Stochastic models of cell cycle regulation in eukaryotes

描述（由申请人提供）：细胞周期是生长中的细胞复制其基因组并在分裂时将每条染色体的两个副本分裂为两个子细胞的过程。这些复制（DNA合成）和分裂（有丝分裂）的过程以极高的保真度进行，对生命的延续至关重要。在真核细胞中，DNA合成（S期）和有丝分裂（M期）在时间上被两个间隙（G1和G2）分开。S期和M期的适当交替是通过“检查点”来执行的，如果细胞的基因组完整性以任何方式受到损害，这些检查点会阻止细胞周期的进展。例如，如果DNA在G1期受损，检查点会阻止其进入S期，直到损伤被修复。如果复制的染色体没有正确地排列在有丝分裂纺锤体上，一个不同的检查点会阻止进入后期（姐妹染色单体分离的阶段），直到所有姐妹染色单体都正确地附着在纺锤体的相反两极。检查点能够通过向控制特定细胞周期转变（G1-S， G2-M和M-G1）的分子机制发送STOP信号来阻断细胞周期进程。控制这些转变的分子机制有一种特殊的性质，叫做“双稳定性”。在生理条件下，控制机制可以无限期地维持在两种特征状态中的任何一种：OFF状态，对应于将细胞周期保持在过渡前阶段；和ON状态，这对应于推动细胞周期进入过渡后阶段。检查点停止信号似乎通过将适当的双稳态开关稳定在其OFF状态来起作用。因为这些检查点对于维持生物体基因组从一代细胞到下一代细胞的完整性至关重要，所以即使在酵母细胞（30 fL）这样的小细胞中不可避免的随机分子波动面前，它们也能可靠地发挥作用。基于控制细胞周期进程的分子机制随机模型的计算表明，检查点功能在野生型出芽酵母细胞中确实是强大的，但在携带特定检查点基因突变的菌株中可能会受到损害。尽管如此，酵母细胞周期进程的精确随机建模仍处于起步阶段，并且由于缺乏可靠的实验而受到阻碍

DESCRIPTION (provided by applicant): The cell cycle is the process by which a growing cell replicates its genome and partitions the two copies of each chromosome to two daughter cells at division. It is of utmost importance to the perpetuation of life that these processes of replication (DNA synthesis) and partitioning (mitosis) be carried out with great fidelity. In eukaryotic cells, DNA synthesis (S phase) and mitosis (M phase) are separated in time by two gaps (G1 and G2). Proper alternation of S phase and M phase is enforced by 'checkpoints' that block progression through the cell cycle if the genomic integrity of the cell is compromised in any way. For example, if DNA is damaged in G1 phase, a checkpoint blocks progression into S phase until the damage can be repaired. If replicated chromosomes are not properly aligned on the mitotic spindle, a different checkpoint blocks progression into anaphase (the phase of sister chromatid separation) until all sister chromatids are properly attached to opposite poles of the spindle. Checkpoints are able to block cell cycle progression by sending a STOP signal to the molecular mechanisms that govern specific cell-cycle transitions (G1-S, G2-M, and M-G1). The molecular mechanisms that govern each of these transitions have a peculiar property called 'bistability.' Under physiological conditions, the control mechanism can persist indefinitely in either of two characteristic states: the OFF state, which corresponds to holding the cell cycle in the pre-transition phase; and the ON state, which corresponds to pushing the cell cycle into the post-transition phase. Checkpoint STOP signals seem to act by stabilizing the appropriate bistable switch in its OFF state. Because these checkpoints are crucial to maintaining the integrity of an organism's genome from one generation of cells to the next, it is vital that they function reliably even in the face of random molecular fluctuations that are inevitable in a cell a small as a yeast cell (30 fL). Calculations based on stochastic models of the molecular mechanisms governing cell cycle progression suggest that checkpoint functions are indeed robust in wild-type budding yeast cells, but they may be compromised in strains carrying mutations of specific checkpoint genes. Nonetheless, accurate stochastic modeling of yeast cell cycle progression is still in its infancy, and it is hampered by a paucity of reliable experimental measurements of molecular abundances in single yeast cells, and of the phenotypic properties of compromised mutant strains. The purpose of this proposal is to provide the mathematical models and experimental data needed to understand how cell cycle checkpoints operate reliably in wild-type yeast cells and how they fail in mutant cells. To reach this goal will require new advances in stochastic modeling, and in the technology of measuring mRNA and protein molecules in single yeast cells. Because all eukaryotic organisms seem to employ the same fundamental molecular machinery that governs progression through the cell division cycle, the understanding of checkpoint operations in yeast cells will translate into a better understanding of checkpoint functions and failures in other types of cells, most notably human cells.