Multifunctional molecular switch essential for cell morphogenesis

细胞增殖过程中细胞周期事件的协调部分是通过监视系统实现的。在芽生酵母中，细胞周期进程受到限制性调控，细胞周期中的一些事件受到监控DNA损伤、DNA复制、纺锤体完整性、纺锤体定位和细胞形态发生的检查点的调控。目前还不清楚是否所有的检查点控制都已确定。在这里，我们发现了一个新的检查点，将细胞壁重塑与纺锤体的形成联系在一起。1，3-β-葡聚糖合成酶活性缺陷的Fks-1突变体未能形成成熟芽。令人惊讶的是，这些细胞带有复制后DNA，但Clb2p水平相当低，并且没有形成双极纺锤体。我们发现，wac1(壁面检查点缺陷)突变取消了这种停滞，导致Clb2p和CLB2 mRNA的积累，并导致尽管葡聚糖合成受到干扰，但仍形成双极纺锤体。这些结果表明存在一种新的检查点机制来协调进入有丝分裂，并表明Wac1p需要通过转录调控CLB2来实现这一检查点功能。此外，我们还发现WAC1与肌动蛋白相关蛋白ARP1相同。Arp1p、Nip100p和Jnm1p是dynactin复合体的组成部分，它们是在保持细胞高度存活的同时实现G2期停滞所必需的。这些结果表明，dynactin复合体在监控细胞壁合成的新检查点中具有调节作用。

The coordination of cell cycle events during cell proliferation is attained, in part, through surveillance systems. In the budding yeast Saccharomyces cerevisiae, cell cycle progression is restrictively regulated and some events during cell cycle are regulated by the checkpoints monitoring DNA damage, DNA replication, integrity of the spindle, spindle positioning and cell morphogenesis. It still remained unclear whether all of the checkpoint controls have been identified.Here we found that a novel checkpoint exists to couple cell wall remodeling with spindle formation. fks1 mutants defective in 1,3-β-glucan synthase activity failed to form a mature bud. Surprisingly, these cells arrested with post-replicative DNA but quite low level of Clb2p, and without forming bipolar spindles. We found that wac1 (wall-checkpoint defective) mutation that abolished this arrest caused the accumulation of Clb2p and CLB2 mRNA and leaded to formation of bipolar spindles despite glucan-synthesis perturbation. These results indicate the existence of a novel checkpoint mechanism to coordinate entry into mitosis, and suggest that Wac1p is required to achieve this checkpoint function through a transcriptional regulation of CLB2. Furthermore, we revealed that WAC1 was identical with ARP1 (actin-related protein). Arp1p, Nip100p and Jnm1p, which are components of the dynactin complex, are required to achieve the G2 arrest while keeping cells highly viable. These results indicate that the dynactin complex have a regulatory role in the novel checkpoint to monitor cell wall synthesis.