Activation of rabbit oocytes: the impact of the Ca2+ signal regime on development

The road to maturation: somatic cell interaction and self-organization of the mammalian oocyte

Mammalian oocytes go through a long and complex developmental process while acquiring the competencies that are required for fertilization and embryogenesis. Recent advances in molecular genetics and quantitative live imaging reveal new insights into the molecular basis of the communication between the oocyte and ovarian somatic cells as well as the dynamic cytoskeleton-based events that drive each step along the pathway to maturity. Whereas self-organization of microtubules and motor proteins direct meiotic spindle assembly for achieving genome reduction, actin filaments are instrumental for spindle positioning and the establishment of oocyte polarity needed for extrusion of polar bodies. Meiotic chromatin provides key instructive signals while being 'chauffeured' by both cytoskeletal systems.

Disparate consequences of heat stress exposure during meiotic maturation: embryo development after chemical activation vs fertilization of bovine oocytes

Consequences of heat stress exposure during the first 12 h of meiotic maturation differed depending on how and when bovine oocytes were activated. If heat-stressed oocytes underwent IVF at ~24 h, blastocyst development was less than for respective controls and similar to that obtained for nonheat-stressed oocytes undergoing IVF at 30 h (i.e. slightly aged). In contrast, if heat-stressed oocytes underwent chemical activation with ionomycin/6-dimethylaminopurine at 24 h, blastocyst development was not only higher than respective controls, but also equivalent to development obtained after activation of nonheat-stressed oocytes at 30 h. Developmental differences in chemically activated vs IVF-derived embryos were not related to fertilization failure or gross alterations in cytoskeletal components. Rather, ionomycin-induced calcium release and MAP kinase activity were less in heat-stressed oocytes. While underlying mechanisms are multifactorial, ability to obtain equivalent or higher development after parthenogenetic activation demonstrates that oocytes experiencing heat stress during the first 12 h of meiotic maturation have the necessary components to develop to the blastocyst stage, but fail to do so after fertilization.

Dynamic analysis of Ca²+ level during bovine oocytes maturation and early embryonic development

Mammalian oocyte maturation and early embryo development processes are Ca²⁺-dependent. In this study, we used confocal microscopy to investigate the distribution pattern of Ca²⁺ and its dynamic changes in the processes of bovine oocytes maturation, in vitro fertilization (IVF), parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT) embryo development. During the germinal vesicle (GV) and GV breakdown stage, Ca²⁺ was distributed in the cortical ooplasm and throughout the oocytes from the MI to MII stage. In IVF embryos, Ca²⁺ was distributed in the cortical ooplasm before the formation of the pronucleus. In 4-8 cell embryos and morulas, Ca²⁺ was present throughout the blastomere. In PA embryos, Ca²⁺ was distributed throughout the blastomere at 48 h, similar to in the 4-cell and 8-cell phase and the morula. At 6 h after activation, there was almost no distribution of Ca²⁺ in the SCNT embryos. However, Ca²⁺ was distributed in the donor nucleus at 10 h and it was distributed throughout the blastomere in the 2-8 cell embryos. In this study, Ca²⁺ showed significant fluctuations with regularity of IVF and SCNT groups, but PA did not. Systematic investigation of the Ca²⁺ location and distribution changes during oocyte maturation and early embryo development processes should facilitate a better understanding of the mechanisms involved in oocyte maturation, reconstructed embryo activation and development, ultimately improving the reconstructed embryo development rate.

Artificial oocyte activation and human failed-matured oocyte vitrification followed by in vitro maturation

The investigation presented in this paper was conducted on the effect of oocytes activation on frozen–thawed human immature oocytes followed by in vitro maturation (IVM). A total of 386 failed-matured oocytes (germinal vesicle (GV) and metaphase I (MI) stages) was randomly divided into two groups: fresh group and vitrification group, GV group and MI group, respectively). The matured oocytes were subject to intracytoplasmic sperm injection (ICSI) after IVM had been carried out. The vitrification group was randomly divided into two groups: controlled and artificial oocyte activation (AOA). The injected oocytes in the controlled group were cultured in cleavage medium. The AOA group oocytes were activated by exposing them to 7% anhydrous alcohol for 6 min then cultured in cleavage medium as well. The rates of fertilization and early embryonic development were compared between the controlled and AOA groups. In MI vitrification group, the high-quality embryo formation rate and blastocyst formation rate were significantly higher in the AOA group than in the controlled group (P < 0.01). In the GV vitrification group, the high-quality embryo formation rate was significantly higher in the AOA group than in the controlled group (P < 0.05). These results indicate that AOA may be good for early embryonic development of vitrified immature human oocytes.

Rhythmic actomyosin-driven contractions induced by sperm entry predict mammalian embryo viability

Fertilization-induced cytoplasmic flows are a conserved feature of eggs in many species. However, until now the importance of cytoplasmic flows for the development of mammalian embryos has been unknown. Here, by combining a rapid imaging of the freshly fertilized mouse egg with advanced image analysis based on particle image velocimetry, we show that fertilization induces rhythmical cytoplasmic movements that coincide with pulsations of the protrusion forming above the sperm head. We find that these movements are caused by contractions of the actomyosin cytoskeleton triggered by Ca²⁺ oscillations induced by fertilization. Most importantly, the relationship between the movements and the events of egg activation makes it possible to use the movements alone to predict developmental potential of the zygote. In conclusion, this method offers, thus far, the earliest and fastest, non-invasive way to predict the viability of eggs fertilized in vitro and therefore can potentially improve greatly the prospects for IVF treatment.

Cytoplasmic flows—the movement of cytoplasmic material—can be detected following the fertilization of an egg by a sperm in many species. In this study, rhythmic cytoplasmic flows are shown to be induced in mice by calcium-induced cytoskeleton contractions which could be used to predict the successful outcome of fertilization.

Cellular and molecular mechanisms of various types of oocyte aging

It is well established that age-related decline of a woman's fertility is related to the poor developmental potential of her gametes. The age-associated decline in female fertility is largely attributable to the oocyte aging caused by ovarian aging. Age-associated oocyte aging results in a decrease in oocyte quality. In contrast to ovarian aging, there is a concept of postovulatory oocyte aging. Postovulatory aging of oocytes, not being fertilized for a prolonged time after ovulation, is known to significantly affect the development of oocytes. Both categories of oocyte aging have similar phenotypes of reproductive failure. However, the mechanisms of the decline in oocyte quality are not necessarily equivalent. An age-dependent increase in aneuploidy is a key determinant of oocyte quality. The reduced expression of molecules regulating cell cycle control during meiosis might be involved in the age-dependent increase in aneuploidy. The mechanism of age-associated oocyte aging might be involved in mitochondrial dysfunction, whose etiologies are still unknown. Alternatively, the mechanism of postovulatory oocyte aging might be involved in reactive oxygen species-induced mitochondrial injury pathways followed by abnormal intracellular Ca²⁺ regulation of the endoplasmic reticulum. We suggest that future research into the mechanism of oocyte aging will be necessary to develop a method to rescue the poor developmental potential of aged oocytes.

