Biology subjects

Gadelha, H.

Publications and source records attributed to Gadelha, H..

5 recordsLinked to original sources

bioRxiv2023

Skeletal actomyosin geometry orchestrates motor cooperativity as a time-variable network

Groups of non-processive myosin motors exhibit complex and non-linear behaviors when binding to actin. These operate at larger scales and time frames than an individual motor, indicating the presence of a strong cooperative disposition. Limits in contemporary microscopy prevent verification of motor-filament binding dynamics, whilst mathematical models rely on continuum abstractions in which cooperativity is implicit and individual motor behavior cannot be separated from the behaviour of the whole. Understanding the fundamental interactions driving the emergent behaviour in actomyosin therefore remains an open question. Here we suggest that the diversity of empirically observed in-vitro oscillations can be explained by a minimal Kuramoto-style phase oscillator model of actomyosin, where cooperativity is orchestrated by the actomyosin geometry and mechanical environment. The model mirrors the irregular and regular saw-tooth oscillations present in in-vitro actomyosin and sarcomeric SPOC experiments with only adjustments of the external mechanical environment, and despite the models simplicity. Actomyosin-like behaviour thus arises as a generic property of the discontinuous mechanical coupling in an incommensurate architecture, rather than specific to molecular motor reaction kinetics. We demonstrate a range of synchronising behaviours arising from the cooperative motor dynamics that, once synchronised, are stable over a large range of external forces. These synchronising behaviours arise from the cooperative motor dynamics that, once synchronised, are stable over a large range of external forces. The nature of the synchronisation patterns allow recruitment of rotors as the external force increases, reducing variance in the backbones velocity. This is a demonstration of morphological control. Due to interest in this behaviour in contemporary robotics, we build a physical experiment, using electric motors to power our oscillators. Using the experiment we verify both the organisational and control properties of the system. This demonstrates non-biological motors can cooperate similarly to biological motors when working within an actomyosin geometry, suggesting that the actomyosin complex may not depend on motor-specific qualities to achieve its biological function. These findings offer novel insights into synchronising networks of oscillators and have potential applications in emulating actomyosin-like behaviors within contemporary robotics using non-biological motors.

biophysics↗

bioRxiv2020

The multi-scale architecture of mammalian sperm flagella and implications for ciliary motility

Motile cilia are molecular machines used by a myriad of eukaryotic cells to swim through fluid environments. However, available molecular structures represent only a handful of cell types, limiting our understanding of how cilia are modified to support motility in diverse media. Here, we use cryo-focused ion beam milling-enabled cryo-electron tomography to image sperm flagella from three mammalian species. We resolve in-cell structures of centrioles, axonemal doublets, central pair apparatus, and endpiece singlets, revealing novel protofilament-bridging microtubule inner proteins throughout the flagellum. We present native structures of the flagellar base, which is crucial for shaping the flagellar beat. We show that outer dense fibers are directly coupled to microtubule doublets in the principal piece but not in the midpiece. Thus, mammalian sperm flagella are ornamented across scales, from protofilament-bracing structures rein-forcing microtubules at the nano-scale to accessory structures that impose micron-scale asymmetries on the entire assembly. Our structures provide vital foundations for linking molecular structure to ciliary motility and evolution.

cell biology↗

bioRxiv2020

Direct Measurement of Unsteady Microscale Stokes Flow Using Optically Driven Microspheres

A growing body of work on the dynamics of eukaryotic flagella has noted that their oscillation frequencies are sufficiently high that the viscous penetration depth of unsteady Stokes flow is comparable to the scales over which flagella synchronize. Incorporating these effects into theories of synchronization requires an understanding of the global unsteady flows around oscillating bodies. Yet, there has been no precise experimental test on the microscale of the most basic aspects of such unsteady Stokes flow: the orbits of passive tracers and the position-dependent phase lag between the oscillating response of the fluid at a distant point and that of the driving particle. Here, we report the first such direct Lagrangian measurement of this unsteady flow. The method uses an array of 30 submicron tracer particles positioned by a time-shared optical trap at a range of distances and angular positions with respect to a larger, central particle, which is then driven by an oscillating optical trap at frequencies up to 400 Hz. In this microscale regime, the tracer dynamics is considerably simplified by the smallness of both inertial effects on particle motion and finite-frequency corrections to the Stokes drag law. The tracers are found to display elliptical Lissajous figures whose orientation and geometry are in agreement with a low-frequency expansion of the underlying dynamics, and the experimental phase shift between motion parallel and orthogonal to the oscillation axis exhibits a predicted scaling form in distance and angle. Possible implications of these results for synchronization dynamics are discussed.

biophysics↗

bioRxiv2020

Computer-assisted segmentation-free analysis for long-term assessment of flagellar beating in free swimming human spermatozoa: the role of emptying calcium stores

Microorganisms perform complex tasks and achieve biological function over long periods of time. Human spermatozoa are the archetype of long-time self-organizing transport in nature, and critical for reproductive success. They utilize the coordinated beating of their flagellum to swim long distances within the female reproductive tract in order to find and fertilize the egg. However, to this date, the long-time coordination of the sperm flagellum beating, or indeed other flagellated microorganisms, remain elusive due to limitations in microscope imaging and flagellar tracking techniques. Here, we present a novel methodology based on local orientation and isotropy of bio-image to obtain long-term kinematic and physiological parameters of individual free-swimming spermatozoa without requiring image segmentation (thresholding). This segmentation-free method allows for immediate evaluation of frequency and amplitude of the flagellar beat and head kinematic parameters for a duration of 9.2 min (limited by the cameras internal memory), corresponding to hundreds of thousands of flagellar beat cycles. We demonstrate the powerful use of this technique by examining how the release of Ca2+ from internal stores alters flagellar beating in the long-term, as Ca2+ is an essential regulator of flagellar beating. We report that increasing intracellular Ca2+ affected head and flagellar beat frequencies and amplitudes nonlinearly over long periods of time, commensurate with physiological conditions. The simplicity and robustness of the method may offer an advantageous alternative to segmentation-based methods, and allows for straightforward generalization to other bio-imaging applications, such as chlamydomonas, trypanosomes, c. elegans, or indeed flagellated microorganisms and slender-body organisms. Thus, this method may appeal to distant communities away from sperm biology.

cell biology↗

bioRxiv2019

The human sperm beats anisotropically and asymmetrically in 3D

The canonical beating of the human sperm flagellum is postulated to be symmetric. This is despite the reported asymmetries inherent to the flagellar axonemal structure, from distribution and activation of molecular motors to, even, the localisation of regulatory ion channels. This raises a fundamental question: how symmetric beating is possible within such intrinsically asymmetric flagellar complex? Here, we employ high-speed 3D imaging with mathematical analysis capable of resolving the flagellar movement in 4D (3D+time). This reveals that the human sperm beating is both anisotropic and asymmetric, and composed by a superposition of two transversal waves: an asymmetric travelling wave and a symmetric standing wave. This novel anisotropic travelling-pulsation mechanism induces sperm rolling self-organisation and causes a flagellar kinematic illusion, so that the beat appears to be symmetric if observed with 2D microscopy. The 3D beating anisotropy thus regularises the intrinsic flagellar asymmetry to achieve symmetric side-to-side movement and straight-line swimming.

cell biology↗