During mammalian fertilization, the contact between sperm and egg triggers increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) in sperm. Voltage-gated Ca(2+) channels (Ca(V)s) are believed to mediate the initial phase of [Ca(2+)](i) increases in sperm induced by egg coat (zona pellucida [ZP]) glycoproteins, while store depletion-activated Ca(2+) entry is thought to mediate the sustained phase. Using patch-clamp recording and Ca(2+) imaging, we show herein that Ca(V) channel currents, while found in spermatogenic cells, are not detectable in epididymal sperm and are not essential for the ZP-induced [Ca(2+)](i) changes. Instead, CATSPER channels localized in the distal portion of sperm (the principal piece) are required for the ZP-induced [Ca(2+)](i) increases. Furthermore, the ZP-induced [Ca(2+)](i) increase starts from the sperm tail and propagates toward the head.
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"Up to date, there is still controversy regarding the origin of the [Ca 2+ ]i increase that leads to AR. Some reports claim that the [Ca 2+ ]i increase induced by ZP initiates in the sperm flagellum , while others describe only the Ca 2+ dynamics in the sperm head without analyzing those occurring in the flagella . Our studies consistently indicated that only the [Ca 2+ ]i rise originated in the sperm head is able to promote AR in response to Progesterone. "
[Show abstract][Hide abstract]ABSTRACT: During capacitation, sperm acquire the ability to undergo the acrosome reaction (AR), an essential step in fertilization. Progesterone produced by cumulus cells has been associated with various physiological processes in sperm, including stimulation of AR. An increase in intracellular Ca(2+) ([Ca(2+)]i) is necessary for AR to occur. In this study, we investigated the spatio-temporal correlation between the changes in ([Ca(2+)]i and AR in single mouse spermatozoa in response to Progesterone. We found that Progesterone stimulates an ([Ca(2+)]i increase in five different patterns: gradual increase, oscillatory, late transitory, immediate transitory and sustained. We also observed that the ([Ca(2+)]i increase promoted by Progesterone starts at either the flagellum or the head. We validated the use of FM4-64 as an indicator for the occurrence of the AR by simultaneously detecting its fluorescence increase and the loss of EGFP in transgenic EGFPAcr sperm. For the first time, we have simultaneously visualized the rise in ([Ca(2+)]i and the process of exocytosis in response to Progesterone and found that only a specific transitory increase in ([Ca(2+)]i originated in the sperm head promotes the initiation of AR.
Full-text · Article · Jan 2016 · Biology of Reproduction
"Ca 2+ channels and Ca 2+ stores are present in mammalian sperm (Publicover et al., 2007; Costello et al., 2009; Darszon et al., 2011) and both play important roles in sperm function. CatSper, a sperm-specific cation channel localized to the flagellum, is the primary Ca 2+ -influx channel in mammalian sperm, is central to the regulation of [Ca 2+ ] i and experiments in CatSper-null mice have shown that the channels play a key role in both regulation of motility and the early phase of zona pellucida-induced acrosome [Ca 2+ ] i signalling (Carlson et al., 2003; Xia and Ren, 2009). Intriguingly, 'late' [Ca 2+ ] i responses persisted in the mutant mice and the zona pellucida-induced acrosome reaction was not inhibited (Xia and Ren, 2009). "
"The contact between a spermatozoon and egg coat (zona pellucida ) triggers Ca 2+ entry into sperm, as suggested by incubation of spermatozoa with solubilized zona pellucida glycoproteins that stimulates an extracellular Ca 2+ -dependent increase in [Ca 2+ ]i in sperm. Zona pellucida induced Catsper channel mediated elevation in Ca 2+ involves an early rapid phase that occurs in milliseconds to seconds and a sustained phase that extends over several minutes (Ren and Xia, 2010; Xia and Ren, 2009b). ZP1, ZP2, and ZP3 are the proteins that constitute the zona pellucida matrix of egg in mouse (Florman et al., 2008; Wassarman and Litscher, 2009) whereas ZP1, ZP2, ZP3, and ZP4 constitute the same in humans (Gupta et al., 2009 ). "
[Show abstract][Hide abstract]ABSTRACT: A number of physiological events, such as sperm hyperactivation, chemotaxis towards the egg, capacitation and acrosome reaction, are triggered by activation of sperm ion channels in response to a diverse range of chemical cues. Cation channel of sperm (CatSper), a sperm-specific ion channel, is unique in orchestrating the events for fertilization, and seems to be exclusively evolved for sperm function and male fertility. CatSper acts as a polymodal, chemosensory calcium channel and plays a vital role in the regulation of sperm hyperactivation. CatSper knockout models and application of patch clamp recordings have shown that it is indispensable for male fertility, and mutations and deletions in CatSper gene(s) may lead to infertility. In fact, mutations in CatSper1 and 2 have been identified in infertile individuals; however, CatSper3 and 4 have not been explored. Restricted localization and expression of CatSper in sperm offer an added advantage to developing gamete-based safe non-hormonal contraceptives. This review concisely covers identification, structure, function, and mechanism of action of CatSper channels. The functional importance of this complex ion channel in sperm motility and male fertility is highlighted for further research on male fertility, infertility, and contraception.
Full-text · Article · Oct 2014 · Reproductive biomedicine online