Reassessing the role of progesterone in fertilization—compartmentalized calcium signalling in human spermatozoa?

Claire V. Harper1,2 and Stephen J. Publicover1,3

1 School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK 2 Present address: School of Biological Sciences, Biosciences Building, Crown Street, University of Liverpool, Liverpool L69 7ZB, UK

3 Corresponding author. E-mail: S.J.PUBLICOVER{at}bham.ac.uk


    Abstract
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
Progesterone is present at micromolar concentrations in the vicinity of the oocyte. Human spermatozoa generate a biphasic rise in intracellular calcium concentration ([Ca2+]i) and undergo the acrosome reaction upon progesterone stimulation, suggesting that the hormone acts as a secondary inducer or ‘primer’ of the acrosome reaction in association with the zona pellucida. However, the sensitivity of human spermatozoa to progesterone is such that many cells may undergo the acrosome reaction prematurely, compromising their ability to fertilize. We have shown that exposing human spermatozoa to a progesterone gradient, simulating the stimulus encountered as sperm approach the oocyte, results in a novel response. A slow rise in [Ca2+]i occurs, upon which, in many cells, [Ca2+]i oscillations are superimposed. Cells showing this pattern of response do not undergo the acrosome reaction, but instead show an alternating pattern of flagellar activity associated with peaks and troughs of [Ca2+]i. A Ca2+ store in the rear of the sperm head apparently generates this complex signal, functioning as an ‘[Ca2+]i oscillator’. We propose that: (i) the acrosome reaction and flagellar beat are regulated by separate Ca2+ stores; (ii) these stores are mobilized through different mechanisms by different agonists; and (iii) progesterone in vivo acts as a switch for the oscillator which regulates the flagellar beat mode.

Key words: calcium/motility/oscillation/progesterone/sperm


    Sperm responses to oocyte-derived factors
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
After deposition in the female tract, a mammalian sperm must swim to the oocyte, requiring both motility through a viscous environment and (probably) chemotactic control of that motility. On reaching the oocyte–cumulus complex, the cell has to penetrate the layers of cumulus and zona pellucida, a process dependent upon both the acrosome reaction (AR) and regulation of motility. The sperm must, therefore, detect and respond appropriately both ‘remotely’ (to factors derived from the oocyte) and also to stimuli presented upon direct contact with the egg. These stimuli must elicit intracellular signals that achieve complex regulation of the flagellum (both beat mode and directional) and appropriately timed activation of the AR. Sperm responses to factors derived from the egg and its vestments are primarily mediated through [Ca2+]i, which is known to control flagellar activity both during regulation of flagellar beat mode (Ho et al., 2002; Harper et al., 2004Go) and during chemotactic responses (Spehr et al., 2003Go, 2004Go). Ca2+ is also pivotal to induction of the AR (Publicover and Barratt, 1999).

At least two components of the egg vestments, zona pellucida and progesterone (secreted at high concentrations by the cumulus cells), activate Ca2+ signalling in mammalian spermatozoa (Florman et al., 1989Go; Blackmore et al., 1990)Go. The induction of the AR by solubilized zona pellucida has been studied in detail in the mouse model and involves activation of a T-type voltage-operated calcium chanel (VOCC) followed by store mobilization and prolonged (probably) capacitative Ca2+ influx (Florman et al., 1992; Evans and Florman, 2002Go). In contrast, the significance of progesterone is much less clear. The responsiveness of human spermatozoa to progesterone correlates with the fertilization rate at IVF (Krausz et al., 1996Go; Forti et al., 1999Go; Giojalas et al., 2004Go), and removal of cumulus cells from oocytes significantly reduces the success rate of IVF in most mammals (Tanghe et al., 2002Go; van Soom et al., 2002). However, the most commonly observed effect of progesterone-induced Ca2+ influx, stimulation of the AR, is arguably not an adaptive response. Human spermatozoa respond with elevation of [Ca2+]i and the AR to doses well below the 1–10 µmol/l that is believed to occur adjacent to the oocyte (Osman et al., 1989Go; Baldi et al., 1991Go; Harper et al., 2003)Go. The AR should therefore occur in many cells before they enter the cumulus, potentially compromising their ability subsequently to penetrate the zona.


    Effect of progesterone on sperm [Ca2+]i
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
The progesterone-induced [Ca2+]i signal has been studied extensively in human sperm cells. Micromolar doses of the hormone induce a rapid, transient (1–2 min) elevation of [Ca2+]i (Blackmore et al., 1990Go, Meizel and Turner, 1991Go; Foresta et al., 1993Go; Plant et al., 1995Go; Aitken et al., 1996Go; Tesarik et al., 1996Go; Kirkman-Brown et al., 2000Go). A role for VOCCs in this effect is disputed (Blackmore and Eisoldt, 1999Go; Garcia and Meizel, 1999Go; Kirkman-Brown et al., 2003Go; Fraire-Zamora and Gonzalez-Martinez, 2004Go), and it appears that receptor-operated mechanisms are largely responsible. As well as the initial transient, a second, sustained elevation of [Ca2+]i occurs (Baldi et al., 1991Go; Yang et al., 1994Go; Bonnacorsi et al., 1995; Tesarik et al., 1996Go; Kirkman-Brown et al., 2000Go). Though it is tempting to suggest that this response resembles that induced by the zona pellucida, possibly involving store-operated Ca2+ influx, studies employing SKF96365, an inhibitor of store-operated Ca2+ influx, and APB [reported to block inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ mobilization and/or store-operated Ca2+ influx] have produced equivocal data (Blackmore, 1999Go; Harper et al., 2004Go). It appears that continuous activation of progesterone-induced signalling is required, since progesterone withdrawal causes immediate reduction or abolition of the sustained [Ca2+]i signal (C.V.Harper, unpublished data).

