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，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，这两个子代基本上都是原始祖细胞的副本，也就是说，它们都是可以继续分裂并制造另外两个细胞的祖细胞。这些细胞分裂被称为对称细胞分裂，因为它们的两个子体具有相似的身份。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会以不同的命运出生。例如，一个女儿将成为另一个祖细胞并能够再次分裂，而另一个女儿将成为一个更专业的细胞，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重复产生更多细胞来变得更大(作为祖先的子代做到了这一点)，同时也制造了一些细胞，这些细胞构建了构成动物行为的神经回路(子代是神经元，通过与其他神经元连接和交流来实现这一点)。这项提议旨在了解决定细胞分裂是对称还是不对称的生物学机制。具体地说，它将检验一个长期坚持的假设，即不对称分裂是由祖细胞到两个子代的特定蛋白质的不对称遗传决定的，例如，一个女儿继承了推动其成为神经元的某些蛋白质，而另一个女儿不继承相同的蛋白质，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，当蛋白质分裂成两个时，将蛋白质只移动到它的一个子体中。我们已经开发出一种新的方法，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。这使我们能够在实验上控制细胞分裂期间的蛋白质定位，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.