Purification of GP-83, a glycoprotein secreted by the human epididymis and conjugated to mature spermatozoa.
(33/514)
Epididymal secretions are critical for mammalian spermatozoa to acquire both forward motility and an ability to recognize and penetrate oocytes. Previous studies identified two glycoproteins, GP-83 and GP-39, which were secreted by the human epididymis and may be related to maturation of sperm function. In this study, GP-83 was purified from human seminal fluid by DEAE-ion exchange, gel filtration chromatography and preparative gel elution. The isoelectric point (pI) of purified GP-83 was 6.57. Monospecific antiserum to GP-83 was induced in male New Zealand rabbits and confirmed on immunoblots. GP-83 was found in fluid, tissue and sperm extracts of corpus and cauda epididymis, but not in the caput. Immunohistochemical localization identified GP-83 in the luminal contents and in the supranuclear region and cell membrane of principal cells of the corpus and cauda epididymis. GP-83 was found on the anterior acrosome in ejaculated spermatozoa, and shifted to the equatorial region after capacitation and the acrosome reaction. (+info)
Sperm function assays and their predictive value for fertilization outcome in IVF therapy: a meta-analysis.
(34/514)
The prevalence of male infertility and the availability of new, highly successful therapeutic options make the testing of sperm functional competence mandatory. An objective, outcome-based examination of the validity of the currently available assays was performed based upon the results obtained from 2906 subjects evaluated in 34 prospectively designed, controlled studies. The aim was carried out through a meta-analytical approach that examined the predictive value of four categories of sperm functional assays: computer-aided sperm motion analysis (CASA); induced-acrosome reaction testing; sperm penetration assay (SPA); and sperm-zona pellucida binding assays for IVF outcome. Results demonstrated a high predictive power of the sperm-zona pellucida binding and the induced-acrosome reaction assays for fertilization outcome. On the other hand, the findings indicated a poor clinical value of the SPA as predictor of fertilization and a real need for standardization and further investigation of the potential clinical utility of CASA systems. This analysis points out to limitations of the current tests and the need for standardization of methodologies and provides objective evidence on which clinical management and future research can be based. (+info)
Enhancement of zona binding using 2-hydroxypropyl- beta-cyclodextrin.
(35/514)
Since membrane cholesterol depletion is known to play an important role in sperm capacitation, we have investigated the effect of 2-hydroxypropyl-beta-cyclodextrin, a cyclic oligosaccharide that mediates cholesterol efflux, on sperm functions. Sperm treatment with cyclodextrin did not affect the motility patterns but induced an increase in sperm binding to zona pellucida (24 +/- 5 versus 13 +/- 4 in control, P < 0.01). Cyclodextrin treatment was associated with an increase in spontaneous acrosome reaction (32 +/- 8% versus 22 +/- 4% in controls after a 4 h incubation, P < 0.05; 61 +/- 10% versus 50 +/- 11% in controls after a 24 h incubation, NS) but with a decrease in acrosome response to ionophore challenge (44 +/- 5% versus 51 +/- 3% in controls, P < 0.05). Concerning cell sterols, cyclodextrin induced a rapid and dramatic fall in the cholesterol and desmosterol content of spermatozoa. We conclude that cyclodextrin is a powerful capacitating agent, but since it induces an increase in spontaneous acrosome loss, it needs to be further evaluated before routine use in assisted reproductive technology media. (+info)
Ca(2+) entry through store-operated channels in mouse sperm is initiated by egg ZP3 and drives the acrosome reaction.
(36/514)
Fertilization occurs after the completion of the sperm acrosome reaction, a secretory event that is triggered during gamete adhesion. ZP3, an egg zona pellucida glycoprotein, produces a sustained increase of the internal Ca(2+) concentration in mouse sperm, leading to acrosome reactions. Here we show that the sustained Ca(2+) concentration increase is due to the persistent activation of a Ca(2+) influx mechanism during the late stages of ZP3 signal transduction. These cells also possess a Ca(2+) store depletion-activated Ca(2+) entry pathway that is open after treatment with thapsigargin. Thapsigargin and ZP3 activate the same Ca(2+) permeation mechanism, as demonstrated by fluorescence quenching experiments and by channel antagonists. These studies show that ZP3 generates a sustained Ca(2+) influx through a store depletion-operated pathway and that this drives the exocytotic acrosome reaction. (+info)
Stimulation of Ca(2+)-dependent exocytosis of the sperm acrosome by cAMP acting downstream of phospholipase A2.
