Regulation of Spindle Positioning

 描述(申请人提供)：在许多组织类型中，细胞命运和随之而来的组织结构由有丝分裂纺锤体相对于细胞边界的取向决定。在生物体发育和组织动态平衡等过程中，纺锤体的取向决定了细胞分裂的平面，从而决定了细胞是对称分裂还是不对称分裂。对称的干细胞分裂产生两个完全相同的干细胞，而切换到不对称分裂产生一个干细胞和一个分化细胞。因此，在许多生物过程中，纺锤体位置与组织或细胞类型的特殊需求的适当协调是至关重要的。不正确的纺锤体方向可能会损害干细胞的不对称分裂，损害分化，并导致组织发育和动态平衡的缺陷。事实上，未经控制的对称性和不对称性分裂都与癌症的发生和发展直接相关。纺锤体定向的一个关键效应器是分子马达胞浆动力蛋白。这个马达被固定在细胞皮质，从那里它通过与微管的精确调节相互作用来定位纺锤体。目前尚不清楚皮质锚定的动力蛋白马达如何通过适当的方向和时间控制来执行这一功能，以实现适当的组织特异性功能。这种信息的缺乏阻碍了有效疗法的发展，这些疗法可以防止或逆转可能导致发育障碍或癌症的组织缺陷。在拟议的研究中，我们将使用简单的生物发芽酵母--其中Dynein及其许多调节器是高度保守的--以及体内、体外和生物物理方法的组合来确定Dynein被激活以执行其纺锤体定向功能的机制，并被调节以实现适当的方向偏差的纺锤体运动。我们的具体目标是：(1)确定皮质动力蛋白活动是如何开启的，以及(2)确定动力蛋白介导的纺锤体运动是如何定向偏向的。

 DESCRIPTION (provided by applicant): In many tissue types, cell fate and consequent tissue organization are dictated by the orientation of the mitotic spindle with respect to the cell boundaries. During such processes as organismal development and tissue homeostasis, spindle orientation dictates the plane of cell division, and thus whether a cell divides symmetrically or asymmetrically. Symmetric stem cell divisions result in two identical stem cells, whereas a switch to asymmetric division results in one stem cell and a differentiated cell. Thus, proper coordination of spindle position with the particular needs of a tissue or cell type is critial during numerous biological processes. Improper spindle orientation can compromise asymmetric stem cell divisions, impair differentiation, and lead to defects in tissue development and homeostasis. In fact, unchecked symmetric and asymmetric divisions have both been directly linked to cancer initiation and progression. A key effector of spindle orientation is the molecular motor cytoplasmic dynein. This motor is anchored at the cell cortex from where it orients the spindle through precisely tuned interactions with microtubules. It is unclear how cortically anchored dynein motors perform this function with appropriate directional and temporal control to achieve proper tissue specific functions. The lack of such information presents an impediment towards the development of effective therapies that may prevent or reverse defects in tissue organization that can lead to developmental disorders or cancer. In the proposed studies, we will use the simple model organism budding yeast - in which dynein and many of its regulators are highly conserved - and a combination of in vivo, in vitro, and biophysical methods to determine the mechanisms by which dynein is activated to perform its spindle orientation function, and regulated to achieve appropriate directionally biased spindle movements. Our specific aims are: (1) determine how cortical dynein activity is switched on, and (2) determine how dynein-mediated spindle movements are directionally biased.