Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 2014 Feb 18;111(7):2602-7. doi: 10.1073/pnas.1311635111. Epub 2014 Feb 3.
The cell cycle is a highly regulated process that enables the accurate transmission of chromosomes to daughter cells. Here we uncover a previously unknown link between the tricarboxylic acid (TCA) cycle and cell cycle progression in the Caenorhabditis elegans early embryo. We found that down-regulation of TCA cycle components, including citrate synthase, malate dehydrogenase, and aconitase, resulted in a one-cell stage arrest before entry into mitosis: pronuclear meeting occurred normally, but nuclear envelope breakdown, centrosome separation, and chromosome condensation did not take place. Mitotic entry is controlled by the cyclin B-cyclin-dependent kinase 1 (Cdk1) complex, and the inhibitory phosphorylation of Cdk1 must be removed in order for the complex to be active. We found that following down-regulation of the TCA cycle, cyclin B levels were normal but CDK-1 remained inhibitory-phosphorylated in one-cell stage-arrested embryos, indicative of a G2-like arrest. Moreover, this was not due to an indirect effect caused by checkpoint activation by DNA damage or replication defects. These observations suggest that CDK-1 activation in the C. elegans one-cell embryo is sensitive to the metabolic state of the cell, and that down-regulation of the TCA cycle prevents the removal of CDK-1 inhibitory phosphorylation. The TCA cycle was previously shown to be necessary for the development of the early embryo in mammals, but the molecular processes affected were not known. Our study demonstrates a link between the TCA cycle and a specific cell cycle transition in the one-cell stage embryo.
细胞周期是一个高度调控的过程，使染色体能够准确地传递给子细胞。在这里，我们揭示了三羧酸（TCA）循环和秀丽隐杆线虫早期胚胎细胞周期进展之间以前未知的联系。我们发现，TCA 循环成分（包括柠檬酸合酶、苹果酸脱氢酶和 aconitase）的下调导致进入有丝分裂之前的单细胞阶段停滞：原核相遇正常发生，但核膜破裂、中心体分离和染色体浓缩没有发生。有丝分裂的进入由细胞周期蛋白 B-细胞周期蛋白依赖性激酶 1（Cdk1）复合物控制，并且为了使复合物具有活性，必须去除 Cdk1 的抑制性磷酸化。我们发现，在 TCA 循环下调后，细胞周期蛋白 B 水平正常，但 CDK-1 在单细胞阶段停滞的胚胎中仍保持抑制性磷酸化，表明存在 G2 样停滞。此外，这不是由于 DNA 损伤或复制缺陷引起的检查点激活的间接影响。这些观察结果表明，秀丽隐杆线虫单细胞胚胎中 CDK-1 的激活对细胞的代谢状态敏感，而 TCA 循环的下调阻止了 CDK-1 抑制性磷酸化的去除。以前已经表明 TCA 循环对于哺乳动物早期胚胎的发育是必需的，但是不知道受影响的分子过程。我们的研究表明 TCA 循环与单细胞阶段胚胎中的特定细胞周期转换之间存在联系。
