Hyperactivation of mammalian sperm regulates navigation through physical boundaries and promotes pseudo-chemotaxis
Migration of sperm from mammals into the female reproductive system requires navigational mechanisms, by which sperm respond to biophysical and biochemical signals. Previous studies have found that biophysical signals for sperm in the female reproductive system include fluid flow, wall architecture, and temperature gradients. Here, by exploring the movement of bovine sperm in microfluidic reservoirs and developing theoretical and computational models, we demonstrate that overactivation of sperm motility, which is part of a process that prepares sperm in the female tract for fertilization and involves an increase in the asymmetry of flagellar sperm. beat, modulates sperm-sidewall interactions and therefore navigation through the architecture of the female tract wall. Specifically, hyperactivation reduces the tendency of sperm to swim along the walls and promotes a response that resembles chemotaxis.
Migration of mammalian sperm through the complex and dynamic environment of the female reproductive system to the fertilization site requires navigational mechanisms, through which the sperm respond to the device environment and maintain swimming behavior. appropriate. In the oviduct (fallopian tube), sperm undergo a process called “hyperactivation,” which involves changing from an almost symmetrical, low amplitude, flagellar beat pattern to an asymmetric high amplitude beat pattern necessary for in vivo fertilization. Here, by exploring the movement of bovine sperm in high aspect ratio microfluidic reservoirs as well as theoretical and computational modeling, we demonstrate that sperm hyperactivation, in response to pharmacological agonists, modulates sperm-sidewall interactions and therefore navigation via physical borders. Before hyperactivation, sperm swam along the side walls of reservoirs; however, once the hyperactivation caused the intrinsic curvature of the sperm to exceed a critical value, swimming along the side walls was reduced. We then studied the effect of noise in the intrinsic curvature near the critical value and found that these non-thermal fluctuations produced an interesting “Run-Stop” motion on the sidewall. Finally, we observed that hyperactivation produced “pseudo-chemotaxis” behavior, in that sperm stayed longer in microfluidic chambers containing higher concentrations of hyperactivation agonists.
- Has received April 20, 2021.
- Accepted September 27, 2021.
Author contributions: research designed by MZ, SSS and AA; MZ carried out research; MZ provided new reagents / analytical tools; MZ analyzed the data; and MZ, SSS and AA wrote the article.
The authors declare no competing interests.
This article is a direct PNAS submission.
This article contains additional information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2107500118/-/DCSupplemental.