Bayesian Inference of Forces Causing Cytoplasmic Streaming in <i>Caenorhabditis elegans</i> Embryos and Mouse Oocytes

Cellular structures are hydrodynamically interconnected, such that force generation in one location can move distal structures. One example of this phenomenon is cytoplasmic streaming, whereby active forces at the cell cortex induce streaming of the entire cytoplasm. However, it is not known how the spatial distribution and magnitude of these forces move distant objects within the cell. To address this issue, we developed a computational method that used cytoplasm hydrodynamics to infer the spatial distribution of shear stress at the cell cortex induced by active force generators from experimentally obtained flow field of cytoplasmic streaming. By applying this method, we determined the shear-stress distribution that quantitatively reproduces in vivo flow fields in Caenorhabditis elegans embryos and mouse oocytes during meiosis II. Shear stress in mouse oocytes were predicted to localize to a narrower cortical region than that with a high cortical flow velocity and corresponded with the localization of the cortical actin cap. The predicted patterns of pressure gradient in both species were consistent with species-specific cytoplasmic streaming functions. The shear-stress distribution inferred by our method can contribute to the characterization of active force generation driving biological streaming.细胞结构在流体动力学层面相互连通，某一位置产生的力可带动远端结构运动。该现象的典型实例为细胞质流动（cytoplasmic streaming）：细胞皮层处的主动力可诱导整个细胞质发生流动。然而，目前尚不清楚此类力的空间分布与强度如何驱动细胞内远端物体的运动。为解决这一问题，我们开发了一种计算方法，该方法借助细胞质流体动力学原理，从实验测得的细胞质流流场中推断主动力发生器所诱导的细胞皮层剪切应力的空间分布。通过应用该方法，我们确定了可定量重现秀丽隐杆线虫（Caenorhabditis elegans）胚胎以及减数分裂II时期小鼠卵母细胞体内流场的剪切应力分布。研究预测，小鼠卵母细胞中的剪切应力定域范围相较于皮层高流速区域更为狭窄，且与皮层肌动蛋白帽的定位特征相吻合。两个物种的压力梯度预测模式均与其物种特异性细胞质流动功能相一致。本方法所推断得到的剪切应力分布，可为表征驱动生物性细胞质流动的主动力产生过程提供助力。