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Biomedical subjects

J Tesarik

Publications and source records attributed to J Tesarik.

At least 91 records · Page 5Linked to original sources
PubMed1996

Fertilization of oocytes by injecting spermatozoa, spermatids and spermatocytes.

The feasibility of fertilization by injecting spermatozoa into oocytes has increased significantly the possibilities for treatment of severe male infertility. However, the rapidity of human application has raised some concern about potential health hazards for the progeny. Human pregnancies and births have also occurred with the use of immature spermatozoa and spermatids, and normal offspring have been born after the injection of secondary spermatocytes into mouse oocytes. This short review deals with the problems that may arise from the injection technique and from the use of deficient or immature sperm cells for fertilization, with particular attention to human applications. Tests for screening parents and follow-up of children are suggested to control the main suspected risk factors.

Animals↗
PubMed1995

Nongenomic steroid action: independent targeting of a plasma membrane calcium channel and a tyrosine kinase.

It is known that steroids can produce nongenomic effects on cells, such as opening of ionic channels, membrane receptor aggregation or changes in protein phosphorylation status. However, it is not known whether these different effects, when occurring concomitantly, are linked by a causal relationship or whether they are triggered independently by the steroid ligand. Here we show that progesterone opens a plasma membrane Ca2+ channel and activates a protein tyrosine kinase of human spermatozoa independently of each other because, on the one hand, tyrosine kinase inhibition does not affect the progesterone-induced Ca2+ influx and, on the other hand, the absence of extracellular Ca2+ does not preclude tyrosine-kinase-mediated progesterone-induced acrosomal exocytosis. These data suggest that steroids interact with multireceptor systems on the surface of responsive cells.

Calcium Channels↗
PubMed1995

Sperm-induced calcium oscillations of human oocytes show distinct features in oocyte center and periphery.

Temporal and spatial characteristics of explosive periodic increases (spikes) of intracellular free Ca2+ concentration ([Ca2+]i) induced by sperm in human oocytes (Ca2+ oscillations) were analyzed by confocal laser scanning microscopy and compared to Ca2+ oscillations induced in oocytes by the thiol reagent thimerosal. During the steady-state period of sperm-induced Ca2+ oscillations, each individual [Ca2+]i spike invariably began from a focus in oocyte periphery and spread throughout the entire peripheral region before propagating to the central ooplasm. This peripheral Ca2+ wave was immediately followed by an explosive [Ca2+]i increase in the central ooplasm. However, this central [Ca2+]i rise only peaked when [Ca2+]i in the peripheral ooplasm was already on the decline. Moreover, the peak [Ca2+]i values were always considerably higher in the oocyte center than in the periphery. In contrast, thimerosal-induced Ca2+ oscillations did not show this particular form of propagation. These data show that sperm-induced Ca2+ oscillations have a unique pattern of spatial dynamics and suggest that the bulk of Ca2+ mobilized during each spike is released from stores that have a relatively high threshold for Ca(2+)-induced Ca2+ release (CICR). These stores are poorly developed, if not absent, in the oocyte cortex, and CICR from them is triggered by previous CICR from another type of store with a lower threshold that are preferentially located in the oocyte cortex and act as a detonator.

Calcium↗
PubMed1995

Alleviation of acrosome reaction prematurity by sperm treatment with egg yolk.

OBJECTIVE: To examine the effects of egg yolk on the spontaneous and ionophore-induced acrosome reaction (AR) and sperm-zona pellucida (ZP) binding in spermatozoa from patients with AR prematurity. DESIGN: Prospective analysis. SETTING: Private hospital, public research center, and a university-based laboratory. PATIENTS: In vitro fertilization patients selected on the basis of previous AR testing. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Frequency of the AR, number of ZP-bound spermatozoa. RESULTS: The pretreatment of spermatozoa with egg yolk decreased the frequency of AR occurring spontaneously during subsequent sperm incubation in capacitating medium but did not modify the sperm response to ionophore. The egg yolk-treated spermatozoa also showed a greater capacity of binding the ZP than their untreated counterparts. CONCLUSIONS: The pretreatment of spermatozoa with egg yolk alleviates the sperm-ZP binding deficiency resulting from premature initiation of the AR and may be helpful in IVF with patients showing this anomaly.

Acrosome↗
PubMed1995

More than 90% fertilization rates after intracytoplasmic sperm injection and artificial induction of oocyte activation with calcium ionophore.