Molecular cloning and characterization of phospholipase C zeta in equine sperm and testis reveals species-specific differences in expression of catalytically active protein

Oocyte activation at fertilization is brought about by the testis-specific phospholipase C zeta (PLCZ), owing to its ability to induce oscillations in intracellular Ca(2+) concentration ([Ca(2+)](i)). Whereas this is a highly conserved mechanism among mammals, important species-specific differences in PLCZ sequence, activity, and expression have been reported. Thus, the objectives of this research were to clone and characterize the intracellular Ca(2+)-releasing activity and expression of equine PLCZ in sperm and testis. Molecular cloning of equine PLCZ yielded a 1914-bp sequence that translated into a protein of the appropriate size (~73 kDa), as detected with an anti-PLCZ-specific antibody. Microinjection of 1 μg/μl of equine PLCZ cRNA supported [Ca(2+)](i) oscillations in murine oocytes that were of a higher relative frequency than those generated by an equivalent concentration of murine Plcz cRNA. Immunofluorescence revealed expression of PLCZ over the acrosome, equatorial segment, and head-midpiece junction; unexpectedly, PLCZ also localized to the principal piece of the flagellum in all epididymal, uncapacitated, and capacitated sperm. Immunostaining over the acrosome was abrogated after induction of acrosomal exocytosis. Moreover, injection of either sperm heads or tails into mouse oocytes showed that PLCZ in both fractions is catalytically active. Immunohistochemistry on equine testis revealed expression as early as the round spermatid stage, and injection of these cells supported [Ca(2+)](i) oscillations in oocytes. In summary, we report that equine PLCZ displays higher intrinsic intracellular Ca(2+)-releasing activity than murine PLCZ and that catalytically active protein is expressed in round spermatids as well as the sperm flagellum, emphasizing important species-specific differences. Moreover, some of these results may suggest potential novel roles for PLCZ in sperm physiology.

Mitochondrial function in the human oocyte and embryo and their role in developmental competence

The role of mitochondria as a nexus of developmental regulation in mammalian oogenesis and early embryogenesis is emerging from basic research in model species and from clinical studies in infertility treatments that require in vitro fertilization and embryo culture. Here, mitochondrial bioenergetic activities and roles in calcium homeostasis, regulation of cytoplasmic redox state, and signal transduction are discussed with respect to outcome in general, and as possible etiologies of chromosomal defects, maturation and fertilization failure in human oocytes, and as causative factors in early human embryo demise. At present, the ability of mitochondria to balance ATP supply and demand is considered the most critical factor with respect to fertilization competence for the oocyte and developmental competence for the embryo. mtDNA copy number, the timing of mtDNA replication during oocyte maturation, and the numerical size of the mitochondrial complement in the oocyte are evaluated with respect to their relative contribution to the establishment of developmental competence. Rather than net cytoplasmic bioenergetic capacity, the notion of functional compartmentalization of mitochondria is presented as a means by which ATP may be differentially supplied and localized within the cytoplasm by virtue of stage-specific changes in mitochondrial density and potential (ΔΨm). Abnormal patterns of calcium release and sequestration detected at fertilization in the human appear to have coincident effects on levels of mitochondrial ATP generation. These aberrations are not uncommon in oocytes obtained after ovarian hyperstimulation for in vitro fertilization. The possibility that defects in mitochondrial calcium regulation or bioenergetic homeostasis could have negative downstream development consequences, including imprinting disorders, is discussed in the context of signaling pathways and cytoplasmic redox state.

Oocyte activation, phospholipase C zeta and human infertility

BACKGROUND

Mammalian oocytes are activated by intracellular calcium (Ca(2+)) oscillations following gamete fusion. Recent evidence implicates a sperm-specific phospholipase C zeta, PLCζ, which is introduced into the oocyte following membrane fusion, as the responsible factor. This review summarizes the current understanding of human oocyte activation failure and describes recent discoveries linking certain cases of male infertility with defects in PLCζ expression and activity. How these latest findings may influence future diagnosis and treatment options are also discussed.

METHODS

Systematic literature searches were performed using PubMed, ISI-Web of Knowledge and The Cochrane Library. We also scrutinized material from the United Nations and World Health Organization databases (UNWHO) and the Human Fertilization and Embryology Authority (HFEA).

RESULTS AND CONCLUSIONS

Although ICSI results in average fertilization rates of 70%, complete or virtually complete fertilization failure still occurs in 1-5% of ICSI cycles. While oocyte activation failure can, in some cases, be overcome by artificial oocyte activators such as calcium ionophores, a more physiological oocyte activation agent might release Ca(2+) within the oocyte in a more efficient and controlled manner. As PLCζ is now widely considered to be the physiological agent responsible for activating mammalian oocytes, it represents both a novel diagnostic biomarker of oocyte activation capability and a possible mode of treatment for certain types of male infertility.

Portrait of an oocyte: our obscure origin

Oocytes play a pivotal role in the cycle of human life. As we discuss here, after emerging from germline stem cells in the fetus, they grow in a follicular niche in which development is harmonized for timely ovulation and hormone secretion after puberty. Most human oocytes have poor developmental competence and are peculiarly vulnerable to chromosomal malsegregation, especially as women pass the optimal years of fertility and may begin to turn to assisted reproductive technologies (ARTs) and egg donation. Research needs to focus on the molecular factors involved and the environmental niche required for optimal development of oocytes, with the aim of increasing their numbers and quality for ARTs, since these are the factors that so often limit human fertility.

Generation of pluripotent stem cells from eggs of aging mice

Oocytes can reprogram genomes to form embryonic stem (ES) cells. Although ES cells largely escape senescence, oocytes themselves do senesce in the ovaries of most mammals. It remains to be determined whether ES cells can be established using eggs from old females, which exhibit reproductive senescence. We attempted to produce pluripotent stem cell lines from artificial activation of eggs (also called pES) from reproductive aged mice, to determine whether maternal aging affects pES cell production and pluripotency. We show that pES cell lines were generated with high efficiency from reproductive aged (old) mice, although parthenogenetic embryos from these mice produced fewer ES clones by initial two passages. Further, pES cell lines generated from old mice showed telomere length, expression of pluripotency molecular markers (Oct4, Nanog, SSEA1), alkaline phosphatase activity, teratoma formation and chimera production similar to young mice. Notably, DNA damage was reduced in pES cells from old mice compared to their progenitor parthenogenetic blastocysts, and did not differ from that of pES cells from young mice. Also, global gene expression differed only minimally between pES cells from young and old mice, in contrast to marked differences in gene expression in eggs from young and old mice. These data demonstrate that eggs from old mice can generate pluripotent stem cells, and suggest that the isolation and in vitro culture of ES cells must select cells with high levels of DNA and telomere integrity, and/or with capacity to repair DNA and telomeres.

