Biology subjects

Bloomfield-Gadelha, H.

Publications and source records attributed to Bloomfield-Gadelha, H..

8 recordsLinked to original sources

bioRxiv2024

Predicting microscale beat patterns from nanoscale chemomechanics in eukaryotic flagella

We present quantitative predictions for experimental observables--amplitude, frequency and wavelength--of the eukaryotic flagellar beat in terms of underlying molecular chemomechanical parameters. Flagellar beating, an incompletely understood self-organized process arising from the collective action of dynein molecular motors, is modelled as a reaction-diffusion (RD) system with an oscillatory instability arising from motor-induced microtubule sliding. While the RD model accurately reproduces beating patterns of bull spermatozoa and C. Reinhardtii, existing linear analyses and simulations are unable to provide a complete framework for understanding nonlinear waveform formation. Here, we derive analytical expressions that reveal the nonlinear dependence of beat characteristics on parameters such as motor binding duty ratio, stepping velocity, and axonemal resistance. Our analysis uncovers a novel out-of-equilibrium mechanism for base-to-tip wave propagation, involving an interference pattern between unstable standing wave modes that generates travelling waves. Predicted beat patterns agree remarkably with numerical simulations, even far from the critical point marking the onset of oscillations. This unveils key molecular parameters that govern oscillation initiation, amplitude saturation, frequency shifts, and the spatial phase gradient crucial for generating propulsive hydrodynamic force. Our results yield biophysical understanding of how molecular interactions shape flagellar beating patterns, allowing for the inference of molecular properties from macroscopic observations. This challenges existing hypotheses on wave generation and demonstrates the power of nonlinear analysis to uncover new phenomena beyond the reach of linear models and computational studies alone.

biophysics↗

bioRxiv2024

A discrete sarcomere model reveals internal unbinding dynamics and conditions for regularity of spontaneous oscillatory contractions

Using a discrete modelling approach for myosin systems we demonstrate how structural differences between single myosin filaments and sarcomeres allow for self similarity during sarcomeric spontaneous oscillatory contractions (SPOC). The form of our modelled SPOC recapitulates the subtleties of in vitro SPOCs more closely than prior modelling methods, suggesting we are capturing internal dynamics of the sarcomere that are either not generally considered or previously unknown. These results reinforce the value of discretely modelling molecular motor systems.

biophysics↗

bioRxiv2024

Fluid flow reconstruction around a free-swimming sperm in 3D

We investigate the dynamics and hydrodynamics of a human spermatozoa swimming freely in 3D. We simultaneously track the sperm flagellum and the sperm head orientation in the laboratory frame of reference via high-speed high-resolution 4D (3D+t) microscopy, and extract the flagellar waveform relative to the body frame of reference, as seen from a frame of reference that translates and rotates with the sperm in 3D. Numerical fluid flow reconstructions of sperm motility are performed utilizing the experimental 3D waveforms, with excellent accordance between predicted and observed 3D sperm kinematics. The reconstruction accuracy is validated by directly comparing the three linear and three angular sperm velocities with experimental measurements. Our microhydrodynamic analysis reveals a novel fluid flow pattern, characterized by a pair of vortices that circulate in opposition to each other along the sperm cell. Finally, we show that the observed sperm counter-vortices are not unique to the experimental beat, and can be reproduced by idealised waveform models, thus suggesting a fundamental flow structure for free-swimming sperm propelled by a 3D beating flagellum.

biophysics↗

bioRxiv2023

Swimming by spinning: spinning-top type rotations regularize sperm swimming into persistently symmetric paths in 3D

Sperm modulate their flagellar symmetry to navigate through complex physico-chemical environments and achieve reproductive function. Yet it remains elusive how sperm swim forwards despite the inherent asymmetry of several components that constitutes the flagellar engine. Despite the critical importance of symmetry, or the lack of it, on sperm navigation and its physiological state, there is no methodology to date that can robustly detect the symmetry state of the beat in free-swimming sperm in 3D. How does symmetric progressive swimming emerge even for asymmetric beating, and how can beating (a)symmetry be inferred experimentally? Here, we numerically resolve the fluid mechanics of swimming around asymmetrically beating spermatozoa. This reveals that sperm spinning critically regularizes swimming into persistently symmetric paths in 3D, allowing sperm to swim forwards despite any imperfections on the beat. The sperm orientation in three-dimensions, and not the swimming path, can inform the symmetry state of the beat, eliminating the need of tracking the flagellum in 3D. We report a surprising correspondence between the movement of sperm and spinning-top experiments, indicating that the flagellum drives "spinning-top" type rotations during sperm swimming, and that this parallel is not a mere analogy. These results may prove essential in future studies on the role of (a)symmetry in spinning and swimming microorganisms and micro-robots, as body orientation detection has been vastly overlooked in favour of swimming path detection. Altogether, sperm rotation may provide a foolproof mechanism for forward propulsion and navigation in nature that would otherwise not be possible for flagella with broken symmetry.