(37/514)
Spermatozoa undergo exocytosis in response to agonists that induce Ca2+ influx and, in turn, activation of phosphoinositidase C, phospholipase C, phospholipase A2, and cAMP formation. Since the role of cAMP downstream of Ca2+ influx is unknown, this study investigated whether cAMP modulates phospholipase C or phospholipase A2 using a ram sperm model stimulated with A23187 and Ca2+. Exposure to dibutyryl-cAMP, phosphodiesterase inhibitors or forskolin resulted in enhancement of exocytosis. However, the effect was not due to stimulation of phospholipase C or phospholipase A2: in spermatozoa prelabelled with [3H]palmitic acid or [14C]arachidonic acid, these reagents did not enhance [3H]diacylglycerol formation or [14C]arachidonic acid release. Spermatozoa were treated with the phospholipase A2 inhibitor aristolochic acid, and dibutyryl-cAMP to test whether cAMP acts downstream of phospholipase A2. Under these conditions, exocytosis did not occur in response to A23187 and Ca2+. However, inclusion of dibutyryl-cAMP and the phospholipase A2 metabolite lysophosphatidylcholine did result in exocytosis (at an extent similar to that seen when cells were treated with A23187/Ca2+ and without the inhibitor). Inclusion of lysophosphatidylcholine alone, without dibutyryl-cAMP, enhanced exocytosis to a lesser extent, demonstrating that cAMP requires a phospholipase A2 metabolite to stimulate the final stages of exocytosis. These results indicate that cAMP may act downstream of phospholipase A2, exerting a regulatory role in the exocytosis triggered by physiological agonists. (+info)
Biphasic elevation of [Ca(2+)](i) in individual human spermatozoa exposed to progesterone.
(38/514)
Fluorimetric studies on progesterone-induced [Ca(2+)](i) signalling in mammalian spermatozoa show both the well-characterised [Ca(2+)](i) transient and a subsequent sustained phase. However, the sustained phase is thought to reflect release of the fluorochrome during the acrosome reaction and has not been subject to critical investigation. We have used single-cell imaging of [Ca(2+)](i) to analyse the progesterone-induced [Ca(2+)](i) response in large numbers (>2000) of capacitated, human spermatozoa. In 70% of cells, treatment with progesterone induced a transient increase, which typically peaked within 1 min and decayed with a similar time course. Upon rapid application of progesterone this response peaked within 5-20 s. In 35% of progesterone-treated spermatozoa a sustained elevation of [Ca(2+)](i) occurred, which became discernible during the falling phase of the transient response and persisted for at least 20 min. Both [Ca(2+)](i) responses were localised to the postacrosomal region. Averaging of large numbers of single cell responses generated traces similar to those seen in fluorimetric studies. Although the sustained response was strongly associated with the initial, transient response, a few spermatozoa generated sustained responses that were not preceded by a significant transient response (5% of cells). It is concluded that a genuine biphasic [Ca(2+)](i) signal is activated by progesterone and that the sustained response is a discrete signalling event with biological significance. (+info)
Steroidal sigma receptor ligands affect signaling pathways in human spermatozoa.
(39/514)
In human spermatozoa, Ca(2+) entry is stimulated by progesterone or prostaglandin E(1) (PGE(1)). The regulation of cation currents by progestins involves sigma receptors, and sigma binding sites are abundant in testis. We examined the effects of sigma ligands on human spermatozoa. Ca(2+) entry induced by progesterone or PGE(1) was not altered by the sigma ligands haloperidol and ditolylguanidine. However, the steroidal sigma ligands RU 3117 and RU 1968 had distinct effects. Stimulation by RU 3117 resulted in activation and homologous desensitization of the sperm progesterone receptor but not of the PGE(1) receptor. Because haloperidol and ditolylguanidine did not affect RU 3117 and progesterone actions in spermatozoa, we conclude that sigma receptors are not involved. However, RU 1968 potently inhibited both the progesterone- and PGE(1)-induced Ca(2+) entry and acrosome reaction. At higher concentrations, RU 1968 also inhibited hormonal Ca(2+) signaling in fibroblasts. Despite suppression of Ca(2+) mobilization, inhibition of phospholipase C by RU 1968 was not observed. Furthermore, RU 1968 did not impair the binding of inositol-1,4,5-trisphosphate to its endoplasmic reticulum receptor. Because RU 1968 preferentially inhibits signaling pathways in spermatozoa, the future development of more selective drugs structurally related to RU 1968 may be a novel approach for pharmacological contraception. (+info)
Vesicular traffic and golgi apparatus dynamics during mammalian spermatogenesis: implications for acrosome architecture.
(40/514)
Vesicular membrane trafficking during acrosome biogenesis in bull and rhesus monkey spermatogenesis differs from the somatic cell paradigm as imaged dynamically using the Golgi apparatus probes beta-COP, giantin, Golgin-97, and Golgin-95/GM130. In particular, sorting and delivery of proteins seemed less precise during spermatogenesis. In early stages of spermiogenesis, many Golgi resident proteins and specific acrosomal markers were present in the acrosome. Trafficking in both round and elongating spermatids was similar to what has been described for somatic cells, as judged by the kinetics of Golgi protein incorporation into endoplasmic reticulum-like structures after brefeldin A treatment. These Golgi components were retrieved from the acrosome at later stages of differentiation and were completely devoid of immature spermatozoa. Our data suggest that active anterograde and retrograde vesicular transport trafficking pathways, involving both beta-COP- and clathrin-coated vesicles, are involved in retrieving Golgi proteins missorted to the acrosome and in controlling the growth and shape of this organelle. (+info)