Effect of maturation medium on in vitro cleavage of canine oocytes fertilized with fresh and cooled homologous semen

This study evaluated the effect of three maturation media on the development of in vitro-matured and in vitro-fertilized dog oocytes. In Experiment 1 (non-comparative experiment) canine cumulus–oocyte complexes (COCs) were matured in vitro in TCM199 supplemented with estrous cow serum (10%) + gonadotropins + steroid (treatment A), TCM199 + estrous cow serum (10%) (treatment B), or TCM199 + polyvinylpyrrolidone (PVP) (4%) (treatment C). All maturation media contained a final concentration of 1 μg/ml of human somatotropin (hST). Oocytes were fertilized with fresh ejaculated sperm and development was assessed by cleavage. The objective of Experiment 2 (comparative experiment) was to compare the rates of cleavage and developmental capacity of COCs matured in vitro in same medium as in Experiment 1, and fertilized either with fresh ejaculated or with cooled extended homologous spermatozoa. In Experiments 1 and 2, oocytes fertilized with fresh semen were in vitro-matured for 48 h, while in Experiment 2 COCs fertilized with cooled semen were matured in vitro for 72 h. The results of Experiments 1 and 2 demonstrated that cleavage was not influenced by the oocyte's maturation environment. The results of Experiment 1 showed that pronucleus formation + cleavage (day 7 after IVF) was similar among treatments A, B and C (p = 0.277). Also, in Experiment 2, pronucleus formation + cleavage (day 7 after IVF) was not different for oocytes fertilized in vitro either with fresh or cooled semen and maturated in media A (p = 0.190), B (p = 0.393) or C (p = 0.687). In both experiments, the numbers of embryos that developed to the 6–8-cell stage were higher for oocytes matured in medium A and fertilized with fresh semen, when compared with numbers of oocytes matured in media B and C. Embryo development to the 6–8-cell stage of oocytes fertilized either with fresh or cooled sperm was observed in treatments A and C in Experiment 2. Cumulus cell expansion was similar among treatments in Experiment 1. In Experiment 2, cumulus cell expansion among treatments A, B and C was similar after 48 h or 72 h of IVM. In both experiments, the greatest expansion category seen was for category 2 (outer cumulus cells slightly expanded). No correlation between cumulus expansion and cleavage were observed. Polyspermy rates in oocytes matured in medium A, and fertilized with fresh sperm were not significantly different from polyspermy rates observed using media B and C, in both experiments. Our findings indicate that treatments A, B and C are similarly effective for the cleavage of dog oocytes. Furthermore, it was demonstrated that canine oocytes matured in vitro could be fertilized by homologous cooled spermatozoa and progress to cleavage.

Analysis of specific factors generating 2-cell block in AKR mouse embryos

The phenomenon of the developmental arrest at the 2-cell stage of 1-cell embryos from some mouse strains during in vitro culture is known as the 2-cell block. We investigated the specific factors involved in the 2-cell block of AKR embryos by means of a modified culture system, the production of reconstructed embryos by pronuclear exchange and a cross experiment. In a culture medium with phosphate, 94.6% of 1-cell embryos from the C57BL mouse strain developed to the blastocyst stage, but 95.7% of embryos from the AKR mouse strain showed 2-cell block. Phosphate-free culture medium rescued the 2-cell block of AKR embryos and accelerated the first cell cycle of the embryos. Co-culture with BRL cells and a BRL-conditioned medium fractionated below 30 kDa also rescued the 2-cell block of AKR embryos. Examinations of in vitro development of reconstructed embryos and of embryos from F1 females between AKR and C57BL strains clearly demonstrated that the AKR cytoplast caused the 2-cell block. In the backcrossed female progeny between (AKR x C57BL) F1 males and AKR females, about three-quarters of the embryos were of the 2-cell blocking phenotype and about one-quarter were of the non-blocking phenotype. These results suggest that two genes are responsible for the 2-cell block of AKR embryos.