The receptor that mediates the response of spermatozoa to progesterone is yet to be characterized, but the rapidity of the response, and the efficacy of progesterone conjugated to bovine serum albumin (BSA) (Meizel and Turner, 1991Go), lead to the conclusion that it is a cell surface, ‘non-genomic’ binding site. Rapid, signalling events activated by progesterone (and estrogen) are known to occur in a range of cells, through either activation of a subpopulation of conventional steroid receptors, activation of modified/truncated conventional receptors, activation of novel transmembrane receptors or possibly by allosteric modulation of receptors for other agonists (Edwards, 2005)Go. Using an antibody to the C-terminus of the conventional progesterone receptor (C262), two proteins resembling N-terminal truncated receptors have been detected in human spermatozoa (Luconi et al., 1998Go, 2002Go). This antibody is able to inhibit the progesterone-induced AR (Sabeur et al., 1996Go; Luconi et al., 1998Go). A progesterone-binding protein unrelated to the nuclear progesterone receptor (mPR), cloned from porcine liver, has also been proposed as the receptor in sperm. Antibodies against this receptor have effects on both the progesterone-induced [Ca2+]i signal and the AR (Buddkikot et al., 1999; Falkenstein et al., 1999Go). These authors recently have proposed that porcine spermatozoa possess both mPR and another receptor that is structurally different (Losel et al., 2004Go). Attempts to localize the sperm progesterone receptor have employed primarily antibodies against the conventional progesterone receptor or fluorescently tagged progesterone. These studies have identified binding on the head, mostly the acrosomal region (Gadkar et al., 2002Go; Huo et al., 2002Go; Shah et al., 2005Go), though Sabeur et al. (1996)Go observed equatorial binding of the C262 antibody. Antisera against the porcine liver progesterone-binding protein (see above) initially localized to a site on the posterior head of human spermatozoa which moved equatorially during capacitation (Buddkikot et al., 1999). The finding that stimulation of human spermatozoa with 3 µmol/l progesterone induces an initial transient that starts in the equatorial region (Meizel et al., 1997Go) is consistent with these observations.

Dose–effect and binding assays identify two receptors for progesterone on human spermatozoa. One is poorly specific and has a Kd of 40 µmol/l, but the other is specific for progesterone and has a much higher affinity (Kd in the nmol/l range; Luconi et al., 1998Go). The progesterone-induced [Ca2+]i response, measured fluorimetrically in populations of human spermatozoa, is dose dependent. An EC50 for the amplitude of the progesterone-induced transient of 50–100 nmol/l has been reported (Baldi et al., 1991Go, Luconi et al., 1998Go; Kumar et al., 2000Go; Schaefer et al., 2000Go; Harper et al., 2003)Go, possibly corresponding to activation of the specific progesterone receptor. We find that both the [Ca2+]i response and induction of the AR saturate at ~300 nmol/l progesterone (Harper et al., 2003)Go. Doses of 1–100 µmol/l progesterone can exert further effects on [Ca2+]i, maybe through the low-affinity receptor (Luconi et al., 1998Go). Although such doses might be encountered within the cumulus, the extreme sensitivity of human spermatozoa to progesterone suggests that this hormone will exert major effects at much lower doses, encountered before the sperm contacts the oocyte–cumulus complex. The stimulus will therefore occur not as a sudden rise in the concentration of progesterone (as is used in pharmacological investigations) but as a gradient generated by diffusion and/or ciliary currents which the cell ascends as it approaches the oocyte (Harper et al., 2004Go).


    Response of human spermatozoa to a progesterone gradient
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
Since progesterone is released from the oocyte–cumulus complex and can be detected by spermatozoa while still remote from the egg, there is potentially an important chemotactic role for the hormone in the female tract. Several authors have described attraction of mammalian sperm to follicular fluid and to factors secreted by cumulus cells and oocytes after ovulation (Ralt et al., 1991Go, 1994Go; Jaiswal et al., 1999Go; Jeon et al., 2001Go; Wang et al., 2001Go; Sun et al., 2005Go), and it has been suggested that progesterone is an ingredient of follicular fluid that contributes to this effect (Vadillo Ortega et al., 1994; Villanueva-Diaz et al., 1995Go; Jeon et al., 2001)Go. However, this is disputed on the basis that any effect of progesterone may be due to induction of hyperactivation, causing accumulation of cells in the presence of the agonist by ‘trapping’ (Jaiswal et al., 1999Go). Olfactory receptors, similar to those in the nasal mucosa, have been described recently in human spermatozoa. Activation of these receptors by burgeonal causes a marked chemotactic response in human spermatozoa via a pathway involving generation of cAMP and activation of Ca2+-permeable cation channels (Spehr et al., 2003Go, 2004Go). An endogenous agonist that would cause oocyte-directed taxis of mammalian spermatozoa in vivo has not yet been described.

