Biology subjects

Corkidi, G.

Publications and source records attributed to Corkidi, G..

4 recordsLinked to original sources

bioRxiv2023

Reorganization of the Flagellum Scaffolding Induces a Sperm Standstill Required for Fertilization

Mammalian sperm delve into the female reproductive tract to fertilize the female gamete. The available information about how sperm regulate their motility during the final journey to the fertilization site is extremely limited. In this work, we investigated the structural and functional changes in the sperm flagellum after AE and during the interaction with the eggs. The evidence demonstrates that the double helix actin network surrounding the mitochondrial sheath of the midpiece undergoes structural changes prior to the motility cessation. This structural modification is accompanied by a decrease in diameter of the midpiece and is driven by intracellular calcium changes that occur concomitant with a reorganization of the actin helicoidal cortex. Midpiece contraction occurs in a subset of cells that undergo AE, live-cell imaging during in vitro fertilization showed that the midpiece contraction is required for motility cessation after fusion is initiated. These findings provide the first evidence of the F-actin networks role in regulating sperm motility, adapting its function to meet specific cellular requirements during fertilization, and highlighting the broader significance of understanding sperm motility. Significant statementIn this work, we demonstrate that the helical structure of polymerized actin in the flagellum undergoes a rearrangement at the time of sperm-egg fusion. This process is driven by intracellular calcium and promotes a decrease in the sperm midpiece diameter as well as the arrest in motility, which is observed after the fusion process is initiated.

cell biology↗

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↗

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↗