Riedel-Kruse Ingmar H, Hilfinger Andreas, Howard Jonathon, Jülicher Frank
HFSP J. 2007 Sep;1(3):192-208. doi: 10.2976/1.2773861.
Cilia and eukaryotic flagella are slender cellular appendages whose regular beating propels cells and microorganisms through aqueous media. The beat is an oscillating pattern of propagating bends generated by dynein motor proteins. A key open question is how the activity of the motors is coordinated in space and time. To elucidate the nature of this coordination we inferred the mechanical properties of the motors by analyzing the shape of beating sperm: Steadily beating bull sperm were imaged and their shapes were measured with high precision using a Fourier averaging technique. Comparing our experimental data with wave forms calculated for different scenarios of motor coordination we found that only the scenario of interdoublet sliding regulating motor activity gives rise to satisfactory fits. We propose that the microscopic origin of such "sliding control" is the load dependent detachment rate of motors. Agreement between observed and calculated wave forms was obtained only if significant sliding between microtubules occurred at the base. This suggests a novel mechanism by which changes in basal compliance could reverse the direction of beat propagation. We conclude that the flagellar beat patterns are determined by an interplay of the basal properties of the axoneme and the mechanical feedback of dynein motors.
纤毛和真核生物鞭毛是细长的细胞附属物，其规则的摆动推动细胞和微生物在水性介质中运动。这种摆动是由动力蛋白产生的一种传播性弯曲的振荡模式。一个关键的开放性问题是这些动力蛋白的活动如何在空间和时间上进行协调。为了阐明这种协调的本质，我们通过分析摆动精子的形状来推断动力蛋白的力学特性：对稳定摆动的公牛精子进行成像，并使用傅里叶平均技术高精度测量其形状。将我们的实验数据与针对动力蛋白协调的不同情况计算出的波形进行比较，我们发现只有双联体间滑动调节动力蛋白活动的情况才能产生令人满意的拟合。我们提出这种“滑动控制”的微观起源是动力蛋白与负载相关的脱离速率。只有当微管基部发生显著滑动时，才能获得观察到的波形与计算波形之间的一致性。这表明了一种新机制，通过该机制基部顺应性的变化可以逆转摆动传播的方向。我们得出结论，鞭毛摆动模式是由轴丝的基部特性和动力蛋白的机械反馈相互作用决定的。