To attempt to mimic the stimulus encountered by sperm approaching the oocyte and to understand better what effect ‘remote detection’ of progesterone by spermatozoa in vivo may have, we investigated the effect of applying progesterone to human spermatozoa as a logarithmic concentration gradient (Harper et al., 2004Go). As the progesterone concentration increased (gradient raised from 0 to 3 µmol/l over a period of 15–25 min), there was a concomitant increase in [Ca2+]i in almost all cells, initiated when progesterone was 1–10 nmol/l and saturating at micromolar levels, possibly reflecting desensitization of the high-affinity progesterone receptor (Aitken et al., 1996Go; Luconi et al., 1998Go; Harper et al., 2003Go). Interestingly, early transient calcium increases were never seen, suggesting that previous studies, conducted by others and ourselves, using stepped progesterone additions were unrepresentative of responses occurring in vivo. The most striking characteristic of progesterone gradient stimulation was the generation of slow [Ca2+]i oscillations in over one-third of cells, typically starting when the progesterone concentration was between 5 and 50 nmol/l. Signals of this complexity in spermatozoa have been described only recently and were thought to occur only rarely (Fukami et al., 2003Go; Wood et al., 2003Go; Kirkman-Brown et al., 2004Go).


    Generation of [Ca2+]i oscillations
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
Study of the [Ca2+]i oscillations showed that they are generated by repetitive mobilization of a Ca2+ store located in the neck region of the sperm (Harper et al., 2004Go, 2005Go). Existence of Ca2+ storage in the redundant nuclear envelope (RNE) has already been proposed (Ho and Suarez, 2001Go; Naaby-Hansen et al., 2001Go; Westbrook et al., 2001Go; Ho and Suarez, 2003Go). The RNE extends from the sperm head into the cytoplasmic droplet surrounding the anterior midpiece (Zamboni et al., 1971Go). Small, osmotically sensitive cytoplasmic droplets are observable in the majority of motile human spermatozoa and are not the large structures observed in air-dried smears which are characteristic of abnormal cells (Cooper et al., 2004)Go. The mechanism by which [Ca2+]i oscillations are generated is most unusual. Though type 3 IP3 receptors have been detected in the neck region of human spermatozoa (Kuroda et al., 1999Go; Naaby-Hansen et al., 2001)Go, Ca2+ mobilization during progesterone-induced [Ca2+]i oscillations is not sensitive to blockade of phospholipase C or of IP3 receptors. Instead, mobilization of Ca2+ is apparently dependent on Ca2+-induced Ca2+ release (CICR) in response to progesterone-induced Ca2+ influx (Harper et al., 2004Go). Consistent with such a mechanism of activation, the frequency of oscillations does not reflect progesterone dose, the agonist acting only as an ‘on’ switch. In fact, withdrawal of progesterone after activation often fails to halt the generation of [Ca2+]i oscillations. Compounds that act at ryanodine receptors (RyRs) regulate the frequency of oscillations, and staining with BODIPY-ryanodine localizes to the sperm neck area (Harper et al., 2004Go). However, the existence of RyRs in sperm is controversial. Trevino et al. (1998)Go detected expression of both RyR1 and RyR3 in mouse spermatogenic cells, RyR3 also being present in mature cells. Other authors reported no detection of RyRs in mouse and bull spermatozoa (Ho and Suarez, 2001Go; Chiarella et al., 2004Go). It is thus possible that CICR in sperm occurs via a RyR-like protein that is not one of the RyRs characterized in somatic cells. The store that is mobilized during [Ca2+]i oscillations does not use sarcoplasmic endoplasmic reticulum Ca2+ ATPases (SERCAs) for Ca2+ uptake but is dependent, at least in part, on the secretory pathway Ca2+ ATPase SPCA1 (Harper et al., 2005Go). These features are strikingly different from those of the acrosomal Ca2+ store, which is mobilized primarily by IP3 and may use a SERCA-like pump for Ca2+ uptake (Rossatto et al., 2001; De Blas et al., 2002Go; Herrick et al., 2005)Go. Interestingly, the ability of cells to generate oscillations appears to develop during capacitation (Kirkman-Brown et al., 2004Go), suggesting that either the ryanodine-type receptor or the mechanism of store filling is subject to regulation as the cells mature.


    Role of progesterone-induced [Ca2+]i oscillations
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 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
The amplitude of progesterone-induced [Ca2+]i oscillations in human spermatozoa is typically similar to that of the 3 µmol/l progesterone transient (although the kinetics are clearly different; Harper et al., 2004Go). Since oscillations persist for at least 40 min (with a frequency of up to 4/min, Harper et al., 2004Go), we expected to see a high frequency of AR in these cells. Surprisingly, the rate of AR in cells that generated oscillations was no higher, and possibly lower, than in cells that failed to oscillate. However, observation of cells in which progesterone-induced [Ca2+]i oscillations were occurring showed that the mode of flagellar beating alternates in synchrony with [Ca2+]i (Figure 1). A low-amplitude beat [that will generate a forward (axial)] force occurs during the oscillation trough, and a much more marked lateral excursion, including bending of the proximal flagellum (which will cause lateral movement of the sperm head) occurs during the oscillation peak. We consider it likely that this confers an advantage to those cells which generate [Ca2+]i oscillations, because alternation between ‘cutting’ and ‘thrusting’ movements of the sperm head will improve zona penetration by avoiding the problem of compaction caused by continuous axial force generation (Bedford, 1998Go; Figure 2). Future studies must address not only the occurrence and effect of this phenomenon in free-swimming cells and in cells penetrating the egg vestments, but also the interaction of mobilization of stored Ca2+ with Ca2+ influx mediated by the recently discovered, sperm-specific Catsper channels. Catspers, which are essential for activation of hyperactivated mobility, are depolarization-activated cation channels, possibly subject to facilitation by cAMP, which are expressed specifically in the principal piece of the sperm tail (Ren et al., 2001Go; Quill et al., 2001Go; Carlson et al., 2003)Go. Some level of regulation of these channels by mobilization of stored Ca2+ is an intriguing possibility.



