Formation of synthetic blastocysts by self-organization of human naïve pluripotent stem cells

胚泡形成在哺乳动物中独特地进化以使子宫着床。胚泡包括三个基本组织，即上胚层、滋养外胚层和下胚层（小鼠中的原始内胚层）。外胚细胞是胚胎本身的起源，也是多能胚胎干细胞的来源。滋养外胚层和下胚层产生胚外组织，胎盘和卵黄囊，支持胚胎在子宫内发育。胚泡如何形成三种不同且精确排列的组织是一个迷人的基本生物学问题。此外，了解人类胚泡发育将在生殖医学中有应用。对人类囊胚的研究受到高质量IVF胚胎可用性和伦理考虑的限制。因此，我们对人类胚胎发育的概念在很大程度上借鉴了小鼠研究。然而，尽管小鼠和人类囊胚看起来相似，但它们至少在一个基本方面有所不同。我们最近发现，与小鼠不同，人类上胚层细胞可以再生真正的滋养外胚层1。这种可塑性在人类幼稚多能干细胞中得以维持，这些干细胞也能够产生原始内胚层。因此，人类幼稚多能干细胞具有重建完整胚胎的独特潜力。基于这些发现，我们的目标是在这个项目中建立第一个合成的人类囊胚模型。利用化学和生长因子信号，我们将指导从幼稚干细胞形成三个谱系，并将自组织引导到准确概括人类囊胚的组成，组织和功能特性的结构中。我们将应用生物工程方法来优化囊胚建模的鲁棒性和吞吐量。我们确定了合成囊胚发育至原肠胚形成的潜力。然后，我们将利用分子和化学遗传学结合高分辨率延时成像来探索早期人类胚胎发育动力学。我们开发的人类合成囊胚将为基础研究提供早期人类发育的机会，提供一个高度可重复和真实的模型，适合任何类型的实验和分析解剖。从幼稚诱导多能干细胞发育的模型胚泡也将在指导干细胞分化用于疾病建模和研究人类不育的遗传基础方面具有重要应用。最后，我们期望从模型囊胚发育和对其发育潜力的评价中获得的知识将能够提高辅助生殖技术的IVF胚胎质量

Blastocyst formation evolved uniquely in mammals to enable uterine implantation. The blastocyst comprises three founding tissues, the epiblast, trophectoderm and hypoblast (primitive endoderm in mice). Epiblast is the origin of the embryo proper and the source of pluripotent embryonic stem cells. Trophectoderm and hypoblast give rise to extra-embryonic tissues, the placenta and yolk sac,that support embryo development in the uterus. How blastocysts form three distinct and precisely arranged tissues is a fascinating fundamental biology question. Furthermore, understanding blastocyst development in humans will have applications in reproductive medicine. Research on human blastocysts is limited by availability of good quality IVF embryos and ethical considerations. Therefore our concept of human embryo development draws heavily on mouse studies. However, although mouse and human blastocysts appear similar, they differ in at least one fundamental aspect. We recently discovered that, unlike in mouse, human epiblast cells can regenerate authentic trophectoderm1. This plasticity is maintained in human naïve pluripotent stem cells, which are also able to produce primitive endoderm. Therefore human naïve pluripotent stem cells have a unique potency to reconstitute an intact embryo. Based on these findings, we aim in this project to establish the first synthetic human blastocyst model. Using chemical and growth factor signals we will direct formation of the three lineages from naïve stem cells and steer self-organization into structures that accurately recapitulate the composition, organization and functional properties of human blastocysts. We will apply bioengineering approaches to optimize robustness and throughput for blastocyst modeling. We establish the potential of the synthetic blastocysts for development up to gastrulation. We will then explore early human embryo developmental dynamics using molecular and chemical genetics in conjunction with high-resolution time-lapse imaging. The human synthetic blastocyst we develop will transform access to early human development for fundamental research, providing a highly reproducible and authentic model amenable to any type of experimental and analytical dissection. Model blastocysts developed from naïve induced pluripotent stem cells will also have important applications in directing stem cell differentiation for disease modeling and in investigation of the genetic basis of human infertility. Finally, we expect that knowledge gained from development of model blastocysts and evaluation of their developmental potential will enable improvement of IVF embryo quality for assisted reproduction technology