Regulation of Key Cell Cycle Events

莱德实验室研究细胞生长控制和组织问题。我们感兴趣的是细胞如何 在没有明显外部输入的情况下做出组织决策；实际上，细胞是如何从混乱中创造秩序的。 我们目前关注的两个特别问题是细胞如何决定何时分裂，以便 维持细胞大小的动态平衡，以及细胞如何决定何时激活单个DNA复制起点 以调节DNA复制的时空组织。 细胞大小调节的机制是细胞生物学中一个经久不衰的谜。保持体型的能力 动态平衡是一种基本的细胞功能，调节适当的细胞大小是分化的关键特征， 细胞功能所必需的，从微小的血小板到巨大的卵母细胞。此外，尺寸动态平衡的丧失是一种 具有许多癌症和组织退行性疾病的特征。尽管最近在以下方面取得了进展 在几个系统中的具体机制中，仍然没有一个系统能够很好地理解问题。我们 研究分裂酵母的细胞大小，因为它提供了一个特征良好的、进化上保守的、实验上易于处理的系统。我们正在研究一种假设，即分裂酵母中的细胞大小受 两种有丝分裂激活因子CDC13和CDC25的大小依赖性表达。我们已经证明了CDC13和 CDC25水平与细胞大小成比例增加，并认为这种大小依赖的表达阻止了细胞 从进入有丝分裂直到它们达到适合分裂的大小。我们目前正在努力直接验证这一假设，并了解这两种蛋白质是如何以大小相关的方式表达的。 DNA复制时间是核代谢的一个基本方面。组织良好的复制时间安排 对于及时完成复制从而稳定的基因组遗传来说是必不可少的。复制时间也是 与基因表达、染色质修饰、染色体 结构和基因组进化。复制时间失调是癌细胞的一个特征，并有助于 它们的基因组不稳定性和病理基因表达表型。复制时间由 复制起始触发的时间，而该定时又由触发概率来调节，该概率在 起源。为了研究起源激发的调节，我们开创了单分子起源映射技术，使我们能够测量整个基因组中起源的位置和激发概率。我们的结果和其他人的结果表明，起源激发的异质性是如何在单细胞水平上 对种群进行平均，以产生紧急复制计时模式。因此，了解原始发射的概率是如何调节的是至关重要的。我们正在两个萌芽酵母中探索这个问题， 这为特定的机械实验提供了定义明确、特征明确的起源，以及哺乳动物细胞，这允许我们将所学应用于更复杂的基因组和发育路径。

The Rhind lab studies questions of cellular growth control and organization. We are interested in how cells make organizational decisions without obvious external input; in effect, how cells create order out of chaos. The two particular questions that we are currently focusing on are how cells decide when to divide, in order to maintain cell-size homeostasis, and how cells decide when to activate individual DNA replication origins, in order to regulate the spatial and temporal organization of DNA replication. The mechanism of cell-size regulation is an enduring mystery in cell biology. The ability to maintain size homeostasis is an essential cellular function, and regulation of proper cell size is a key feature of differentiation, required for cellular function from tiny platelets to enormous oocytes. Moreover, loss of size homeostasis is a characteristic of many cancers and tissue-degenerative diseases. Although recent progress has been made on specific mechanisms in several systems, there is still no system in which the problem is well understood. We study cell size in fission yeast because it affords a well-characterized, evolutionarily conserved and experimentally tractable system. We are investigating the hypothesis that cell size in fission yeast is controlled by the size-dependent expression of two mitotic activators: Cdc13 and Cdc25. We have shown that both Cdc13 and Cdc25 levels increase in proportion to cell size, and propose that this size-dependent expression prevents cells from entering mitosis until they reach their correct size for division. We are currently working to test that hypothesis directly and to understand how these two proteins are expressed in size-dependent manners. DNA replication timing is a fundamental aspect of nuclear metabolism. Well-organized replication timing is essential for timely completion of replication and thus stable genome inheritance. Replication timing is also correlated with, and has been proposed to regulate, gene expression, chromatin modification, chromosome structure, and genome evolution. Dysregulated replication timing is a feature of cancer cells and contributes to their genome instability and pathological gene-expression phenotypes. Replication timing is regulated by the timing of replication origin firing, which is in turn regulated by the probability of firing, which varies between origins. To investigate the regulation of origin firing, we have pioneered single-molecule origin mapping techniques that allow us to measure both the location and firing probability of origins across the genome. Our results and the results of others that have shown how the heterogeneity of origin firing at the single cell level is averaged over the population to produce emergent replication timing patterns. It is therefore critical to understand how the probability of origin firing is regulated. We are pursuing this question in both budding yeast, which affords well-defined and well-characterized origins for specific mechanistic experiments, and mammalian cells, which allow us to apply what we learn to more complicated genomes and developmental pathways.