Revealing how the mitotic spindle controls asymmetric cell division in vivo

总结 这项提案的目标是发现新形式的微管组织如何驱动第一个不对称细胞 哺乳动物生物体在体内的分裂。多细胞生物最显著的特征之一是 大量的细胞类型。其中许多是由不对称的细胞分裂产生的，在这种分裂中， 不对称分布细胞命运决定子，或产生不同形状、体积或细胞大小的子细胞。 极性特征 在大多数细胞类型中，有丝分裂纺锤体在不对称细胞分裂中起着重要作用。它包括 两个关键部分，与染色体相互作用并促进细胞动力学沟形成的中央纺锤体， 和一系列星状微管。这些星形微管起源于纺锤体两极的中心体 并允许极化的皮层元件和力调节器差动地控制纺锤体以驱动不对称的 细胞分裂细胞不对称分裂的机制已经在培养细胞和非培养细胞中进行了详细的研究。 哺乳动物有机体。然而，小鼠胚胎并不从其亲本细胞中继承中心粒， 提出缺乏功能性中心体和星形微管阵列。因此，仍不清楚有丝分裂如何 纺锤体是在发育的最早阶段组织起来的，以及它们如何有助于不对称性。 细胞分裂以驱动第一种哺乳动物细胞类型的分化。 在这里，我们将联合收割机活体成像方法与分子和生物物理方法相结合，以测试一种新的 有丝分裂纺锤体组织的形式，我们发现它在体内驱动不对称细胞分裂。不同于以往 假设缺乏中心体和星形微管阵列，我们发现一些细胞建立了一个高度 不对称纺锤体，只有一个星状微管阵列。操纵这种不对称的纺锤体， 第一类细胞的分离。因此，这一建议的核心假设是， 这种新形式的不对称纺锤体组织驱动体内第一次不对称细胞分裂。为了验证这个， 我们的目标是研究非对称主轴的组装机制（目标1），并能驱动 不对称细胞分裂（Aim 2）。 目标1将特别侧重于解剖所需的分子调节剂的来源和功能， 组装不对称的纺锤体，细胞极性组件的作用，以及带来所需的物理力量 星形阵列和中央纺锤体一起组装成完整的有丝分裂纺锤体装置。 目的2将探讨不对称纺锤体驱动细胞不对称分裂的机制。我们将 具体测试基于细胞分裂方向的差异调节的三种基本机制， 子细胞体积和细胞皮层张力。

Summary The goal of this proposal is to discover how new forms of microtubule organization drive the first asymmetric cell divisions of a mammalian organism in vivo. One of the most salient features of multicellular organisms is their vast number of cell types. Many of these are produced by asymmetric cell division, in which a parental cell asymmetrically distributes cell fate determinants, or generates daughter cells with different shape, volume or cell polarity features. In most cell types, the mitotic spindle apparatus plays a fundamental role in asymmetric cell division. It comprises two key parts, the central spindle that interacts with chromosomes and promotes cytokinetic furrow formation, and an array of astral microtubules. These astral microtubules originate from centrosomes at the spindle poles and allow polarized cortical elements and force regulators to differentially control the spindle to drive asymmetric cell division. The mechanisms of asymmetric cell division have been studied in detail in cultured cells and non- mammalian organisms. Yet, the mouse embryo does not inherit centrioles form its parental cells and has been proposed to lack functional centrosomes and astral microtubule arrays. Therefore, it remains unclear how mitotic spindles are organized during the earliest stages of development, and how they may contribute to asymmetric cell division to drive the differentiation of the first mammalian cell types. Here, we combine live-imaging approaches with molecular and biophysical methods to test the function of a new form of mitotic spindle organization, which we found to drive asymmetric cell division in vivo. Unlike previous assumptions of lack of centrosomes and astral microtubule arrays, we found that some cells establish a highly asymmetric spindle with only one astral-like microtubule array. Manipulations of this asymmetric spindle disrupt the segregation of the first cell types. Thus, the central hypothesis of this proposal is that the establishment of this new form of asymmetric spindle organization drives the first asymmetric cell divisions in vivo. To test this, our aims will investigate the mechanisms by which the asymmetric spindle is assembled (Aim 1) and can drive asymmetric cell division (Aim 2). Aim 1 will specifically focus on dissecting the source and function of the molecular regulators required to assemble the asymmetric spindle, the role of cell polarity components, and the physical forces required to bring together the astral array and the central spindle to assemble a complete mitotic spindle apparatus. Aim 2 will investigate the mechanisms by which the asymmetric spindle drives asymmetric cell division. We will specifically test three fundamental mechanisms based on the differential regulation of cell cleavage orientation, daughter cell volume and cell cortex tension.