Mechanisms of ventral body wall closure

婴儿的腹部是在子宫内由内部器官的包裹形成的，首先是一层薄薄的所谓的中胚层和外胚层（“初级体壁”），然后是肌肉和结缔组织（“次级体壁”）。次级壁如何取代初级壁尚不清楚，但由于内部器官同时快速生长，因此在整个过程中保持了紧密配合。大约每2000个婴儿中就有一个婴儿出生时腹壁有缺陷，临床上最常见的表现是腹部有一个洞，部分肠道和肝脏通过这个洞突出（疝出）。腹壁缺陷的原因也不是很清楚，部分原因是涉及的基本胚胎学尚未以详细的定量方式进行研究。在拟议的项目中，我们将使用小鼠胚胎作为模型，其中腹壁闭合与人类非常相似，以了解生长，重塑和物理力量的细节，这些必须共同努力才能形成第二体壁。我们将首先对腹壁进行“生长图谱”，以确定整个过程是如何在包含内部器官的情况下协调主壁被副壁取代的。为了将解剖变化与我们对细胞生物学的理解联系起来，我们将观察构成所有组织的细胞的固定标本，以了解细胞增殖、重排和大小变化是如何实现生长和重塑的，并取一些活体胚胎组织，其中的细胞被荧光标记，以便我们可以在显微镜下单独观察这些细胞的行为。我们将比较来自健康小鼠的胚胎和那些已知经常有腹部闭合缺陷的突变小鼠的胚胎，以了解哪些细胞过程异常从而导致腹部缺陷。最后，我们将验证腹壁生长是由机械张力触发和协调的观点，机械张力是由初级体壁变窄和对次级体壁的拉动以及正在生长的内脏器官的扩张所施加的。为了做到这一点，我们将绘制腹壁的张力图，看看它是否在空间或时间上与细胞增殖相关，并做小切口来缓解局部张力，研究这是否会减少局部增殖。我们还将研究一种分子信号通路，称为Yap/Taz，已知在其他情况下刺激细胞增殖以应对紧张，并询问它是否存在，活跃，以及腹壁生长所必需的。总之，本项目的调查将提供对腹壁闭合的综合理解，建立基本生物学并阐明出生缺陷可能发生的方式。

The abdomen (belly) of a baby is formed in the womb by the wrapping of the internal organs, first by a thin layer of so-called mesoderm and ectoderm ("primary body wall") and then by muscle and connective tissue ("secondary body wall"). How the secondary wall replaces the primary is not understood, but a snug fit is maintained throughout the process because the internal organs are growing rapidly at the same time. About one in 2000 babies are born with a defect in the abdominal wall, which most often presents clinically as a hole in the abdomen through which parts of the gut and sometimes the liver protrude (herniate). The causes of abdominal wall defects are also not well understood, in part because the basic embryology involved has not been studied in a detailed quantitative way. In the proposed project, we will use the mouse embryo, in which abdominal wall closure is very similar to that in humans, as a model to understand the details of growth, reshaping and physical forces that must work together to enable the secondary body wall to form. We will first make a 'growth atlas' of the abdominal wall to determine how the entire process coordinates replacement of the primary wall by the secondary wall while containing the internal organs. To link the anatomical changes with our understanding of cell biology, we will look in fixed specimens at the cells that make up all the tissues to see how the growth and re-shaping are achieved by cell multiplication, rearrangement, and size change, and take pieces of living embryonic tissue in which cells are fluorescently labelled so that we can microscopically observe these cell behaviours individually. We will compare embryos from healthy mice with those from mouse mutants known to have frequent abdominal closure defects to see which cellular processes are abnormal so as to cause abdominal defects. Finally, we will test the idea that the abdominal wall growth is triggered and coordinated by mechanical tension, exerted by primary body wall narrowing and pulling on the secondary body wall and by expansion of the growing internal organs. To do this, we will map tension across the growing abdominal wall and see if it correlates in space or time with cell proliferation and make small incisions to relieve local tension, investigating whether this reduces local proliferation. We will also investigate a molecular signalling pathway, known as Yap/Taz, that is known in other situations to stimulate cell proliferation in response to tension, and ask if it is present, active, and necessary for abdominal wall growth. Together the investigations in this project will provide an integrated understanding of abdominal wall closure, establishing the basic biology and elucidating ways in which birth defects might occur.