Cell-cell interactions in the regulation of neural progenitor fate: the role of PCDH19

大脑是一个复杂而高度有序的结构，是所有脊椎动物和一些无脊椎动物的控制中心。在哺乳动物中，大脑的一个区域，称为大脑新皮层，对记忆，注意力，思想，感知和语言等复杂过程特别重要。哺乳动物新皮层中的神经元分布在特定的层中，并且具有独特的形态和功能特性。这些神经元在发育过程中由特定的细胞产生，称为神经祖细胞。这些祖细胞需要为每一层产生正确数量的神经元，并且它们按顺序进行。它们首先为最深的一层生成神经元，然后为最深的一层生成神经元，以此类推，直到生成所有层。这意味着祖细胞需要在产生神经元和维持自己的种群之间保持平衡，以避免在所有神经元产生之前耗尽。祖先可以以两种不同的方式分裂：对称和不对称。对称分裂产生两个相同的子细胞，两个祖细胞或两个神经元。不对称分裂产生两种不同的细胞：一种祖细胞和一种神经元。在皮层形成的早期阶段，祖细胞对称分裂以增加其数量。但在某些时候，它们需要改变为不对称分裂，以开始产生神经元。祖先是如何做出这一决定的，目前还不清楚。我的实验室正在研究控制大脑皮层发育的机制。我们最近发现，一种细胞-细胞粘附蛋白，原钙粘蛋白19（PCDH 19），参与调节神经祖细胞的行为。PCDH 19在人类疾病中发生突变，导致癫痫和非常年轻的女孩中不同程度的认知障碍。这种分子存在于神经祖细胞的对称到不对称分裂开关的时间。我们已经发现，具有PCDH 19的祖细胞在单独时产生神经元的速率与它们与缺乏这种蛋白质的祖细胞共存时不同。对于PCDH 19缺陷的祖细胞也是如此。这表明细胞之间的交流对于调节祖细胞行为很重要，我们可以使用PCDH 19来研究这一过程。我们将首先确定我们在胚胎E11.5天看到的变化是否及时维持，以及它们如何影响整体神经元的产生。然后，我们将分析分裂的祖细胞，以找出是什么使具有PCDH 19的祖细胞与没有这种蛋白质的祖细胞不同。最后，我们将使用直接和无偏见的方法来找出哪些分子和信号通路负责两种祖细胞类型之间的差异行为。我们将研究已被证明在祖细胞的维持中发挥作用的特定分子途径。与此同时，我们将对PCDH 19阳性和阴性祖细胞表达的所有基因进行分析，以公正的方式评估其他潜在的差异。这些实验将提供有价值的信息来解释祖细胞如何决定开始产生神经元，但它们也将揭示细胞间通讯如何影响这一过程。这些信息对于理解大脑是如何正确形成的至关重要，这是研究神经发育障碍时的基本知识。

The brain is a complex, yet highly ordered structure serving as the control centre for all vertebrates and some invertebrates. In mammals, one region of the brain, designated the cerebral neocortex, is particularly important for elaborate processes such as memory, attention, thoughts, perception and language. Neurons in the mammalian neocortex are distributed in specific layers and have distinct morphological and functional properties. These neurons are generated during development by specific cells, called neural progenitors. These progenitors need to produce the correct amount of neurons for each of the layers, and they do it sequentially. They first produce neurons for the deepest layer, then for the layer on top of that, and so on until all layers are generated. This means that progenitors need to maintain a balance between giving rise to neurons and maintaining their own population, to avoid getting depleted before all neurons are produced. Progenitors can divide in two different ways: symmetrically and asymmetrically. Symmetric divisions produce two identical daughter cells, either two progenitors or two neurons. Asymmetric divisions give rise to two different cells: one progenitor and one neuron. At very early stages in the formation of the cortex, progenitors divide symmetrically to increase their numbers. But at some point they need to change to asymmetric divisions to start producing neurons. How progenitors make this decision is currently not understood. My laboratory is investigating the mechanisms that control development of the cerebral cortex. We have recently found that one cell-cell adhesion protein, protocadherin 19 (PCDH19), is involved in the regulation of neural progenitor behaviour. PCDH19 is mutated in a human disorder leading to epilepsy and varying degrees of cognitive impairment in very young girls. This molecule is present in neural progenitors around the time of the symmetric to asymmetric division switch. We have found that progenitors with PCDH19 produce neurons at different rates when they are alone than when they coexist with progenitors that lack this protein. The same is true for the PCDH19-deficient progenitors. This suggests that communication between cells is important to regulate progenitor behaviour and that we can use PCDH19 to investigate this process. We will first determine if the changes that we have seen at embryonic day E11.5 are maintained in time and how they affect overall neuronal production. We will then analyse the dividing progenitor cells to find out what makes the progenitors with PCDH19 different from the ones without this protein. Finally, we will use both direct and unbiased approaches to figure out which molecules and signalling pathways are responsible for the differential behaviour between the two progenitor types. We will investigate particular molecular pathways that have been shown to play a role in the maintenance of progenitor cells. At the same time, we will carry out an analysis of all genes expressed by PCDH19-positive and -negative progenitors to assess other potential differences in an unbiased way.These experiments will provide valuable information to explain how progenitors decide to start producing neurons, but they will also reveal how cell-cell communication influences this process. This information is crucial to understand how brains are formed correctly, an essential knowledge when studying neurodevelopmental disorders.