Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation

Abstract

Summary: Ion channels control sperm navigation within the female reproductive tract and, thus, are critical for their ability to find and fertilize an egg. The flagellar calcium channel CatSper controls sperm hyperactivated motility and is dependent on an alkaline cytoplasmic pH. The latter is accomplished by either proton transporters or, in human sperm, via the voltage-gated proton channel Hv1. To provide concerted regulation, ion channels and their regulatory proteins must be compartmentalized. Here, we describe flagellar regulatory nanodomains comprised of Hv1, CatSper, and its regulatory protein ABHD2. Super-resolution microscopy revealed that Hv1 is distributed asymmetrically within bilateral longitudinal lines and that inhibition of this channel leads to a decrease in sperm rotation along the long axis. We suggest that specific distribution of flagellar nanodomains provides a structural basis for the selective activation of CatSper and subsequent flagellar rotation. The latter, together with hyperactivated motility, enhances the fertility of sperm. : Miller et al. use super-resolution microscopy, electrophysiology, and electron microscopy to show that the sperm proton channel Hv1 forms bilateral lines positioned asymmetrically down the sperm flagellum. Hv1 inhibition leads to a decrease in sperm rotation, suggesting an important role for this channel in sperm motility. Keywords: hydrogen voltage-gated channel 1, Hv1, CatSper, STORM, super-resolution imaging, ion channels, rotation, sperm flagellum