Schiffer, Christian, Rieger, Steffen, Brenker, Christoph, Young, Samuel, Hamzeh, Hussein, Wachten, Dagmar, Tüttelmann, Frank, Röpke, Albrecht, Kaupp, U Benjamin, Wang, Tao, Wagner, Alice, Krallmann, Claudia, Kliesch, Sabine, Fallnich, Carsten, and Strünker, Timo
Navigation of sperm in fluid flow, called rheotaxis, provides long‐range guidance in the mammalian oviduct. The rotation of sperm around their longitudinal axis (rolling) promotes rheotaxis. Whether sperm rolling and rheotaxis require calcium (Ca2+) influx via the sperm‐specific Ca2+ channel CatSper, or rather represent passive biomechanical and hydrodynamic processes, has remained controversial. Here, we study the swimming behavior of sperm from healthy donors and from infertile patients that lack functional CatSper channels, using dark‐field microscopy, optical tweezers, and microfluidics. We demonstrate that rolling and rheotaxis persist in CatSper‐deficient human sperm. Furthermore, human sperm undergo rolling and rheotaxis even when Ca2+ influx is prevented. Finally, we show that rolling and rheotaxis also persist in mouse sperm deficient in both CatSper and flagellar Ca2+‐signaling domains. Our results strongly support the concept that passive biomechanical and hydrodynamic processes enable sperm rolling and rheotaxis, rather than calcium signaling mediated by CatSper or other mechanisms controlling transmembrane Ca2+ flux. Synopsis: Mammalian sperm navigation in the oviductal fluid is considered to depend on calcium signaling via the CatSper channel. Here, newly‐developed live imaging microscopy of trapped sperm suggests that passive biomechanical processes, rather than channel‐mediated ion fluxes instruct sperm motility. Rolling and rheotaxis persist in CatSper‐deficient human sperm from infertile patients.Sperm display continuous full 360° rotations, rather than incomplete rotations.Calcium influx is not required for sperm movements.Rolling and rheotaxis persist in CatSper‐deficient mouse sperm. [ABSTRACT FROM AUTHOR]