Developmental arrest induced in cleavage stage porcine embryos following microinjection of mRNA encodingBrahma (Smarca 2), a chromatin remodeling protein

Smarca 2 (Brahma) and Smarca 4 (Brahma related gene 1, BRG1) alternatively occupy the catalytic site of SWI/SNF chromatin remodeling complexes. Mammalian embryos undergo a dramatic amount of epigenetic remodeling during cleavage development, which plays key roles in regulating both gene transcription and the developmental potential of the embryo. In order to understand how the epigenetic state of cleavage stage embryos is regulated, it is important to identify the factors that mediate epigenetic changes during cleavage development. In this study we hypothesized that altered expression of Smarca 2 would have profound effects on embryo development. The objectives of this study were to determine the expression pattern of Smarca 2 and determine the effects of Smarca 2 overexpression in cleavage stage parthenogenetic porcine embryos. Smarca 2 transcripts are most abundant in germinal vesicle (GV) stage oocytes and decline progressively during cleavage development. At the blastocyst stage, Smarca 2 transcripts are reduced by 18-fold (GV stage oocyte vs. blastocyst stage embryo, P < 0.05). Parthenogenetic porcine embryos injected with mRNA encoding wild type human Smarca 2 exhibited a dramatic developmental arrest as compared to noninjected embryos, embryos injected with GFP mRNA, or mRNA encoding a dominant negative version of human Smarca 2 (P < 0.01). This work demonstrates the importance of Smarca 2 containing SWI/SNF chromatin remodeling complexes in preimplantation porcine embryos and how perturbing the amount of Smarca 2 in porcine embryos disrupts cleavage development.

Vitrification of Immature Bovine Oocytes by the Microdrop Method

This study was conducted to determine the optimal vitrification conditions for immature bovine oocytes using the microdrop method. In experiment 1, the optimal pre-equilibration period for microdrop vitrification was examined. The maturation rate of vitrified oocytes with a 3 min first pre-equilibration period (41.1%) was higher than that of vitrified oocytes with a 0 min first pre-equilibration period (21.4%), and the values of those with a 1 (33.9%) or 5 min (27.4%) first pre-equilibration period were intermediate. The value for a 1 min second pre-equilibration period (44.4%) was significantly higher (P<0.05) than those for a 0.5 (28.6%) and 2 min (21.4%) second pre-equilibration period. In experiment 2, the distribution of microtubules in matured oocytes was investigated. There was no difference among the first pre-equilibration times in terms of the rates of normal spindles in vitrified oocytes. However, this value was significantly higher (P<0.05) in the 1 min group (52.8%) compared with the 0.5 (16.7%) and 2 min groups (12.3%). In experiment 3, we investigated the developmental capacity of immature bovine oocytes vitrified under optimal pre-equilibration conditions (3 min and 1 min for the first and second pre-equilibrations, respectively). Although the total fertilization rates were significantly lower (P<0.05) in the vitrified oocytes (65.6%) compared with the control oocytes (92.4%), there was no difference in the rate of normal fertilization (2PN) between the vitrified (78.6%) and control (82.0%) oocytes. Cleavage and blastocyst rates were significantly lower (P<0.05) in vitrified oocytes (55.7 and 2.3%) than in control oocytes (84.4 and 34.7%). Thus, these results indicated that immature bovine oocytes can survive after microdrop vitrification and subsequently can be cultured to mature oocytes capable of undergoing fertilization in vitro and developing into blastocysts.

Infertility in murine acute Trypanosoma cruzi infection is associated with inhibition of pre-implantation embryo development

We previously showed that Trypanosoma cruzi acute infection induced infertility in a great proportion of female mice, which resulted from a defect taking place before implantation. In this study, we have analyzed every step of reproduction from mating to implantation to identify the most sensitive event. Our results show that mating, ovulation, fertilization, and first division of the zygote of infected mice take place normally compared with uninfected mice, indicating that the defect occurred after the two-cell stage. In vivo development of two-cell embryos to the blastocyst stage was indeed dramatically delayed; some embryos even arrested their development before having reached the eight-cell stage while others degenerated. The effect was less pronounced when embryos were allowed to develop in vitro, indicating that the infectious context of the mother plays a role in maintaining growth retardation. The delay of embryonic development was associated with insufficient divisions of the blastomeres and led to abnormal blastocyst outgrowth that may explain implantation failure. Inhibition of cell division was correlated with the maternal parasitemia. This work clearly shows that T. cruzi infection dramatically impedes embryonic development, offering a model for further in vivo studies of embryotrophic factors produced by the oviduct of infected females.