Qualitative and morphometric analysis of the ultrastructure of human oocytes cryopreserved by two alternative slow cooling protocols

PURPOSE

To ascertain possible cell damage from cryopreservation, the ultrastructure of human oocytes cryopreserved by slow cooling was assessed.

MATERIALS AND METHODS

Cryopreservation was performed through two protocols with one-step or two-step propanediol. Fresh control oocytes were examined for comparison. Samples were processed for transmission electron microscopy analysis.

RESULTS

By light microscopy, both fresh and frozen-thawed oocytes appeared regularly rounded, with intact zona pellucida, and homogeneous cytoplasm. By electron microscopy observation, organelles were abundant and uniformly dispersed. Mitochondria-smooth endoplasmic reticulum associations appeared regular. However, both the amount and density of cortical granules appeared abnormally reduced in frozen-thawed samples. Slight to moderate vacuolization was also found in the ooplasm of oocytes of both frozen groups.

CONCLUSIONS

Slow cooling ensures a good overall preservation of human oocytes. However, cytoplasmic vacuolization and cortical granule loss appears associated with cryopreservation, irrespective of the protocol used.

Analysis of cat oocyte activation methods for the generation of feline disease models by nuclear transfer

BACKGROUND

Somatic cell nuclear transfer in cats offers a useful tool for the generation of valuable research models. However, low birth rates after nuclear transfer hamper exploitation of the full potential of the technology. Poor embryo development after activation of the reconstructed oocytes seems to be responsible, at least in part, for the low efficiency. The objective of this study was to characterize the response of cat oocytes to various stimuli in order to fine-tune existing and possibly develop new activation methods for the generation of cat disease models by somatic cell nuclear transfer.

METHODS

First, changes in the intracellular free calcium concentration [Ca2+]i in the oocytes induced by a number of artificial stimuli were characterized. The stimuli included electroporation, ethanol, ionomycin, thimerosal, strontium-chloride and sodium (Na+)-free medium. The potential of the most promising treatments (with or without subsequent incubation in the presence of cycloheximide and cytochalasin B) to stimulate oocyte activation and support development of the resultant parthenogenetic embryos was then evaluated. Finally, the most effective methods were selected to activate oocytes reconstructed during nuclear transfer with fibroblasts from mucopolysaccharidosis I- and alpha-mannosidosis-affected cats.

RESULTS

All treatments were able to elicit a [Ca2+]i elevation in the ooplasm with various characteristics. Pronuclear formation and development up to the blastocyst stage was most efficiently triggered by electroporation (60.5 +/- 2.9 and 11.5 +/- 1.7%) and the combined thimerosal/DTT treatment (67.7 +/- 1.8 and 10.6 +/- 1.9%); incubation of the stimulated oocytes with cycloheximide and cytochalasin B had a positive effect on embryo development. When these two methods were used to activate oocytes reconstructed during nuclear transfer, up to 84.9% of the reconstructed oocytes cleaved. When the 2 to 4-cell embryos (a total of 220) were transferred into 19 recipient females, 4 animals became pregnant. All of the fetuses developed from oocytes activated by electroporation followed by cycloheximide and cytochalasin B incubation; no fetal development was detected as a result of thimerosal/DTT activation. Although heartbeats were detected in two of the cloned fetuses, no term development occurred.

CONCLUSION

Electroporation proved to be the most effective method for the activation of cat oocytes reconstructed by nuclear transfer. The combined thimerosal/DTT treatment followed by cycloheximide and cytochalasin B incubation triggered development effectively to the blastocyst stage; whether it is a viable option to stimulate term development of cloned cat embryos needs further investigations.

Inositol 1,4,5-trisphosphate receptor 1 degradation in mouse eggs and impact on [Ca2+]i oscillations

The initiation of normal embryo development depends on the completion of all events of egg activation. In all species to date, egg activation requires an increase(s) in the intracellular concentration of calcium ([Ca(2+)](i)), which is almost entirely mediated by inositol 1,4,5-trisphosphate receptor 1 (IP(3)R1). In mammalian eggs, fertilization-induced [Ca(2+)](i) responses exhibit a periodic pattern that are called [Ca(2+)](i) oscillations. These [Ca(2+)](i) oscillations are robust at the beginning of fertilization, which occurs at the second metaphase of meiosis, but wane as zygotes approach the pronuclear stage, time after which in the mouse oscillations cease altogether. Underlying this change in frequency are cellular and biochemical changes associated with egg activation, including degradation of IP(3)R1, progression through the cell cycle, and reorganization of intracellular organelles. In this study, we investigated the system requirements for IP(3)R1 degradation and examined the impact of the IP(3)R1 levels on the pattern of [Ca(2+)](i) oscillations. Using microinjection of IP(3) and of its analogs and conditions that prevent the development of [Ca(2+)](i) oscillations, we show that IP(3)R1 degradation requires uniform and persistently elevated levels of IP(3). We also established that progressive degradation of the IP(3)R1 results in [Ca(2+)](i) oscillations with diminished periodicity while a near complete depletion of IP(3)R1s precludes the initiation of [Ca(2+)](i) oscillations. These results provide insights into the mechanism involved in the generation of [Ca(2+)](i) oscillations in mouse eggs.

Calmodulin-dependent protein kinase gamma 3 (CamKIIgamma3) mediates the cell cycle resumption of metaphase II eggs in mouse

Mature mammalian eggs are ovulated arrested at meiotic metaphase II. Sperm break this arrest by an oscillatory Ca(2+) signal that is necessary and sufficient for the two immediate events of egg activation: cell cycle resumption and cortical granule release. Previous work has suggested that cell cycle resumption, but not cortical granule release, is mediated by calmodulin-dependent protein kinase II (CamKII). Here we find that mouse eggs contain detectable levels of only one CamKII isoform, gamma 3. Antisense morpholino knockdown of CamKIIgamma3 during oocyte maturation produces metaphase II eggs that are insensitive to parthenogenetic activation by Ca(2+) stimulation and insemination. The effect is specific to this morpholino, as a 5-base-mismatch morpholino is without effect, and is rescued by CamKIIgamma3 or constitutively active CamKII cRNAs. Although CamKII-morpholino-treated eggs fail to exit metaphase II arrest, cortical granule exocytosis is not blocked. Therefore, CamKIIgamma3 plays a necessary and sufficient role in transducing the oscillatory Ca(2+) signal into cell cycle resumption, but not into cortical granule release.