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Figure 1. Example of a cell in which treatment with a logarithmic gradient of progesterone (0–3 µmol/l over 20 min, shown by a bar above the trace) caused [Ca2+]i oscillations and alternation of flagellar beat mode. Cells were loaded with Oregon Green BAPTA-1 to report [Ca2+]i, and fluorescence was monitored at intervals of 10 s. The intensity has been normalized to the pre-stimulation level and is expressed as percentage change. After 30 min fluorescence, imaging was stopped, the cells were observed under phase contrast and a second series of images was collected at 500 ms intervals. The flagellar position in each frame was recorded using a scale (normal to the axis of the sperm) superimposed on the image and used to provide a semi-quantitative measurement of lateral excursion (see Harper et al., 2004Go for details). Examination of the images showed that high values were representative of flagellar excursion and bending of the proximal flagellum.

 


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Figure 2. Tentative model summarizing the proposed role of progesterone in events preceding gamete fusion. The graded blue background indicates increasing progesterone concentration on approach to the oocyte. Red ‘paths’ show cells which progress and are potential fertilizers; blue, broken paths indicate events which probably only occur in vitro; black paths show cells which are abnormal/non-motile, are removed from the population of potential fertilizers or are poorly competitive. At each stage, a number of those cells that would be assessed as ‘normal’ are lost by premature acrosome reaction (AR). During capacitation, this occurs spontaneously. Upon approaching the oocyte, the ramped [Ca2+]i response occurs, leading to activation of the Ca2+ store in the sperm neck and regulation of motility. A proportion of cells undergo the AR because inadequate [Ca2+]i homeostasis leads to spill-over of the progesterone signal, potentially a mechanism for removal of poor quality cells. The possibility of occurrence of biphasic responses in vivo is shown (though this is considered unlikely). During penetration of the cumulus, cells generating alternating cut and thrust movements due to [Ca2+]i oscillations are at an advantage and reach the zona more rapidly (shown by heavier arrows). Upon AR, the combination of enzyme activity and alternating motility pattern permits penetration of the zona, whereas cells generating uniform flagellar movement are less well able to penetrate the zona.

 


    Compartmentalized [Ca2+]I signalling in human spermatozoa
 Top
 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
We consider that it is most unlikely that the function in vivo of the well-characterized progesterone sensitivity of human spermatozoa is to activate the AR (though action to prime sensitivity of the response to progesterone in mouse and human sperm clearly does occur; Roldan et al., 1994Go; Schuffner et al., 2002Go). Instead, we propose that the primary role of progesterone is to activate the endogenous [Ca2+]i oscillator which is positioned behind the nucleus and which acts as a ‘throttle’, regulating activity of the flagellum. Separation of two Ca2+-regulated processes, induction of AR and regulation of flagellar beat, in a minute cell requires strict spatial organization. This is apparently achieved by the existence of two Ca2+ stores, with distinct functions and with separate regulatory mechanisms. AR requires emptying of the acrosomal store (De Blas et al., 2002; Herrick et al., 2005)Go. This store probably responds to IP3 generated in response to zona binding (Roldan et al., 1994Go; Walensky and Snyder, 1995Go; O’Toole et al., 2000Go; Evans and Florman, 2002Go). Type 1 IP3 receptors are localized primarily to the outer acrosomal membrane of human spermatozoa (Kuroda et al., 1999Go) so will empty into the small cytoplasmic compartment between the outer acrosomal membrane and the plasmalemma (Figure 3). The second Ca2+ store in the sperm neck region (probably the RNE) empties into the rear of the sperm head and midpiece (Figure 3) and regulates flagellar beat mode. A role for the RNE in regulation of hyperactivation of bovine spermatozoa has already been proposed (Ho and Suarez, 2001Go, 2003Go). This store is mobilized by CICR and thus, although apparently not co-localized with progesterone-binding sites (see above), will respond to the modest rise in sperm [Ca2+]i that occurs as the cell ascends the progesterone gradient around the oocyte (Harper et al., 2004Go). Studies on the spread of Ca2+ from an apparently localized source suggest that true isolation of subcellular compartments is not achieved within the head of mammalian spermatozoa (Meizel et al., 1997Go; Fukami et al., 2003Go). However, the restricted communication between compartments (due to the close association between plasma and organelle membranes) in combination with effective Ca2+ buffering, particularly in the cytoplasmic compartment between the outer acrosomal membrane and the plasmalemma, should significantly ‘blunt’ the signal as it spreads, leading to functional separation. This is consistent with the observations of Suarez and Dai (1995)Go that, in hamster sperm, [Ca2+]i in the head and in the midpiece showed independence. Strikingly, levels in the head were higher in acrosome-reacted sperm but the converse was true in hyperactivated cells. The ability of progesterone to induce the AR is, we consider, a result of unsuccessful Ca2+ buffering permitting excessive signal spill-over between the two Ca2+ signalling processes. In this context, it is noteworthy that stimulation of human spermatozoa with 3 µmol/l progesterone has been shown to stimulate generation of IP3, an effect that is dependent on Ca2+ influx and has kinetics similar to those of the [Ca2+]i transient that occurs in response to this stimulus (Thomas and Meizel, 1989Go). Activation of phospholipase C in response to progesterone may be, in part, a function of the cell’s ability to regulate [Ca2+]i and may thus serve to remove poor quality cells by acting on the acrosomal store to permit premature AR (Figure 2).



