Determining the mechanisms linking cell growth to the cell cycle in the liver

项目总结 在复制脱氧核糖核酸之前，细胞生长在G1/S过渡期触发人类细胞分裂。这一过程很重要 因为它决定了增殖细胞的大小，这对它们的生理功能很重要。更大 细胞，包括巨噬细胞和肝细胞，通常有额外的基因组拷贝，其比例与其 增加了单元格大小。通常，这样的大细胞通过触发DNA合成来维持其DNA与细胞质的比例， 但不是分裂，分裂的细胞大小与倍性成比例。然而，尽管细胞大小和倍性经常 相互关联，维持DNA与细胞质比例的功能尚不清楚。此外，我们不知道 尽管已经确定了许多关键的细胞周期，但控制DNA与细胞质比例的分子机制 调节蛋白。在这里，我们建议确定DNA与细胞质比例的功能和 通过检测小鼠肝细胞在体内将细胞生长与DNA复制联系起来的调节机制 发展和再生的背景。这项工作的科学前提是最近的一项突破，我的 实验室在了解细胞生长如何触发分裂方面取得了进展。与预期的增长将 增加Cyclin D-CDK4，6的活性，我们发现相反，细胞生长稀释了细胞周期抑制物Rb来触发 培养细胞的分裂。我们在体外发现的Rb稀释机制提出了一个问题，如果这个机制 在活体内运作。在这里，我们建议最终测试RB稀释，以及一个替代模型，在该模型中， 细胞激活p38抑制小鼠肝细胞分裂。我们将测量肝细胞大小的变化 以及Rb1在一系列小鼠系中的细胞生长与细胞周期进程是如何耦合的 有条件地删除、删除或过度表达。初步数据表明，对于小鼠的肝细胞 同一倍体，DNA/细胞质比与Rb1基因剂量呈负相关，与Rb-1基因剂量呈正相关。 稀释模型。我们将使用这些改变DNA与细胞质比例的遗传模型来测试它在 肝脏。更具体地说，我们将使用可诱导的敲除和过度表达的等位基因来产生肝细胞 它们比野生型大小不一，并且DNA与细胞质的比例异常。然后我们将执行一项 肝功能和再生测试小组。这一点很重要，因为异常的DNA与细胞质的比例 与多种病理状态有关，但其在体内的功能在任何细胞类型中仍不清楚。加在一起， 这项拟议的工作很重要，因为确定细胞生长如何触发细胞分裂是一个基本的 细胞和发育生物学中的问题。它的理解还将提供对癌症的洞察，在这些癌症中 流程不规范。

PROJECT SUMMARY Cell growth triggers human cell division at the G1/S transition before DNA is replicated. This process is important because it determines the size of proliferating cells, which is important for their physiological functions. Larger cells, including macrophages and hepatocytes, often have additional copies of their genome in proportion to their increased cell size. Typically, such large cells maintain their DNA-to-cytoplasm ratio by triggering DNA synthesis, but not division, at cell sizes in proportion to their ploidy. However, while cell size and ploidy are frequently correlated, the function of maintaining the DNA-to-cytoplasm ratio is unclear. Moreover, we do not know the molecular mechanisms controlling the DNA-to-cytoplasm ratio despite having identified many key cell cycle regulatory proteins. Here, we propose to determine both the function of the DNA-to-cytoplasm ratio and the regulatory mechanisms linking cell growth to DNA replication in vivo by examining mouse hepatocytes in developmental and regenerative contexts. The scientific premise of this work is a recent breakthrough that my laboratory made in understanding how cell growth triggers division. Contrary to expectations that growth would increase Cyclin D-Cdk4,6 activity, we found instead that cell growth dilutes the cell cycle inhibitor Rb to trigger division in cultured cells. Our discovery of the Rb dilution mechanism in vitro raises the question if this mechanism operates in vivo. Here, we propose to definitively test the Rb dilution, and an alternative model in which small cells activate p38 to inhibit cell division in mouse hepatocytes. We will measure changes in hepatocyte cell size and how cell growth is coupled to cell cycle progression in a series of mouse lines in which Rb1 has been conditionally deleted, knocked down or over-expressed. Preliminary data indicate that for hepatocytes of the same ploidy, the DNA-to-cytoplasm ratio is inversely correlated with Rb1 gene dosage, consistent with the Rb- dilution model. We will use these genetic models that change the DNA-to-cytoplasm ratio to test its function in the liver. More specifically, we will use inducible knockdown and over-expression alleles to generate hepatocytes that are larger and smaller than wild type and have aberrant DNA-to-cytoplasm ratios. We will then perform a panel of liver function and regeneration tests. This is important because aberrant DNA-to-cytoplasm ratio is associated with various pathological states, but its function in vivo is still unclear in any cell type. Taken together, the proposed work is important because determining how cell growth triggers cell division is a fundamental question in cell and developmental biology. Its understanding will also provide insight into cancers, where this process is misregulated.