PT  - JOURNAL ARTICLE
AU  - Soheil Mojiri
AU  - Sebastian Isbaner
AU  - Steffen Mühle
AU  - Hongje Jang
AU  - Albert Johann Bae
AU  - Ingo Gregor
AU  - Azam Gholami
AU  - Jörg Enderlein
TI  - Three-dimensional beating dynamics of <em>Chlamydomonas</em> flagella
AID  - 10.1101/2020.07.20.212159
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.07.20.212159
4099  - http://biorxiv.org/content/early/2020/07/21/2020.07.20.212159.short
4100  - http://biorxiv.org/content/early/2020/07/21/2020.07.20.212159.full
AB  - Axonemes are the basic structure of motile cilia and flagella, and the investigation of how they function and move requires rapid three-dimensional imaging. We built a multi-plane phase-contrast microscope for imaging the three-dimensional motion of unlabeled flagella of the model organism Chlamydomonas reinhardtii with sub-μm spatial and 4 ms temporal resolution. This allows us to observe not only bending but also the three-dimensional torsional dynamics of these small structures. We observe that flagella swim counter-clockwise close to a surface, with negatively-valued torsion at their basal and positively-valued torsion at their distal tips. To explain the torsional dynamics and signature, we suggest the existence of an intrinsic negative twist at the basal end that is untwisted by active positive-twist-inducing dynein motor proteins. Moreover, dyneins walking towards the basal induce an opposite twist at the distal tip. Bending of the whole axoneme structure then translates this twist into an observable torsion. This interconnection between chiral structure, twist, curvature, and torsion is fundamental for understanding flagellar mechanics.Competing Interest StatementThe authors have declared no competing interest.