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Figure 3. Compartmentalized [Ca2+]i signalling in human spermatozoa. Two separate stores are shown. The acrosome (purple) releases Ca2+ (shown by pseudo-colouring) into the space between the outer acrosomal membrane and the plasmalemma in response to IP3 (purple arrow) generated upon activation of zona receptors (purple box). Mobilization of this store leads to the acrosome reaction. Putative progesterone receptors (blue box) situated equatorially (and possibly over the acrosome) permit Ca2+ influx as the sperm acends the progesterone gradient around the oocyte, leading to a slow, ramped rise in [Ca2+]i (see Figure 1). A store in the sperm neck (blue), probably the redundant nuclear envelope (RNE; Naaby-Hansen et al., 2001Go; Ho and Suarez, 2001Go; Westbrook et al., 2001Go; Ho and Suarez, 2003Go), releases Ca2+ upon activation of ryanodine (-like) receptors by Ca2+-induced Ca2+ release (CICR; shown by a dashed blue arrow) in response to this elevation of [Ca2+]i. Mobilization of this store into the sperm neck and midpiece regulates flagellar beat (Ho and Suarez, 2001Go, 2003Go), providing the signal that leads to the alternating cut and thrust motility that facilitates penetration of the cumulus and zona (Bedford, 1998Go).

 


    References
 Top
 Abstract
 Sperm responses to oocyte...
 Effect of progesterone on...
 Response of human spermatozoa...
 Generation of [Ca2+]i...
 Role of progesterone-induced...
 Compartmentalized [Ca2+]I...
 References
 
Aitken RJ, Buckingham DW and Irvine DS (1996) The extragenomic action of progesterone on human spermatozoa: evidence for a ubiquitous response that is rapidly down-regulated. Endocrinology 137,3999–4009.[Abstract]

Baldi E, Casano R, Falsetti C, Krausz C, Maggi M and Forti G (1991) Intracellular calcium accumulation and responsiveness to progesterone in capacitating human spermatozoa. J Androl 12,323–330.[Abstract/Free Full Text]

Bedford JM (1998) Mammalian fertilization misread? Sperm penetration of the eutherian zona pellucida is unlikely to be a lytic event. Biol Reprod 59,1275–1287.[Free Full Text]

Blackmore PF (1999) Extragenomic actions of progesterone in human sperm and progesterone metabolites in human platelets. Steroids 64,149–156.

Blackmore PF and Eisoldt S (1999) The neoglycoprotein mannose–bovine serum albumin, but not progesterone, activates T-type calcium channels in human spermatozoa. Mol Hum Reprod 5,498–506.[Abstract/Free Full Text]

Blackmore PF, Beebe SJ, Danforth DR and Alexander N (1990) Progesterone and 17 alpha-hydroxyprogesterone. Novel stimulators of calcium influx in human sperm. J Biol Chem 265,1376–1380.[Abstract/Free Full Text]

Buddhikot M, Falkenstein E, Wehling M and Meizel S (1999) Recognition of a human sperm surface protein involved in the progesterone-initiated acrosome reaction by antisera against an endomembrane progesterone binding protein from porcine liver. Mol Cell Endocrinol 158,187–193.[CrossRef][ISI][Medline]

Chiarella P, Puglisi R, Sorrentino V, Boitani C and Stefanini M (2004) Ryanodine receptors are expressed and functionally active in mouse spermatogenic cells and their inhibition interferes with spermatogonial differentiation. J Cell Sci 117,4127–4134.[Abstract/Free Full Text]

Carlson AE, Westenbroek RE, Quill T, Ren D, Clapham DE, Hille B, Garbers DL and Babcock DF (2003) CatSper1 required for evoked Ca2+ entry and control of flagellar function in sperm. Proc Natl Acad Sci USA 100,14864–14868.[Abstract/Free Full Text]

Cooper TG, Yeung CH, Fetic S, Sobhani A and Nieschlag E (2004) Cytoplasmic droplets are normal structures of human sperm but are not well preserved by routine procedures for assessing sperm morphology. Hum Reprod 19,2283–2288.[Abstract/Free Full Text]

De Blas G, Michaut M, Trevino CL, Tomes CN, Yunes R, Darszon A and Mayorga LS (2002) The intraacrosomal calcium pool plays a direct role in acrosomal exocytosis. J Biol Chem 277,49326–49331.[Abstract/Free Full Text]

Edwards DP (2005) Regulation of signal transduction pathways by estrogen and progesterone. Annu Rev Physiol 67, 335–376.[CrossRef][ISI][Medline]

Evans JP and Florman HM (2002) The state of the union: the cell biology of fertilization. Nat Med Suppl S57–S63.

