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.

Rotational motion and rheotaxis of human sperm do not require functional CatSper channels and transmembrane Ca 2+ signaling

“…The Ca 2+ channel CatSper has been implicated in rolling and rheotactic steering of mammalian sperm (Miki & Clapham, 2013; (Zhang et al, 2016). Furthermore, it has been proposed that the quadrilateral organization of CatSper and associated signaling components provides the flagellar ultrastructure required for rolling and rheotaxis (Miller et al, 2018). The CatSper complex and the quadrilateral Ca 2+ -signaling domains are abolished in Catsper1 À/À mouse sperm (Chung et al, 2014), but not in human CATSPER2 À/À sperm.…”

“…Semi-automated analysis of blinking events revealed the rotation frequency of each sperm cell in the field of view. In non-capacitated and capacitated control sperm from healthy donors, the rotation frequency was normally distributed ( Fig 2D) with a mean value of 4.8 AE 1.5 Hz (n = 1,455) and 7.0 AE 2.2 Hz (n = 1,097), respectively ( Fig 2E) (Rigler & Thyberg, 1984;Aitken et al, 1985;Miller et al, 2018). Bicarbonate (25 mM) used for capacitation stimulates cAMP synthesis (Carlson et al, 2007;Tresguerres et al, 2011;Brenker et al, 2012) and, thereby, accelerates the flagellar beat (Esposito et al, 2004;Xie et al, 2006) and rotation frequency (Miki & Clapham, 2013).…”

“…In Catsper1 À/À mouse sperm, longitudinal rolling and rheotaxis were abolished (Miki & Clapham, 2013), suggesting that control of [Ca 2+ ] i by CatSper is required for rolling and rheotaxis of mammalian sperm. For human sperm, it was specifically proposed that rolling is created by asymmetrical Ca 2+ influx via CatSper channels, stimulated by local pH i signaling (Miller et al, 2018). The H + channel Hv1 is organized along the flagellum of human sperm in two threads near two of the four CatSper threads (Miller et al, 2018).…”

“…For human sperm, it was specifically proposed that rolling is created by asymmetrical Ca 2+ influx via CatSper channels, stimulated by local pH i signaling (Miller et al, 2018). The H + channel Hv1 is organized along the flagellum of human sperm in two threads near two of the four CatSper threads (Miller et al, 2018). It was proposed that H + efflux via Hv1 organizes localized Ca 2+ signaling that, ultimately, creates an asymmetry in calcium-dependent inhibition of dynein-powered microtubule sliding (Miller et al, 2018).…”

“…The H + channel Hv1 is organized along the flagellum of human sperm in two threads near two of the four CatSper threads (Miller et al, 2018). It was proposed that H + efflux via Hv1 organizes localized Ca 2+ signaling that, ultimately, creates an asymmetry in calcium-dependent inhibition of dynein-powered microtubule sliding (Miller et al, 2018). However, the concept that rolling and rheotaxis are enabled by Ca 2+ influx cannot be reconciled with the finding that rolling of mouse sperm does not require extracellular Ca 2+ (Babcock et al, 2014;Muschol et al, 2018), and that exposure of human sperm to gradients of flow velocities does not evoke measurable changes in [Ca 2+ ] i (Zhang et al, 2016).…”