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导航-对于细菌觅食，免疫反应和受精过程中精子细胞对卵子的引导至关重要。细胞导航代表了微观尺度上自主运动的物理学模型系统及其通过感官线索的控制。以前的工作主要集中在理想化的条件下完美的化学梯度。然而，自然环境的特点是扰动，扭曲细胞外化学梯度。一个典型的例子是海洋中的湍流，在海洋无脊椎动物的模型物种中，精子和卵细胞直接在开放水域产卵，精子细胞沿着螺旋路径使用专门的梯度感应算法来控制卵释放的信号分子的浓度梯度。小尺度的湍流扭曲了这些浓度梯度，并使游泳细胞对流。我们建议开发一个理论的精子趋化性在湍流条件下，通过结合现有的模拟框架的螺旋趋化性与湍流平流的流体动力学计算，这是新颖的。使用这个模型系统，我们将针对（i）被动颗粒的湍流搅拌和（ii）在没有外部流动的情况下先前研究的主动游泳细胞的趋化性之间的知识差距。因此，我们将解决一个基本的和很大程度上未探索的问题：生物细胞如何在动态和无序的环境中导航。我们将阐明湍流的正面效应和负面效应之间的竞争，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，我们将确认和解释存在一个最佳的湍流强度，最大限度地提高精卵相遇的概率。在更精细的尺度上，我们的初步模拟表明，小规模的湍流会产生高浓度的延伸细丝，精子细胞可以沿着这些细丝沿着“冲浪”向卵子运动。我们将了解的机制'丝冲浪'的趋化转向和旋转的局部剪切流。接下来，我们将研究在局部浓度最大值和这些最大值之间的随机过渡，以及它对梯度传感的空间和时间分辨率的依赖性的精子细胞的捕获。因此，我们期望真正的物理洞察的探索/开发权衡的背景下，蜂窝导航。在此之前，我们开创了螺旋趋化性理论，它代表了生物细胞的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。拟议的项目将联合收割机这两个研究领域结合成一个新的方向。因此，我们将提供一个简明的理解细胞导航在动态和无序的外部领域中的一个重要的模型系统。