OBJECTIVE: To examine whether fertilization rates after intracytoplasmic sperm injection can be increased by artificial oocyte activation. DESIGN: Oocytes that failed to fertilize spontaneously by 24 hours after intracytoplasmic sperm injection were treated either with calcium ionophore to induce activation or with solvent only to serve as control. The ability of ionophore-treated and control oocytes to achieve delayed fertilization was compared. SETTING: Private hospital and public research center. PATIENTS: Infertile couples treated by intracytoplasmic sperm injection. INTERVENTIONS: Intracytoplasmic sperm injection. MAIN OUTCOME MEASURES: Fertilization and cleavage rates. RESULTS: The mean rate of spontaneous fertilization after intracytoplasmic sperm injection was 32%, but 88% of the oocytes that failed to fertilize spontaneously did so after subsequent exposure to calcium ionophore. Most of these oocytes underwent at least one apparently normal cleavage division. In contrast, delayed fertilization of oocytes not treated with ionophore was an exceptional finding. If only oocytes remaining intact after intracytoplasmic sperm injection are taken into account, the mean global fertilization rate of ionophore-enhanced intracytoplasmic sperm injection was 91%. CONCLUSIONS: These results show that the failure of oocyte activation is the main cause of fertilization failure after intracytoplasmic sperm injection. If an appropriate, clinically applicable treatment is found to overcome this problem, intracytoplasmic sperm injection can be expected to yield fertilization rates far exceeding those of standard IVF with normal spermatozoa.

Adult↗
PubMed1995

Key elements of a highly efficient intracytoplasmic sperm injection technique: Ca2+ fluxes and oocyte cytoplasmic dislocation.

OBJECTIVE: To analyze the mechanism by which modifications of the intracytoplasmic sperm injection (ICSI) technique influence success rates. DESIGN: Prospective clinical study supplemented with an experimental analysis of Ca2+ fluxes provoked by the injection procedure. SETTING: Private hospital and public research center. PATIENTS: Patients treated by IVF and ICSI. INTERVENTIONS: Intracytoplasmic sperm injection. MAIN OUTCOME MEASURES: Fertilization and pregnancy rates and intracellular free Ca2+ concentration. RESULTS: The inclusion of vigorous aspiration of oocyte cytoplasm improved outcomes of ICSI. In a series of 100 consecutive cases treated with this technique, the fertilization and pregnancy rates were 87% of total metaphase II oocytes injected and 52% of total treatment cycles, respectively. Enhanced Ca2+ influx into the injected oocytes and dislocation of the oocyte cytoplasm, including the development of a focus of persistent Ca2+ discharge around the injected sperm head, were the main characteristics of this highly successful technique. CONCLUSIONS: Vigorous aspiration of oocyte cytoplasm may facilitate fertilization after ICSI by increasing the oocyte Ca2+ load at the time of injection, by establishing a more intimate contact of the injected sperm head with oocyte intracellular Ca2+ stores, or by a conjunction of these mechanisms.

Aniline Compounds↗
PubMed1995

Targeting the zona pellucida for immunocontraception: a minireview.

This minireview summarizes the main data relevant to the development of contraceptive vaccines based on zona pellucida (ZP) antigens, as well as the pros and the cons of this immunocontraceptive strategy. Even though the antifertility efficacy of anti-ZP antibodies in humans is not corroborated by a clear relationship between spontaneous autoimmunization against the ZP and infertility, passive and active immunization studies in laboratory animals have provided convincing results. The contraceptive action of anti-ZP antibodies, targeting events situated upstream of gamete fusion, is devoid of potential ethical concerns related to the destruction of early embryos. The high protein content of the mammalian ZP, knowledge of the complete amino acid sequence of the major ZP proteins, and the high degree of sequence homology between individual species all favour the rapid advancement of anti-ZP vaccine projects. However, certain sequences of ZP proteins, when incorporated into the vaccine construct, activate CD4+ T cells of the recipient organism to direct a cellular immune attack (autoimmune oophoritis) to other functionally relevant ovarian components (primordial follicles, steroidogenic cells). The search for the optimal combination of B cell and T cell epitopes in the vaccine construct will hopefully overcome this problem.

Antigen-Antibody Reactions↗
PubMed1995

Nongenomic effects of 17 beta-estradiol on maturing human oocytes: relationship to oocyte developmental potential.

There is increasing evidence for nongenomic steroid effects in various cell types. This study is the first to demonstrate that 17 beta-estradiol (E2) exerts a direct nongenomic effect on maturing human oocytes by inducing a series of transient increases in the intracellular free calcium concentration ([Ca2+]i). This effect of E2 appeared to be specific and was mediated by steroid action on the cell surface. The first of the E2-induced [Ca2+]i increases was induced by an influx of extracellular Ca2+ ions. However, the release of Ca2+ from intracellular stores contributed more significantly to [Ca2+]i waves characterizing the subsequent series of secondary [Ca2+]i increases, although the presence of extracellular Ca2+ still was an absolute requirement for these [Ca2+]i oscillations. The addition of E2 to oocyte maturation medium did not produce any apparent effects on either germinal vesicle breakdown or further progression of meiosis, but it did increase the fertilization and cleavage rates of the in vitro matured oocytes. These findings show that E2 can directly influence the quality of maturing oocytes. This effect is due to steroid action on the cell surface, implies Ca2+ as a second messenger, and contributes to oocyte capacitation for fertilization and early postfertilization development.

