A perinuclear theca substructure is formed during epididymal guinea pig sperm maturation and disappears in acrosome reacted cells

Cryopreservation, in addition to protein tyrosine phosphorylation, alters the distribution of phosphatidyl inositol bisphosphate and the localization of cytoskeletal and signaling proteins (gelsolin, tyrosine kinase c-SRC and phospholipase C-ζ) in the perinuclear theca of boar sperm

Cryopreservation of boar spermatozoa affects the perinuclear theca (PT) and involves several proteins and molecules that play important roles during capacitation and the acrosomal reaction. The objective of the present study was to evaluate whether the deleterious effects of cryopreservation in addition to protein tyrosine phosphorylation are accompanied by changes in the distribution of phosphatidyl inositol bisphosphate (PIP2) and the localization of cytoskeletal and signaling proteins in the perinuclear theca of cryopreserved boar spermatozoa. For this purpose, by immunocytochemistry (IC) the changes in localization of phosphorylated proteins in tyrosine residues, gelsolin, c-SRC kinase and PLC-ζ, as well as in the distribution of phosphatidyl inositol bisphosphate were analyzed in thawed spermatozoa (T) non capacitated (NC), capacitated (C) and in those with acrosomal reaction (AR) and compared with fresh spermatozoa (F) under the same physiological status. Western blotting (WB) and co-immunoprecipitation were performed to confirm the presence of these proteins in PT and to determine the interaction between these molecules. IC showed that immunostaining for phosphorylated proteins significantly increased in the acrosomal region and flagellum in TNC spermatozoa (p < 0.05). The proportion of cells displaying immunolabeling for gelsolin in the acrosomal region decreased after capacitation in cryopreserved spermatozoa; the same change was found (p < 0.05) in the proportion of spermatozoa immunoreactive to PIP2 in the sperm head. c-SRC was observed in the equatorial segment and acrosomal region, subdomains that coincide with the site where phosphorylated proteins were detected. PLC-ζ immunolocalization in fresh spermatozoa underwent changes after capacitation and acrosomal reaction, with a significant increase in the equatorial segment and post-acrosomal region in cryopreserved spermatozoa (p < 0.05). WB analysis indicated the presence of gelsolin, c-SRC and PLC-ζ in PT; besides, we confirmed that gelsolin co-immunoprecipitated with c-SRC and PLC-ζ, which changes according to the physiological state of spermatozoa. As a conclusion, cryopreservation together with increased immunodetection of tyrosine phosphorylated proteins decreases the detection of PIP2 and alters the immunolocalization patterns of gelsolin, c-SRC and PLC-ζ in the PT in boar spermatozoa.

During capacitation in bull spermatozoa, actin and PLC-ζ undergo dynamic interactions

The migration pattern of sperm-specific phospholipase C-ζ (PLC-ζ) was followed and the role of this migration in actin cytoskeleton dynamics was determined. We investigated whether PLC-ζ exits sperm, opening the possibility that PLC-ζ is the 'spermatozoidal activator factor' (SOAF). As capacitation progresses, the highly dynamic actin cytoskeleton bound different proteins to regulate their location and activity. PLC-ζ participation at the start of fertilization was established. In non-capacitated spermatozoa, PLC-ζ is in the perinuclear theca (PT) and in the flagellum, therefore it was decided to determine whether bovine sperm actin interacts with PLC-ζ to direct its relocation as it progresses from non-capacitated (NC) to capacitated (C) and to acrosome-reacted (AR) spermatozoa. PLC-ζ interacted with actin in NC spermatozoa (100%), PLC-ζ levels decreased in C spermatozoa to 32% and in AR spermatozoa to 57% (P < 0.001). The level of actin/PLC-ζ interaction was twice as high in G-actin (P < 0.001) that reflected an increase in affinity. Upon reaching the AR spermatozoa, PLC-ζ was partially released from the cell. It was concluded that actin cytoskeleton dynamics control the migration of PLC-ζ during capacitation and leads to its partial release at AR spermatozoa. It is suggested that liberated PLC-ζ could reach the egg and favour fertilization.

