Biology subjects

Struenker, T.

Publications and source records attributed to Struenker, T..

3 recordsLinked to original sources

bioRxiv2022

Cylicins are a structural component of the sperm calyx being indispensable for male fertility in mice and human

Cylicins are testis-specific proteins, which are exclusively expressed during spermiogenesis. In mice and humans, two Cylicins, the gonosomal X-linked Cylicin 1 (Cylc1/CYLC1) and the autosomal Cylicin 2 (Cylc2/CYLC2) genes have been identified. Cylicins are cytoskeletal proteins with an overall positive charge due to lysine-rich repeats. While Cylicins have been localized in the acrosomal region of round spermatids, they resemble a major component of the calyx within the perinuclear theca at the posterior part of mature sperm nuclei. However, the role of Cylicins during spermiogenesis has not yet been investigated. Here, we applied CRISPR/Cas9-mediated gene-editing in zygotes to establish Cylc1- and Cylc2-deficient mouse lines as a model to study the function of these proteins. Cylc1 deficiency resulted in male subfertility, whereas Cylc2-/-, Cylc1-/y Cylc2+/-, and Cylc1-/y Cylc2-/- males were infertile. Phenotypical characterization revealed that loss of Cylicins prevents proper calyx assembly during spermiogenesis. This results in decreased epididymal sperm counts, impaired shedding of excess cytoplasm, and severe structural malformations, ultimately resulting in impaired sperm motility. Furthermore, exome sequencing identified an infertile man with a hemizygous variant in CYLC1 and a heterozygous variant in CYLC2, displaying morphological abnormalities of the sperm including the absence of the acrosome. Thus, our study highlights the relevance and importance of Cylicins for spermiogenic remodeling and male fertility in human and mouse, and provides the basis for further studies on unraveling the complex molecular interactions between perinuclear theca proteins required during spermiogenesis.

developmental biology↗

bioRxiv2021

External fertilization is orchestrated by a pH-regulated soluble adenylyl cyclase controlling sperm motility and chemotaxis

The reaction of CO2 with H2O to form HCO3- and H+ is one of the most important chemical equilibria in cells. In mammalian sperm, a soluble adenylyl cyclase (sAC) serves as cellular HCO3- sensor that conveys the equilibrium state via cAMP synthesis to cAMP-signaling molecules. The function of sAC and cAMP in non-mammalian sperm is largely unknown. Here, we identify sAC orthologs in sea urchin and salmon sperm that, surprisingly, are activated by alkaline pH rather than HCO3-. Two amino-acid residues required for HCO3- binding of mammalian sAC are lacking in pH-regulated sAC. Orthologs identified in ten other phyla are also lacking either one of these key residues, suggesting that pH control is widespread among non-mammalian metazoan. The pH-sensitive sAC controls several functions of sperm from external fertilizers. Upon spawning, alkalization triggers cAMP synthesis and, thereby, activates motility of quiescent sperm. Egg-derived chemoattractants also alkalize sperm and elevate cAMP, which then-modulates pacemaker HCN channels to trigger a chemotactic Ca2+ response. Finally, the sAC and the voltage- and cAMP-activated Na+/H+ exchanger sNHE mutually control each other. A picture of evolutionary significance is emerging: motility and sensory signaling of sperm from both internal and external fertilizers rely on cAMP, yet, their sAC is regulated by HCO3- or pHi, respectively. Acidification of aquatic habitats due to climate change may adversely affect pH-sensing by sAC and thereby sexual reproduction in the sea. Statement of significanceAdenylyl cyclases synthesize cAMP, a prominent cellular messenger. A bicarbonate-sensitive AC family member, soluble AC (sAC), is tied to the chemical equilibrium: H2O + CO2 {leftrightarrow} HCO3- (bicarbonate) + H+. The sAC is required for fertilization: Mammals lacking sAC are infertile and sperm immotile. We now identify a new sAC form in sperm of non-mammalian animals that reproduce in the sea. This novel sAC is activated at alkaline pH rather than bicarbonate. It controls sperm motility and chemotaxis. The switch from HCO3- to pH rests on substitution of two amino-acids, which represents an adaptation to aquatic environments low in bicarbonate. Acidification of aquatic habitats due to climate change may adversely affect sAC activity and, thereby, fertilization.

biophysics↗

bioRxiv2020

Shedding light on the control of CatSper Ca2+ channels by cAMP and chemicals used to probe cAMP signaling

The sperm-specific CatSper channel controls the influx of Ca2+ into the flagellum and, thereby, the swimming behavior of sperm. A hallmark of human CatSper is its polymodal activation by membrane voltage, intracellular pH, and oviductal hormones. Whether CatSper is also activated by signaling pathways involving an increase of cAMP and ensuing activation of protein kinase A (PKA) is, however, a matter of controversy. Here, using kinetic ion-sensitive fluorimetry and patch-clamp recordings, we study transmembrane Ca2+ flux and membrane currents in human sperm from healthy donors and from patients that lack functional CatSper channels. We show that human CatSper is neither activated by intracellular cAMP directly nor indirectly by the cAMP/PKA-signaling pathway. Moreover, we demonstrate that non-physiological concentrations of cAMP and membrane-permeable cAMP analogs used to mimic the action of intracellular cAMP activate human CatSper from the outside via a previously unknown extracellular cyclic nucleotide-binding site. Finally, we demonstrate that the effects of common PKA inhibitors on human CatSper rest on off-target drug actions on CatSper itself rather than on inhibition of PKA. We conclude that the concept of an intracellular cAMP/PKA-activation of CatSper is primarily based on unspecific effects of chemical probes used to interfere with cAMP signaling. Altogether, our findings solve several controversial issues, which has important bearings on future studies of cAMP and Ca2+ signaling and the ligand-control of CatSper in sperm.

cell biology↗