Tissue Tectonics During Gastrulation In Bilaminar Disc Embryos

哺乳动物的身体计划是在原肠形成过程中建立的，所有成年组织的基本细胞层都是第一次奠定的。在人类中，这一过程在植入后立即开始，在发育的第三周，并与大多数胚胎损失(~40%)发生在怀孕期间的时期一致。在这个非常早期的发育阶段，胚胎建立了由基因控制的细胞组织的空间模式，并在一定程度上受到构成胎盘的周围组织的影响。在这个阶段，胚胎的对称性被打破：胚胎不再是一个圆盘，而是一端的细胞表达与另一端不同的基因(换句话说，出现了前后轴)。这种对称性的断裂是如何在非啮齿哺乳动物(即人类)身上确定的，目前尚不清楚。我们对人类原肠发育的了解非常有限，因为在这一时期不能直接研究人类胚胎。然而，人类和猪的胚胎(和大多数其他哺乳动物)从平盘上胚层开始原肠形成。扁平盘由上胚层细胞和下胚层细胞组成的双层细胞层组成，周围环绕着滋养外胚层细胞。在双层盘状胚胎中协调原肠形成开始的生化信号(称为形态原)还不是很清楚。此外，在扁平盘状上皮细胞原肠形成过程中，上皮细胞在大小、形状和运动方面的生物物理特性的变化也是未知的。在这个方案中，我们将使用猪胚胎作为模型系统来研究这些过程，因为它们在现阶段与人类胚胎相似。此外，我们将使用人和猪的原肠形成干细胞模型(原肠突)来研究对称破坏和跨物种轴向模式的共同机制。我们将使用体内、体外和计算模型的组合来整合不同发育阶段的生化、细胞几何和形状信息，以建立哺乳动物胚胎发生的基本原理。为该项目选择的多尺度(从单个细胞到复杂组织)、多物种和多学科方法将提供对动物关键发育过程之一的全面新理解。在这个项目中获得的关于双层盘状胚胎原肠形成机制的新知识将为哺乳动物胚胎形成的关键原理提供蓝图。这项工作将影响我们对哺乳动物物种的发育、多样性和进化的理解；将通过提高我们对早期胚胎丧失原因的理解而在医学上产生影响；并将有助于开发用于异种移植的动物体内产生人类器官的新方法。

The mammalian body plan is established during gastrulation, where the basic cell layers from which all adult tissues derive are laid down for the first time. In humans, this process starts immediately after implantation, during the third week of development, and coincides with the period when most embryonic losses (~40%) occur during pregnancy. In this very early phase of development, the embryo establishes a spatial pattern of cellular organization controlled by genes and is, in part, influenced by the surrounding tissues contributing to the placenta. At this stage, the symmetry of the embryo breaks: the embryo is no longer a round disc, but instead cells on one end express different genes to those in the other end (in other words, the anterior-posterior axis emerges). How this break in symmetry is determined in non-rodent mammals (i.e. humans) is not yet clear. Our knowledge of gastrulation in humans is very limited because human embryos cannot be directly studied during this period. However, human and pig embryos (and most other mammals) start gastrulation from a flat disc epiblast. The flat disc is made of a bilaminar cell layer of epiblast and hypoblast cells and is surrounded by trophectoderm cells. Biochemical signals (known as morphogens) that orchestrate the onset of gastrulation in bilaminar disc embryos are not well known. Furthermore, the changes in the biophysical characteristics of epiblast cells in terms of size, shape, and movement during gastrulation in flat disc epiblasts are also unknown. In this proposal, we will study these processes using pig embryos as model system, due to their resemblance to human embryos at this stage. Furthermore, we will use human and pig stem cells model of gastrulation (gastruloids) to study the shared mechanisms of symmetry breaking and axial patterning across species. We will use a combination of in vivo, in vitro, and computational models to integrate biochemical, cell geometry and shape information across different developmental stages to establish fundamental principles of mammalian embryogenesis. The multi-scale (from individual cells to complex tissues), multispecies and multidisciplinary approaches selected for this project will provide a holistic new understanding of one of the key developmental processes of animals. The new knowledge of the mechanisms of gastrulation in bilaminar disc embryos gained in this project will provide a blueprint of the key principles governing the formation of a mammalian embryo. This work will impact our understanding of the development diversity and evolution of mammalian species; will have an impact in medicine by improving our understanding of the causes of early embryonic loss; and will enable the development of new methodologies for the generation of human organs in animals for xenotransplantation.