Falkenstein E, Heck M, Gerdes D, Grube D, Christ M, Weigel M, Buddhikot M, Meizel S and Wehling M (1999) Specific progesterone binding to a membrane protein and related nongenomic effects on Ca2+-fluxes in sperm. Endocrinology 140,5999–6002.

Florman HM, Tombes RM, First NL and Babcock DF (1989) An adhesion-associated agonist from the zona pellucida activates G protein-promoted elevations of internal Ca2+ and pH that mediate mammalian sperm acrosomal exocytosis. Dev Biol 135,133–146.[CrossRef][ISI][Medline]

Foresta C, Rossato M and Di Virgilio F (1993) Ion fluxes through the progesterone-activated channel of the sperm plasma membrane. Biochem J 294,279–283.[ISI][Medline]

Forti G, Baldi E, Krausz C, Luconi M, Bonaccorsi L, Maggi M, Bassi F and Scarselli G (1999) Effects of progesterone on human spermatozoa: clinical implications. Ann Endocrinol (Paris) 60,107–110.[ISI][Medline]

Fraire-Zamora JJ and Gonzalez-Martinez MT (2004) Effect of intracellular pH on depolarization-evoked calcium influx in human sperm. Am J Physiol 287, C1688–C1696.[CrossRef][ISI]

Fukami K, Yoshida M, Inoue T, Kurokawa M, Fissore RA, Yoshida N, Mikoshiba K and Takenawa T (2003) Phospholipase Cdelta4 is required for Ca2+ mobilization essential for acrosome reaction in sperm. J Cell Biol 161,79–88.[Abstract/Free Full Text]

Gadkar S, Shah CA, Sachdeva G, Samant U and Puri CP (2002) Progesterone receptor as an indicator of sperm function. Biol Reprod 67,1327–1336.[Abstract/Free Full Text]

Garcia MA and Meizel S (1999) Progesterone-mediated calcium influx and acrosome reaction of human spermatozoa: pharmacological investigation of T-type calcium channels. Biol Reprod 60,102–109.[Abstract/Free Full Text]

Giojalas LC, Iribarren P, Molina R, Rovasio RA and Estofan D (2004) Determination of human sperm calcium uptake mediated by progesterone may be useful for evaluating unexplained sterility. Fertil Steril 82,738–740.[CrossRef][ISI][Medline]

Harper CV, Kirkman-Brown JC, Barratt CL and Publicover SJ (2003) Encoding of progesterone stimulus intensity by intracellular [Ca2+] ([Ca2+]i) in human spermatozoa. Biochem J 372,407–417.[CrossRef][ISI][Medline]

Harper CV, Barratt CL and Publicover SJ (2004) Stimulation of human spermatozoa with progesterone gradients to simulate approach to the oocyte. Induction of [Ca2+]i oscillations and cyclical transitions in flagellar beating. J Biol Chem 279,46315–46325.[Abstract/Free Full Text]

Harper, C, Wootton, L, Michelangeli, F, Lefièvre, L, Barratt, C and Publicover, S (2005) Secretory pathway Ca2+-ATPase (SPCA1) Ca2+ pumps, not SERCAs, regulate complex [Ca2+]i signals in human spermatozoa. J Cell Sci 118,1673–1685.[Abstract/Free Full Text]

Herrick SB, Schweissinger DL, Kim SW, Bayan KR, Mann S and Cardullo RA (2005) The acrosomal vesicle of mouse sperm is a calcium store. J Cell Physiol 202,663–67[CrossRef][ISI][Medline]

Ho HC and Suarez SS (2001) An inositol 1,4,5-trisphosphate receptor-gated intracellular Ca2+ store is involved in regulating sperm hyperactivated motility. Biol Reprod 65,1606–1615.[Abstract/Free Full Text]

Ho HC and Suarez SS (2003) Characterization of the intracellular calcium store at the base of the sperm flagellum that regulates hyperactivated motility. Biol Reprod 68,1590–1596.[Abstract/Free Full Text]

Huo YW, Qiu SD, Xu YJ, Cheng SL, Wu J, Wang LR and Ge L (2002) Investigation of progesterone receptor on human sperm plasma membrane. Zhonghua Nan Ke Xue 8,277–280.[Medline]

Jaiswal BS, Tur-Kaspa I, Dor J, Mashiach S and Eisenbach M (1999) Human sperm chemotaxis: is progesterone a chemoattractant? Biol Reprod 60,1314–1319.[Abstract/Free Full Text]

Jeon BG, Moon JS, Kim KC, Lee HJ, Choe SY and Rho GJ (2001) Follicular fluid enhances sperm attraction and its motility in human. J Assist Reprod Genet 18,407–412.[CrossRef][ISI][Medline]

Kirkman-Brown JC, Bray C, Stewart PM, Barratt CL and Publicover SJ (2000) Biphasic elevation of [Ca2+]i in individual human spermatozoa exposed to progesterone. Dev Biol 222,326–335.[CrossRef][ISI][Medline]