Role of Wasp and the small GTPases RhoA, RhoB, and Cdc42 during capacitation and acrosome reaction in spermatozoa of English guinea pigs

Cytoskeleton remodeling is necessary for capacitation and the acrosome reaction in spermatozoa. F-actin is located in the acrosome and equatorial region during capacitation, but is relocated in the post-acrosomal region during the acrosome reaction in spermatozoa from bull, rat, mice, and guinea pig. Actin polymerization and relocalization are generally regulated by small GTPases that activate Wasp protein, which coordinates with Arp2/3, profilin I, and profilin II to complete cytoskeletal remodeling. This sequence of events is not completely described in spermatozoa, though. Therefore, the aim of this study was to determine if Wasp interacts with small GTPases (RhoA, RhoB, and Cdc42) and proteins (Arp2/3, profilin I, and profilin II) that co-localize with F-actin during capacitation and the acrosome reaction in English guinea pig spermatozoa obtained from the vas deferens. The spermatozoa were capacitated in calcium-free medium, incubated with an activator or an inhibitor of GTPases, and then induced to acrosome react using calcium. The distribution patterns of F-actin were compared to the patterns of Wasp and its putative interaction partners: Wasp and RhoB, but not RhoA or Cdc42, localization overlap with F-actin during capacitation and the acrosome reaction. Activation of small GTPases localized RhoB to the post-acrosomal region whereas their inhibition prevented acrosome exocytosis. Arp2/3 and profilin II appear to interact with Wasp in the post-acrosomal region and flagellum, while profilin I and Wasp could be found in the equatorial region. Thus, Wasp and F-actin distribution overlap during capacitation and acrosome reaction, and small GTPases play an important role in cytoskeleton remodeling during these processes in spermatozoa. Mol. Reprod. Dev. 83: 927-937, 2016 © 2016 Wiley Periodicals, Inc.

Glycerol decreases the integrity of the perinuclear theca in boar sperm

We evaluated the effect of glycerol on the perinuclear theca (PT) of boar sperm. Samples from six ejaculates obtained from three different boars were incubated in the detergent Brij 36-T. Spermatozoa were treated with a glycerol concentration of either 2 or 4%, and incubated for 10 or 30 min; two other samples were treated with protease inhibitors (PI; leupeptin or an inhibitor commercial cocktail), mixed with 4% glycerol, and incubated for 30 min. A third glycerol-free group was used as the control. The samples were processed for electron microscopy evaluation. The PT remained intact in 78% of the control samples while, after addition of glycerol for 30 min, the proportion of spermatozoa with disrupted or absent PT increased (P < 0.05). PT was preserved in PI samples, but PT changes increased (P < 0.05). Differences due to treatment with glycerol (2 or 4%) at 10 or 30 min were not observed. These results show, to our knowledge for the first time, the adverse effect of glycerol on the integrity of the PT.

Cytoskeletal proteins F-actin and β-dystrobrevin are altered by the cryopreservation process in bull sperm

The cryopreservation process has an important impact on sperm structure and physiology. The negative effects have been mainly observed on the plasma membrane, which is directly stabilized by the cytoskeleton. Since cytoskeleton proteins are osmosensitive and thermosensitive, the aim of this study was to evaluate the damage caused to the bull sperm cytoskeleton by cryopreservation (freezing-thawing). Fresh and frozen-thawed bull semen samples were exposed to a treatment with the neutral detergent Brij 36-T. Electron microscopy evidenced important damages at the sperm perinuclear theca after the protein extraction protocol; the perinuclear theca was partially solubilized, the perinuclear theca substructure disappeared in the cryopreserved samples. Furthermore, the sperm head's shape was significantly altered on the cryopreserved samples. Fluorescence analysis showed a decrease of the intensity of actin and dystrobrevin on the frozen-thawed samples. Western blot assays revealed a stronger signal for actin and β-dystrobrevin in the frozen-thawed sperm samples than in the fresh ones. Our results suggest that the cryopreservation process highly alters the sperm cytoskeleton stability, causing its proteins to become more fragile and therefore more susceptible to be extracted.

Selective diffusion barriers separate membrane compartments

We have investigated exchange of molecules between different membrane domains on a highly compartmentalized cell, the spermatozoon. Using Alexa Fluor 555-cholera toxin B-subunit we have observed clustering of preexisting GM1 gangliosides which diffused across the anterior acrosome-equatorial segment interface but did not access the postacrosome. By contrast, single lipid and protein molecules readily exchanged between all three domains, although they diffused more slowly on nearing and crossing to the postacrosome. Thus, two types of diffusion interfaces are present on sperm heads, an "open" interface and a "mass filter" interface. The latter seems to be due to a protein-cytoskeleton network.