Calcium↗
PubMed1994

Mouse oocyte maturation is affected by lithium via the polyphosphoinositide metabolism and the microtubule network.

The incubation of mechanically denuded mouse oocytes in medium containing LiCl delayed both germinal vesicle breakdown (GVBD) and polar body extrusion in a dose-dependent and reversible manner. When myo-inositol alone was added to the culture medium, we observed that it accelerated GVBD and increased the rate of polar body extrusion, whereas, when combined with LiCl, the normal timing of GVBD was recovered. In the same way, when inositol trisphosphate (InsP3) was microinjected into the ooplasma, we observed an important improvement of the rate of GVBD, as compared to control oocytes, and prevention of lithium inhibition. However, neither myo-inositol nor InsP3 were able to rescue totally the oocytes from the negative effect of lithium on polar body extrusion. Moreover, lithium induced some important changes in microtubule and chromosome organizations. Before extrusion of the first polar body, the reduction of the spindle size or the appearance of short individualized chromosomes dispersed around a large aster of microtubules were often observed, whereas, after polar body extrusion, the spindle appeared smaller and chromosomes were often trapped in the midbody. Thus lithium affects mouse oocyte maturation at two different levels: GVBD and polar body extrusion. Whereas the former seems to be affected via polyphosphoinositide turnover, the latter is InsP3-independent and seems to be influenced negatively via underdevelopment of microtubular structures.

Actin Cytoskeleton↗
PubMed1994

Most living acrosome-reacted spermatozoa do not fuse with the oocyte when inserted into the perivitelline space.

OBJECTIVE: To evaluate the frequency with which acrosome-reacted spermatozoa fuse with the oocyte after subzonal insemination (SUZI). DESIGN: The acrosome reaction frequency determined in sperm suspensions used for SUZI was related with the frequency of sperm-oocyte fusion after the microinsemination procedure. In some experiments, the acrosome reaction frequency was compared in sperm suspensions aspirated into the microinjection needle and in those leaving the needle. SETTING: Private hospital, public research center, and university-based laboratory. PATIENTS, PARTICIPANTS: Patients involved in a program of micromanipulation-assisted fertilization and healthy sperm donors. INTERVENTIONS: IVF-ET. MAIN OUTCOME MEASURES: Frequency of the acrosome reaction, frequency of sperm-oocyte fusion. RESULTS: The procedure of sperm aspiration to the microinjection needle followed by active swim-out of motile spermatozoa did not change the overall percentage of acrosome-reacted spermatozoa even though the subpopulation of acrosome-reacted spermatozoa leaving the needle was enriched in recently reacted cells. The frequency of sperm-oocyte fusion was considerably lower than the frequency of the acrosome reaction in both patient and donor sperm samples, irrespective of the number of spermatozoa inserted per egg. CONCLUSIONS: A spontaneous acrosome reaction does not necessarily predispose a spermatozoon to fuse with the oocyte after SUZI. It remains to be elucidated whether this relative inefficiency of acrosome-reacted spermatozoa is related to technical aspects of SUZI or whether, in a more general sense, the acrosomal exocytosis and the development of sperm-oocyte fusion capacity are distinctly regulated, though closely related, phenomena.

Acrosome↗
PubMed1994

Comparison of Ca2+ responses in human oocytes fertilized by subzonal insemination and by intracytoplasmic sperm injection.

OBJECTIVE: To evaluate the consequences of bypassing the normal interaction between the sperm and oocyte surfaces for the form of Ca2+ responses developing in oocytes at fertilization. DESIGN: Oocytes were fertilized by subzonal insemination (SUZI) (maintaining the normal interaction between cell surfaces of both gametes) or by direct intracytoplasmic sperm injection, and changes in intracellular free Ca2+ concentration were evaluated by confocal laser scanning microscopy after loading oocytes with a fluorescent Ca2+ indicator. SETTING: Private hospital, public research center, and university-based laboratory. PATIENTS, PARTICIPANTS: Patients participating in an assisted reproduction program. INTERVENTIONS: In vitro fertilization, SUZI, intracytoplasmic sperm injection. MAIN OUTCOME MEASURES: Changes in intracellular free Ca2+ concentration. RESULTS: All oocytes fertilized after SUZI showed an oscillatory Ca2+ response introduced by a short initial phase with faster Ca2+ oscillations. In contrast, oocytes fertilized after intracytoplasmic sperm injection did not show a similar change in the oscillation rhythm. In both cases, Ca2+ increases were propagated throughout the ooplasm in a wave-like manner. CONCLUSIONS: The results show that there is a relationship between gamete surface contact and the form of Ca2+ fluxes accompanying fertilization. When the contact between gamete surfaces is skipped by direct sperm injection to the ooplasm, a delayed, truncated Ca2+ response is produced which, however, can maintain the form of Ca2+ waves and Ca2+ oscillations typical of normal fertilization.

