胚胎结纤毛运动机理及左右方向信号传递过程：实验与理论模拟研究

The left-right differentiation during embryogenesis is necessary for the normal development of human beings and other vertebrates. The nodal ciliary movement and the cilia-driven unidirectional flow are two key factors to this process. Purely experimental studies can hardly provide direct evidence for the mechanism of the ciliary motion or the left-right signal transmission process by the unidirectional flow. To make up this limitation, in this project, we combine experimental observations and computational simulations to explore these two issues. We establish cilium-specific ultrastructure model based on the electronic tomography data via ultra-high voltage electron microscope, and simulate the ciliary motion driven by the dynein activity as well as the viscous force of the surrounding fluid via Finite Element analysis, Finite Volume method and fluid-structure interaction techniques. By comparing the computed ciliary motion to the data captured by high-speed microscope photography, the mechanism of the protein-driven ciliary motility can be proposed. The simulated ciliary motion is integrated into the model simulating the fluid environment of the embryonic node. By employing the IB-LBM method, we simulate the flow motion generated by a number of cilia. The computed results for in vitro situation is compared to particle image velocimetry to validate the model; while, the results for in vivo situation is employed in further studies regarding the sided information transmission process. The proposed computational platform for the ciliary ultrastructure and the nodal environment may further our understandings regarding the ciliary motion and provide more detailed explanations for the left-right differentiation process during embryogenesis. The proposed computational platform can be also applied in the studies of mutant cilia, in order to explore the dysfunction of their movement and the relations of them to the abnormality of the left-right axis establishment.

胚胎对左右方向的感知过程是人体及其他脊椎动物正常发育的必要环节。其中，胚胎结纤毛的运动及其产生的单向流场是实现此过程的关键因素。目前，单纯的实验研究难以为纤毛运动机理及单向流场对左右方向信号的传递过程提供直接证据。为弥补这一不足，本课题将结合实验与理论模拟对这两个科学问题进行探讨。我们将基于超高压电子断层数据建立纤毛个体化超微结构模型并嵌入流场，通过有限元、有限体积及流固耦合技术模拟纤毛在内、外力作用下的运动形态。对比高速显微照相数据，推测纤毛内部动力蛋白活动方式。计算所获纤毛运动形态将被整合入胚胎结内环境模型，通过IB-LBM方法模拟多纤毛运动产生的流场。借助粒子图像测速法验证模拟结果，并将流场数据用于对左右方向信息传递过程的研究。此方案所建立的"纤毛-胚胎结内环境"模拟平台将为纤毛运动机理及胚胎左右区划过程提供更明确的解释，并将应用于结构变异纤毛，探讨其运动障碍机理及与发育疾病的关系。

【研究背景】 胚胎对左右方向的感知及后续区化过程是人体及其他脊椎动物正常发育的必要环节，此过程受到胚胎结纤毛旋转运动所产生的胚胎结内单向流场控制，异常的胚胎结内流场可导致如先心病等多种遗传疾病的发生。目前，实验技术难以对运动中纤毛的内部结构进行直接观测，而碍于胚胎外膜的半透明性，针对其内部流体运动及化学成分的活体内研究也受到限制，亟需结合实验与理论模拟技术，对胚胎结纤毛的运动机理及左右方向信号传递过程进行深入研究。.【研究内容】本项目的研究内容包括：1）针对胚胎结纤毛内部动力蛋白活动规律研究；和 2）针对胚胎结内左右方向信号传递过程的研究。结合实验与模拟计算技术，分别为纤毛运动机理和胚胎左右方向信号传导过程这两个科学问题提供解释。.【重要结果】本项目构建了：1）基于超高压电子断层数据，建立纤毛个体化超微结构模型，并进行流固耦合分析的建模及计算流程；2）基于高速显微成像的纤毛运动捕捉算法；3）基于IB-LBM的多纤毛流场计算方法及物质对流扩散过程模拟。相关技术应用于正常和变异胚胎结环境的数值分析，重要结果包括：1）确定了可引导胚胎结纤毛旋转运动的动力蛋白活动方式，发表于Biophys J（2区Top）等期刊；2）揭示了微管变异纤毛复杂运动的力学机理；3）量化分析了纤毛运动及其对周围流场产生的运动和物质传输作用，发表于Dev Cell（1区Top）等期刊，并将该复杂系统建模算法拓展应用，发表于Theranostics（1区Top）等期刊。目前，此项目共发表具有基金标注的SCI期刊论文12篇、授权专利1项、授权软件著作权1项。.【科学意义】此项目所建立的“纤毛-胚胎结内环境”模拟方法为纤毛运动机理及胚胎左右区化过程提供了更明确的解释，通过将其应用于结构变异的纤毛，定量的分析其运动障碍机理及周围流场运动变化，从而阐明其与发育疾病的关系。