Dynamical Localization of DivL and PleC in the Asymmetric Division Cycle of Caulobacter crescentus: A Theoretical Investigation of Alternative Models.
Dynamical Localization of DivL and PleC in the Asymmetric Division Cycle of Caulobacter crescentus: A Theoretical Investigation of Alternative Models.
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DOI：
10.1371/journal.pcbi.1004348
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发表时间：
2015-07
影响因子：
4.3
通讯作者：
Tyson JJ
中科院分区：
文献类型：
--
作者：
Subramanian K;Paul MR;Tyson JJ
新月柄杆菌分裂前细胞中的细胞命运不对称性要求调节蛋白 DivL 定位于细胞的新极，在该极上调 CckA 激酶，从而导致整个细胞内出现 CtrA~P 梯度。在细胞周期的前一阶段（“有茎”细胞），DivL 沿着细胞膜均匀定位，并通过 DivK~P 维持非活性形式。目前还不清楚 DivL 如何通过简单地将其位置改变到新的极来克服分裂前细胞中 DivK~P 的抑制。有人认为，DivL 与 PleC 磷酸酶在新极的共定位对于 DivL 在那里的活性至关重要。然而，对于双功能酶 PleC 在新极点是否充当激酶或磷酸酶，存在不同的观点。为了探索这些模糊性，我们制定了杆杆菌细胞不对称分裂周期期间 DivL、PleC 和相关蛋白（DivJ、DivK、CckA 和 CtrA）时空分布的数学模型。通过在我们的模型中改变 DivL 和 PleC 的定位概况，我们展示了生理学观察到的这些蛋白质的空间分布对于从有茎细胞到预分裂细胞的转变至关重要。我们的模拟表明，PleC 是分裂前细胞中的一种激酶，并且通过隔离 DivK~P，PleC 的激酶形式使 DivL 在新极处重新激活。因此，PleC 激酶和 DivL 的共定位对于建立细胞不对称性至关重要。我们的模拟再现了实验观察到的野生型和突变细胞中 CtrA 的空间分布和磷酸化状态。基于该模型，我们探索突变等位基因的新组合，做出可以通过实验测试的预测。水生细菌新月柄杆菌不对称地分裂成留在其出生地的非运动“茎”细胞和分散到不同地点的运动“群”细胞。在细胞分裂之前，细胞会经历“分裂前”阶段，此时细胞的“旧”端有柄，“新”端有鞭毛。这些形态学的时空变化部分是由信号蛋白亚细胞定位的变化驱动的。为了了解细胞如何利用蛋白质定位来产生不同的细胞命运，我们制定了杆杆菌细胞周期期间六种调节蛋白（DivJ、DivK、PleC、DivL、CckA 和 CtrA）的时空动力学数学模型。与一些建议相反，我们的模型预测 PleC 在细胞周期的预分裂阶段充当激酶。此外，我们表明 DivL 和 PleC 激酶在茎阶段的空间分离是 DivL 失活和 DNA 合成起始所必需的。随后，DivL 和 PleC 激酶在细胞新极的共定位恢复了细胞半群中的 DivL 活性，导致细胞周期预分裂阶段复制不对称性的建立。
Cell-fate asymmetry in the predivisional cell of Caulobacter crescentus requires that the regulatory protein DivL localizes to the new pole of the cell where it up-regulates CckA kinase, resulting in a gradient of CtrA~P across the cell. In the preceding stage of the cell cycle (the “stalked” cell), DivL is localized uniformly along the cell membrane and maintained in an inactive form by DivK~P. It is unclear how DivL overcomes inhibition by DivK~P in the predivisional cell simply by changing its location to the new pole. It has been suggested that co-localization of DivL with PleC phosphatase at the new pole is essential to DivL’s activity there. However, there are contrasting views on whether the bifunctional enzyme, PleC, acts as a kinase or phosphatase at the new pole. To explore these ambiguities, we formulated a mathematical model of the spatiotemporal distributions of DivL, PleC and associated proteins (DivJ, DivK, CckA, and CtrA) during the asymmetric division cycle of a Caulobacter cell. By varying localization profiles of DivL and PleC in our model, we show how the physiologically observed spatial distributions of these proteins are essential for the transition from a stalked cell to a predivisional cell. Our simulations suggest that PleC is a kinase in predivisional cells, and that, by sequestering DivK~P, the kinase form of PleC enables DivL to be reactivated at the new pole. Hence, co-localization of PleC kinase and DivL is essential to establishing cellular asymmetry. Our simulations reproduce the experimentally observed spatial distribution and phosphorylation status of CtrA in wild-type and mutant cells. Based on the model, we explore novel combinations of mutant alleles, making predictions that can be tested experimentally. The aquatic bacterium, Caulobacter crescentus, divides asymmetrically into a non-motile “stalked” cell that stays at its place of birth, and a motile “swarmer” cell that disperses to a different locale. Prior to cell division, the cell passes through a “predivisional” stage, when it has a stalk at its “old” end and a flagellum at its “new” end. These spatiotemporal changes in morphology are driven, in part, by changes in subcellular localization of signaling proteins. To understand how the cell exploits protein localization to generate distinct cell fates, we formulated a mathematical model of the spatiotemporal dynamics of six regulatory proteins (DivJ, DivK, PleC, DivL, CckA and CtrA) during the Caulobacter cell cycle. Contrary to some suggestions, our model predicts that PleC functions as a kinase during the predivisional stage of the cell cycle. Further, we show that spatial separation of DivL and PleC kinase in the stalked stage is required for inactivation of DivL and for initiation of DNA synthesis. Later, co-localization of DivL and PleC kinase at the new pole of the cell restores DivL activity in the swarmer-half of the cell, resulting in the establishment of replicative asymmetry in the predivisional stage of the cell cycle.