Data from: Simulation of the nodal flow of mutant embryos with small number of cilia: comparison of mechanosensing and vesicle transport hypotheses

Left-right (L-R) asymmetry in the body plan is determined by nodal flow in vertebrate embryos. Shinohara et al. used Dpcd and Rfx3 mutant mouse embryos and showed that only a few cilia were sufficient to achieve L-R asymmetry. However, the mechanism underlying the breaking of symmetry by such weak ciliary flow is unclear. The flow-mediated signals related to L-R asymmetry have not been clarified; there are two models for L-R symmetry breaking: vesicle transport and mechanosensing. In this study, we developed a computational model of the node system reported by Shinohara et al. and examined feasibilities of two hypotheses with a small number of cilia. With the small number of rotating cilia, flow was induced locally and global strong flow was not observed in the node. Particles were then effectively transported only when they were close to the cilia, and particle transport was strongly dependent on the ciliary positions. Although the maximum wall shear rate was also influenced by ciliary position, the mean wall shear rate at the perinodal wall increased monotonically with the number of cilia. We also investigated membrane tension of immotile cilia, which is relevant to the regulation of mechanotransduction. The results indicated that tension of about 0.1 uN/m was exerted at the base even when the fluid shear rate was applied about 0.1 1/s. The area of high tension was also localised at the upstream side, and negative tension appeared at the downstream side. Such localisation may be useful to sense the flow direction at the periphery, as time-averaged anticlockwise circulation was induced in the node by rotation of a few cilia. Our numerical results support the mechanosensing hypothesis, and we expect that our study will stimulate further experimental investigations of mechanotransduction in the near future.脊椎动物胚胎体轴的左右（L-R）不对称性由节点流（nodal flow）决定。Shinohara等利用Dpcd与Rfx3突变小鼠胚胎开展实验，证实仅需少量纤毛即可实现左右不对称发育。然而，此类微弱纤毛流打破对称性的具体机制仍未阐明；目前针对左右对称性破缺存在两种假说模型：囊泡运输与机械感知。本研究针对Shinohara等报道的原结系统构建了计算模型，并针对少量纤毛条件下的两种假说展开可行性验证。在少量旋转纤毛的作用下，流场仅在局部被诱导产生，原结内部未观测到全局强流。仅当粒子贴近纤毛时，方可被有效输运，且粒子输运过程强烈依赖于纤毛的空间位置。尽管最大壁面剪切速率同样受纤毛位置影响，但原结周边壁面的平均壁面剪切速率随纤毛数量单调递增。我们还探究了不动纤毛的膜张力，该指标与机械转导的调控密切相关。研究结果表明，即使流体剪切速率约为0.1 s⁻¹，纤毛基部仍会承受约0.1 μN/m的张力。高张力区域同样定位于上游侧，而下流侧则出现负张力。此类张力分布可用于感知外周的流动方向，因为少量纤毛的旋转会在原结内诱导出时间平均的逆时针环流。本研究的数值结果支持机械感知假说，我们期望本研究能够在未来推动机械转导相关的更多实验研究。