Human sperm rheotaxis: a passive physical process.

Zhuoran Zhang,Changhai Ru,Yu Sun,Jun Liu,Shaorong Xie,Jim Meriano,Jun Luo

doi:10.1038/srep23553

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.

Highlights

We summarized the percentage of sperm showing rheotactic movement
These results were consistent with data previously reported in the literature[4,14], confirming that the reorientation behavior observed in our experiments was caused by fluid flow instead of other factors
Difference was found among the groups [p = 0.3 by ANOVA, see Fig. 4(c)]. These results suggest that no calcium signaling occurs in the process of rheotaxis reorientation, and explain the measurement results presented in the section of ‘Unchanging flagellar beating in rheotaxis reorientation’

Summary

Introduction

To normalize flagellar beating of sperm swimming towards different directions, the whole sperm was rotated so that the head and midpiece were horizontally facing left [Fig. 1(c)]. The flagella beat periodically around the head axis in the same way as under the no-flow condition, and no obvious asymmetrically flagellar bending was observed (Supplementary Video 1).

Results

Conclusion