Molecular mechanisms controlling entry into mitosis

描述（由申请人提供）：单细胞生物显示出在广泛变化的外部条件下保持相同大小的非凡能力。多细胞生物还显示出控制细胞大小的非凡能力，因为它们能够产生许多不同大小的不同类型的细胞。尽管细胞大小控制具有重要的基础意义，但我们对控制细胞大小和细胞生长的分子机制知之甚少。维持特定的细胞大小需要细胞生长和细胞分裂的协调。在裂变酵母中，Wee1激酶和Cdc25磷酸酶在G2/M下协调细胞生长和细胞分裂。Wee1磷酸化并抑制周期蛋白依赖性激酶，从而延迟进入有丝分裂，直到达到临界大小。Cdc25去除Wee1添加的抑制性磷酸盐，从而促进进入有丝分裂。对控制Wee1和Cdc25活性的信号机制的理解将为细胞如何感知和维持特定的细胞大小提供重要线索。然而，令人惊讶的是，这些机制在很大程度上是未知的。Wee1和Cdc25的芽殖酵母同源物称为Swel和Mih1。我们最近的研究表明，在G2/M状态下，Swel和Mih1是协调细胞生长和细胞分裂所必需的，这表明裂变酵母的Wee1和Cdc25的基本功能在出芽酵母中得到了保留。本提案中描述的实验目标将是利用出芽酵母中可用的强大实验方法来了解G2/M下细胞生长和细胞分裂的协调。我们将首先描述在正常细胞周期和Swe1依赖性检查点延迟期间调节Swe1和Mih1的分子机制。然后，我们将确定负责调节Swe1和Mih1的蛋白质，并确定它们是如何被控制的。我们的长期目标是发现调节Swe1和Mih1的上游生理信号，以协调G2/M的细胞生长和细胞分裂。了解协调细胞生长和细胞分裂的机制可能与癌症有关，因为它们代表了旨在阻止肿瘤细胞生长的药物的潜在靶点。

DESCRIPTION (provided by applicant): Single-celled organisms show a remarkable ability to maintain the same size over widely varying external conditions. Multicellular organisms also show a remarkable ability to control cell size, as they are able to generate many different cell types of different sizes. Despite the fundamental importance of cell size control, we know little about the molecular mechanisms that control cell size and cell growth. Maintenance of a specific cell size requires coordination of cell growth and cell division. In fission yeast, the Wee1 kinase and the Cdc25 phosphatase are required for coordination of cell growth and cell division at G2/M. Wee1 phosphorylates and inhibits cyclin-dependent kinases, thereby delaying entry into mitosis until a critical size has been reached. Cdc25 removes the inhibitory phosphate added by Wee1, thereby promoting entry into mitosis. An understanding of the signaling mechanisms that control the activity of Wee1 and Cdc25 should provide important clues to how cells sense and maintain a specific cell size. Surprisingly, however, these mechanisms are largely unknown. The budding yeast homologs of Wee1 and Cdc25 are called Swel and Mih1. Our recent work has shown that Swel and Mih1 are required for coordination of cell growth and cell division at G2/M, indicating that the basic functions of fission yeast Wee1 and Cdc25 have been conserved in budding yeast. The goal of the experiments described in this proposal will be to use the powerful experimental approaches available in budding yeast to understand coordination of cell growth and cell division at G2/M. We will first characterize the molecular mechanisms that regulate Swe1 and Mih1 during a normal cell cycle and during a Swe1 dependent checkpoint delay. We will then identify proteins responsible for regulation of Swe1 and Mih1 and determine how they are controlled. Our long-term goal is to discover the upstream physiological signals that regulate Swe1 and Mih1 to coordinate cell growth and cell division at G2/M. An understanding of the mechanisms that coordinate cell growth and cell division may be relevant to cancer, since they represent potential targets for drugs aimed at blocking the growth of tumor cells.