Bimodal rheotactic behavior reflects flagellar beat asymmetry in human sperm cells

Abstract

Rheotaxis, the directed response to fluid velocity gradients, has been shown to facilitate stable upstream swimming of mammalian sperm cells along solid surfaces, suggesting a robust physical mechanism for long-distance navigation during fertilization. However, the dynamics by which a human sperm orients itself relative to an ambient flow is poorly understood. Here, we combine microfluidic experiments with mathematical modeling and 3D flagellar beat reconstruction to quantify the response of individual sperm cells in time-varying flow fields. Single-cell tracking reveals two kinematically distinct swimming states that entail opposite turning behaviors under flow reversal. We constrain an effective 2D model for the turning dynamics through systematic large-scale parameter scans, and find good quantitative agreement with experiments at different shear rates and viscosities. Using a 3D reconstruction algorithm to identify the flagellar beat patterns causing left or right turning, we present comprehensive 3D data demonstrating the rolling dynamics of freely swimming sperm cells around their longitudinal axis. Contrary to current beliefs, this 3D analysis uncovers ambidextrous flagellar waveforms and shows that the cell's turning direction is not defined by the rolling direction. Instead, the different rheotactic turning behaviors are linked to a broken mirror symmetry in the midpiece section, likely arising from a buckling instability. These results challenge current theoretical models of sperm locomotion.sperm swimming | rheotaxis | fluid dynamics | microfluidics | simulations T axis, the directed kinematic response to external signals, is a defining feature of living things that affects their reproduction, foraging, migration, and survival strategies (1-4). Higher organisms rely on sophisticated networks of finely tuned sensory mechanisms to move efficiently in the presence of chemical or physical stimuli. However, various fundamental forms of taxis are already manifest at the unicellular level, ranging from chemotaxis in bacteria (5) and phototaxis in unicellular green algae (2) to the mechanical response (durotaxis) of fibroblasts (6) and rheotaxis (7, 8) in spermatozoa (3, 9-12). Over the last few decades, much progress has been made in deciphering chemotactic, phototactic, and durotactic pathways in prokaryotic and eukaryotic model systems. In contrast, comparatively little is known about the physical mechanisms that enable flow gradient sensing in sperm cells (3, 9-13). Recent studies (3, 12) suggest that mammalian sperm use rheotaxis for long-distance navigation, but it remains unclear how shear flows alter flagellar beat patterns in the vicinity of surfaces and, in particular, how such changes in the beat dynamics affect the steering process. Answering these questions will be essential for evaluating the importance of chemical (14) and physical (4) signals during mammalian fertilization (15-17).A necessary requirement for any form of directed kinematic response is the ability to change the direction of loco...

Rotational motion and rheotaxis of human sperm do not require functional CatSper channels and transmembrane Ca 2+ signaling

“…In fluid flow, mammalian sperm realign their swimming path and move upstream-a mechanism called rheotaxis (Miki & Clapham, 2013;El-Sherry et al, 2014;Kantsler et al, 2014;Tung et al, 2014Tung et al, , 2015Bukatin et al, 2015). In the oviduct, long-range navigation via rheotaxis directs sperm to the site of fertilization (Miki & Clapham, 2013).…”

“…In the oviduct, long-range navigation via rheotaxis directs sperm to the site of fertilization (Miki & Clapham, 2013). An important ingredient of rheotaxis is the rotation of sperm around their longitudinal axis, called rolling (e.g., Miki & Clapham, 2013;Kantsler et al, 2014;Bukatin et al, 2015), resulting in a coneshaped beating envelope. Through this mechanism, vertical shear flow, e.g., near boundary surfaces, exerts a torque that aligns the longitudinal axis of sperm against the flow direction (Miki & Clapham, 2013;Kantsler et al, 2014;Bukatin et al, 2015).…”

“…An important ingredient of rheotaxis is the rotation of sperm around their longitudinal axis, called rolling (e.g., Miki & Clapham, 2013;Kantsler et al, 2014;Bukatin et al, 2015), resulting in a coneshaped beating envelope. Through this mechanism, vertical shear flow, e.g., near boundary surfaces, exerts a torque that aligns the longitudinal axis of sperm against the flow direction (Miki & Clapham, 2013;Kantsler et al, 2014;Bukatin et al, 2015). However, whether sperm rolling involves full 360°or incomplete rotations of alternating direction is debated (Miki & Clapham, 2013;Muschol et al, 2018).…”

Mechanical tuning of mammalian sperm behaviour by hyperactivation, rheology and substrate adhesion: a numerical exploration

“…Such behaviour also would require an appropriate choice of sperm species and viscosity to maintain helical waves, with Woolley [44] reporting that three-dimensional flagellar beating can be suppressed near surfaces, though this is not universal [45,46]. While such dynamics does not appear to be common, and is predicted to require stringent restrictions, mouse sperm can be observed to tightly cycle on a surface before detaching [47], which shares similar dynamical features to the rolling motility predicted here.…”

Análisis de Métricas Sobre el Flagelo de Espermatozoides de Humano en 3D para su Clasificación entre Activados e Hiperactivados

“…Con la información tridimensional que proporciona este sistema, ha sido posible concluir que el movimiento del flagelo es diferente de lo que se esperaba y que se está perdiendo información relevante cuando solamente es estudiado en 2D [3,4]. Lo anterior es de gran importancia para entender el funcionamiento de dichas células, ya que naturalmente, éstas no se mueven únicamente sobre una superficie, sino que también lo hacen libremente en un espacio tridimensional.Actualmente ya existen diversos sistemas que permiten la reconstrucción en tercera dimensión del flagelo de los espermatozoides, una de las más novedosas es la microscopía sin lentes, la cual permite analizar múltiples células al mismo tiempo mediante detección holográfica [5], otra de ellas es el algoritmo de "Rayleigh-Sommerfeld Back-Propagation" sobre un video bidimensional tomado a un solo plano focal [6], sin embargo, en ninguna de estas técnicas puede ser utilizada la fluorescencia, que es empleada para la detección de los procesos bioquímicos básicos que ocurren en el espermatozoide, por la naturaleza incoherente de la luz emitida. La aplicación final de los resultados del desarrollo de este trabajo pretende realizarse sobre imágenes con fluorescencia, por tal motivo el empleo de dichas técnicas fue descartado, optándose por utilizar el sistema desarrollado por Corkidi et al [2,3] que es lo suficientemente sensible para medir la diferencia entre los distintos tipos de batido, y el cual no presenta dicha limitante.…”