Biology subjects

Geyer, V. F.

Publications and source records attributed to Geyer, V. F..

3 recordsLinked to original sources

bioRxiv2024

Active fluctuations of axoneme oscillations scale with number of dynein motors

Fluxes of energy generate active forces in living matter, yet also active fluctuations. As canonical example, collections of molecular motors exhibit spontaneous oscillations with frequency jitter caused by non-equilibrium phase fluctuations. We investigate phase fluctuations in reactivated Chlamydomonas axonemes, which are accessible to direct manipulation. We quantify the precision of axonemal oscillations after controlled chemical removal of dynein motors, providing an experimental test for the theory prediction that the quality factor of motor oscillations should increase with motor number. Our quantification reveals specialized roles of inner and outer arm dynein motors. This supports a model in which inner dyneins serve as master pace-makers, to which outer arm dyneins become entrained, consistent with recent insight provided by structural biology.

biophysics↗

bioRxiv2024

Twist - torsion coupling in beating axonemes

Motile cilia and flagella are ubiquitous cell appendages whose regular bending waves pump fluids across tissue surfaces and enable single-cell navigation. Key to these functions are their non-planar waveforms with characteristic torsion. It is not known how torsion, a purely geometric property of the shape, is related to mechanical deformations of the axoneme, the conserved cytoskeletal core of cilia and flagella. Here, we assess torsion and twist in reactivated axonemes isolated from the green alga Chlamydomonas reinhardtii. Using defocused darkfield microscopy and beat-cycle averaging, we resolve the 3D shapes of the axonemal waveform with nanometer precision at millisecond timescales. Our measurements reveal regular hetero-chiral torsion waves propagating base to tip with a peak-to-peak amplitude of 22 {o}/{micro}m. To investigate if the observed torsion results from axonemal twist, we attach gold nanoparticles to axonemes to measure its cross-section rotation during beating. We find that locally, the axonemal cross-section co-rotates with the bending plane. This co-rotation presents the first experimental evidence for twist-torsion coupling and indicates that twist waves propagate along the axoneme during beating. Our work thus links shape to mechanical deformation of beating axonemes, informing models of motor regulation that shape the beat of motile cilia.

biophysics↗

bioRxiv2024

Gliding motility of the diatom Craspedostauros australis correlates with the intracellular movement of raphid-specific myosins

Raphid diatoms are one of the few eukaryotes capable of gliding motility, which is remarkably fast and allows for quasi-instantaneous directional reversals. Besides other mechanistic models, it has been suggested that an actomyosin system provides the force for diatom gliding. However, in vivo data on the dynamics of actin and myosin in diatoms are lacking. In this study we demonstrate that the raphe-associated actin bundles required for diatom movement do not exhibit a directional turnover of subunits and thus their dynamics do not contribute directly to force generation. By phylogenomic analysis we identified four raphid diatom-specific myosins in Craspedostauros australis (CaMyoA-D) and investigated their in vivo localization and dynamics through GFP-tagging. Only CaMyoB-D but not CaMyoA exhibited coordinated movement during gliding, consistent with a role in force generation. The characterization of raphid diatom-specific myosins lays the foundation for unraveling the molecular mechanisms that underlie the gliding motility of diatoms.

cell biology↗