Effect of sperm extract injection volume, injection of PLCzeta cRNA, and tissue cell line on efficiency of equine nuclear transfer

We evaluated the effect of different activation methods on blastocyst development after equine nuclear transfer. All activation treatments were followed by incubation in 2 mM 6-dimethylaminopurine for 4 h. In Experiment 1, reconstructed oocytes were injected with sperm extract for 0.1, 0.2, 0.4, 0.8, or 1.6 sec using a FemtoJet injection device, then treated with ionomycin. The blastocyst rate (9.8%) for 0.1-sec injection was significantly higher than that for 0.2 sec (0%) or 0.8 sec (1.4%). In Experiment 2, injection of murine PLCzeta cRNA before or after ionomycin treatment did not increase blastocyst development (0 and 4.5%) over a control treatment (injection of sperm extract after ionomycin exposure; 5.6%). Transfer of 10 blastocysts produced in Experiments 1 and 2 resulted in five pregnancies, all lost before 70 days of gestation. In Experiment 3, cells from a second biopsy sample from the same horse produced significantly more blastocysts than did the original sample (4/44 vs. 0/58; p < 0.05). Transfer of these four blastocysts produced two viable foals. In Experiment 4, blastocyst development rates did not differ between oocytes in metaphase I or II at the time of nuclear transfer (16.7 and 3.0%, respectively). A healthy foal was produced from a blastocyst originating from a metaphase I oocyte.

Activation regimens for full-term development of rabbit oocytes injected with round spermatids

The present study was designed to investigate the effect of activation regimens on full-term development of rabbit oocytes after round spermatid injection (ROSI). In the first series, rabbit oocytes were treated with 5 microM ionomycin before ROSI, after ROSI, or before and after ROSI. In addition, non-treated oocytes were subjected to intracytoplasmic sperm injection (ICSI) using ejaculated spermatozoa. Cleavage rate of ROSI oocytes activated before and after ROSI (55%) was comparable with that of ICSI oocytes (60%), and significantly higher than those of ROSI oocytes activated either before or after ROSI (29-39%; P < 0.05). No offspring were produced by transfer of the cleaving ROSI oocytes, while 8% of the cleaving ICSI oocytes transferred gave birth to offspring. In the second series, oocytes were exposed to 5, 10, or 20 microM ionomycin, followed by ROSI, 5 microM ionomycin treatment, and incubation with 5 microg/ml cycloheximide (CHX) + 2 mM 6-dimethylaminopurine (DMAP). Significantly higher cleavage rates were derived from oocytes activated with 10 and 20 microM ionomycin before ROSI (91% and 82%, respectively; P < 0.05) compared to those activated with 5 microM ionomycin before ROSI (53%). Live offspring were obtained when the cleaving ROSI oocytes with the initial ionomycin treatment at 5 and 10 microM were transferred (offspring rate 2% and 4%, respectively). These activation regimens, however, were not valid for the ROSI using cryopreserved round spermatids. In conclusion, rabbit ROSI oocytes were capable of developing into full-term when the oocytes were activated with a combined treatment of ionomycin and CHX/DMAP.

Live birth of somatic cell-cloned rabbits following trichostatin A treatment and cotransfer of parthenogenetic embryos

Somatic cell nuclear transfer (SCNT) efficiency is still low in rabbit. Previous studies indicated that trichostatin A (TSA) treatment could improve cloning efficiency and term development in the mouse, and cotransfer of parthenogenetic (PA) embryos benefited the pregnancy of cloned embryos in porcine and the mouse. In this study we investigated the effect of TSA treatment on the term development of the SCNT rabbit embryos, and the possibility of the pregnancy maintenance of clones by cotransfer of PA embryos. The SCNT embryos were produced by fusing cumulus cells with enucleated cytoplasts before activation by electrical stimulation, and Dimethylaminopurine (6-DMAP) and Cyclohexamide (CHX) treatments. They were cultured in EBSS-complete medium regardless of their treatment with or without TSA. In vitro developmental data showed no differences in the cleavage and the blastocyst rates, and the blastocyst cell number between the TSA-treated and the untreated SCNT embryos. Two of the six recipients became pregnant after the embryo transfer (ET) in the TSA-treated group, and one pregnant female delivered seven live and three stillborn pups. The death of all live pups occurred within an hour to 19 days. Four of the seven recipients became pregnant in the TSA-untreated group. Three of them gave birth to six live and eight stillborn pups. Four pups of the TSA-untreated group have grown into adulthood, and three of them produced progeny. Cotransfer of three to four PA embryos with 26-32 SCNT embryos to the same recipient resulted in pregnancy and birth rates statistically no different compared to the control SCNT ET group. In conclusion, our results indicate that TSA treatment has a limited effect on the in vitro development of the SCNT embryos; furthermore, both the TSA-treated and the untreated clones can develop to term in rabbits, but none of the offspring from TSA-treated embryos survived to adulthood in our experiment.

Mouse androgenetic embryonic stem cells differentiated to multiple cell lineages in three embryonic germ layers in vitro

The embryos of some rodents and primates can precede early development without the process of fertilization; however, they cease to develop after implantation because of restricted expressions of imprinting genes. Asexually developed embryos are classified into parthenote/gynogenote and androgenote by their genomic origins. Embryonic stem cells (ESCs) derived from asexual origins have also been reported. To date, ESCs derived from parthenogenetic embryos (PgESCs) have been established in some species, including humans, and the possibility to be alternative sources for autologous cell transplantation in regenerative medicine has been proposed. However, some developmental characteristics, which might be important for therapeutic applications, such as multiple differentiation capacity and transplantability of the ESCs of androgenetic origin (AgESCs) are uncertain. Here, we induced differentiation of mouse AgESCs and observed derivation of neural cells, cardiomyocytes and hepatocytes in vitro. Following differentiated embryoid body (EB) transplantation in various mouse strains including the strain of origin, we found that the EBs could engraft in theoretically MHC-matched strains. Our results indicate that AgESCs possess at least two important characteristics, multiple differentiation properties in vitro and transplantability after differentiation, and suggest that they can also serve as a source of histocompatible tissues for transplantation.

Cryopreservation of manipulated embryos: tackling the double jeopardy

The aim of the present review is to provide information to researchers and practitioners concerning the reasons for the altered viability and the medium- and long-term consequences of cryopreservation of manipulated mammalian embryos. Embryo manipulation is defined herein as the act or process of manipulating mammalian embryos, including superovulation, AI, IVM, IVF, in vitro culture, intracytoplasmic sperm injection, embryo biopsy or splitting, somatic cell nuclear transfer cloning, the production of sexed embryos (by sperm sexing), embryo cryopreservation, embryo transfer or the creation of genetically modified (transgenic) embryos. With advances in manipulation technologies, the application of embryo manipulation will become more frequent; the proper prevention and management of the resulting alterations will be crucial in establishing an economically viable animal breeding technology.