Possible participation of calmodulin in the decondensation of nuclei isolated from guinea pig spermatozoa

The guinea pig spermatozoid nucleus contains actin, myosin, spectrin and cytokeratin. Also, it has been reported that phalloidin and/or 2,3-butanedione monoxime retard the sperm nuclear decondensation caused by heparin, suggesting a role for F-actin and myosin in nuclear stability. The presence of an F-actin/myosin dynamic system in these nuclei led us to search for proteins usually related to this system. In guinea pig sperm nuclei we detected calmodulin, F-actin, the myosin light chain and an actin-myosin complex. To define whether calmodulin participates in nuclear-dynamics, the effect of the calmodulin antagonists W5, W7 and calmidazolium was tested on the decondensation of nuclei promoted by either heparin or by a Xenopus laevis egg extract. All antagonists inhibited both the heparin- and the X. laevis egg extract-mediated nuclear decondensation. Heparin-mediated decondensation was faster and led to loss of nuclei. The X. laevis egg extract-promoted decondensation was slower and did not result in loss of the decondensed nuclei. It is suggested that in guinea pig sperm calmodulin participates in the nuclear decondensation process.

In guinea pig sperm, aldolase A forms a complex with actin, WAS, and Arp2/3 that plays a role in actin polymerization

Glycolytic enzymes have, in addition to their role in energy production, other functions in the regulation of cellular processes. Aldolase A has been reported to be present in sperm, playing a key role in glycolysis; however, despite its reported interactions with actin and WAS, little is known about a non-glycolytic role of aldolase A in sperm. Here, we show that in guinea pig spermatozoa, aldolase A is tightly associated to cytoskeletal structures where it interacts with actin, WAS, and Arp2/3. We show that aldolase A spermatozoa treatment increases their polymerized actin levels. In addition, we show that there is a direct correlation between the levels of polymerized actin and the levels of aldolase A-actin interaction. Our results suggest that aldolase A functions as a bridge between filaments of actin and the actin-polymerizing machinery.

Cryopreservation of bull spermatozoa alters the perinuclear theca

The perinuclear theca (PT) is involved in several important sperm functions leading to fertilization. The objective of this study was to investigate the effect of cryopreservation of bull spermatozoa on the integrity of the PT and the relationship between PT integrity and semen characteristics. Semen from seven bulls was evaluated before and after cryopreservation, comparing the integrity of the plasma membrane (hypo-osmotic test), percentage of live and dead spermatozoa (triple stain), acrosome integrity (triple stain) and the integrity of the PT (negative stain by electron microscopy). Cryopreservation of bull semen caused substantial damage to the PT; the proportion of spermatozoa with a damaged PT was 15.2% versus 52.5% (P<0.05) in fresh versus frozen-thawed spermatozoa, respectively. Furthermore, on average, 67.4% (range, 64-72%) of fresh spermatozoa were live, compared to 53.1% (range, 49-58%) for frozen-thawed spermatozoa; there was an inverse correlation between the percentage of live spermatozoa and the percentage with damage to the PT. Although 59.1% of frozen-thawed spermatozoa had an intact acrosome, only 43.7% of them still remained alive. In frozen-thawed semen, there was a high correlation (r=0.69) between live spermatozoa with an intact acrosome and spermatozoa that maintained an intact PT. In conclusion, freezing/thawing of bull spermatozoa altered the PT and maintaining PT integrity may be necessary to maintain acrosome integrity.

