Anisotropy links cell shapes to tissue flow during convergent extension
Anisotropy links cell shapes to tissue flow during convergent extension
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DOI：
10.1073/pnas.1916418117
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发表时间：
2020-06-16
影响因子：
11.1
通讯作者：
Kasza, Karen E.
中科院分区：
文献类型：
--
作者：
Wang, Xun;Merkel, Matthias;Kasza, Karen E.
在发育中的胚胎中，组织流动和重组的时间尺度短至几分钟。这包括上皮组织，由于外力或细胞内力的各向异性，上皮组织在会聚伸展运动中经常变窄和拉长。然而，允许或阻止组织重组的机制，特别是在存在强各向异性力的情况下，仍不清楚。我们在收敛和延伸的果蝇胚带上皮中研究了这个问题，它显示平面极化的肌球蛋白II，并受到来自邻近组织的各向异性力。我们表明，与各向同性组织相反，细胞形状本身不足以预测快速细胞重排的开始。从理论考虑和顶点模型模拟，我们预测在各向异性组织中，需要两个实验可获得的细胞模式指标——细胞形状指数和细胞排列指数——来确定各向异性组织是处于固体状还是流体状状态。我们表明，随着时间的推移，果蝇胚带中细胞形状和排列的变化预测了野生型和蜗牛扭曲突变胚胎中快速细胞重排的开始，当我们也考虑到细胞包装紊乱时，我们的理论预测进一步得到改进。这些发现表明，趋同扩展与向更流体样的组织行为过渡有关，这可能有助于适应快速发育过程中组织形状的变化。
Within developing embryos, tissues flow and reorganize dramatically on timescales as short as minutes. This includes epithelial tissues, which often narrow and elongate in convergent extension movements due to anisotropies in external forces or in internal cell-generated forces. However, the mechanisms that allow or prevent tissue reorganization, especially in the presence of strongly anisotropic forces, remain unclear. We study this question in the converging and extending Drosophila germband epithelium, which displays planar-polarized myosin II and experiences anisotropic forces from neighboring tissues. We show that, in contrast to isotropic tissues, cell shape alone is not sufficient to predict the onset of rapid cell rearrangement. From theoretical considerations and vertex model simulations, we predict that in anisotropic tissues, two experimentally accessible metrics of cell patterns-the cell shape index and a cell alignment index-are required to determine whether an anisotropic tissue is in a solid-like or fluid-like state. We show that changes in cell shape and alignment over time in the Drosophila germband predict the onset of rapid cell rearrangement in both wild-type and snail twist mutant embryos, where our theoretical prediction is further improved when we also account for cell packing disorder. These findings suggest that convergent extension is associated with a transition to more fluid-like tissue behavior, which may help accommodate tissue-shape changes during rapid developmental events.