Navigation of sperm cells in scalar turbulence: Theory of sperm chemotaxis in turbulent flow and its adaptation to dynamic concentration and velocity gradients

标量湍流中精子细胞的导航：湍流中精子趋化性理论及其对动态浓度和速度梯度的适应

• 批准号: 391963627
• 负责人: Professor Dr. Benjamin M. Friedrich
• 金额: --
• 依托单位: Exzellenzcluster Physics of Life (PoL)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/391963627?language=en
• 关键词: Navigation; sperm; cells; scalar; turbulence

Chemotaxis - the navigation of biological cells guided by chemical gradients - is crucial for bacterial foraging, immune responses, and guidance of sperm cells to the egg during fertilization. Cellular navigation represents a model system for the physics of autonomous motility at the microscale and its control by sensory cues. Previous work focused predominantly on idealized conditions of perfect chemical gradients. Yet, natural environments are characterized by perturbations, which distort extracellular chemical gradients. A prototypical example are turbulent flows of the ocean.In the model species of marine invertebrates, sperm and egg cells are directly spawned into open water, where sperm cells employ a dedicated gradient-sensing algorithm along helical paths to steer up concentration gradients of signaling molecules released by the egg. Small-scale turbulence distorts these concentration gradients and convects swimming cells. We propose to develop a theory of sperm chemotaxis in turbulent flow conditions, by combining an existing simulation framework of helical chemotaxis with hydrodynamic computations of turbulent advection, which is novel. Using this model system, we will target a gap in knowledge between (i) turbulent stirring of passive particles and (ii) chemotaxis of actively swimming cells studied previously in the absence of external flow. Thereby, we will address a fundamental and largely unexplored question: how biological cells navigate in dynamic and disordered environments. We will elucidate the competition between positive and negative effects of turbulence, i.e. faster establishment of concentration gradients and random distortion of these gradients. By this, we will confirm and explain the existence of an optimal turbulence strength that maximizes the probability of sperm-egg encounters. On a finer scale, our preliminary simulations suggest that small-scale turbulence creates extended filaments of high concentration along which sperm cell can 'surf' towards the egg. We will understand the mechanism of 'filament surfing' in terms of chemotactic steering and rotation by local shear flow. Next, we will study trapping of sperm cells in local concentration maxima and stochastic transitions between such maxima, and its dependence on the spatial and temporal resolution of gradient sensing. Thereby, we expect genuine physical insight into the exploration/exploitation trade-off in the context of cellular navigation. Previously, we pioneered the theory of helical chemotaxis, which represents one out of three basic gradient-sensing strategies of biological cells. Additionally, our group established a solid competence in hydrodynamic simulations. The proposed project will combine these two research fields into a new direction. Thereby, we will provide a concise understanding of cellular navigation in dynamic and disordered external fields in an important model system.

趋化性--由化学梯度引导的生物细胞的导航--对于细菌觅食、免疫反应以及受精期间精子细胞对卵子的引导至关重要。细胞导航代表了一个模型系统，用于研究微观尺度上的自主运动及其由感官线索控制的物理过程。以前的工作主要集中在完美化学梯度的理想化条件。然而，自然环境的特点是扰动，这扭曲了细胞外的化学梯度。一个典型的例子是海洋的湍流。在海洋无脊椎动物的模式物种中，精子和卵细胞直接产卵到开放水域，在那里精子细胞沿着螺旋路径使用专门的梯度传感算法来引导卵子释放的信号分子的浓度梯度。小尺度湍流扭曲了这些浓度梯度，并使游泳圈对流。通过将现有的螺旋趋化模拟框架与湍流平流的流体力学计算相结合，我们提出了一种湍流条件下精子趋化的理论。利用这个模型系统，我们将针对(I)被动粒子的湍流搅拌和(Ii)在没有外部流动的情况下主动游泳细胞的趋化性这两个方面的知识差距。因此，我们将解决一个基本且在很大程度上未被探索的问题：生物细胞如何在动态和无序的环境中导航。我们将阐明湍流的积极和消极影响之间的竞争，即更快地建立浓度梯度和这些梯度的随机扭曲。通过这一点，我们将证实和解释最优湍流强度的存在，从而最大化精子-卵子相遇的可能性。在更精细的尺度上，我们的初步模拟表明，小范围的湍流产生了高浓度的延伸细丝，精子细胞可以沿着这些细丝向卵子‘冲浪’。我们将从化学趋化导向和局部剪切流旋转的角度来理解“丝状冲浪”的机制。接下来，我们将研究精子细胞在局部浓度极大值中的捕获以及这些极大值之间的随机转换，以及它对梯度传感的时空分辨率的依赖。因此，我们期望对蜂窝导航背景下的勘探/开采权衡有真正的物理洞察。在此之前，我们开创了螺旋趋化理论，它代表了生物细胞三种基本梯度传感策略之一。此外，我们的团队在流体动力学模拟方面建立了坚实的能力。拟议的项目将把这两个研究领域结合起来，形成一个新的方向。因此，我们将在一个重要的模型系统中提供一个关于动态和无序外场中的蜂窝导航的简明理解。