Cell Progression Through Meiosis: A Signal from Recombination to the First Division

减数分裂的细胞进展：从重组到第一次分裂的信号

• 批准号: 0083816
• 负责人: Robert Malone
• 金额: $ 39万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-05-15 至 2004-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0083816&HistoricalAwards=false
• 关键词: Cell; Progression; Through; Meiosis; Signal

Meiosis, the special division process in eukaryotes wherein chromosome number is reduced from diploid to haploid during the production of gametes, is complex and highly conserved. It is possible to think of the various steps of meiosis somewhat like an intracellular developmental pathway. Mitotic cells get a signal to enter meiosis and must go through premeiotic DNA synthesis, recombination and synapsis, reductional division, equational division, and packaging of the haploid nuclei in the proper order. An interesting and important question is how the various steps of meiosis communicate with each other to ensure that they occur at the right time and in the right sequence. In the budding yeast, Saccharomyces cerevisiae, answers to some of the questions are known. A key feature ensuring that events occur properly is ordered transcriptional regulation. Entry into meiosis involves the loss of a mitotic repressor (RME1) and expression of a meiotic activator (IME1). This results in the transcription of the "Early Meiotic Genes", which include the genes necessary for meiotic recombination. These early events activate a second transcriptional regulator, NDT80, which is required for expression of the "Middle Meiotic Genes" and the first and second meiotic division. NDT80 activation also results in the expression of "Late Meiotic Genes", though it is not yet completely clear whether this is direct or/and a consequence of NDT80 activation of the Middle genes. A second layer of regulation in meiosis is meiotic checkpoints. For example, a failure to perform premeiotic replication results in cell arrest. Recent interest has been stimulated by the realization that cells also have a checkpoint that assesses the state of meiotic recombination. In certain recombination mutants (e.g., dmc1) blocked at intermediate points in the meiotic recombination pathway, the cell arrests before the first division. This arrest requires several genes (e.g., RAD17, MEC1 ) known to be involved in mitotic DNA damage recognition checkpoints. It has been proposed that this checkpoint assessing the state of recombination is a key feature of normal progression through meiosis and that the "dmc1 checkpoint" also occurs in wildtype cells, as the intermediate is made normally during recombination. It makes good sense that the high frequency of breaking and rejoining chromosomes during recombination is a process which the cell should be able to sense. Attempts to segregate chromosomes before recombination was finished would be disastrous. There is yet another mode whereby meiotic recombination communicates with the first division, and that this communication occurs as recombination starts in wild type cells. It has been shown that meiotic cells are capable of recognizing that recombination has been started; the response is to delay the first division for a time equivalent to the time necessary to accomplish recombination. Null mutations in four genes required to initiate recombination ("EE" genes) result in a earlier first division. This is intuitively pleasing; it seems eminently reasonable that starting the complex process of recombination should signal the next meiotic step, the first division. It appears that this signaling process is complex since null mutations in different EE genes can have somewhat different effects on the timing of the first division. It has been shown that the signal is not the formation of double strand breaks (the first easily observed DNA intermediate in recombination initiation). The importance of this initiation signal is indicated by noting that, in its absence, the first division occurs at the time when homologs would normally be recombining. This indicates that the first division segregation apparatus can be ready and functional considerably earlier than it normally acts. Data from this laboratory indicates that the start of recombination prevents this premature division. This project asks how this novel signal from recombination to the first division works. Does it require the majority of the initiation genes, consistent with the idea that the signal is the formation of an initiation complex? What is the role of the synaptonemal complex and its component parts in sending the signal? Is the normal signal from recombination initiation recognized and communicated by the checkpoint genes that also respond to the dmc1 mutant block which occurs at later stages? Does the signal work by affecting activation of the central meiotic regulator NDT80? Finally, what are the other genes involved in this signal from recombination to the first division? This work will define how this intracellular signaling process, crucial for the proper progression through meiosis, functions to ensure that two critical steps in meiosis happen at the proper times.

减数分裂是真核生物的特殊分裂过程，在配子产生过程中染色体数目从二倍体减少到单倍体，减数分裂是复杂且高度保守的。可以将减数分裂的各个步骤视为细胞内发育途径。 有丝分裂细胞获得进入减数分裂的信号，并且必须经历减数分裂前的DNA合成、重组和联会、还原分裂、等式分裂以及以正确的顺序包装单倍体核。一个有趣且重要的问题是减数分裂的各个步骤如何相互沟通以确保它们在正确的时间以正确的顺序发生。在芽殖酵母（酿酒酵母）中，一些问题的答案是已知的。确保事件正常发生的一个关键特征是有序转录调控。 进入减数分裂涉及有丝分裂阻遏物（RME1）的丧失和减数分裂激活物（IME1）的表达。 这导致“早期减数分裂基因”的转录，其中包括减数分裂重组所需的基因。这些早期事件激活第二个转录调节因子NDT80，它是“减数分裂中期基因”表达以及第一次和第二次减数分裂所需的。 NDT80 激活也会导致“减数分裂晚期基因”的表达，尽管尚不完全清楚这是否是NDT80 激活中间基因的直接结果。 减数分裂的第二层调节是减数分裂检查点。例如，未能进行减数分裂前复制会导致细胞停滞。最近人们认识到细胞也有一个评估减数分裂重组状态的检查点，这激发了人们的兴趣。在减数分裂重组途径的中间点被阻断的某些重组突变体（例如 dmc1）中，细胞在第一次分裂之前停滞。这种停滞需要已知参与有丝分裂 DNA 损伤识别检查点的多个基因（例如 RAD17、MEC1）。有人提出，评估重组状态的检查点是减数分裂正常进展的关键特征，并且“dmc1检查点”也出现在野生型细胞中，因为中间体在重组过程中正常产生。重组过程中染色体断裂和重新连接的高频率是细胞应该能够感知的过程，这是有道理的。 在重组完成之前尝试分离染色体将是灾难性的。 还有另一种模式，减数分裂重组与第一次分裂进行通讯，并且这种通讯在野生型细胞中重组开始时发生。研究表明，减数分裂细胞能够识别重组已经开始。响应是将第一次分裂延迟相当于完成重组所需时间的时间。 启动重组所需的四个基因（“EE”基因）的无效突变导致较早的第一次分裂。这在直觉上是令人愉悦的；开始复杂的重组过程应该标志着减数分裂的下一个步骤，即第一次分裂，这似乎是非常合理的。这个信号传导过程似乎很复杂，因为不同 EE 基因的无效突变可能对第一次分裂的时间产生不同的影响。已表明信号不是双链断裂的形成（重组起始中第一个容易观察到的 DNA 中间体）。该起始信号的重要性可以通过注意到，如果没有该起始信号，则第一次分裂发生在同源物通常重组时。 这表明第一分区分离装置可以比其正常工作更早地准备好并投入使用。该实验室的数据表明重组的开始可以防止这种过早分裂。 该项目询问这种从重组到第一次分裂的新颖信号是如何工作的。它是否需要大部分起始基因，与信号是起始复合物形成的观点一致？联会复合体及其组成部分在发送信号中起什么作用？来自重组起始的正常信号是否被检查点基因识别和传达，这些检查点基因也对后期发生的 dmc1 突变块做出反应？该信号是否通过影响中央减数分裂调节因子 NDT80 的激活来发挥作用？最后，参与从重组到第一次分裂的信号的其他基因是什么？这项工作将定义这种细胞内信号传导过程（对于减数分裂的正确进展至关重要）如何发挥作用，以确保减数分裂中的两个关键步骤在适当的时间发生。