Kirkman-Brown JC, Barratt CL, and Publicover SJ (2003) Nifedipine reveals the existence of two discrete components of the progesterone-induced [Ca2+]i transient in human spermatozoa. Dev Biol 259,71–82[CrossRef][ISI][Medline]

Kirkman-Brown JC, Barratt CL and Publicover SJ (2004) Slow calcium oscillations in human spermatozoa. Biochem J 378,827–832.[CrossRef][ISI][Medline]

Krausz C, Bonaccorsi L, Maggio P, Luconi M, Criscuoli L, Fuzzi B, Pellegrini S, Forti G and Baldi E (1996) Two functional assays of sperm responsiveness to progesterone and their predictive values in in-vitro fertilization. Hum Reprod 11,1661–1667.[Abstract]

Kumar S, Ying YK, Hong P and Maddaiah VT (2000) Potassium increases intracellular calcium simulating progesterone action in human sperm. Arch Androl 44,93–101.[CrossRef][ISI][Medline]

Kuroda Y, Kaneko S, Yoshimura Y, Nozawa S and Mikoshiba K (1999) Are there inositol 1,4,5-triphosphate (IP3) receptors in human sperm? Life Sci 65,135–143.[CrossRef][ISI][Medline]

Losel R, Dorn-Beineke A, Falkenstein E, Wehling M and Feuring M (2004) Porcine spermatozoa contain more than one membrane progesterone receptor. Int J Biochem Cell Biol 36,1532–1541.[CrossRef][ISI][Medline]

Luconi M, Bonaccorsi L, Maggi M, Pecchioli P, Krausz C, Forti G and Baldi E. (1998) Identification and characterization of functional nongenomic progesterone receptors on human sperm membrane. J Clin Endocrinol Metab. 83,877–885.[Abstract/Free Full Text]

Luconi M, Bonaccorsi L, Bini L, Liberatori S, Pallini V, Forti G and Baldi E (2002) Characterization of membrane nongenomic receptors for progesterone in human spermatozoa. Steroids 67,505–509.[CrossRef][ISI][Medline]

Meizel S and Turner KO (1991) Progesterone acts at the plasma membrane of human sperm. Mol Cell Endocrinol 77, R1–R5.[CrossRef][ISI][Medline]

Meizel S, Turner KO and Nuccitelli R (1997) Progesterone triggers a wave of increased free calcium during the human sperm acrosome reaction. Dev Biol 182,67–75.[CrossRef][ISI][Medline]

Naaby-Hansen S, Wolkowicz MJ, Klotz K, Bush LA, Westbrook VA, Shibahara H, Shetty J, Coonrod SA, Reddi PP, Shannon J et al. (2001) Co-localization of the inositol 1,4,5-trisphosphate receptor and calreticulin in the equatorial segment and in membrane bounded vesicles in the cytoplasmic droplet of human spermatozoa. Mol Hum Reprod 7,923–933.[Abstract/Free Full Text]

Osman RA, Andria ML, Jones AD and Meizel S (1989) Steroid induced exocytosis: the human sperm acrosome reaction. Biochem Biophys Res Commun 160,828–833.[CrossRef][ISI][Medline]

O’Toole CM, Arnoult C, Darszon A, Steinhardt RA and Florman HM (2000) Ca(2+) entry through store-operated channels in mouse sperm is initiated by egg ZP3 and drives the acrosome reaction. Mol Biol Cell 11,1571–1584.[Abstract/Free Full Text]

Plant A, McLaughlin EA and Ford WC (1995) Intracellular calcium measurements in individual human sperm demonstrate that the majority can respond to progesterone. Fertil Steril 64,1213–1215.[ISI][Medline]

Quill TA, Ren D, Clapham DE and Garbers DL (2001) A voltage-gated ion channel expressed specifically in spermatozoa. Proc Natl Acad Sci USA 98,12527–12531.[Abstract/Free Full Text]

Ralt D, Goldenberg M, Fetterolf P, Thompson D, Dor J, Mashiach S, Garbers DL and Eisenbach M (1991) Sperm attraction to a follicular factor(s) correlates with human egg fertilizability. Proc Natl Acad Sci USA 88,2840–2844.[Abstract/Free Full Text]

Ralt D, Manor M, Cohen-Dayag A, Tur-Kaspa I, Ben-Shlomo I, Makler A, Yuli I, Dor J, Blumberg S, Mashiach S and Eisenbach M (1994) Chemotaxis and chemokinesis of human spermatozoa to follicular factors. Biol Reprod 150,774–785.

Ren D, Navarro B, Perez G, Jackson AC, Hsu S, Shi Q, Tilly JL and Clapham DE (2001) A sperm ion channel required for sperm motility and male fertility. Nature 413,603–609.[CrossRef][ISI][Medline]

Roldan ERS, Murase T and Shi Q-X (1994) Exocytosis in spermatozoa in response to progesterone and zona pellucida. Science 266,1578–1581.[ISI][Medline]

Rossato M, Di Virgilio F, Rizzuto R, Galeazzi C and Foresta C (2001) Intracellular calcium store depletion and acrosome reaction in human spermatozoa: role of calcium and plasma membrane potential. Mol Hum Reprod 7,119–128.[Abstract/Free Full Text]

Sabeur K, Edwards DP and Meizel S (1996) Human sperm plasma membrane progesterone receptor(s) and the acrosome reaction. Biol Reprod 54,993–1001.[Abstract]