Activation of bovine somatic cell nuclear transfer embryos by PLCZ cRNA injection

The production of cloned animals by the transfer of a differentiated somatic cell into an enucleated oocyte circumvents fertilization. During fertilization, the sperm delivers a sperm-specific phospholipase C (PLCZ) that is responsible for triggering Ca(2)(+) oscillations and oocyte activation. During bovine somatic cell nuclear transfer (SCNT), oocyte activation is artificially achieved by combined chemical treatments that induce a monotonic rise in intracellular Ca(2)(+) and inhibit either phosphorylation or protein synthesis. In this study, we tested the hypothesis that activation of bovine nuclear transfer embryos by PLCZ improves nuclear reprogramming. Injection of PLCZ cRNA into bovine SCNT units induced Ca(2)(+) oscillations similar to those observed after fertilization and supported high rates of blastocyst development similar to that seen in embryos produced by IVF. Furthermore, gene expression analysis at the eight-cell and blastocyst stages revealed a similar expression pattern for a number of genes in both groups of embryos. Lastly, levels of trimethylated lysine 27 at histone H3 in blastocysts were higher in bovine nuclear transfer embryos activated using cycloheximide and 6-dimethylaminopurine (DMAP) than in those activated using PLCZ or derived from IVF. These results demonstrate that exogenous PLCZ can be used to activate bovine SCNT-derived embryos and support the hypothesis that a fertilization-like activation response can enhance some aspects of nuclear reprogramming.

Porcine cumulus cell influences ooplasmic mitochondria-lipid distributions, GSH-ATP contents and calcium release pattern after electro-activation

The objective was to explore mechanisms of the influence of porcine cumulus cells (CC) on oocyte maturation. Immature porcine oocytes were matured in groups of denuded oocyte (DOs), cumulus-oocyte complexes (COCs), denuded oocytes co-cultured with CC (DoCC), or with cumulus-oocyte complexes (DoCOCs). Ooplasmic mitochondria-lipid distributions, glutathione (GSH)-adenosine triphosphate (ATP) contents, calcium release pattern, and developmental competence after parthenogenetic activation were assessed after IVM. The portion of matured oocytes after IVM and the developmental competence and GSH content in single oocytes were lower in DOs than in COCs (P<0.05). In contrast, the maturation rate and development in DoCOCs and COCs were higher than in DoCC and DOs (P<0.05). The blastocyst rate in DoCOCs was higher than in DOs (P<0.05), and ATP content in COCs was higher than in all other groups (P<0.01). In addition, the rate of oocytes with damaged oolemma in DOs (35%) was significantly higher than in COCs (3%), DoCOCs (7%), and DoCC (10%). The rate of oocytes with evenly distributed mitochondria was 70% in DOs, which was significantly lower than in COCs and DoCC (89 and 84%, respectively). The percentage of oocytes with normal lipid droplets distributions in COCs (70%) was significantly higher than in three other groups, whereas both percentages in DoCC and DoCOCs were higher than in DOs (P<0.05). The duration of [Ca(2+)] rise in DOs was longer than in three other groups, whereas the duration was shortest in COCs. The amplitude of the [Ca(2+)] rise in DOs was significantly lower than in other groups (P<0.05), but the amplitude did not differ significantly among DoCC, DoCOCs and COCs. In conclusion, the presence of porcine CC during IVM functionally affected ooplasmic mitochondria-lipid distributions and GSH-ATP contents, which may affect the calcium release pattern and developmental competence of oocytes after electro-activation.

The present status of artificial oocyte activation in assisted reproductive technology

Intracytoplasmic sperm injection (ICSI) is the most effective treatment for achieving fertilization in assisted reproductive technology (ART). However, fertilization failure occurs. The incidence of fertilization failure after ICSI is 1-5%. Approximately 50% of fertilization failure cases could be attributed to the abnormality of sperm factor. As the fertilization fails after ICSI using mature sperm, round spermatids and globozoospermia, artificial oocyte activation may provide a means of improving fertilization rates in such cases. The oocyte activation treatments used in clinical research include calcium (Ca) ionophore treatment, electrostimulation and strontium treatment. In terms of the efficiency of oocyte activation, electrostimulation and Ca ionophore gave better outcomes than strontium treatment. Strontium treatment causes Ca2+ oscillations in mice, so it has been viewed favorably. However, in human oocytes calcium oscillation has not been observed. The fertilization rate after ICSI was low in the case of globozoospermia and wiht round spermatids. Some cases of pregnancy were achieved by ICSI alone and oocyte activation methods were not essential in these cases. Among the various oocyte activation methods currently used, it should be noted that issues of genetic safety have not been addressed for the combined use of these oocyte activation methods. (Reprod Med Biol 2008; 7: 133-142).

Artificial oocyte activation with calcium ionophore A23187 in intracytoplasmic sperm injection cycles using surgically retrieved spermatozoa

OBJECTIVE

To evaluate the effect of artificial oocyte activation (AOA) on intracytoplasmic sperm injection (ICSI) cycles using surgically retrieved sperm.

DESIGN

Laboratory study.

SETTING

Fertility/assisted fertilization center.

PATIENT(S)

Couples undergoing surgical sperm retrieval for ICSI (n = 204).

INTERVENTION(S)

Application of calcium ionophore A23187 for AOA.

MAIN OUTCOME MEASURE(S)

Cycles were divided into experimental groups according to the origin of the sperm used for injection and the type of azoospermia: [1] testicular sperm aspiration in nonobstructive-azoospermic patients (TESA-NOA group, n = 58), [2] TESA in obstructive-azoospermic patients (TESA-OA group, n = 48), [3] and percutaneous epididymal sperm aspiration in obstructive-azoospermic patients (PESA-OA, n = 98). For each experimental group, cycles where AOA was applied (subgroup: activation) were compared with cycles in which AOA was not applied (subgroup: control). The fertilization, high-quality embryo, implantation, and pregnancy rates were compared among the subgroups.

RESULT(S)

For patients undergoing TESA, AOA did not improve ICSI outcomes for either type of azoospermia. However, for cases in which the injected sperm were retrieved from the epididymis, a statistically significantly increased rate of high-quality embryos was observed with AOA.

CONCLUSION(S)

Artificial oocyte activation may improve ICSI outcomes in azoospermic patients when epididymal, but not testicular spermatozoa, are injected.

