Shiba Kogiku, Inaba Kazuo
Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, 415-0025, Japan.
J Plant Res. 2017 May;130(3):465-473. doi: 10.1007/s10265-017-0931-7. Epub 2017 Apr 19.
Symmetry/asymmetry conversion of eukaryotic flagellar waveform is caused by the changes in intracellular Ca. Animal sperm flagella show symmetric or asymmetric waveform at lower or higher concentration of intracellular Ca, respectively. In Chlamydomonas, high Ca induces conversion of flagellar waveform from asymmetric to symmetry, resulting in the backward movement. This mirror image relationship between animal sperm and Chlamydomonas could be explained by the distinct calcium sensors used to regulate the outer arm dyneins (Inaba 2015). Here we analyze the flagellar Ca-response of the prasinophyte Pterosperma cristatum, which shows backward movement by undulating four flagella, the appearance similar to animal sperm. The moving path of Pterosperma shows relatively straight in artificial seawater (ASW) or ASW in the presence of a Ca ionophore A23187, whereas it becomes circular in a low Ca solution. Analysis of flagellar waveform reveals symmetric or asymmetric waveform propagation in ASW or a low Ca solution, respectively. These patterns of flagellar responses are completely opposite to those in sperm flagella of the sea urchin Anthocidaris crassispina, supporting the idea previously proposed that the difference in flagellar response to Ca attributes to the evolutional innovation of calcium sensors of outer arm dynein in opisthokont or bikont lineage.
真核生物鞭毛波形的对称/不对称转换是由细胞内钙离子的变化引起的。动物精子鞭毛在细胞内钙离子浓度较低或较高时分别呈现对称或不对称波形。在衣藻中，高钙离子浓度会诱导鞭毛波形从不对称转换为对称，从而导致向后运动。动物精子和衣藻之间的这种镜像关系可以通过用于调节外臂动力蛋白的不同钙传感器来解释（稻场，2015年）。在这里，我们分析了绿藻Pterosperma cristatum的鞭毛钙反应，它通过四条鞭毛的波动进行向后运动，外观类似于动物精子。在人工海水（ASW）或存在钙离子载体A23187的ASW中，Pterosperma的运动路径相对较直，而在低钙溶液中则变为圆形。鞭毛波形分析显示，在ASW或低钙溶液中分别传播对称或不对称波形。这些鞭毛反应模式与海胆Anthocidaris crassispina精子鞭毛的反应模式完全相反，支持了先前提出的观点：鞭毛对钙离子反应的差异归因于后鞭毛生物或双鞭毛生物谱系中外臂动力蛋白钙传感器的进化创新。
