Dissociation between intracellular calcium elevation and development of human oocytes treated with calcium ionophore

Design of novel oocyte activation methods: The role of zinc

Oocyte activation occurs at the time of fertilization and is a series of cellular events initiated by intracellular Ca2+ increases. Consequently, oocytes are alleviated from their arrested state in meiotic metaphase II (MII), allowing for the completion of meiosis. Oocyte activation is also an essential step for somatic cell nuclear transfer (SCNT) and an important tool to overcome clinical infertility. Traditional artificial activation methods aim to mimic the intracellular Ca2+ changes which occur during fertilization. Recent studies emphasize the importance of cytoplasmic Zn2+ on oocyte maturation and the completion of meiosis, thus suggesting artificial oocyte activation approaches that are centered around the concentration of available Zn2+in oocytes. Depletion of intracellular Zn2+ in oocytes with heavy metal chelators leads to successful oocyte activation in the absence of cellular Ca2+ changes, indicating that successful oocyte activation does not always depends on intracellular Ca2+ increases. Current findings lead to new approaches to artificially activate mammalian oocytes by reducing available Zn2+ contents, and the approaches improve the outcome of oocyte activation when combined with existing Ca2+ based oocyte activation methods. Here, we review the important role of Ca2+ and Zn2+ in mammalian oocyte activation and development of novel oocyte activation approaches based on Zn2+ availability.

Sperm-oocyte interplay: an overview of spermatozoon's role in oocyte activation and current perspectives in diagnosis and fertility treatment

The fertilizing spermatozoon is a highly specialized cell that selects from millions along the female tract until the oocyte. The paternal components influence the oocyte activation during fertilization and are fundamental for normal embryo development; however, the sperm-oocyte interplay is in a continuous debate. This review aims to analyze the available scientific information related to the role of the male gamete in the oocyte activation during fertilization, the process of the interaction of sperm factors with oocyte machinery, and the implications of any alterations in this interplay, as well as the advances and limitations of the reproductive techniques and diagnostic tests. At present, both PLCζ and PAWP are the main candidates as oocyte activated factors during fertilization. While PLCζ mechanism is via IP₃, how PAWP activates the oocyte still no clear, and these findings are important to study and treat fertilization failure due to oocyte activation, especially when one of the causes is the deficiency of PLCζ in the sperm. However, no diagnostic test has been developed to establish the amount of PLCζ, the protocol to treat this type of pathologies is broad, including treatment with ionophores, sperm selection improvement, and microinjection with PLCζ protein or RNA.

Essential Role of Sperm-Specific PLC-Zeta in Egg Activation and Male Factor Infertility: An Update

Sperm-specific phospholipase C zeta (PLCζ) is widely considered to be the physiological stimulus responsible for generating calcium (Ca²⁺) oscillations that induce egg activation and early embryonic development during mammalian fertilization. In the mammalian testis, PLCζ expression is detected at spermiogenesis following elongated spermatid differentiation. Sperm-delivered PLCζ induces Ca²⁺ release via the inositol 1,4,5-trisphosphate (InsP₃) signaling pathway. PLCζ is the smallest known mammalian PLC isoform identified to date, with the simplest domain organization. However, the distinctive biochemical properties of PLCζ compared with other PLC isoforms contribute to its unique potency in stimulating cytosolic Ca²⁺ oscillations within mammalian eggs. Moreover, studies describing PLCζ “knockout” mouse phenotypes confirm the supreme importance of PLCζ at egg activation and monospermic fertilization in mice. Importantly, a number of clinical reports have highlighted the crucial importance of PLCζ in human fertilization by associating PLCζ deficiencies with certain forms of male factor infertility. Herein, we give an update on recent advances that have refined our understanding of how sperm PLCζ triggers Ca^{2 +} oscillations and egg activation in mammals, while also discussing the nature of a potential “alternative” sperm factor. We summarise PLCζ localization in mammalian sperm, and the direct links observed between defective PLCζ protein in sperm and documented cases of male infertility. Finally, we postulate how this sperm protein can be used as a potential diagnostic marker, and also as a powerful therapeutic agent for treatment of certain types of male infertility due to egg activation failure or even in more general cases of male subfertility.