Morphologic changes in boar sperm nuclei with reduced disulfide bonds in electrostimulated porcine oocytes

In pigs, failure of sperm nuclear decondensation has been reported after injection into oocytes. We examined the effects of pretreating sperm heads with Triton X-100 (TX-100) and dithiothreitol (DTT) and of electrical stimulation of oocytes after sperm head injection on time-dependent morphologic changes in sperm nuclei andin vitrodevelopment to the blastocyst stage. In experiment 1, spermatozoa were pretreated with 1% TX-100 and 5 mM DTT (T + D) or not treated, and then injected intoin vitromatured oocytes. Electrical stimulation (1.5 kV/cm, 20 μs DC pulse) was applied to the oocytes 1 h after injection (stimulated group) or was not applied (unstimulated group). Some of the oocytes in each group were evaluated at hourly intervals until 10 h after injection for morphologic changes in the sperm nuclei. Unstimulated oocytes injected with untreated spermatozoa showed a delayed peak in the rate of nuclear decondensation (39.4–44.1%, 3–6 h after injection) compared with oocytes injected with T + D-treated spermatozoa (57.0% and 52.6%, 1 and 2 h, respectively). The rate of male pronucleus formation peaked 6 h after stimulation (by 40–60%) after injected oocytes had been stimulated with an electrical pulse, irrespective of whether or not the spermatozoa had been pretreated. In unstimulated oocytes, the rate of male pronucleus formation did not increase and stayed at the basal level (less than 20%) throughout the culture period, regardless of the sperm treatment. Thus, T + D treatment of spermatozoa did not affect completion of fertilization. In experiment 2, we evaluated the effects of electrical stimulation and sperm treatment with T + D on the rate of blastocyst formation and the mean number of cells per blastocyst. Oocytes stimulated after injection with either T + D-treated or untreated spermatozoa showed significantly higher percentages of blastocyst formation (24.8% and 27.1% respectively) than did unstimulated oocytes (1.1% and 4.1% for T + D-treated and untreated respectively;P< 0.01 by Duncan’s multiple-range test). The rate of blastocyst formation did not differ between the T + D-treated and untreated groups. The mean number of cells per blastocyst did not differ among any of the groups (14.0–29.4 cells). These results suggest that pretreatment of sperm with TX-100 and DTT shifted the timing of sperm nuclear decondensation forward. However, pronucleus formation and development to the blastocyst stagein vitrowere not improved by sperm treatment. Thus, electrical stimulation of injected oocytes enhancesin vitrodevelopment to the blastocyst stage in pigs.

Actin, myosin, cytokeratins and spectrin are components of the guinea pig sperm nuclear matrix

The nuclear matrix (NM) of somatic cells is an internal nuclear framework structure, with a structural function and participation in DNA replication and transcription. The NM has been described in mouse, hamster and human spermatozoa. In this study, an NM structural component of the guinea pig sperm nucleus was obtained by removing nuclear proteins and DNA from DTT-CTAB nuclei. Removal was achieved with high ionic strength salt and microccocal nuclease treatments including a heparin treatment to cause a slight swelling of the nucleus and facilitate material extraction. Actin, myosin, cytokeratins and spectrin were detected associated to NM by indirect immunofluorescence, immunogold staining and Western blotting analysis using specific antibodies. The presence of NM in guinea pig sperm nucleus is shown for the first time and some of its components are identified. This is also the first report on cytokeratins and myosin presence in guinea pig sperm. A retarding effect of nuclear decondensation caused by heparin is induced after phalloidin and/or diacetyl-monoxime (a myosin ATPase activity inhibitor) treatment, suggesting a role for F-actin and myosin in the maintenance of nuclear stability in sperm. The actin role was supported by the decondensing effect that citochalasin D and gelsolin had on sperm nuclei.

Actin polymerization in the equatorial and postacrosomal regions of guinea pig spermatozoa during the acrosome reaction is regulated by G proteins

The acrosome reaction (AR) is an exocytotic process of spermatozoa, and an absolute requirement for fertilization. During AR, actin polymerization is necessary in the equatorial and postacrosomal regions of guinea pig sperm for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane (PM) fusion nor the early steps of egg activation. To identify the mechanisms involved in this sperm actin polymerization, we searched for the protein members, known to be involved in a highly conserved model, that may apply to any cellular process in which de novo actin polymerization occurs from G protein activation. WASP, Arp 2/3, profilins I and II, and Cdc42, RhoA and RhoB GTPases were localized by indirect immunofluorescence (IIF) in guinea pig spermatozoa and their presence corroborated by Western blotting. WASP and profilin II were translocated to the postacrosomal region (Arp2/3 already were there) in long-term capacitated and acrosome-reacted spermatozoa, at the same time as actin polymerization occurred. These events were inhibited by GDP-beta-S and promoted by lysophosphatidic acid (LPA) and GTP-gamma-S, a small GTPase inhibitor and two activators, respectively. By immunoprecipitation, Cdc42-WASp association was identified in capacitated but not in noncapacitated gametes. Polymerized actin in the postacrosomal region is apparently anchored both to the postacrosomal perinuclear theca region and the overlying PM. Results suggest that GTPases are involved in sperm actin polymerization, in the postacrosomal region and the mechanism for polymerization might fit a previously proposed model (Mullins, 2000: Curr Opin Cell Biol 12:91-96).

