Function and regulation of the spindle positioning checkpoint (SPOC) kinase Kin4 of budding yeast

细胞经历不对称细胞分裂并形成不同细胞命运的子细胞的能力是一种保守的机制，涉及多细胞和单细胞生物中细胞多样性的产生。在大多数细胞类型中，纺锤体的位置在决定细胞是不对称分裂还是对称分裂方面起着至关重要的作用。几年前，我和其他人已经确定纺锤体位置检查点（SPOC）是一种重要的机制，可以感知纺锤体相对于出芽酵母细胞分裂轴的位置。如果纺锤体错位，SPOC会延迟有丝分裂和细胞质分裂的过渡。到目前为止，仅鉴定出5种SPOC成分：激酶Cdc5 （polo样激酶）、Elm1和Kin4、Bfa1-Bub2 GAP复合物和PP2A亚基Rts1。Kin4激酶是一种关键的SPOC成分，可以抵消Cdc5 polo激酶对Bfa1-Bub2 GAP复合物的失活。Rts1和Elm1分别调控Kin4激酶的定位和活性。有趣的是，涉及Kin4同源物的类似检查点机制可能存在于果蝇干细胞中。在高等真核生物中，这种检查点对细胞周期调节的重要性刚刚出现。Kin4激酶在SPOC的中心起作用，协调正确的纺锤体排列并退出有丝分裂。然而，对于纺锤体的位置如何控制Kin4激酶，人们知之甚少。因此，该项目旨在揭示在正常细胞周期进程和SPOC激活下调节Kin4激酶定位和活性的分子机制。

The ability of cells to undergo asymmetric cell divisions and to form daughter cells of distinct cell fates is a conserved mechanism that is involved in the generation of cell diversity in multiand unicellular organisms. In most cell types the position of the spindle plays a crucial role in determining whether a cell will divide asymmetrically or symmetrically. A couple of years ago, I and others have identified the spindle position checkpoint (SPOC) as an essential mechanism that senses the position of the spindle in respect to the division axis of a budding yeast cell. If the spindle is misaligned the SPOC delays both the transition out of mitosis and cytokinesis.So far, only five SPOC components have been identified: the kinases Cdc5 (polo-like kinase), Elm1 and Kin4, the Bfa1-Bub2 GAP complex, and the PP2A subunit Rts1. The Kin4 kinase is a key SPOC component that counteracts the inactivation of Bfa1-Bub2 GAP complex by Cdc5 polo kinase. Rts1 and Elm1 regulate the localisation and activity of Kin4 kinase, respectively. Interestingly, a similar checkpoint mechanism involving the homologue of Kin4 might exist in Drosophila stem cells. The im-portance of this checkpoint for cell cycle regulation in higher eukaryotes is just emerging.Kin4 kinase functions at the centre of the SPOC coordinating correct spindle alignment and exit from mitosis. However, relatively little is know about how the position of the spindle controls Kin4 kinase. This project therefore aims to unravel the molecular mechanisms that regulate localisation and activity of Kin4 kinase under normal cell cycle progression and upon SPOC activation.