Analysis of Notch signalling pathway activation in controlling arteryformation during sprouting angiogenesis

脉管系统是胚胎发育过程中形成的第一个器官之一，对于为身体提供营养很重要。在第一个血管由前体细胞形成后，新的血管从这些细胞中发芽，连接到一个网络。这个过程称为血管生成。在血管生成过程中，内皮细胞必须以受控的方式生长到非灌注组织中，在那里它们形成管。这些最终必须以协调的方式与已经存在的血管系统连接，以确保从动脉到静脉的适当血液流动。生长通过所谓的“尖端”细胞的特化而发生，尖端细胞导致新生长的血管芽和“茎”细胞，茎细胞跟随尖端细胞。我们和其他实验室已经能够确定几个信号通路的重要提示和茎细胞规格。其中一个途径是Notch。这些研究提供了一个概念，其中notch配体dll4在血管生成发芽期间在尖端细胞中表达，其激活柄细胞中的Notch信号传导，从而防止它们本身成为尖端细胞。然而，过去几年在我的实验室里的观察使我们怀疑这个概念。例如，我们可以观察到新的血管芽主要来自静脉，这些静脉芽的尖端细胞随后形成新的动脉。还已知动脉需要Notch信号通路的激活来进行分化。那么，Notch信号通路激活程度较低的尖端细胞是如何变成动脉的呢？新的延时记录中，我们使用一个记者来监测激活的Notch信号通路在斑马鱼现在已经显示激活的Notch信号通路的提示，而不是在柄细胞。在这个应用程序中，我们现在将研究尖端和柄细胞如何协调Notch信号通路激活。我们将研究转化生长因子β（TGF β）信号传导如何影响Notch通路的激活。此外，我们将探讨这两种途径如何影响趋化因子受体cxcr4a的表达，cxcr4a对尖端细胞的正常迁移非常重要。最后，我们将研究只有静脉而没有动脉形成的组织中的血管生成。在这种情况下，我们预计Notch信号通路不会显著影响静脉形成。总之，我们期待对血管生成和动脉形成的协调调节以及Notch和TGF β信号通路对这些过程的影响有新的见解。

The vasculature is one of the first organs formed during embryonic development important for providing the body with nutrients. After the first blood vessels have formed from precursor cells, new blood vessels sprout from these, which connect to a network. This process is called angiogenesis. During angiogenesis, endothelial cells must grow in a controlled manner into non-perfused tissues, where they form tubes. These must eventually connect in a coordinated fashion with the already existing blood vessel system in order to ensure proper blood flow from arteries into veins. The growth takes place via the specification of so-called "tip" cells, which lead newly growing blood vessel sprouts and "stalk" cells, which follow the tip cells. We and other laboratories have been able to identify several signalling pathways important for tip and stalk cell specification. One of these pathways is Notch. These studies provided a concept in which a notch ligand, dll4, is expressed in tip cells during angiogenic sprouting, which activates Notch signalling in stalk cells, thereby preventing them from becoming tip cells themselves. Observations in the last few years in my laboratory, however, made us doubt this concept. For instance, we could observe that new blood vessel sprouts mainly originated from veins, and that the tip cells of these venous sprouts subsequently formed new arteries. It was also known that arteries need activation of the Notch signalling pathway for their differentiation. How could tip cells, then, which showed a low activation of the Notch signalling pathway become arteries? New time-lapse recordings in which we were using a reporter to monitor the activation of the Notch signalling pathway in zebrafish have now shown activation of the Notch signalling pathway in tip and not in stalk cells. In this application we will now examine how tip and stalk cells coordinate Notch signalling pathway activation. We will investigate how Transforming Growth Factor beta (TGF beta) signalling affects Notch pathway activation. In addition, we will explore how these two pathways influence the expression of a chemokine receptor, cxcr4a, which is important for the proper migration of tip cells. Finally, we will study angiogenesis in a tissue in which only veins and no arteries are being formed. In this setting, we would expect the Notch signalling pathway to not significantly influence vein formation. In summary, we expect new insights into the coordinated regulation of angiogenesis and artery formation and the influence of both the Notch and TGF beta signalling pathways on these processes.