Flagellar synchronization through direct hydrodynamic interactions.
Flagellar synchronization through direct hydrodynamic interactions.
复制标题
DOI：
10.7554/elife.02750
复制
发表时间：
2014-07-29
期刊：
影响因子：
7.7
通讯作者：
Goldstein RE
中科院分区：
文献类型：
--
作者：
Brumley DR;Wan KY;Polin M;Goldstein RE
鞭毛集合产生的流动对发育、运动和感觉至关重要，但这种惊人的协调背后的机制仍不清楚。我们提出了新的实验，其中两个微吸管持有的体细胞，具有不同的固有心跳频率，通过高速成像研究它们的分离和定向的函数。对时间序列的分析表明，鞭毛间的耦合受细胞之间缺乏流体动力学连接的限制，表现出与理论一致的空间相关性。在近距离时，它产生数千次拍子的稳健同步，而在增加间隔时，同步被随机过程降级。对相对鞭毛取向的操纵揭示了同相态和反相态，这与动力学理论一致。鞭毛跟踪以精确的精度揭示了流体动力耦合导致的波形变化。这项研究明确地证明，仅通过流体连接的鞭毛可以实现稳健的同步，尽管它们的内在性质不同。DOI：http://dx.doi.org/10.7554/eLife.02750.001精子细胞，以及许多细菌和藻类，利用鞭毛般的附属物推进自己。在许多细胞的表面也发现了类似的被称为纤毛的较短的结构，在那里它们起到了在细胞上移动液体的作用。每个纤毛或鞭毛都以其特有的节奏跳动，但在许多情况下，纤毛或鞭毛必须与附近的其他细胞同步跳动。例如，卵细胞通过管内纤毛的协调拍打而沿着输卵管扫过。公牛的精子细胞在彼此靠近时，也会同步鞭毛的跳动。有人提出，围绕鞭毛跳动的流体的运动可能是这种同步的来源。实验产生的结果与描述这种流体运动的数学模型相匹配。然而，这些实验的设计方式往往没有完全排除其他可能的同步源，例如化学信号，或者--对于位于同一细胞的鞭毛--鞭毛之间的物理连接。为了克服这一缺点，Brumley等人。使用高速成像观察了绿藻Volvox carteri细胞的鞭毛，这些细胞被分开，因此它们只能通过周围液体的运动进行交流。鞭毛仍然能够同步它们的跳动，即使这两个鞭毛以非常不同的速度自然跳动。鞭毛之间的距离影响跳动同步的程度。当鞭毛靠在一起时，鞭毛可以锁定在同一节奏中数千次。然而，随着它们移动得更远，细胞内的随机生化波动会降低鞭毛同步的程度。鞭毛也可以同步，这样它们就可以同时向同一方向移动，也可以向相反的方向移动，这取决于它们相对于彼此的方向。此外，结果还证实，一个鞭毛拍打产生的流体流量足以与附近其他鞭毛的拍打同步。DOI：http://dx.doi.org/10.7554/eLife.02750.002
Flows generated by ensembles of flagella are crucial to development, motility and sensing, but the mechanisms behind this striking coordination remain unclear. We present novel experiments in which two micropipette-held somatic cells of Volvox carteri, with distinct intrinsic beating frequencies, are studied by high-speed imaging as a function of their separation and orientation. Analysis of time series shows that the interflagellar coupling, constrained by lack of connections between cells to be hydrodynamical, exhibits a spatial dependence consistent with theory. At close spacings it produces robust synchrony for thousands of beats, while at increasing separations synchrony is degraded by stochastic processes. Manipulation of the relative flagellar orientation reveals in-phase and antiphase states, consistent with dynamical theories. Flagellar tracking with exquisite precision reveals waveform changes that result from hydrodynamic coupling. This study proves unequivocally that flagella coupled solely through a fluid can achieve robust synchrony despite differences in their intrinsic properties. DOI: http://dx.doi.org/10.7554/eLife.02750.001 Sperm cells, as well as many bacteria and algae, propel themselves using whip-like appendages called flagella. Similar, shorter structures called cilia are also found on the surface of many cells, where they perform roles such as moving liquids over the cell. Each cilium or flagellum beats at its own characteristic rhythm, but there are many situations where cilia or flagella must synchronize their beating with other nearby cells. For example, an egg cell is swept along the Fallopian tube by the coordinated beating of the cilia lining the tube. Bull sperm cells are also known to synchronize the beating of their flagella when swimming close to each other. It has been suggested that the movement of the fluid surrounding the beating flagella could be the source of this synchronization. Experiments have produced results that match up with mathematical models describing this fluid movement. However, these experiments have often been designed in ways that didn’t fully exclude other possible sources of synchronization, such as chemical signalling, or—for flagella located on the same cell—a physical connection between the flagella. To overcome this shortcoming, Brumley et al. used high-speed imaging to watch the flagella of cells of Volvox carteri—a species of green alga—that were separated so that they could only communicate through the movement of the fluid around them. The flagella were still able to synchronize their beating, even when the two flagella naturally beat at substantially different rates. The distance between the flagella affects how well the beating synchronizes. When close together, the flagella can lock into the same rhythm for thousands of beats. However, as they move further apart, random biochemical fluctuations within the cells reduce the extent to which the flagella can synchronize. The flagella can also synchronize so that they move in the same direction at the same time, or in opposite directions, depending on how they are oriented relative to each other. Moreover, the results confirm that the fluid flow produced by a beating flagellum is sufficient to synchronize the beating of other nearby flagella. DOI: http://dx.doi.org/10.7554/eLife.02750.002