The role of Ca2+ in oocyte activation during In Vitro fertilization: Insights into potential therapies for rescuing failed fertilization

At fertilization the mature mammalian oocyte is activated to begin development by a sperm-induced series of increases in the cytosolic free Ca²⁺ concentration. These so called Ca²⁺ oscillations, or repetitive Ca²⁺ spikes, are also seen after intracytoplasmic sperm injection (ICSI) and are primarily triggered by a sperm protein called phospholipase Czeta (PLCζ). Whilst ICSI is generally an effective way to fertilizing human oocytes, there are cases where oocyte activation fails to occur after sperm injection. Many such cases appear to be associated with a PLCζ deficiency. Some IVF clinics are now attempting to rescue such cases of failed fertilization by using artificial means of oocyte activation such as the application of Ca²⁺ ionophores. This review presents the scientific background for these therapies and also considers ways to improve artificial oocyte activation after failed fertilization.

The establishment of appropriate methods for egg-activation by human PLCZ1 RNA injection into human oocyte

Phospholipase C-zeta (PLCZ1), a strong candidate of egg-activating sperm factor, can induce Ca²⁺ oscillations and cause egg activation. For the application of PLCZ1 to clinical use, we examined the pattern of Ca²⁺ responses and developmental rate by comparing PLCZ1 RNA injection methods with the other current methods, such as cytosolic aspiration, electrical stimulation and ionomycin treatment in human oocytes. We found that the pattern of Ca²⁺ oscillations after PLCZ1 RNA injection exhibited similar characteristics to that after ICSI treatment. We also determined the optimal concentration of human PLCZ1 RNA to activate the human oocytes. Our findings suggest that human PLCZ1 RNA is a better therapeutic agent to rescue human oocytes from failed activation, leading to normal and efficient development.

Rescue of failed oocyte activation after ICSI in a mouse model of male factor infertility by recombinant phospholipase Cζ

Artificial oocyte activation to overcome failed fertilization after intracytoplasmic sperm injection (ICSI) in human oocytes typically employs Ca(2+) ionophores to produce a single cytosolic Ca(2+) increase. In contrast, recombinant phospholipase Czeta (PLCζ) causes Ca(2+) oscillations indistinguishable from those occurring during fertilization, but remains untested for its efficacy in a scenario of ICSI fertilization failure. Here, we compare PLCζ with other activation stimuli in a mouse model of failed oocyte activation after ICSI, in which heat-treated sperm are injected into mouse oocytes. We show that increasing periods of 56 °C exposure of sperm produces a progressive loss of Ca(2+) oscillations after ICSI. The decrease in Ca(2+) oscillations produces a reduction in oocyte activation and embryo development to the blastocyst stage. We treated such oocytes that failed to activate after ICSI either with Ca(2+) ionophore, or with Sr(2+) media which causes Ca(2+) oscillations, or we injected them with recombinant human PLCζ. All these treatments rescued oocyte activation, although Sr(2+) and PLCζ gave the highest rates of development to blastocyst. When recombinant PLCζ was given to oocytes previously injected with control sperm, they developed normally to the blastocyst stage at rates similar to that after control ICSI. The data suggest that recombinant human PLCζ protein is an efficient means of rescuing oocyte activation after ICSI failure and that it can be effectively used even if the sperm already contains endogenous Ca(2+) releasing activity.