Calcium↗
PubMed1994

Ultrastructural analysis of fertilization failure after intracytoplasmic sperm injection.

Human oocytes that failed to display signs of fertilization by 44 h after intracytoplasmic sperm injection (ICSI) were processed for electron microscopic analysis. All oocytes were arrested at metaphase II. The first polar body contained intact cortical granules and chromosome clumps, which were not surrounded by a nuclear envelope but still associated with microtubules. When a second globular body was present, it always showed the same ultrastructure, indicating that it had originated from fragmentation of the first polar body and not from the resumption of the second meiotic division. The most prominent organelles of the oocyte cytoplasm were the smooth endoplasmic reticulum and mitochondria. In the oocyte cortex, cortical granules were intact, with no signs of incipient or incomplete cortical reaction. Oocyte chromosomes were found in the oocyte periphery near the locality of the first polar body extrusion. They consisted of dense aggregates of chromatin associated with microtubules. The chromatin of the injected spermatozoon was demembranated and partially decondensed. In some cases, vesicular and tubular structures, apparently of oocyte origin, were associated with the periphery of the sperm chromatin mass but they never formed a continuous layer. These data suggest that fertilization failure after ICSI is basically a failure of oocyte activation.

Cell Nucleus↗
PubMed1994

Human oocyte activation after intracytoplasmic sperm injection.

Oocyte activation is a series of events triggered by the fertilizing spermatozoon and necessary for the beginning of the embryonic development. Calcium plays a pivotal role in this process. Here we used confocal laser scanning microscopy to examine the changes in the concentration of intracellular free calcium ([Ca2+]i) in human oocytes after intracytoplasmic sperm injection (ICSI). The first considerable but short (< 2 min) increase in [Ca2+]i was detected immediately after the penetration of the microinjection needle into the ooplasm. This rise by itself did not provoke oocyte activation and was also obtained after the injection of medium without spermatozoa. After a lag period of 4-12 h, oocytes that were subsequently activated initiated a second period of [Ca2+]i changes. These changes were sperm-dependent and followed one of two alternative patterns, a non-oscillatory one and an oscillatory one. The non-oscillatory pattern resembled the changes described previously during parthenogenetic activation of mammalian oocytes. The oscillatory pattern was similar to the changes accompanying normal fertilization in different mammalian species. It is concluded that the initial [Ca2+]i rise provoked by the ICSI procedure is not responsible for oocyte activation, and that a release of a sperm factor(s) is required to initiate this process.

Calcium↗
PubMed1994

Treatment of sperm-injected human oocytes with Ca2+ ionophore supports the development of Ca2+ oscillations.

Oscillations of intracellular free Ca2+ concentration are an essential component of the oocyte response to the fertilizing spermatozoon. Ca2+ oscillations have also been observed in human oocytes fertilized by intracytoplasmic sperm injection (ICSI), but only after a considerable delay. The present study was performed to determine whether or not the development of Ca2+ oscillations in sperm-injected oocytes is influenced by exposure of the oocytes to Ca2+ ionophore. The treatment (5 min) of sperm-injected, but not sham-injected, oocytes with 10 microM ionophore A23187 augmented significantly the percentage of oocytes that developed Ca2+ oscillations and accelerated the onset of the oscillations as compared to the values for solvent-treated controls. However, the oscillations developed only after a lag period, which ranged between 25 min and 88 min after the removal of ionophore, during which intracellular Ca2+ levels returned nearly to the basal value. Each of the subsequent periodic Ca2+ rises was initiated from a focus in the oocyte cortex and spread throughout the ooplasm as a Ca2+ wave. These data suggest that ionophore treatment supports the physiological pattern of oocyte activation when applied after ICSI. This effect is probably indirect, implying the stimulation of an unknown process continuing during the lag period.

Calcimycin↗
PubMed1993

A plasma-membrane progesterone receptor in human sperm is switched on by increasing intracellular free calcium.

Recent studies have revealed the presence of an atypical progesterone receptor on the plasma membrane of a relatively small subpopulation of human sperm cells. In this study, we show that the receptor is present in many cells in a latent form and that the receptor function in these cells is switched on asynchronously by increasing intracellular free Ca2+ levels. Under physiological conditions, this process occurs during sperm capacitation, but it can be mimicked by a short sperm exposure to the Ca(2+)-mobilizing agent thapsigargin. These observations suggest a role of Ca2+ as a modulator of nongenomic steroid effects on the cell surface.

Biological Transport↗