肌球蛋白分布的定量预测苍蝇胚胎中的整体形态发生流
Quantification of myosin distribution predicts global morphogenetic flow in the fly embryo
摘要：
在胚胎发生过程中，组织层不断重新排列并折叠成特定的形状。发育生物学确定了局部组织动力学基础的基因表达和细胞骨架调节模式，但不同细胞类型的多个结构域如何协调作用以在器官尺度上重塑组织仍不清楚。我们使用全光片显微镜，自动图像分析和物理建模，定量研究全球组织转化动力学和果蝇原肠胚形成过程中的力生成模式之间的联系。我们发现胚胎尺度的形状变化是由三个简单的流场配置的时间序列。每个阶段都伴随着一个特征性的空间肌球蛋白分布，量化的粗粒度的“肌球蛋白张量”，捕获浓度和各向异性。我们的模型假设组织流动是由肌球蛋白张量成比例的应力驱动的，并且是有效的粘弹性的，具有控制流动的“无旋转”和“无发散”分量的两个参数。该模型仅使用三个全局参数，预测流量和测量流量之间的一致性高达90%。该分析揭示了a）肌球蛋白分布的空间调制和b）由于细胞的机械相互作用而使其作用的长程扩散的重要性。特别是，我们发现胚带延伸阶段与上皮的有效面积不可压缩性的发生有关，这使得流动和肌球蛋白强迫的关系强烈非局部。我们的分析还揭示了一个新的功能，为基础肌球蛋白在产生背侧定向流，并结合突变体分析，确定了一个非常规的控制机制，通过扭转依赖性减少基础肌球蛋白水平的腹侧。我们的结论是，理解形态发生流需要一个从根本上全球的角度来看。
英文摘要：
During embryogenesis tissue layers continuously rearrange and fold into specific shapes. Developmental biology identified patterns of gene expression and cytoskeletal regulation underlying local tissue dynamics, but how actions of multiple domains of distinct cell types coordinate to remodel tissues at the organ scale remains unclear. We use in toto light-sheet microscopy, automated image analysis, and physical modeling to quantitatively investigate the link between kinetics of global tissue transformations and force generation patterns during Drosophila gastrulation. We find embryo-scale shape changes are represented by a temporal sequence of three simple flow field configurations. Each phase is accompanied by a characteristic spatial myosin distribution, quantified in terms of a coarse-grained 'myosin tensor' that captures both concentration and anisotropy. Our model assumes tissue flow is driven by stress proportional to the myosin tensor, and is effectively visco-elastic with two parameters that control 'irrotational' and 'divergence-less' components of the flow. With just three global parameters, this model achieves up to 90% agreement between predicted and measured flow. The analysis uncovers importance of a) spatial modulation of myosin distribution and b) long-range spreading of its effect due to mechanical interaction of cells. In particular, we find germband extension phase is associated with the onset of effective areal incompressibility of the epithelium, which makes the relation of flow and myosin forcing strongly non-local. Our analysis also revealed a new function for basal myosin in generating a dorsally directed flow and, combined with mutant analysis, identified an unconventional control mechanism through twist dependent reduction of basal myosin levels on the ventral side. We conclude that understanding morphogenetic flow requires a fundamentally global perspective.
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