CatSperζ regulates the structural continuity of sperm Ca2+ signaling domains and is required for normal fertility

Abstract

We report that the Gm7068 (CatSpere) and Tex40 (CatSperz) genes encode novel subunits of a 9-subunit CatSper ion channel complex. Targeted disruption of CatSperz reduces CatSper current and sperm rheotactic efficiency in mice, resulting in severe male subfertility. Normally distributed in linear quadrilateral nanodomains along the flagellum, the complex lacking CatSperζ is disrupted at ~0.8 μm intervals along the flagellum. This disruption renders the proximal flagellum inflexible and alters the 3D flagellar envelope, thus preventing sperm from reorienting against fluid flow in vitro and efficiently migrating in vivo. Ejaculated CatSperz-null sperm cells retrieved from the mated female uterus partially rescue in vitro fertilization (IVF) that failed with epididymal spermatozoa alone. Human CatSperε is quadrilaterally arranged along the flagella, similar to the CatSper complex in mouse sperm. We speculate that the newly identified CatSperζ subunit is a late evolutionary adaptation to maximize fertilization inside the mammalian female reproductive tract.DOI: http://dx.doi.org/10.7554/eLife.23082.001

Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation

“…Although ABHD2 could be used as a marker for sperm flagellar diameter and has an average distance between lines of at least 400 nm (Figure 4C), the distance between Hv1 bilateral lines is around 230 nm (Figures 2 and 4C). Based on Hv1 immunogold labeling, which indicates a close proximity of one of the Hv1 lines to the LC (Figures S5D and S5E), previously reported evidence that two CatSper lines closely “sandwich” each LC (Chung et al, 2017; Chung et al, 2014), and our assumption that CatSper and ABHD2 are positioned closely to each other, we suggest that one of the Hv1 lines is also in close proximity, if not in the complex, with CatSper channels. This suggestion supports our simulations, which imply a strong interaction of Hv1induced pH rise on some CatSpers.…”

“…To overcome this, three-dimensional stochastic optical reconstruction microscopy (3D-STORM) (Huang et al, 2008; Rust et al, 2006) was used to reveal the detailed organization of flagellar elements in human sperm. The same method has been successfully used before to reveal the quadrilateral line arrangement of CatSper (Chung et al, 2014, 2017). In human sperm, CatSper activation has two prerequisites: intraflagellar alkalinity and sperm exposure to progesterone.…”

“…To enable the rapid progesterone-triggered activation of CatSper, it follows that the turnover of 2-AG should occur in close proximity to the channel itself. Therefore, we hypothesized that, like CatSper in human and mouse sperm (Chung et al, 2017; Chung et al, 2014), its regulator ABHD2 follows a quadrilateral distribution. With 3D-STORM imaging, we assessed the localization of ABHD2 in the flagella of human sperm and found that this enzyme also follows CatSper distribution (Figures 1C and 1D).…”

“…Interestingly, although both human and mouse sperm hyperactivate, only human spermatozoa display full 360 rotation along the long axis, whereas mouse sperm alternate between 180 turns (Babcock et al, 2014). CatSper, which is organized in quadrilateral longitudinal nanodomains along the sperm flagellum (Chung et al, 2014, 2017) is also regulated by species-specific cues (Miller et al, 2015). In human sperm, CatSper is activated by both flagellar alkalinity and progesterone (Lishko et al, 2011; Strünker et al, 2011), whereas, in murine sperm, CatSper is only regulated by the former modality (Kirichok et al, 2006).…”

Intramembranal disulfide cross-linking elucidates the super-quaternary structure of mammalian CatSpers

“…The requirement for four CatSper genes in mammals suggests that there is a structural selective pressure that goes beyond the form and function of the individual channel, since one gene would do if sperm required only a voltage-dependent and ion selective channel. The arrangement of CatSper into four lines extending the length of the principal piece of the sperm flagellum [60], and the observed association of defects in this architecture with reduced motility [7], suggests a connection between the CatSper macromolecular architecture and hyperactive motility.…”