Parthenogenetic development of in vitro matured porcine oocytes treated with chemical agents

Parthenogenetic activation is a possible way to produce homogeneous embryos with the same ploidy. These embryos could develop to the blastocyst stage during the cultivation. Probably such embryos could be used in other areas of biotechnology. The objectives of the present study were first to assess the ability of strontium-chloride to induce activation and parthenogenetic development in porcine oocytes in comparison with cycloheximide and 6-dimethylaminopurine; second to verify whether the combination of the two treatments improved activation and parthenogenetic development rates. At first, the effects of cycloheximide, 6-dimethylaminopurine and strontium-chloride on oocyte activation and embryonic development were compared. Oocytes from slaughterhouse ovaries were matured for 42h in tissue culture medium (TCM) 199 at 38.5 degrees C, 5% CO(2) in air. Matured oocytes were activated with 10mM strontium-chloride (S), 0.04mM cycloheximide (CX), 2mM 6-dimethylaminopurine (D) for 5h. The activation rate was judged by pronuclear formation of oocytes. Following the activation, oocytes were incubated in NCSU 37 medium for 6 days and in all groups more than 45% of oocytes activated. The activation rate for CX treatment was significantly higher (P<0.05) than for D (57.37+/-4.21% and 48.09+/-3.43%, respectively). In a second experiment in vitro matured porcine oocytes were activated using a combined treatment of strontium-chloride with cycloheximide (SCX) and strontium-chloride combined with 6-dimethylaminopurine (SD). In S and SCX groups more than 50% of oocytes were activated (53.29+/-5.39% and 54.3+/-7.29%, respectively). However a large portion of embryos stopped their development at the two- or four-cell stage. Significantly higher numbers of embryos could reach the eight-cell stage in SD and SCX than for S (7.8+/-1.0%, 7.2+/-4.0% and 3.9+/-3.1%, respectively). Blastocyst formation was only observed in S, CX and SCX. These results show that porcine in vitro matured oocytes can be artificially activated by cycloheximide, 6-dimethylaminopurine and strontium-chloride.

Verapamil reversibly inhibits spontaneous parthenogenetic activation in aged rat eggs cultured in vitro

The present study was designed to investigate whether verapamil could inhibit spontaneous parthenogenetic activation in aged rat eggs cultured in vitro. Eggs collected from oviduct after 19 h post human chorionic gonadotropin (hCG) were arrested at the metaphase-II (M-II) stage and exhibited a first polar body. Culture of these aged eggs in calcium/magnesium (Ca(2+)/Mg(2+))-deficient and serum-free medium for 3 h induced exit from M-II, a morphological sign of spontaneous parthenogenetic activation in all eggs. However, verapamil reversibly inhibited spontaneous parthenogenetic activation in a dose-dependent manner. Further, lower doses (6.25, 12.5, and 25 muM) of verapamil induced egg survival, while higher doses (50 and 100 muM) were associated with the appearance of morphological apoptotic features such as shrinkage, membrane blebbing and cytoplasmic granulation prior to degeneration. The DNA fragmentation was induced [as evidenced by terminal deoxynucleotidyl transferase (TdT) nick-end labeling (TUNEL) positive staining] in eggs undergoing morphological apoptotic changes. On the other hand, caspase-3 inhibitor (1 muM) partially inhibited morphological apoptotic changes (44.34+/-3.53%) suggesting the involvement of both Ca(2+)and caspase-3-mediated apoptotic pathways. These findings suggest that verapamil reversibly inhibits spontaneous parthenogenetic activation and induces egg survival at lower doses, while higher doses induce cell death via apoptosis.

Reactive oxygen species and oocyte aging: role of superoxide, hydrogen peroxide, and hypochlorous acid

Aging of the unfertilized oocyte inevitably occurs following ovulation, limiting its fertilizable life span. However, the mechanisms that regulate oocyte aging are still unclear. We hypothesize that reactive oxygen species such as superoxide (O2-), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl) are likely candidates that may initiate these changes in the oocyte. In order to test this hypothesis, we investigated direct effects of O2- [hypoxanthine/xanthine oxidase system generating 0.12 (n=42) and 0.25 (n=45) microM O2-/min], H2O2 (20 or 100 microM, n=60), and HOCl, (1, 10, and 100 microM, n=50) on freshly ovulated or relatively old mouse oocytes, while their sibling oocytes were fixed immediately or cultured under physiological conditions (n=96). The aging process was assessed by the zona pellucida dissolution time (ZPDT), ooplasm microtubule dynamics (OMD), and cortical granule (CG) status. The ZPDT increased 2-fold in relatively old, compared to young, untreated oocytes (P<0.0001). Exposure to O2- increased it even further (P<0.0001). Similarly, more O2- exposed oocytes exhibited increased OMD and major CG loss, with fewer having normal OMD and intact CG compared to untreated controls. Interestingly, young oocytes resisted "aging," when exposed to 20 microM H2O2, while the same enhanced the aging phenomena in relatively old oocytes (P<0.05). Exposure to even very low levels of HOCl induced the aging phenomena in young and relatively old oocytes, and higher concentrations of HOCl compromised oocyte viability. Overall, O2-, H2O2, and HOCl each augment oocyte aging, more so in relatively old oocytes, suggesting compromised antioxidant capacity in aging oocytes.

The roles of Ca2+, downstream protein kinases, and oscillatory signaling in regulating fertilization and the activation of development

Reviews in Developmental Biology have covered the pathways that generate the all-important intracellular calcium (Ca(2+)) signal at fertilization [Miyazaki, S., Shirakawa, H., Nakada, K., Honda, Y., 1993a. Essential role of the inositol 1,4,5-trisphosphate receptor/Ca(2+) release channel in Ca(2+) waves and Ca(2+) oscillations at fertilization of mammalian eggs. Dev. Biol. 158, 62-78; Runft, L., Jaffe, L., Mehlmann, L., 2002. Egg activation at fertilization: where it all begins. Dev. Biol. 245, 237-254] and the different temporal responses of Ca(2+) in many organisms [Stricker, S., 1999. Comparative biology of calcium signaling during fertilization and egg activation in animals. Dev. Biol. 211, 157-176]. Those reviews raise the importance of identifying how Ca(2+) causes the events of egg activation (EEA) and to what extent these temporal Ca(2+) responses encode developmental information. This review covers recent studies that have analyzed how these Ca(2+) signals are interpreted by specific proteins, and how these proteins regulate various EEA responsible for the onset of development. Many of these proteins are protein kinases (CaMKII, PKC, MPF, MAPK, MLCK) whose activity is directly or indirectly regulated by Ca(2+), and whose amount increases during late oocyte maturation. We cover biochemical progress in defining the signaling pathways between Ca(2+) and the EEA, as well as discuss how oscillatory or multiple Ca(2+) signals are likely to have specific advantages biochemically and/or developmentally. These emerging concepts are put into historical context, emphasizing that key contributions have come from many organisms. The intricate interdependence of Ca(2+), Ca(2+)-dependent proteins, and the EEA raise many new questions for future investigations that will provide insight into the extent to which fertilization-associated signaling has long-range implications for development. In addition, answers to these questions should be beneficial to establishing parameters of egg quality for human and animal IVF, as well as improving egg activation protocols for somatic cell nuclear transfer to generate stem cells and save endangered species.