Generation of parthenogenetic goat blastocysts: effects of different activation methods and culture media

The present study was carried out to investigate the effects of different activation methods and culture media on the in vitro development of parthenogenetic goat blastocysts. Calcium (Ca2+) ionophore, ethanol or a combination of the two, used as activating reagents, and embryo development medium (EDM), modified Charles Rosenkrans (mCR2a) medium and research vitro cleave (RVCL) medium were used to evaluate the developmental competence of goat blastocysts. Quantitative expression of apoptosis, stress and developmental competence-related genes were analysed in different stages of embryos. In RVCL medium, the cleavage rate of Ca2+ ionophore-treated oocytes (79.61 ± 0.86) was significantly (P < 0.05) higher than in ethanol (74.90 ± 1.51) or in the combination of both Ca2+ ionophore and ethanol. In mCR2a or EDM, hatched blastocyst production rate of Ca2+ ionophore-treated oocytes (8.33 ± 1.44) was significantly higher than in ethanol (6.46 ± 0.11) or in the combined treatment (6.70 ± 0.24). In ethanol, the cleavage, blastocyst and hatched blastocyst production rates in RVCL medium (74.90 ± 1.51, 18.30 ± 1.52 and 8.24 ± 0.15, respectively) were significantly higher than in EDM (67.81 ± 3.21, 14.59 ± 0.27 and 5.59 ± 0.42) or mCR2a medium (65.09 ± 1.57, 15.36 ± 0.52 and 6.46 ± 0.11). The expression of BAX, Oct-4 and GlUT1 transcripts increased gradually from 2-cell stage to blastocyst-stage embryos, whereas the transcript levels of Bcl-2 and MnSOD were significantly lower in blastocysts. In addition, different activation methods and culture media had little effect on the pattern of variation and relative abundance of the above genes in different stages of parthenogenetic activated goat embryos. In conclusion, Ca2+ ionophore as the activating agent, and RVCL as the culture medium are better than other tested options for development of parthenogenetic activated goat blastocysts.

Toxic effects of Hoechst staining and UV irradiation on preimplantation development of parthenogenetically activated mouse oocytes

Parthenogenetic activation of oocytes is a helpful tool to obtain blastocysts, of which the inner cell mass may be used for derivation of embryonic stem cells. In order to improve activation and embryonic development after parthenogenesis, we tried to use sperm injection and subsequent removal of the sperm head to mimic the natural Ca2+ increases by release of the oocyte activating factor. Visualization of the sperm could be accomplished by Hoechst staining and ultraviolet (UV) light irradiation. To exclude negative effects of this treatment, we examined toxicity on activated mouse oocytes. After activation, oocytes were incubated in Hoechst 33342 or 33258 stain and exposed to UV irradiation. The effects on embryonic development were evaluated. Our results showed that both types of Hoechst combined with UV irradiation have toxic effects on parthenogenetically activated mouse oocytes. Although activation and cleavage rate were not affected, blastocyst formation was significantly reduced. Secondly, we used MitoTracker staining for removal of the sperm. Sperm heads were stained before injection and removed again after 1 h. However, staining was not visible anymore in all oocytes after intracytoplasmic sperm injection. In case the sperm could be removed, most oocytes died after 1 day. As MitoTracker was also not successful, alternative methods for sperm identification should be investigated.

Developmental competence of parthenogenetic mouse and human embryos after chemical or electrical activation

Parthenogenetic reconstruction is one major strategy to create patient-specific stem cells. The aim of this study was to find the best artificial activation protocol for parthenogenetic activation of mouse and human oocytes comparing different methods. In a first set of experiments, in-vivo matured mouse oocytes and human failed-fertilized, in-vitro and in-vivo matured oocytes were artificially activated by a chemical (ionomycin) or electrical stimulus. In a second set of experiments, a combination of activating agents (electrical pulses followed by ionomycin or SrCl(2)) was applied in an aim to improve developmental competence. All embryos were evaluated daily until day 6 after activation. Mouse blastocysts were differentially stained to evaluate blastocyst quality. For mouse oocytes and human failed-fertilized oocytes, blastocyst development was significantly higher after electrical activation (P<0.05). For human in-vitro and in-vivo matured oocytes, blastocyst formation was only obtained after electrical activation of in-vitro matured oocytes. After combining activating agents, no differences in development could be observed. In conclusion, this study revealed that for both mouse and human oocytes development to the blastocyst stage was significantly better after electrical activation compared with chemical activation. Combining activating agents had no further positive effect on developmental potential.