biophysics↗

bioRxiv2023

The reaction-diffusion basis of animated patterns in eukaryotic flagella

We show that the flagellar beat of bull spermatozoa and Chlamydomonas Reinhardtii can be modelled by a minimal, geometrically nonlinear, sliding-controlled, reaction-diffusion system. Model solutions are spatio-temporally animated patterns describing flagellar bending waves, further connecting beating patterns of cilia and flagella with, seemly unrelated, chemical patterns from classical reaction-diffusion systems. Instead of chemical species freely reacting and diffusing in space, our system describes the tug-of-war reaction-kinetics of molecular motors that are anchored in the flagellar structure, but the shear deformation that they generate can diffuse away via the bending elasticity of the flagellum. Synchronization of the reaction-kinetics in neighbouring elements occurs via a sliding-control mechanism. We derive from first principles the reaction-diffusion basis of animated patterns, and show that this is a direct consequence of the high internal energy dissipation by the flagellum relative to the external dissipation by the fluid environment. By fitting, for the first time, nonlinear, large-amplitude solutions of a specific motor cross-bridge reaction-kinetics, we show that reaction-diffusion successfully accounts for beating patterns of both bull sperm and Chlamydomonas (wild-type and mbo2-mutant), unifying these distant eukaryotic species under the same minimal model. Our results suggest that the flagellar beat occurs far from equilibrium, in the strongly nonlinear regime, and that in contrary to the conclusions of small amplitude studies, a unified mechanism may exist for dynein molecular motor control that is regulated by axonemal sliding, without requiring curvature-sensing or the fine-tuning of basal compliance, and only weakly influenced by hydrodynamic dissipation and the cell body boundary condition. High internal dissipation allows the emergence of base-to-tip autonomous travelling waves, independently of, and without relying on, the external fluid viscosity, when small. This enables progressive swimming, otherwise not possible, in low viscosity environments, and may be critical for external fertilizers and aquatic microorganisms. The reaction-diffusion model may prove a powerful tool for studying the pattern formation of movement in flagella, cilia, and more generally, oscillations of animated filament-bundles at the microscale.

biophysics↗

bioRxiv2023

The 3D coarse-graining formulation of interacting elastohydrodynamic filaments and multi-body microhydrodynamics

Elastic filaments are vital to biological, physical and engineering systems, from cilia driving fluid in the lungs to artificial swimmers and micro-robotics. Simulating slender structures requires intricate balance of elastic, body, active, and hydrodynamic moments, all in three-dimensions. Here, we present a generalised 3D coarse-graining formulation that is efficient, simple-to-implement, readily extendable and usable for a wide array of applications. Our method allows for simulation of collections of 3D elastic filaments, capable of full flexural and torsional deformations, coupled non-locally via hydrodynamic interactions, and including multi-body microhydrodynamics of structures with arbitrary geometry. The method exploits the exponential mapping of quaternions for tracking three-dimensional rotations of each interacting element in the system, allowing for computation times up to 150 times faster than a direct quaternion implementation. Spheres are used as a building block of both filaments and solid micro-structures for straightforward and intuitive construction of arbitrary three-dimensional geometries present in the environment. We highlight the strengths of the method in a series of non-trivial applications including bi-flagellated swimming, sperm-egg scattering, and particle transport by cilia arrays. Applications to lab-on-a-chip devices, multi-filaments, mono-to-multi flagellated microorganisms, Brownian polymers, and micro-robotics are straightforward. A Matlab code is provided for further customization and generalizations.

biophysics↗

bioRxiv2022

The human sperm head spins with a conserved direction during swimming in 3D

In human sperm, head spinning is essential for sperm swimming and critical for fertilization. Measurement of head spinning has not been straightforward due to its symmetric head morphology, its translucent nature and fast 3D motion driven by its helical flagellum movement. Microscope image acquisition has been mostly restricted to 2D single focal plane images limited to head position tracing, in absence of head orientation and rotation in 3D. To date, human sperm spinning has been reported to be mono or bidirectional, and even intermittently changing direction. This variety in head spinning direction, however, appears to contradict observations of conserved helical beating of the human sperm flagellum. Here, we reconcile these observations by directly measuring the head spinning movement of freely swimming human sperm with multi-plane 4D microscopy. We show that 2D microscopy is unable to distinguish the spinning direction in human sperm. We evaluated the head spinning of 409 spermatozoa in four different conditions: in non-capacitating and capacitating solutions, for both aqueous and viscous media. All spinning spermatozoa, regardless of the experimental conditions spun counterclockwise (CCW) as seen from head-to-tail. Head spinning was suppressed in 57% of spermatozoa swimming in non-capacitating viscous media, though, interestingly, they recovered the CCW spinning after incubation in capacitating conditions within the same viscous medium. Our observations show that the spinning direction in human sperm is conserved, even when recovered from non-spin, indicating the presence of a robust and persistent helical driving mechanism powering the human sperm flagellum, thus of critical importance in future sperm motility assessments, human reproduction research and microorganism self-organised swimming.

cell biology↗

bioRxiv2021

Does the rainbow trout ovarian fluid guide the spermatozoon on its way to the egg?

Fertilization of freshwater fish occurs in an environment that may negatively affect the gametes; therefore, the specific mechanisms triggering the encounters of gametes would be highly expedient. The egg and ovarian fluid (OF) are likely the primary sources of these triggers in fish that we confirmed here for rainbow trout Oncorhynchus mykiss. The ovarian fluid significantly affected the spermatozoa performance: it supported high velocity for a more extended period and changed the motility pattern from tumbling in water to straightforward moving in the ovarian fluid. Rainbow trout OF induced a trapping chemotaxis-like effect on activated male gametes, and this effect depended on the properties of the activating media. The interaction of the spermatozoa with the attracting agents was accompanied by their "turn-and-run" behavior involving asymmetric flagellar beating and Ca2+ concentration bursts in the bent flagella segment, characteristic of the chemotactic response. Collectively, the ovarian fluid creates the optimal environment for rainbow trout spermatozoa performance, being an effective promoter of fertilization. The individual peculiarities of the egg (ovarian fluid) - sperm interaction in rainbow trout reflect the specific features of the spawning process in this species.

ecology↗