Absence of Dp71 in mdx3cv mouse spermatozoa alters flagellar morphology and the distribution of ion channels and nNOS

In muscle, the absence of dystrophin alters the dystrophin-associated protein complex (DAPC), which is involved in the clustering and anchoring of signaling proteins and ion and water channels. Here we show that mice spermatozoa express only dystrophin Dp71 and utrophin Up71. The purpose of this study was to explore the effect of the absence of Dp71 on the morphology and membrane distribution of members of the DAPC, ion channels and signaling proteins of spermatozoa obtained from dystrophic mutant mdx3cv mice. Our work indicates that although the absence of Dp71 results in a dramatic decrease in beta-dystroglycan, it induces membrane redistribution and an increase in the total level of alpha-syntrophin, voltage-dependent Na+ (micro1) and K+ (Kv1.1) channels and neural nitric oxide synthase (nNOS). The short utrophin (Up71) was upregulated and redistributed in the spermatozoa of mdx3cv mice. A significant increase in abnormal flagella morphology was observed in the absence of Dp71, which was partially corrected when the plasma membrane was eliminated by detergent treatment. Our observations point to a new phenotype associated with the absence of Dp71. Abnormal flagellar structure and altered distribution of ion channels and signaling proteins may be responsible for the fertility problems of mdx3cv mice.

Electron microscopic observations of human sperm whole-mounts after extraction for nuclear matrix and intermediate filaments (NM-IF)

The extraction for nuclear matrix and intermediate filaments (NM-IF) is used to reveal, isolate and study these highly resistant structures in different cell types. We applied for the first time this chemical dissection to human spermatozoa and observed them as whole-mounts by unembedded electron microscopy. The general appearance of NM-IF extracted sperm cells was preserved, showing the intermediate filament-like properties of their cytoskeletal components. In most heads, a network was observed in subacrosomal position, consisting of hubs interconnected by filaments. It seemed to be overlaid on another, finer network. The neck retained its integrity, allowing observations of the three-dimensional structure of the segmented columns. More distally, axoneme and outer dense fibres were covered by submitochondrial cytoskeleton in the middle piece and fibrous sheath in the principal piece, with the annulus usually detached from the fibrous sheath. End piece microtubules were retained in most cells and showed a tendency of cohesion, remaining in a parallel bundle or forming flat sheets. In conclusion, our results provided additional structural details of human sperm cytoskeleton and demonstrated the advantages of combining different methodological approaches in ultrastructural research.

Interactions of sperm perinuclear theca with the oocyte: implications for oocyte activation, anti-polyspermy defense, and assisted reproduction

Perinuclear theca (PT) is the cytoskeletal coat of mammalian sperm nucleus that is removed from the sperm head at fertilization. PT harbors the sperm borne, oocyte-activating factor (SOAF), a yet-to-be-characterized substance responsible for triggering the signaling cascade of oocyte activation, thought to be dependent on intra-oocyte calcium release. The present article reviews the current knowledge on the biogenesis and molecular composition of sperm PT. Possible functions of sperm PT during natural and assisted fertilization, and in the initiation of embryonic development are discussed. Furthermore, evidence is provided that SOAF is transferred from the sperm PT to oocyte cytoplasm through the internalization and rapid solubilization of the post-acrosomal PT. It is shown that during natural fertilization the sperm PT dissolves in the oocyte cytoplasm concomitantly with sperm nuclear decondensation and the initiation of pronuclear development. SOAF activity is preserved in the differentially extracted sperm heads only if the integrity of PT is maintained. After intracytoplasmic sperm injection (ICSI), activation occurs only in those oocytes in which the injected spermatozoon displays complete or partial dissolution of PT. In the latter case, the residual PT of the sub-acrosomal and/or post-acrosomal sperm region may persist on the apical surface of the sperm nucleus/male pronucleus and may cause a delay or arrest of zygotic development. We propose that the sperm PT harbors SOAF in the post-acrosomal sheath, as this is the first part of the sperm cytosol to enter the oocyte cytoplasm and its disassembly appears sufficient to initiate the early events of oocyte activation. Dissolution of the sub-acrosomal part of the PT, on the other hand, appears necessary to insure complete DNA decondensation in the internalized sperm nucleus and initiate DNA synthesis of both pronuclei. The release of the SOAF from the sperm head into oocyte cytoplasm at fertilization ultimately leads to the activation of oocyte mechanism including the completion of the meiotic cell cycle, pronuclear development and anti-polyspermy defense.