Spontaneous in vitro maturation and artificial activation of human germinal vesicle oocytes recovered from stimulated cycles

PURPOSE

To define germinal vesicles (GV) by morphometric and morphologic examination and by chromatin compaction and to assess their spontaneous nuclear and cytoplasmic competence.

MATERIALS

131 GV were cultured for 42.7 ± 2.4 h. Nuclear maturation was evaluated at four time points. Sixty-seven in vitro and twenty-five in vivo metaphase II (MII) were activated. Parthenotes with 2 PB and one pronucleus (NA) were studied for ploidy.

RESULTS

A total of 74.8% GV matured to MII: 55% at 21.4 ± 2.4 h and 47.3% in the following 24 h. Artificial activation induced NA in 79.2% of in vivo-MII and in 22.4% of in vitro-MII. All NA were haploid.

CONCLUSIONS

GV spontaneously mature at the nuclear level. Their NA are haploid, but their cytoplasmic competence is compromised. Variables were not found to be predictors of oocyte competence, probably due to our population being homogeneous with respect to most of the variables studied.

Parthenogenesis as an approach to pluripotency: advantages and limitations involved

Embryonic stem cells (ESCs) are invaluable cells derived from the inner cell mass of the mammalian blastocyst. They have nearly indefinite self-renewal, retain their developmental potential after prolonged periods in culture and display great plasticity that allow them to differentiate into all cell types of the body. They provide exciting opportunities to develop unique models for developmental research and hold great potential for cell and tissue replacement therapy. However, these unique cells cannot be obtained without destroying an embryo and, despite the potential therapeutic usefulness, their derivation in the human raises substantial ethical as well as legal and political concerns because it unavoidably involves the destruction of viable embryos. In the recent years a number of scientific proposals that do not require the generation and subsequent destruction of human embryos have been put forward in an attempt to fill the gap between ethical questions and potential scientific and medical benefits. In this review we briefly summarize data obtained from the literature related to these different alternative approaches and focus in more details on our experience in the derivation of parthenothes, as a possible alternative source for pluripotent cells, discussing the advantages as well as the limits of these cell lines.

Parthenotes as a source of embryonic stem cells

The derivation and study of human embryonic stem cell lines, despite their potential therapeutic usefulness, raise considerable ethical, religious, legal and political concerns because it inevitably leads to the destruction of viable embryos. In an attempt to bridge the division between ethical questions and potential scientific and medical benefits, considerable efforts have been devoted to the search for alternative sources of pluripotent cell lines. In this review we discuss the use of artificial parthenogenesis as a way to create entities, called parthenotes, that may represent an alternative ethical source for pluripotent cell lines. We describe the biological differences between parthenotes and embryos, in order to provide a rationale for the discussion on whether their use can be acceptable as a source of stem cells. We present data derived from animal models on the extent parthenogenetic stem cells are similar to biparental cell lines and discuss these aspects in the context of their extension to the human species. Finally, we present experiments recently carried out in our laboratory that allowed us to generate human parthenotes through artificial activation of human oocytes and to use them as a source for the derivation of parthenogenetic pluripotent cell lines.

Production of cloned horse foals using roscovitine-treated donor cells and activation with sperm extract and/or ionomycin

We evaluated the effect of different activation treatments on the production of blastocysts and foals by nuclear transfer. Donor cells were prepared using roscovitine treatment, which has previously been associated with increased production of viable offspring. All activation treatments were followed by culture in 6-dimethylaminopurine (6-DMAP) for 4 h. In experiment 1, blastocyst production after activation by injection of sperm extract followed by treatment with ionomycin was significantly higher than that for activation with a serial treatment of ionomycin, 6-DMAP, and ionomycin (12.5 vs 2.8%; P < 0.05) and tended to be higher than that for injection of sperm extract alone (3.4%; P = 0.07). In experiment 2, there were no significant differences in blastocyst development among treatments with ionomycin once or twice, sperm extract then ionomycin, or ionomycin then sperm extract (range 4.6-7.3%). Overall, transfer of 26 blastocysts resulted in 16 pregnancies (62%) and 9 live foals (35% of transferred embryos). Treatment with sperm extract followed by ionomycin produced a live foal rate per embryo transferred of 5/10 (50%). One foal died of pneumonia 48 h post partum and one foal died at 1 week of age after complications during induction of anesthesia; the remaining seven foals are currently 10-14 months of age.

