The axoneme is an intricate nanomachine responsible for generating the propulsive oscillations of cilia and flagella in an astonishing variety of organisms. New imaging techniques based on cryoelectron‐tomography (cryo‐ET) and subtomogram averaging have revealed the detailed structures of the axoneme and its components with sub‐nm resolution, but the mechanical function of each component and how the assembly generates oscillations remains stubbornly unclear. Most explanations of oscillatory behavior rely on the dynamic regulation of dynein by some signal, but this may not be necessary if the system of dynein‐driven slender filaments is dynamically unstable. Understanding the possibility of instability‐driven oscillations requires a multifilament model of the axoneme that accounts for distortions of the axoneme as it bends. Active bending requires forces and bending moments that will tend to change the spacing and alignment of doublets. We hypothesize that components of the axoneme resist and respond to these loads in ways that are critical to beating. Specifically, we propose (i) that radial spokes provide torsional stiffness by resisting misalignment (as well as spacing) between the central pair and outer doublets, and (ii) that the kinematics of dynein arms affect the relationships between active forces and bending moments on deforming doublets. These proposed relationships enhance the ability of theoretical, multifilament models of axonemal beating to generate propulsive oscillatory waveforms via dynamic mechanical instability.

中文翻译：

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轴丝扭曲与纤毛跳动中的内力和扭矩之间的理论关系

轴丝是一种复杂的纳米机器，负责在多种生物体中产生纤毛和鞭毛的推进振动。基于冷冻电子断层扫描（cryo-ET）和次断层平均的新成像技术以亚纳米分辨率揭示了轴丝及其组件的详细结构，但每个组件的机械功能以及组件如何产生振荡仍然不清楚。大多数振荡行为的解释依赖于某些信号对动力蛋白的动态调节，但如果动力蛋白驱动的细长丝系统动态不稳定，这可能就没有必要。了解不稳定驱动振荡的可能性需要轴丝的多丝模型，该模型可以解释轴丝弯曲时的扭曲。主动弯曲需要力和弯矩，这往往会改变双峰的间距和对齐方式。我们假设轴丝的组成部分以对跳动至关重要的方式抵抗和响应这些负载。具体来说，我们建议（i）径向辐条通过抵抗中心对和外部双峰之间的错位（以及间距）来提供扭转刚度，以及（ii）动力蛋白臂的运动学影响主动力和弯矩之间的关系使双峰变形。这些提出的关系增强了轴丝跳动的理论多丝模型通过动态机械不稳定性产生推进振荡波形的能力。