Mechanisms of ventral body wall closure

婴儿的腹部(腹部)是在子宫中由内脏包裹形成的，首先是一层薄薄的所谓中胚层和外胚层(“初级体壁”)，然后是肌肉和结缔组织(“次级体壁”)。次生壁如何取代初级壁尚不清楚，但在整个过程中保持着舒适的配合，因为内脏在同一时间快速生长。大约每2000名婴儿中就有一名出生时腹壁有缺陷，临床上最常见的表现为腹部有一个洞，部分肠道，有时还有肝脏突出(突出)。腹壁缺陷的原因也不是很清楚，部分原因是所涉及的基础胚胎学还没有得到详细的定量研究。在拟议的项目中，我们将使用小鼠胚胎作为模型，了解生长、重塑和物理力量的细节，这些细节必须共同作用才能形成次级体壁。我们将首先制作腹壁的“生长图谱”，以确定在包含内脏的同时，整个过程是如何协调由次生壁替换主壁的。为了将解剖变化与我们对细胞生物学的理解联系起来，我们将在固定的标本中观察组成所有组织的细胞，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，并取一些活的胚胎组织，其中的细胞被荧光标记，以便我们可以显微镜下观察这些细胞的单独行为。我们将比较来自健康小鼠的胚胎和已知有频繁腹部闭合缺陷的小鼠突变的胚胎，看看哪些细胞过程异常，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缩小和对次级体壁的拉动以及正在生长的内脏的扩张所施加的。为此，我们将绘制不断生长的腹壁上的张力图，看看它在空间或时间上是否与细胞增殖相关，并进行小切口以缓解局部紧张，研究这是否会减少局部增殖。我们还将研究分子信号通路，称为YAP/Taz，在其他情况下已知为刺激细胞增殖以应对紧张，并询问它是否存在、活跃和对腹壁生长是必要的。这一项目的研究将提供对腹壁关闭的综合理解，建立基本的生物学基础，并阐明可能发生出生缺陷的方式。

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.