In vitro development of human oocytes after parthenogenetic activation or intracytoplasmic sperm injection

OBJECTIVE

To compare directly in vitro developmental competence between parthenogenetically activated and intracytoplasmic sperm injection (ICSI)-fertilized oocytes.

DESIGN

For each patient, three metaphase II oocytes were randomized to the ICSI procedure, while n-3 were allocated to parthenogenetic activation.

SETTING

University hospital infertility unit.

PATIENTS

Thirty-eight patients, aged 35.2 +/- 3.3 years (mean +/- SD) selected for ICSI.

INTERVENTIONS

After 1 hour from denudation, oocytes were either fertilized by ICSI (n = 114) or chemically activated (n = 104). Fertilized and activated oocytes were cultured for up to 3 and 5 days, respectively.

MAIN OUTCOME MEASURES

Development rate, cell number, and morphological grade during culture.

RESULTS

The two groups showed no significant differences between rates of fertilization and parthenogenetic activation, development, and blastomere number on days 2 and 3 of culture. However, parthenotes showed a lower morphological grade, and a significantly lower proportion went on cleaving to day 3, when only activated rather than total numbers of oocytes were considered. On day 5 after activation, nine oocytes (8.6%) reached the blastocyst stage, representing 12.9% of parthenotes.

CONCLUSIONS

Since most parameters examined in this study were similar between activated and fertilized oocytes, parthenogenetic activation may be a useful tool for the preclinical evaluation of experimental procedures.

Human therapeutic cloning (NTSC)

Human therapeutic cloning or nuclear transfer stem cells (NTSC) to produce patient-specific stem cells, holds considerable promise in the field of regenerative medicine. The recent withdrawal of the only scientific publications claiming the successful generation of NTSC lines afford an opportunity to review the available research in mammalian reproductive somatic cell nuclear transfer (SCNT) with the goal of progressing human NTSC. The process of SCNT is prone to epigenetic abnormalities that contribute to very low success rates. Although there are high mortality rates in some species of cloned animals, most surviving clones have been shown to have normal phenotypic and physiological characteristics and to produce healthy offspring. This technology has been applied to an increasing number of mammals for utility in research, agriculture, conservation, and biomedicine. In contrast, attempts at SCNT to produce human embryonic stem cells (hESCs) have been disappointing. Only one group has published reliable evidence of success in deriving a cloned human blastocyst, using an undifferentiated hESC donor cell, and it failed to develop into a hESC line. When optimal conditions are present, it appears that in vitro development of cloned and parthenogenetic embryos, both of which may be utilized to produce hESCs, may be similar to in vitro fertilized embryos. The derivation of ESC lines from cloned embryos is substantially more efficient than the production of viable offspring. This review summarizes developments in mammalian reproductive cloning, cell-to-cell fusion alternatives, and strategies for oocyte procurement that may provide important clues facilitating progress in human therapeutic cloning leading to the successful application of cell-based therapies utilizing autologous hESC lines.

Developmental competence of human in vitro aged oocytes as host cells for nuclear transfer

BACKGROUND

Improving human nuclear transfer (NT) efficiencies is paramount for the development of patient-specific stem cell lines, although the opportunities remain limited owing to difficulties in obtaining fresh mature oocytes.

METHODS

Therefore, the developmental competence of aged, failed-to-fertilize human oocytes as an alternate cytoplasmic source for NT was assessed and compared with use of fresh, ovulation-induced oocytes. To further characterize the developmental potential of aged oocytes, parthenogenetic activation, immunocytochemical analysis of essential microtubule proteins involved in meiotic and mitotic division, and RT-PCR in single oocytes (n = 6) was performed to determine expression of oocyte-specific genes [oocyte-specific histone 1 (H1FOO), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), zygote arrest 1 (ZAR1)] and microtubule markers [nuclear mitotic arrest (NuMA), minus-end directed motor protein HSET and the microtubule kinesin motor protein EG5].