Schaefer M, Habenicht UF, Brautigam M and Gudermann T (2000) Steroidal sigma receptor ligands affect signaling pathways in human spermatozoa. Biol Reprod 63,57–63.[Abstract/Free Full Text]

Schuffner AA, Bastiaan HS, Duran HE, Lin ZY, Morshedi M, Franken DR and Oehninger S (2002) Zona pellucida-induced acrosome reaction in human sperm: dependency on activation of pertussis toxin-sensitive G(i) protein and extracellular calcium, and priming effect of progesterone and follicular fluid. Mol Hum Reprod 8,722–727.[Abstract/Free Full Text]

Shah C, Modi D, Sachdeva G, Gadkar S and Puri C (2005) Coexistence of intracellular and membrane-bound progesterone receptors in human testis. J Clin Endocrinol Metab 90,474–483.[Abstract/Free Full Text]

Spehr M, Gisselmann G, Poplawski A, Riffell JA, Wetzel CH, Zimmer RK and Hatt H (2003) Identification of a testicular odorant receptor mediating human sperm chemotaxis. Science 299,2054–2058.[Abstract/Free Full Text]

Spehr M, Schwane K, Riffell JA, Barbour J, Zimmer RK, Neuhaus EM and Hatt H (2004) Particulate adenylate cyclase plays a key role in human sperm olfactory receptor-mediated chemotaxis. J Biol Chem 279,40194–40203.[Abstract/Free Full Text]

Suarez SS and Dai X (1995) Intracellular calcium reaches different levels of elevation in hyperactivated and acrosome-reacted hamster sperm. Mol Reprod Dev 42,325–333.[CrossRef][ISI][Medline]

Sun F, Bahat A, Gakamsky A, Girsh E, Katz N, Giojalas LC, Tur-Kaspa I and Eisenbach M (2005) Human sperm chemotaxis: both the oocyte and its surrounding cumulus cells secrete sperm chemoattractants. Hum Reprod 20,761–767.[Abstract/Free Full Text]

Tanghe S, Van Soom A, Nauwynck H, Coryn M and de Kruif A (2002) Minireview: functions of the cumulus oophorus during oocyte maturation, ovulation, and fertilization. Mol Reprod Dev 61,414–424.[CrossRef][ISI][Medline]

Tesarik J, Carreras A and Mendoza C (1996) Single cell analysis of tyrosine kinase dependent and independent Ca2+ fluxes in progesterone induced acrosome reaction. Mol Hum Reprod 2,225–232.[Abstract]

Thomas P and Meizel S (1989) Phosphatidylinositol 4,5-bisphosphate hydrolysis in human sperm stimulated with follicular fluid or progesterone is dependent upon Ca2+ influx. Biochem J 264,539–546.[ISI][Medline]

Trevino CL, Santi CM, Beltran C, Hernandez-Cruz A, Darszon A and Lomeli H (1998) Localisation of inositol trisphosphate and ryanodine receptors during mouse spermatogenesis: possible functional implications. Zygote 6,159–172.[CrossRef][ISI][Medline]

Vadillo Ortega F, Villanueva Diaz C, Arias Martinez QB, Bermejo L and Bustos Lopez H (2001) Chemotactic factor for spermatozoa: a new biological function of progesterone. Ginecol Obstet Mex 62,127–130.

Van Soom A, Tanghe S, De Pauw I, Maes D and de Kruif A (2002) Function of the cumulus oophorus before and during mammalian fertilization. Reprod Domest Anim. 37,144–151.[CrossRef][ISI][Medline]

Villanueva-Diaz C, Arias-Martinez J, Bermejo-Martinez L and Vadillo-Ortega F (1995) Progesterone induces human sperm chemotaxis. Fertil Steril 64,1183–1188.[ISI][Medline]

Walensky LD and Snyder SH (1995) Inositol 1,4,5-trisphosphate receptors selectively localized to the acrosomes of mammalian sperm. J Cell Biol 130,857–869.[Abstract]

Wang Y, Storeng R, Dale PO, Abyholm T and Tanbo T (2001) Effects of follicular fluid and steroid hormones on chemotaxis and motility of human spermatozoa in vitro. Gynecol Endocrinol 15,286–292.[ISI][Medline]

Westbrook VA, Diekman AB, Naaby-Hansen S, Coonrod SA, Klotz KL, Thomas TS, Norton EJ, Flickinger CJ and Herr JC (2001) Differential nuclear localization of the cancer/testis-associated protein, SPAN-X/CTp11, in transfected cells and in 50% of human spermatozoa. Biol Reprod 64,345–358.[Abstract/Free Full Text]

Wood CD, Darszon A and Whitaker M (2003) Speract induces calcium oscillations in the sperm tail. J Cell Biol 161,89–101.[Abstract/Free Full Text]

Yang J, Serres C, Philibert D, Robel P, Baulieu EE and Jouannet P (1994) Progesterone and RU486: opposing effects on human sperm. Proc Natl Acad Sci USA 91,529–533.[Abstract/Free Full Text]

Zamboni L, Zemjanis R and Stefanini M (1971) The fine structure of monkey and human spermatozoa. Anat Rec 169,129–154.[CrossRef][ISI][Medline]

Submitted on March 24, 2005; resubmitted on April 29, 2005; accepted on May 24, 2005.





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