化受到干扰后的表型效应。在首批丢失Oct4的上胚层细胞中，Nanog同源框蛋白（Nanog）的表达会上调，进而导致Nanog阳性细胞区域发生扩张。原条会在预设的近端后部区域形成，但由于E-钙粘蛋白（E-cadherin）的表达大幅上调，上皮间质转化（EMT）过程受到阻滞，最终引发胚胎完全紊乱且无法生成胚层。此外，谱系标志物的表达区域出现紊乱：具体而言，定型内胚层发生扩张，预设的前后结构域之间的边界变得模糊，且前部出现了异位的类后部区域，这表明Oct4在维持胚胎轴稳态中发挥着重要作用。尽管突变体中谱系标志物的表达区域发生了混杂，但并未观察到同时表达多种不同谱系基因的细胞，这表明Oct4的敲除并不会改变体内调控细胞命运决策的转录网络的连接性。分子谱分析证实了突变体全基因组范围内的后部化转变，并干扰了原肠胚形成相关基因的表达。最后，我们通过对植入后阶段Oct4阳性与Oct4阴性小鼠样本进行体外mRNA表达谱分析，证实了Oct4在植入后上胚层的自我更新中具有必需作用。