Novel actin-related proteins Arp-T1 and Arp-T2 as components of the cytoskeletal calyx of the mammalian sperm head

The calyx is a large cytoskeletal component of the perinuclear theca of the mammalian sperm head, displaying remarkable morphological interspecies differences, which is biochemically characterized by resistance to high ionic strength and detergents and by a special protein composition, including the basic proteins calicin, cylicin I and II, and two major actin-capping proteins. In our calyx preparations from bull spermatozoa we have noted two major acidic components which upon partial amino acid sequencing have been identified as novel members of the subfamily of actin-related proteins (Arps). Antibodies raised against the corresponding human proteins, termed Arp-T1 and Arp-T2, have been used to detect the proteins by immunoblotting and immunofluorescence microscopy, demonstrating their specific synthesis in the testis, late in spermatid differentiation, and their localization in the calyx. The discovery of two novel Arps as major components in a cytoskeletal, nonmotile structure of mammalian spermatozoa suggests that certain members of this family of proteins may serve functions other than nucleation of actin filaments, and possible biological roles of such Arps in spermatozoa are discussed.

Post-testicular development of a novel membrane substructure within the equatorial segment of ram, bull, boar, and goat spermatozoa as viewed by atomic force microscopy

Atomic force microscopy has been used to investigate changes in the plasma membrane overlying the head region of mammalian spermatozoa (bull, boar, ram, goat, stallion, mouse, and monkey) during post-testicular development, after ejaculation, and after exocytosis of the acrosomal vesicle. On ejaculated ram, bull, boar, and goat spermatozoa the postacrosomal plasma membrane has a more irregular surface than that covering the acrosome. The equatorial segment, by contrast, is relatively smooth except for an unusual semicircular substructure within it that has a coarse uneven appearance. This substructure (referred to as the equatorial subsegment) is situated adjacent to the boundary between the postacrosomal region and the equatorial segment itself and seems to be confined to the order Artiodactyla as it has not been observed on stallion, mouse, or monkey spermatozoa. The equatorial subsegment develops during epididymal maturation, and following induction of the acrosome reaction with Ca(2+) ionophore A23187, its topography changes from a finely ridged appearance to that resembling truncated papillae. A monoclonal antibody to the equatorial subsegment binds only to permeabilized spermatozoa, suggesting that the subsegment is related to the underlying perinuclear theca that surrounds the sperm nucleus. A role for the equatorial subsegment in mediating fusion with the oolemma at fertilization is discussed.

Comparative distribution of short dystrophin superfamily products in various guinea pig spermatozoa domains

In this study, the presence and cellular distribution of dystrophin family products (i.e. Dp71d, Dp71f-like protein and dystrobrevin) was examined by indirect immunofluorescence and Western blotting in guinea pig spermatozoa. Two dystrophin-associated proteins, beta-dystroglycan and alpha-syntrophin, and nNOS a protein frequently associated with alpha-syntrophin, were determined. In spermatozoa lacking plasma membrane and acrosome, Dp71f-like protein was found in the postacrosomal perinuclear theca and also in the middle piece of the flagellum. In the flagellum, Dp71f-like protein is localized together with alpha-syntrophin and nNOS. Dp71d was present in the plasma membrane of the middle piece with beta-dystroglycan, alpha-syntrophin and nNOS. Dp71d was also present in plasma membrane of the post acrosomal region, but only with nNOS. Finally, dystrobrevin was located all along skeletal flagellum structures and in the subacrosomal hemisphere of the perinuclear theca. This distinct and complementary distribution in various domains of spermatozoa may reveal a specific function for each short dystrophin family product, in the stabilization of the domains where they are located.

