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

大脑是一个复杂而又高度有序的结构，是所有脊椎动物和一些无脊椎动物的控制中心。在哺乳动物的大脑中，有一个区域被称为大脑新皮层，它对记忆、注意力、思维、感知和语言等复杂的过程尤为重要。哺乳动物新皮层的神经元分布在特定的层，具有不同的形态和功能特性。这些神经元是在发育过程中由称为神经祖细胞的特定细胞产生的。这些祖细胞需要为每一层产生正确数量的神经元，而且它们是依次产生的。它们首先生成最深层的神经元，然后生成最上层的神经元，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身数量之间保持平衡，以避免在所有神经元产生之前耗尽。祖细胞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，要么是两个祖细胞，要么是两个神经元。不对称分裂产生两个不同的细胞：一个祖细胞和一个神经元细胞。在皮层形成的早期阶段，祖细胞对称分裂以增加它们的数量。但在某些时候，它们需要转变为不对称分裂，开始产生神经元。祖先是如何做出这个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 (PCDH19)，参与神经祖细胞行为的调节。PCDH19在一种人类疾病中发生突变，导致非常年幼的女孩癫痫和不同程度的认知障碍。这种分子存在于神经祖细胞中，大约在对称分裂到不对称分裂切换的时候。我们发现含有PCDH19的祖细胞单独存在时与与缺乏这种蛋白质的祖细胞共存时产生神经元的速率不同。缺乏pcdh19的祖细胞也是如此。这表明细胞间的交流对于调节祖细胞的行为很重要，我们可以使用PCDH19来研究这一过程。我们将首先确定我们在胚胎期E11.5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，找出是什么使带有PCDH19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倚的方法来弄清楚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维持祖细胞中起作用的特定分子途径。同时，我们将对pcdh19阳性和阴性祖细胞表达的所有基因进行分析，以不偏不倚地评估其他潜在差异。这些实验将为解释祖细胞如何决定开始产生神经元提供有价值的信息，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，是研究神经发育障碍的基本知识。

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.