Investigating cellular plasticity in the avian primitive streak

“大”图景：生物学中一个引人入胜的问题是，多细胞生物是如何从一个单细胞——受精卵——产生的。在胚胎发生过程中naïve和仍可塑祖细胞相互作用，首先形成不同的胚胎层和组织主体轴，然后形成具有高度分化的细胞类型和功能的特化器官。胚胎中的细胞通过分子信号机制相互沟通来协调这些复杂的事件。细胞间的交流在生物体的整个生命过程中都很重要，例如在损伤后的修复或生长和重塑中。骨骼肌就是一个很好的例子，骨骼肌是一种可以自我再生和重建的组织（在受伤或运动后）。这是可能的，因为肌肉和其他组织中都有专门的细胞，它们在受到刺激时可以分裂，并在需要时产生更多分化的细胞。这些特化的细胞是组织内的干细胞，它们对与胚胎中相同的通信信号作出反应。我们需要了解这些信号的细节复杂性，因为它们会根据它们所处的环境产生不同的影响。信号机制的缺陷可能对胚胎有害，但它们也可能导致成年人的疾病，如癌症，当细胞“行为不当”并忽略信号或做出错误反应并因此不受控制地生长时。实验模型系统：我们使用形态与早期人类胚胎非常相似的早期鸡胚胎，研究了两种重要的细胞-细胞信号通路的影响。从这些研究中我们知道BMP和WNT信号在不同类型的早期祖细胞中有不同的作用，这取决于发育阶段。我们还知道这些途径是通过一个共同的转录调节因子（SMAD）起作用的，它可以开关其他基因的“开启”或“关闭”。在“HH 3期”胚胎中，这些信号改变了细胞的迁移方式，但在“HH 4期”胚胎中，相同的信号对迁移没有影响，而是改变了细胞的命运；因此，在这个后期阶段，细胞的反应是改变它们将要变成的样子。我们将使用最先进的分子协议来识别这些细胞群中由smad开关打开或关闭的基因。我们在鸡胚胎中有这些方法的经验，这是一个容易获得的实验系统，我们已经组建了一支高技能的研究人员团队来执行这一研究计划。为什么这很重要？BMP和Wnt信号是广泛应用于多种组织器官的细胞通讯信号。我们知道许多通路的组成部分，但我们仍然不明白为什么细胞对（显然）相同的触发因素的反应会因环境而异。我们现在有一个定义良好的系统，其中细胞对相同信号的反应已经被表征，并且相当不同：要么细胞迁移受到影响，要么细胞规格受到影响。这给我们提供了一个独特的机会来确定哪些基因在反应细胞中被打开或关闭，并在分子水平上提供更深入的机制洞察。这是充分了解特化细胞如何形成以及它们如何构建功能器官所必需的。这不仅与胚胎发育有关，如果出现问题，胚胎将无法存活或畸形，而且与干细胞科学和组织工程有关，这些新兴领域越来越重要，在医学和健康方面具有重大的未来潜力。具体目标：我们将利用我们最近的观察结果，并使用我们完善的模型系统来(1)识别在BMP和Wnt信号响应中差异表达的基因，以及(2)测试这些基因在细胞迁移和细胞规范/分化中的表达和功能。

THE 'BIG' PICTURE: A fascinating question in biology asks how multicellular organisms arise from a single cell: the fertilized egg. During embryogenesis naïve and still plastic progenitor cells interact with each other, first to form different embryonic layers and to organize the main body axes, and later to build specialized organs with highly differentiated cell types and functions. The cells in an embryo coordinate these complex events by communicating with each other using molecular signalling mechanisms. Cell-cell communication is important throughout the life of an organism, for example for repair after injury or for growth and remodelling. A good example for this is skeletal muscle, a tissue that can regenerate and rebuild itself (after injury or after exercise). This is possible, because there are specialized cells in muscle, but also in other tissues, which can divide when stimulated and make more differentiated cells when needed. These specialized cells are tissue-resident stem cells and they respond to the same communication signals that act in the embryo. We need to understand the detailed intricacies of these signals, as they can have different effects depending on the context in which they act. Defects in signalling mechanisms can be detrimental to an embryo, but they can also lead to diseases in adults such as cancer, when cells "mis-behave" and ignore the signals or respond incorrectly and grow uncontrollably as a result.EXPERIMENTAL MODEL SYSTEM: We have used the early chick embryo, which is very similar in its morphology to early human embryos, and investigated the effects of two important cell-cell signaling pathways. From these studies we know that BMP and WNT signals have different effects in different types of early progenitor cells, depending on the stage of development. We also know that these pathways act via a common transcriptional regulator (SMAD), which can switch other genes 'on' or 'off'. In a "HH stage 3" embryo the signals change how cells migrate, but in a "HH stage 4" embryo the SAME signals have no effect on migration but instead alter the fate of the cells; thus at this later stage the cells respond by changing what they will become. We will use state-of-the-art molecular protocols to identify the genes that are switched on or off by the SMAD-switch in these cell populations. We have experience with these methods in the chick embryo, an accessible experimental system and we have assembled a highly skilled team of researchers to execute this programme of research.WHY IS THIS IMPORTANT? BMP and Wnt signaling are widely used cell communication signals that act in many tissues and organs. We know many of the components of the pathways, but we still do not understand why cellular responses to the (apparently) same trigger vary depending on the context. We now have a well-defined system where the cellular response to the same signals has been characterized and is quite divergent: EITHER cell migration is affected OR cell specification is affected. This gives us the unique opportunity to identify which genes have been switched on or off in the responding cells and provide a deeper mechanistic insight at the molecular level. This is needed in order to fully understand how specialised cells form and how they build functional organs. This is not only relevant in developing embryos, if things go wrong the embryo will not survive or become malformed, but is also relevant for stem cell science and tissue engineering, emerging fields of increasing importance and with significant future potential for medicine and health.SPECIFIC OBJECTIVES: We will capitalize on our recent observations and use our well established model system to (1) identify genes that are differentially expressed in response to BMP and Wnt signaling, and to (2) test the expression and function of these genes in both cell migration and cell specification/differentiation.