Exocytosis of a 60 kDa protein (calreticulin) from activated hamster oocytes

The sp50 protein localized at the acrosomal region of guinea pig sperm was suggested to participate in acrosome exocytosis, the acrosome reaction (AR). On the other hand, the cortical reaction (CR), also an exocytotic event, occurs during egg activation. The aim of the present work was to identify sp50 and also to define if sp50 is present in hamster eggs, as well as its location before and after CR. Sp50 was identified as calreticulin (CRT), based on: (a) its NH(2)-terminal amino acid (25 aa) sequence, (b) a cross-recognition of pure sp50 and pure CRT with anti-CRT (from Santa Cruz, anti-CRTsc), and anti-sp50 (anti-sp50/CRT) antibodies, respectively, and (c) that both antibodies revealed a 50 kDa protein in a Brij sperm extract. On the other hand, CRT presence in eggs was positively determined by Western blotting (Wb) using anti-sp50/CRT antibody which recognized a 60 kDa protein in the egg extract, and by indirect immunofluorescence (IIF), CRT was located in the cortical granules (CG). It was defined by a granular pattern and co-localization with mannose, a specific carbohydrate of the CG. Additionally, a decrease in CRT concentration occurred in eggs after their activation and, in parallel, the protein was revealed in the egg's incubation medium. In activated eggs with zona pellucida (ZP), CRT remains as a halo in the perivitelline space and around the polar body. From these results we suggest that: (1) CRT is present in the CG of non-activated hamster eggs, (2) CRT is exocytosed during the CR, in response to egg activation, and (3) CRT might participate in the block to polyspermy, together with other CG components.

Mobility shift assay of calcium-binding proteins of mouse epididymal spermatozoa

The calcium-binding proteins (CBPs) of mouse epididymal spermatozoa were analysed by mobility changes in the presence of added Ca2+ in two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The expression patterns of relatively high molecular weight CBPs (Mr > 20 kDa) were different between caput and cauda epididymal spermatozoa. There was a constitutive expression of low molecular weight CBPs (Mr < 20 kDa) regardless of the epididymal region. Most of the CBPs disappeared after the acrosome reaction (AR) induced by Ca2+ ionophore A23187, suggesting that they originated from the acrosome and/or the plasma membrane overlaying the acrosome. Taken together, it can be suggested that changes in CBPs of spermatozoa are important features of sperm maturation during epididymal transit, and that they may be related to the fertilizing ability of mouse epididymal spermatozoa.

Induction of the acrosome reaction in dog sperm cells is dependent on epididymal maturation: the generation of a functional progesterone receptor is involved

In the current study we investigated the progesterone receptor exposure on the sperm from the testis and different parts of the epididymis, the relation to the sperm maturation stage, the functionality of the progesterone receptor and the capacity of sperm to undergo acrosome reaction. Exposed progesterone receptors on spermatozoa were detected using Progesterone-BSA conjugate labeled with fluorescein isothiocyanate (P-BSA-FITC) or a monoclonal antibody against progesterone receptor, C-262. Either progesterone or calcium ionophore was used to induce acrosome reaction. A high percentage (69 +/- 8%; mean +/- SD) of spermatozoa from the cauda epididymis showed P-BSA-FITC labeling at the onset of incubation, whereas only 0.1 +/- 1 and 4 +/- 2%, of spermatozoa from the testes, caput, and corpus epididymis, respectively, were labeled. There was no significant increase in P-BSA-FITC binding during the course of a 6 hr incubation. Treatment with either 10 microM progesterone or 5 microM calcium ionophore induced acrosome reaction in cauda epididymal sperm but not in testicular sperm, caput or corpus epipidymal sperm. It is concluded that the matured sperm of the dog from cauda epididymis and freshly ejaculated sperm demonstrate a functional membrane-bound progesterone receptor while less matured spermatozoa from the testicle, caput, and corpus epididymis fail to demonstrate such a receptor. Acrosome reaction of dog sperm can be induced using either progesterone or calcium ionophore; however, the maturation stages of spermatozoa influence this occurrence.