Microinjection of mouse phospholipase Cζ complementary RNA into mare oocytes induces long-lasting intracellular calcium oscillations and embryonic development

Methods presently used to activate mare oocytes for assisted reproduction technologies provide low rates of advanced embryonic development. Because phospholipase Cζ (PLCζ) is the postulated sperm-borne factor responsible for oocyte activation at fertilisation, the aim of the present study was to investigate the pattern of [Ca2+]i oscillations and developmental rates achieved by microinjection of three concentrations of mouse PLCζ complementary (c) RNA (1, 0.5 or 0.25 μg μL–1) into mare oocytes. The frequency of [Ca2+]i oscillations was no different (P > 0.05) after injection of 1, 0.5 or 0.25 μg μL–1 PLCζ cRNA (41.1 ± 5.3, 47 ± 4.0 and 55.4 ± 9.0, respectively). However, [Ca2+]i oscillations persisted longest (P < 0.05) for oocytes injected with 0.5 μg μL–1 PLCζ cRNA (570.7 ± 64.2 min). There was no significant difference in cleavage rates after injection of the three concentrations of PLCζ (P > 0.05; range 97–100%), but the proportion of oocytes reaching advanced stages of embryonic development (>64 nuclei) was significantly lower for oocytes injected with 0.25 μg μL–1 PLCζ cRNA (3%) than for those injected with 1 μg μL–1 PLCζ cRNA (15%). Based on these results, microinjection of PLCζ may prove an effective and consistent method for the parthenogenetic activation of mare oocytes for nuclear transfer and provides a physiologically relevant tool with which to study fertilisation-dependent [Ca2+]i signalling in this species.

Alterations of PLCbeta1 in mouse eggs change calcium oscillatory behavior following fertilization

Inositol 1,4,5-trisphosphate generated by the action of a phospholipase C (PLC) mediates release of intracellular Ca2+ that is essential for sperm-induced activation of mammalian eggs. Much attention currently focuses on the role of sperm-derived PLCzeta in generating changes in egg intracellular Ca2+ despite the fact that PLCzeta constitutes a very small fraction of the total amount of PLC in a fertilized egg. Eggs express several isoforms of PLC, but a role for an egg-derived PLC in sperm-induced Ca2+ oscillations has not been examined. Reducing egg PLCbeta1 by a transgenic RNAi approach resulted in a significant decrease in Ca2+ transient amplitude, but not duration or frequency, following insemination. Furthermore, overexpressing PLCbeta1 by microinjecting a Plcb1 cRNA significantly perturbed the duration and frequency of Ca2+ transients and disrupted the characteristic shape of the first transient. These results provide the first evidence for a role of an egg-derived PLC acting in conjunction with a sperm-derived PLCzeta in egg activation.

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.

INTRACELLULAR CALCIUM IN THE FERTILIZATION AND DEVELOPMENT OF MAMMALIAN EGGS

1. Mammalian eggs are arrested at metaphase of their second meiotic division when ovulated and remain arrested until fertilized. The sperm delivers into the egg phospholipase C (PLC) zeta, which triggers a series of Ca(2+) spikes lasting several hours. The Ca(2+) spikes provide the necessary and sufficient trigger for all the events of fertilization, including exit from metaphase II arrest and extrusion of cortical granules that block the entry of other sperm. 2. The oscillatory Ca(2+) signal switches on calmodulin-dependent protein kinase II (CaMKII), which phosphorylates the egg-specific protein Emi2, earmarking it for degradation. To remain metaphase II arrested, eggs must maintain high levels of maturation-promoting factor (MPF) activity, a heterodimer of CDK1 and cyclin B1. Emi2 prevents loss of MPF by blocking cyclin B1 degradation, a process that is achieved by inhibiting the activity of the anaphase-promoting complex/cyclosome. However, CaMKII is not the primary initiator in the extrusion of cortical granules. 3. Ca(2+) spiking is also observed in mitosis of one-cell embryos, probably because PLCzeta contains a nuclear localization signal and so is released into the cytoplasm following nuclear envelope breakdown. The function of these mitotic Ca(2+) spikes remains obscure, although they are not absolutely required for passage through mitosis. 4. Intriguingly, the pattern of Ca(2+) spikes observed at fertilization has an effect on both pre- and postimplantation development in a manner that is independent of their ability to activate eggs. This suggests that the Ca(2+) spikes set in train at fertilization are having effects on processes initiated in the newly fertilized egg but whose influences are only observed several cell divisions later. The nature of the signals remains little explored, but their importance is clear and so warrants further investigation.

Chemical activation of parthenogenetic and nuclear transfer porcine oocytes using ionomycin and strontium chloride

Effective protocols for oocyte activation are crucial for study of parthenogenetic development and to produce nuclear transfer reconstructed embryos. This study investigated the use of ionomycin (ION) and strontium chloride (Sr(2+)) in the activation of parthenogenetic and nuclear transfer porcine oocytes. In-vitro-matured oocytes with a polar body were treated with varying concentrations of ION, Sr(2+) or its combinations, and then fixed or cultured to assess activation and development rates, respectively. Ionomycin concentrations of 10 and 15 microM resulted in more frequent oocyte activation and the 15 microM in advanced development compared to 5 microM (71.8 and 70%vs. 47.5%; P=0.04, and 43.7%vs. 19.3%; P=0.008, respectively). Oocytes treated with 10, 20 or 30 mM of Sr(2+) for 2 or 4h displayed a pronuclear formation rate ranging from 46.7 to 70%. When employed after a 5 min treatment with 10 or 15 microM ION, exposure to 10 mM Sr(2+) for 4 h resulted in higher pronuclear formation than did the 20 mM concentration (82 and 88.6%vs. 63.3 and 73.2%; P=0.03). Nuclear transfer reconstructed oocytes treated with 15 microM/5 min ION followed by 10 mM/4 h Sr(2+) resulted in a higher development to blastocyst stage compared to those treated with 15 microM ION alone (17.7 vs. 11.3%; P=0.06). In conclusion, we inferred that the inclusion of Sr(2+) in the activation protocol can benefit the development of nuclear transfer reconstructed porcine oocytes.

The MEK inhibitor, U0126, alters fertilization-induced [Ca2+]i oscillation parameters and secretion: differential effects associated with in vivo and in vitro meiotic maturation

Although mitogen-activated protein kinase (MAPK) is a well-known cell cycle regulator, emerging studies have also implicated its activity in the regulation of intracellular calcium concentration ([Ca2+](i)) and secretion. Those studies raise the hypothesis that MAPK activity during oocyte maturation and early fertilization is required for normal egg Ca2+ oscillations and cortical granule (CG) secretion. We extend the findings of [Lee, B., Vermassen, E., Yoon, S.-Y., Vanderheyden, V., Ito, J., Alfandari, D., De Smedt, H., Parys, J.B., Fissore, R.A., 2006. Phosphorylation of IP(3)R1 and the regulation of [Ca2+](i) responses at fertilization: a role for the MAP kinase pathway. Development 133, 4355-4365] by demonstrating acute effects on Ca2+ oscillation frequency, amplitude, and duration in fertilized mouse eggs matured in vitro with the MAPK inhibitor, U0126. Frequency was increased, whereas amplitude and duration were greatly decreased. These effects were significantly reduced in eggs matured in vivo and fertilized in the presence of the inhibitor. Ionomycin studies indicated that intracellular Ca2+ stores were differentially affected in eggs matured in vitro with U0126. Consistent with these effects on [Ca2+](i) elevation, fertilization-induced CG exocytosis and metaphase II exit were also reduced in in vitro-matured eggs with U0126, but not in those similarly treated after in vivo maturation. These results indicate that MAPK targets Ca2+ regulatory proteins during both maturation and fertilization, as well as provide a new hypothesis for MAPK function, which is to indirectly regulate events of early development by controlling Ca2+ oscillation parameters.

