Article

Egg Coat Proteins Activate Calcium Entry into Mouse Sperm via CATSPER Channels

Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Biology of Reproduction (Impact Factor: 3.45). 03/2009; 80(6):1092-8. DOI: 10.1095/biolreprod.108.074039
Source: PubMed

ABSTRACT 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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    • "Finally, CatSper is the only voltage-activated Ca 2 þ channel that can be detected by patch-clamp recordings from ejaculated human and epididymal mouse sperm (Kirichok et al, 2006; Navarro et al, 2008; Xia and Ren, 2009; Lishko et al, 2010, 2011; Kirichok and Lishko, 2011; Strü nker et al, 2011). Currents carried by other Ca v channels have only been recorded from precursor cells or testicular sperm (Martinez-Lopez et al, 2009; Xia and Ren, 2009). The only other Ca 2 þ -permeable ion channel that has been functionally characterized is a purinergic P2X2 receptor present in mouse sperm (Navarro et al, 2011). "
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    ABSTRACT: The sperm-specific CatSper channel controls the intracellular Ca(2+) concentration ([Ca(2+)](i)) and, thereby, the swimming behaviour of sperm. In humans, CatSper is directly activated by progesterone and prostaglandins-female factors that stimulate Ca(2+) influx. Other factors including neurotransmitters, chemokines, and odorants also affect sperm function by changing [Ca(2+)](i). Several ligands, notably odorants, have been proposed to control Ca(2+) entry and motility via G protein-coupled receptors (GPCRs) and cAMP-signalling pathways. Here, we show that odorants directly activate CatSper without involving GPCRs and cAMP. Moreover, membrane-permeable analogues of cyclic nucleotides that have been frequently used to study cAMP-mediated Ca(2+) signalling also activate CatSper directly via an extracellular site. Thus, CatSper or associated protein(s) harbour promiscuous binding sites that can host various ligands. These results contest current concepts of Ca(2+) signalling by GPCR and cAMP in mammalian sperm: ligands thought to activate metabotropic pathways, in fact, act via a common ionotropic mechanism. We propose that the CatSper channel complex serves as a polymodal sensor for multiple chemical cues that assist sperm during their voyage across the female genital tract.
    The EMBO Journal 02/2012; 31(7):1654-65. DOI:10.1038/emboj.2012.30 · 10.75 Impact Factor
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    • "Finally, all attempts to identify voltagegated Ca 2+ currents electrophysiologically in mature mouse or human spermatozoa have failed. T-type Ca 2+ channels could be recorded from mouse testicular sperm (Darszon et al., 2006b), but they seemed to be silenced via an unknown mechanism and are undetectable in the epididymal mouse sperm (Xia and Ren, 2009b). Ejaculated human spermatozoa do not posses functional Ca v channels as recorded with the patch-clamp technique (Lishko and Kirichok, unpublished data). "
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    ABSTRACT: Upon ejaculation, mammalian spermatozoa have to undergo a sequence of physiological transformations within the female reproductive tract that will allow them to reach and fertilize the egg. These include initiation of motility, hyperactivation of motility and perhaps chemotaxis toward the egg, and culminate in the acrosome reaction that permits sperm to penetrate the protective vestments of the egg. These physiological responses are triggered through the activation of sperm ion channels that cause elevations of sperm intracellular pH and Ca(2+) in response to certain cues within the female reproductive tract. Despite their key role in sperm physiology and their absolute requirement for the process of fertilization, sperm ion channels remain poorly understood due to the extreme difficulty in application of the patch-clamp technique to spermatozoa. This review covers the topic of sperm ion channels in the following order: first, we discuss how the intracellular Ca(2+) and pH signaling mediated by sperm ion channels controls sperm behavior during the process of fertilization. Then, we briefly cover the history of the methodology to study sperm ion channels, which culminated in the recent development of a reproducible whole-cell patch-clamp technique for mouse and human cells. We further discuss the main approaches used to patch-clamp mature mouse and human spermatozoa. Finally, we focus on the newly discovered sperm ion channels CatSper, KSper (Slo3) and HSper (H(v)1), identified by the sperm patch-clamp technique. We conclude that the patch-clamp technique has markedly improved and shifted our understanding of the sperm ion channels, in addition to revealing significant species-specific differences in these channels. This method is critical for identification of the molecular mechanisms that control sperm behavior within the female reproductive tract and make fertilization possible.
    Molecular Human Reproduction 06/2011; 17(8):478-99. DOI:10.1093/molehr/gar044 · 3.48 Impact Factor
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    • "Secondly, during the burst of InsP 3 generation that follows zona pellucida binding and mediates emptying of the acrosomal store, the store in the midpiece/sperm neck may be strongly activated through its InsP 3 Rs. In addition, zona binding mat activate CatSpers (Xia & Ren, 2009; section 6.1) If either or both these processes occur, arrival of the sperm at the zona pellucida will initiate a combination of acrosome reaction and intense hyperactivation to facilitate penetration of the zona pellucida (fig. "
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    ABSTRACT: Intracellular Ca2+ stores play a central role in the regulation of cellular [Ca2+](i) and the generation of complex [Ca2+] signals such as oscillations and waves. Ca2+ signalling is of particular significance in sperm cells, where it is a central regulator in many key activities (including capacitation, hyperactivation, chemotaxis and acrosome reaction) yet mature sperm lack endoplasmic reticulum and several other organelles that serve as Ca2+ stores in somatic cells. Here, we review i) the evidence for the expression in sperm of the molecular components (pumps and channels) which are functionally significant in the activity of Ca2+ stores of somatic cells and ii) the evidence for the existence of functional Ca2+ stores in sperm. This evidence supports the existence of at least two storage organelles in mammalian sperm, one in the acrosomal region and another in the region of the sperm neck and midpiece. We then go on to discuss the probable identity of these organelles and their discrete functions: regulation by the acrosome of its own secretion and regulation by membranous organelles at the sperm neck (and possibly by the mitochondria) of flagellar activity and hyperactivation. Finally, we consider the ability of the sperm discretely to control mobilisation of these stores and the functional interaction of stored Ca2+ at the sperm neck/midpiece with CatSper channels in the principal piece in regulation of the activities of mammalian sperm.
    Reproduction 07/2009; 138(3):425-37. DOI:10.1530/REP-09-0134
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