Department of Genetics, School of Life Science, The Graduate University for Advanced Studies (Sokendai), Yata 1111, Mishima, Shizuoka 411-8540, Japan.
Proc Natl Acad Sci U S A. 2011 Jul 19;108(29):11900-5. doi: 10.1073/pnas.1101853108. Epub 2011 Jul 5.
Cytoplasmic streaming is a type of intracellular transport widely seen in nature. Cytoplasmic streaming in Caenorhabditis elegans at the one-cell stage is bidirectional; the flow near the cortex ("cortical flow") is oriented toward the anterior, whereas the flow in the central region ("cytoplasmic flow") is oriented toward the posterior. Both cortical flow and cytoplasmic flow depend on non-muscle-myosin II (NMY-2), which primarily localizes in the cortex. The manner in which NMY-2 proteins drive cytoplasmic flow in the opposite direction from remote locations has not been fully understood. In this study, we demonstrated that the hydrodynamic properties of the cytoplasm are sufficient to mediate the forces generated by the cortical myosin to drive bidirectional streaming throughout the cytoplasm. We quantified the flow velocities of cytoplasmic streaming using particle image velocimetry (PIV) and conducted a three-dimensional hydrodynamic simulation using the moving particle semiimplicit method. Our simulation quantitatively reconstructed the quantified flow velocity distribution resolved through PIV analysis. Furthermore, our PIV analyses detected microtubule-dependent flows during the pronuclear migration stage. These flows were reproduced via hydrodynamic interactions between moving pronuclei and the cytoplasm. The agreement of flow dynamics in vivo and in simulation indicates that the hydrodynamic properties of the cytoplasm are sufficient to mediate cytoplasmic streaming in C. elegans embryos.
细胞质流动是一种在自然界中广泛存在的细胞内运输方式。在单细胞期的秀丽隐杆线虫中，细胞质流动是双向的；靠近皮层的流动（“皮层流动”）朝向前端，而中央区域的流动（“细胞质流动”）朝向后端。皮层流动和细胞质流动都依赖于非肌肉肌球蛋白 II（NMY-2），它主要定位于皮层。NMY-2 蛋白如何从远处驱动细胞质向相反方向流动的机制尚未完全了解。在这项研究中，我们证明了细胞质的流体力学特性足以介导由皮层肌球蛋白产生的力，从而在整个细胞质中驱动双向流动。我们使用粒子图像测速法（PIV）量化了细胞质流动的速度，并使用移动粒子半隐式方法进行了三维流体动力学模拟。我们的模拟通过 PIV 分析定量重建了量化的流速分布。此外，我们的 PIV 分析在原核迁移阶段检测到微管依赖性流动。这些流动是通过移动原核和细胞质之间的流体动力学相互作用产生的。体内和模拟中的流动动力学的一致性表明，细胞质的流体力学特性足以介导秀丽隐杆线虫胚胎中的细胞质流动。