Comparison of Ca2+ and CaMKII responses in IVF and ICSI in the mouse

Novel methods of egg activation in human assisted reproductive technologies and animal somatic cell nuclear transfer are likely to alter the signalling process that occurs during normal fertilization. Intracytoplasmic sperm injection (ICSI) bypasses the normal processes of the acrosome reaction, sperm-egg fusion, and processing of the sperm plasma membrane, as well as alters some parameters of intracellular calcium ([Ca(2+)](i)) dynamics (reported previously by Kurokawa and Fissore (2003)). Herein, we extend these studies to determine if ICSI alters the activity of the Ca(2+)-dependent protein, Ca(2+)/calmodulin-dependent kinase II (CaMKII), which is responsible for the completion of meiosis in vertebrate eggs. After ICSI or in vitro fertilization (IVF), individual mouse eggs were monitored for their relative changes in both [Ca(2+)](i) and CaMKII activity during the first [Ca(2+)](i) rise and a subsequent rise associated with second polar body extrusion. The duration of the first [Ca(2+)](i) rise was greater in ICSI than in IVF, but the amplitude of the rise was transiently higher for IVF than ICSI. However, a similar mean CaMKII activity was observed in both procedures. During polar body extrusion, the amplitude and duration of the Ca(2+) rises were increased by a small amount in ICSI compared with IVF, whereas the CaMKII activities were similar. Thus, compared with IVF, ICSI is not associated with decreased or delayed CaMKII activity in response to these Ca(2+) signals in the mouse.

Truths and myths of oocyte sensitivity to controlled rate freezing

The mammalian oocyte is especially sensitive to cryopreservation. Because of its size and physiology, it can easily undergo cell death or sub-lethal damage as a consequence of intracellular ice formation, increase in the concentration of solutes and other undesired effects during the conversion of extracellular water into ice. This has generated the belief that oocyte storage cannot be achieved with the necessary efficiency and safety. However, many concerns raised by oocyte freezing are the result of unproven hypotheses or observations conducted under sometimes inappropriate conditions. For instance, spindle organization can undergo damage under certain freezing conditions but not with other protocols. The controversial suggestion that cryopreservation induces cortical granule discharge and zona pellucida hardening somehow questions the routine use of sperm microinjection. Damage to mouse oocytes caused by solute concentration is well documented but, in the human, there is no solid evidence that modifications of freezing mixtures, to prevent this problem, provide an actual advantage. The hope of developing oocyte cryopreservation as a major IVF option is becoming increasingly realistic, but major efforts are still required to clarify the authentic implications of oocyte cryopreservation at the cellular level and identify freezing conditions compatible with the preservation of viability and developmental ability.

Activation of fertilized and nuclear transfer eggs

In all animal species, initiation of embryonic development occurs shortly after the joining together of the gametes from each of the sexes. The first of these steps, referred to as "egg activation", is a series of molecular events that results in the syngamy of the two haploid genomes and the beginning of cellular divisions for the new diploid embryo. For many years it has been known that the incoming sperm drives this process, as an unfertilized egg will remain dormant until it can no longer sustain normal metabolic processes. Until recently, it was also believed that the sperm was the only cell capable of creating a viable embryo and offspring. Recent advances in cell biology have allowed researchers to not only understand the molecular mechanisms of egg activation, but to exploit the use of pharmacological agents to bypass sperm-induced egg activation for the creation of animals by somatic cell nuclear transfer. This chapter will focus on the molecular events of egg activation in mammals as they take place during fertilization, and will discuss how these mechanisms are successfully bypassed in processes such as somatic cell nuclear transfer.

Efficient establishment of mouse embryonic stem cell lines from single blastomeres and polar bodies

Recently, ES cell lines were established from single blastomeres taken from eight-cell embryos in mice and humans with success rates of 4% and 2%, respectively, which suggests that the method could be used in regenerative medicine to reduce ethical concerns over harm to embryos. However, those studies used other ES cells as supporting cells. Here, we report a simple and highly efficient method of establishing mouse ES cell lines from single blastomeres, in which single blastomeres are simply plated onto a feeder layer of mouse embryonic fibroblasts with modified ES cell medium. A total of 112 ES cell lines were established from two-cell (establishment rate, 50%-69%), early four-cell (28%-40%), late four-cell (22%), and eight-cell (14%-16%) stage embryos. We also successfully established 18 parthenogenetic ES cell lines from first (36%-40%) and second polar bodies (33%), the nuclei of which were reconstructed to embryos by nuclear transfer. Most cell lines examined maintained normal karyotypes and expressed markers of pluripotency, including germline transmission in chimeric mice. Our results suggest that the single cells of all early-stage embryos or polar bodies have the potential to be converted into ES cells without any special treatment.

The absence of a Ca(2+) signal during mouse egg activation can affect parthenogenetic preimplantation development, gene expression patterns, and blastocyst quality

A series of Ca(2+) oscillations during mammalian fertilization is necessary and sufficient to stimulate meiotic resumption and pronuclear formation. It is not known how effectively development continues in the absence of the initial Ca(2+) signal. We have triggered parthenogenetic egg activation with cycloheximide that causes no Ca(2+) increase, with ethanol that causes a single large Ca(2+) increase, or with Sr(2+) that causes Ca(2+) oscillations. Eggs were co-treated with cytochalasin D to make them diploid and they formed pronuclei and two-cell embryos at high rates with each activation treatment. However, far fewer of the embryos that were activated by cycloheximide reached the blastocyst stagecompared tothose activated by Sr(2+) orethanol. Any cycloheximide-activated embryos that reached the blastocyst stage had a smaller inner cell mass number and a greater rate of apoptosis than Sr(2+)-activated embryos. The poor development of cycloheximide-activated embryos was due to the lack of Ca(2+) increase because they developed to blastocyst stages at high rates when co-treated with Sr(2+) or ethanol. Embryos activated by either Sr(2+) or cycloheximide showed similar signs of initial embryonic genome activation (EGA) when measured using a reporter gene. However, microarray analysis of gene expression at the eight-cell stage showed that activation by Sr(2+) leads to a distinct pattern of gene expression from that seen with embryos activated by cycloheximide. These data suggest that activation of mouse eggs in the absence of a Ca(2+) signal does not affect initial parthenogenetic events, but can influence later gene expression and development.

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.