Biology subjects

Kage, A.

Publications and source records attributed to Kage, A..

3 recordsLinked to original sources

bioRxiv2026

Diurnal regulation of flagellar length and swimming speed in the red-tide raphidophyte Chattonella marina

The raphidophyte Chattonella marina is a harmful algal bloom (HAB) species known for its distinct diurnal vertical migration (DVM), a behavior important for its survival and bloom formation. However, the single-cell mechanisms governing this migration remain unclear. In this study, we investigated the swimming characteristics of individual C. marina cells during day (light) and night (dark) phases. We observed a strong positive correlation between the length of the propulsive anterior flagellum and the cells swimming speed. We discovered that the length distribution of the anterior flagellum is different during the day and at night. We also found that the beat frequency of the anterior flagellum was significantly higher during the day compared to the night. This resulted in faster mean swimming speeds during the light phase. To investigate the mechanism of length regulation, we tested the role of intraflagellar transport (IFT) using the IFT dynein inhibitor, ciliobrevin D. Treatment with ciliobrevin D induced a time- and concentration-dependent shortening of the anterior flagellum. This is the first pharmacological evidence to suggest that an IFT-like mechanism may actively control motile flagellar length in C. marina. These findings suggest that C. marina modulates its swimming speed through diurnal changes in both flagellar length and beat frequency, likely as an energy-saving strategy coupled to its DVM.

biophysics↗

bioRxiv2025

Dynein-2 is tuned for the A-tubule of the ciliary doublet through tubulin tyrosination

Eukaryotic cilia and flagella are thin structures present on the surface of cells, playing vital roles in signaling and cellular motion. Cilia structures rely on intraflagellar transport (IFT), which involves dynein-2 for retrograde and kinesin-2 for anterograde movements along doublet microtubules. Unlike dynein-1, which works on singlet microtubules within the cytoplasm, dynein-2 specifically works on the doublet microtubules inside the cilia. Previous cryo-electron tomography studies have shown that retrograde IFT, driven by dynein-2, occurs on the A-tubule of the doublet, suggesting a specialized regulatory mechanism involving dynein-2. However, the molecular basis of this specificity remains unclear. Here, we investigated this mechanism using cryo-electron tomography (cryo-ET) with Volta Phase Plate (VPP), molecular dynamics (MD) simulations, and biochemical analysis. Our biochemical assay revealed that the microtubule-binding domain of dynein-2 exhibits a higher affinity for the ciliary doublet microtubule compared to dynein-1. Cryo-ET with VPP further visualized the preferential binding of dynein-2 to the A-tubule of the doublet microtubule. MD simulations suggest that the preferential binding of dynein-2 is attributed to the tyrosinated tubulin in the A-tubule. These findings uncover a tyrosination-dependent regulatory mechanism that governs the bidirectional transport of IFT on doublet microtubules, providing new insights into the spatial and functional specialization of ciliary transport systems.

biophysics↗

bioRxiv2023

Swimming ability and flagellar motility of sperm packets of the volvocine green alga Pleodorina starrii

Eukaryotic flagella collectively form metachronal waves that facilitate the ability to cause flow or swim. Among such flagellated and planktonic swimmers, large volvocine genera such as Eudorina, Pleodorina and Volvox form bundles of small male gametes (sperm) called "sperm packets" for sexual reproduction. Although these sperm packets reportedly have flagella and the ability to swim, previous studies on volvocine motility have focused on asexual forms and the swimming characteristics of sperm packets remain unknown. However, it is important to quantify the motility of sperm packets and sperm in order to gain insights into the significance of motility in the sexual reproduction of planktonic algae. In this study, we quantitatively described the behavior of three flagellated forms of a male strain of Pleodorina starrii--asexual colonies, sperm packets, and single dissociated sperm--with emphasis on comparison of the two multicellular forms. Despite being smaller, sperm packets swam approximately 1.4 times faster than the asexual colonies of the same male strain. Body length was approximately 0.5 times smaller in the sperm packets than in asexual colonies. The flagella from sperm packets and asexual colonies showed asymmetric waveforms, whereas those from dissociated single sperm showed symmetric waveforms, suggesting the presence of a switching mechanism between sperm packets and dissociated sperm. Flagella from sperm packets were approximately 0.5 times shorter and had a beat period approximately twice as long as those from asexual colonies. The flagella of sperm packets were densely distributed over the anterior part of the body, whereas the flagella of asexual colonies were sparse and evenly distributed. The distribution of flagella, but not the number of flagella, appear to illustrate a significant difference in the speeds of sperm packets and asexual colonies. Our findings reveal novel aspects of the regulation of eukaryotic flagella and shed light on the role of flagellar motility in sexual reproduction of planktonic algae.

biophysics↗