RESULTS

For NT, enucleation and fusion rates of aged oocytes were significantly lower compared with fresh oocytes (P < 0.05). Cleavage rates and subsequent development were poor. In addition, parthenote cleavage was low. Immunocytochemical analysis revealed that many oocytes displayed aberrant expression of NuMA and EG5, had disrupted meiotic spindles and tetrapolar spindles. One of the six oocytes misexpressed GDF9, BMP15 and ZAR1. Two oocytes expressed EG5 messenger RNA (mRNA), and HSET and NuMA were not detectable. RT-PCR of mRNA for oocyte specific genes and microtubule markers in single aged oocytes.

CONCLUSIONS

Thus, aneuploidy and spindle defects may contribute to poor parthenogenetic development and developmental outcomes following NT.

Screening for hereditary hemochromatosis: a clinical practice guideline from the American College of Physicians

Hereditary hemochromatosis is a genetic disorder of iron metabolism. Diagnosis of hereditary hemochromatosis is usually based on a combination of various genetic or phenotypic criteria. Decisions regarding screening are difficult because of the variable penetrance of mutations of the HFE gene and the absence of any definitive trials addressing the benefits and risks of therapeutic phlebotomy in asymptomatic patients or those with only laboratory abnormalities. The purpose of this guideline is to increase physician awareness of hereditary hemochromatosis, particularly the variable penetrance of genetic mutations; aid in case finding; and explain the role of genetic testing. This guideline provides recommendations based on a review of evidence in the accompanying background paper by Schmitt and colleagues. The target audience for this guideline is internists and other primary care physicians. The target patient population is all persons who have a probability or susceptibility of developing hereditary hemochromatosis, including the relatives of individuals who already have the disease.

Phospholipase Cζ causes Ca2+ oscillations and parthenogenetic activation of human oocytes

At fertilization in mammals the sperm activates development of the oocyte by inducing a prolonged series of oscillations in the cytosolic free Ca2+concentration. One theory of signal transduction at fertilization suggests that the sperm cause the Ca2+oscillations by introducing a protein factor into the oocyte after gamete membrane fusion. We recently identified this sperm-specific protein as phospholipase Cζ (PLCζ), and we showed that PLCζ triggers Ca2+oscillations in unfertilized mouse oocytes. Here we report that microinjection of the complementary RNA for human PLCζ causes prolonged Ca2+oscillations in aged human oocytes that had failed to fertilize duringin vitrofertilization or intracytoplasmic sperm injection. The frequency of Ca2+oscillations was related to the concentration of complementary RNA injected. At low concentrations, PLCζ stimulated parthenogenetic activation of oocytes. These embryos underwent cleavage divisions and some formed blastocysts. These data show that PLCζ is a novel parthenogenetic stimulus for human oocytes and that it is unique in its ability to mimic the repetitive nature of the Ca2+stimulus provided by the sperm during human fertilization.

Activation of mouse oocytes requires multiple sperm factors but not sperm PLCgamma1

A sperm cytosolic factor is responsible for oocyte activation at fertilization in mammals. The molecular identity of this factor is not yet known, although a sperm phospholipase Cgamma (PLCgamma) is a potential candidate. In this study, cation-exchange chromatography with a Heparin column was used for the fractionation of porcine sperm cytosolic extracts. Oocyte activation potential of the resulting fractions was tested and active fractions were subjected to Western blot analysis using antibodies specific to PLCgamma1. PLCgamma1 was detected in fractions other than those supporting oocyte activation (Ca(2+)-release and pronuclear formation). The active Heparin fraction was then purified on a Mono Q anion-exchange column. One of the resulting fractions still contained Ca(2+)-releasing activity, but pronuclear formation did not occur. We conclude that sperm PLCgamma1 is not involved in oocyte activation and that Ca(2+)-release and pronuclear formation requires multiple factors from sperm cytosol.