Optogenetic protein manipulation during asymmetric divisions in vertebrate brain development

在脊椎动物胚胎（包括人类）的大脑发育过程中，被称为祖细胞的单个细胞分裂产生两个子细胞。在早期发育中，两个子细胞基本上都是原始祖细胞的复制品，也就是说，它们都是祖细胞，它们自己可以继续分裂并产生另外两个细胞。这种细胞分裂被称为对称细胞分裂，因为它们的两个子细胞具有相似的身份。在发育稍晚的时候，许多祖先会改变他们的分裂方式，这样他们的两个女儿就有了不同的命运。例如，一个子代将成为另一个祖细胞并能够再次分裂，而另一个子代将成为一个更专门的细胞，如不能分裂的神经元。这种类型的细胞分裂被称为不对称细胞分裂，对大脑发育至关重要，因为它允许大脑通过反复产生更多的细胞（作为祖细胞的子细胞）而变得更大，同时也制造一些构建神经回路的细胞，这些神经回路是动物行为的基础（作为神经元的子细胞通过与其他神经元连接和交流来实现这一点）。该提案旨在了解决定细胞分裂是对称还是不对称的生物学机制。具体来说，它将测试一个长期持有的假设，即不对称分裂是由特定蛋白质从祖细胞到两个子代的不对称遗传决定的，例如一个子代遗传了某些蛋白质，这些蛋白质将其推向成为神经元，而另一个子代没有遗传相同的蛋白质，因此具有不同的身份。为了实现蛋白质的不对称遗传，祖细胞需要有一种机制，当它分裂成两个时，它只将蛋白质转移到它的一个子代中。我们开发了一种新方法，允许我们使用特定波长的光来操纵活胚胎中单个祖细胞中的蛋白质定位。这使我们能够通过实验控制细胞分裂过程中的蛋白质定位，从而控制蛋白质是对称遗传还是不对称遗传。这将使我们能够确定不对称蛋白质遗传是否可以解释脊椎动物胚胎中不对称分裂的发生。

During brain development in vertebrate embryos (including man) individual cells known as progenitors divide to generate two daughter cells. In early development the two daughters are essentially both copies of the original progenitor cell, i.e. they are both also progenitors that can themselves go on to divide and make two more cells. These cell divsions are called symmetric cell divisions because their two daughters have similar identities. A little later in development many progenitors will change the way they divide so that their two daughters are generated with different fates. For example one daughter will become another progenitor and be capable of dividing again, while the other daughter becomes a more specialised cell such as a neuron which is incapable of dividing. This type of cell division is called an asymmetric cell division and is of fundamental importance to brain development because it allows the brain to get bigger by repeatedly generating more cells (the daughter that is the progenitor does this) while also making some cells that construct the neural circuits that underlie animal behaviour (the daughter that is the neuron does this by connecting and communicating to other neurons). This proposal aims to understand the biological mechanisms that determine whether a cell division is symmetric or asymmetric. Specifically it will test a long held hypothesis that asymmetric divisions are determined by the asymmetric inheritance of specific proteins from the progenitor cell to the two daughters, for example one daughter inherits certain proteins that push it towards becoming a neuron, while the other daughter does not inherit the same proteins and therefore has a different identity. To achieve asymmetric inheritance of a protein the progenitor cell needs to have a mechanism that moves the protein into only one of its daughters as it splits into two. We have developed a new method that allows us to use light of particular wavelength to manipulate protein localisation in individual progenitor cells in a living embryo. This allows us to experimentally control protein localisation during cell divisions and thus control whether proteins are symmetrically or asymmetrically inherited. This will allow us to determine whether asymmetric protein inheritance can explain the occurrence of asymmetric divisions in a vertebrate embryo.