Inverse relationship of Ca2+-dependent flagellar response between animal sperm and prasinophyte algae
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Symmetry/asymmetry conversion of eukaryotic flagellar waveform is caused by the changes in intracellular Ca2+. Animal sperm flagella show symmetric or asymmetric waveform at lower or higher concentration of intracellular Ca2+, respectively. In Chlamydomonas, high Ca2+ 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 Ca2+-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 Ca2+ ionophore A23187, whereas it becomes circular in a low Ca2+ solution. Analysis of flagellar waveform reveals symmetric or asymmetric waveform propagation in ASW or a low Ca2+ 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 Ca2+ attributes to the evolutional innovation of calcium sensors of outer arm dynein in opisthokont or bikont lineage.
KeywordsCalaxin Cilia Dynein Opisthokont Prasinophyte Sperm flagella
We thank National Institute for Environmental Studies (NIES) for providing a strain of Pterosperma cristatum (NIES-626). This work was supported in part by Grant-in-Aid 15H01201 for Scientific Research on Innovative Areas and 22370023 for Scientific Research (B) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT).
Movie S1. Flagellar movement of the sea urchin A. crassispina sperm. Five hundred frames were recorded per second. The movie plays at 0.06× speed. (MOV 644 KB)
Movie S2. Flagellar movement of the prasinophyte P. cristatum. Five hundred frames were recorded per second. The movie plays at 0.06× speed. (MOV 222 KB)
Movie S3. Turn movement of the prasinophyte P. cristatum. Five hundred frames were recorded per second. The movie plays at 0.06× speed. (MOV 171 KB)
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