Human sperm rheotaxis: a passive physical process

Abstract

A long-standing question in natural reproduction is how mammalian sperm navigate inside female reproductive tract and finally reach the egg cell, or oocyte. Recently, fluid flow was proposed as a long–range guidance cue for sperm navigation. Coitus induces fluid flow from oviduct to uterus, and sperm align themselves against the flow direction and swim upstream, a phenomenon termed rheotaxis. Whether sperm rheotaxis is a passive process dominated by fluid mechanics, or sperm actively sense and adapt to fluid flow remains controversial. Here we report the first quantitative study of sperm flagellar motion during human sperm rheotaxis and provide direct evidence indicating that sperm rheotaxis is a passive process. Experimental results show that there is no significant difference in flagellar beating amplitude and asymmetry between rheotaxis-turning sperm and those sperm swimming freely in the absence of fluid flow. Additionally, fluorescence image tracking shows no Ca2+ influx during sperm rheotaxis turning, further suggesting there is no active signal transduction during human sperm rheotaxis.

Strictures of a microchannel impose fierce competition to select for highly motile sperm

“…Therefore, the probability of the sperm to be closer than to the stricture is . [ 20] in which and ′ are the corresponding times of = , in which because of the periodic motion, the sperm pass through this situation twice.…”

A Bistable Mechanism Mediated by Integrins Controls Mechanotaxis of Leukocytes

“…Chemical guiding, or chemotaxis, has long been studied and many mechanistic elements have been identified (1,2). In contrast, mechanical guiding, or mechanotaxis, has been acknowledged more recently, and although physiological roles have been identified in cell/organism swimming (3,4), differentiation (5), morphogenesis (6,7), or leukocyte activation (8), its basic functioning remains largely open. The regulation of immune cells trafficking between lymphoid organs, blood system, and inflamed or infected zones involves robust guiding mechanisms by chemical signals (9)(10)(11) and also mechanical signals like hydrodynamic shear stress (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”

Sperm motility in modulated microchannels

“…Passive guidance, on the other hand, relies solely on given sperm shape and beat pattern, and the physical effects of the suroundings. Rheotaxis [5,6], where the sperm orients against a flow gradient, is such a passive guidance effect: similar to a flag in the wind, the flagellum is rotated against the flow [7]. Because mammalian sperm swim in closed confinement of the winded Fallopian tube, interactions with boundaries provide another important mechanism for active or passive guidance.…”