Intracellular density impacts the physical nature of the cytoplasm and can globally affect cellular processes, yet density regulation remains poorly understood. Here, using a new quantitative phase imaging method, we determined that dry-mass density varies during the cell cycle in fission yeast. Density decreased during G2, increased in mitosis and cytokinesis, and rapidly dropped at cell birth. These density variations were explained by a constant rate of biomass synthesis, coupled to slowdown of volume growth during cell division and rapid expansion post-cytokinesis. Arrest at specific cell-cycle stages led to continued increases or decreases in density. Spatially heterogeneous patterns of density suggested links between density regulation and tip growth, and septum bending away from higher-density daughters linked density to intracellular osmotic pressure. Our results demonstrate that systematic density variations during the cell cycle are predominantly due to modulation of volume expansion, and reveal functional consequences of density gradients and cell-cycle arrests.

中文翻译：

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细胞周期中细胞内密度的变化是由裂变酵母中的尖端生长调节引起的

细胞内密度影响细胞质的物理性质，并可以整体上影响细胞过程，但密度调节仍然知之甚少。在这里，使用新的定量相成像方法，我们确定了裂变酵母在细胞周期中干物质密度会发生变化。在G2期间密度降低，有丝分裂和胞质分裂增加，并在细胞出生时迅速下降。这些密度变化是由恒定的生物质合成速率解释的，再加上细胞分裂过程中体积增长的减慢和胞质分裂后的快速扩张。在特定细胞周期阶段的逮捕导致密度的持续增加或减少。密度的空间异质性模式表明密度调节与尖端生长之间存在联系，远离高密度女儿的隔膜弯曲将密度与细胞内渗透压联系起来。我们的结果表明，细胞周期中的系统密度变化主要归因于体积膨胀的调节，并揭示了密度梯度和细胞周期停滞的功能后果。