Impact of the assessment of early cleavage in a single embryo transfer policy

The policy of single embryo transfer (SET) adopted for women <36 years old since 1 July 2003, strongly calls for improvement of embryo selection. A total of 196 cycles in which SET was performed were randomly allocated to two groups. In the first group, early cleavage was assessed (ECA) 25 h after insemination. The embryo with the best score that cleaved early, if present, was selected for transfer. In the second group, early cleavage was not assessed (ECNA) and embryo selection was based solely on the embryo score. Ninety-eight cycles were allocated in the ECA and ECNA group respectively. Early cleavage occurred in 64% of cycles and 32.2% of embryos. Patient population and embryo morphology were similar between the two groups, and similar delivery rates were observed (27.6 versus 24.5% respectively in the ECA and ECNA groups). The assessment of early cleavage as additional parameter did not improve the delivery rate in the single embryo transfer policy.

Where do we stand now? Mouse early embryo patterning meeting in Freiburg, Germany (2005)

Mechanism underlying mammalian preimplantation development has long been a subject of controversy and the central question has been if any "determinants" play a key role in a manner comparable to the non-mammalian "model" system. During the last decade, this issue has been revived (Pearson, 2002; Rossant and Tam, 2004) by claims that the axes of the mouse blastocyst are anticipated at the egg ("prepatterning model"; Gardner, 1997; Gardner, 2001; Piotrowska et al., 2001; Piotrowska and Zernicka-Goetz, 2001; Zernicka-Goetz, 2005), suggesting that a mechanism comparable to that operating in non-mammals may be at work. However, recent studies by other laboratories do not support these claims ("regulative model"; Alarcon and Marikawa, 2003; Chroscicka et al., 2004; Hiiragi and Solter, 2004; Alarcon and Marikawa, 2005; Louvet-Vallee et al., 2005; Motosugi et al., 2005) and the issue is currently under hot debate (Vogel, 2005). Deepening our knowledge of this issue will not only provide an essential basis for understanding mammalian development, but also directly apply to ongoing clinical practices such as intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis (PGD). These practices were originally supported by a classical premise that mammalian preimplantation embryos are highly regulative (Tarkowski, 1959; Tarkowski, 1961; Tarkowski and Wroblewska, 1967; Rossant, 1976), in keeping with the "regulative model". However, if the "prepatterning model" is correct, the latter will require critical reassessment.

Role of TIF1alpha as a modulator of embryonic transcription in the mouse zygote

The first events of the development of any embryo are under maternal control until the zygotic genome becomes activated. In the mouse embryo, the major wave of transcription activation occurs at the 2-cell stage, but transcription starts already at the zygote (1-cell) stage. Very little is known about the molecules involved in this process. We show that the transcription intermediary factor 1 α (TIF1α) is involved in modulating gene expression during the first wave of transcription activation. At the onset of genome activation, TIF1α translocates from the cytoplasm into the pronuclei to sites of active transcription. These sites are enriched with the chromatin remodelers BRG-1 and SNF2H. When we ablate TIF1α through either RNA interference (RNAi) or microinjection of specific antibodies into zygotes, most of the embryos arrest their development at the 2–4-cell stage transition. The ablation of TIF1α leads to mislocalization of RNA polymerase II and the chromatin remodelers SNF2H and BRG-1. Using a chromatin immunoprecipitation cloning approach, we identify genes that are regulated by TIF1α in the zygote and find that transcription of these genes is misregulated upon TIF1α ablation. We further show that the expression of some of these genes is dependent on SNF2H and that RNAi for SNF2H compromises development, suggesting that TIF1α mediates activation of gene expression in the zygote via SNF2H. These studies indicate that TIF1α is a factor that modulates the expression of a set of genes during the first wave of genome activation in the mouse embryo.

Blastocyst culture for deriving human embryonic stem cells

Success in producing a human embryonic stem cell line depends largely on the quality of the 5-d-old embryo (blastocyst) used. Such blastocysts are grown from frozen-thawed d 1-3 surplus embryos left over from infertility clinics and donated for stem cell research with informed patient consent. Knowledge, therefore, of the culture conditions and embryo scoring systems that are used to generate high-quality blastocysts are crucial. This chapter describes an extended microdroplet culture protocol using two-stage sequential culture media with morphological and polarized optical parameters for embryo scoring for each day of embryonic growth to help produce high-quality blastocysts.

Embryology: does prepatterning occur in the mouse egg?

A recurring question in developmental biology has been whether localized determinants play any role in mammalian preimplantation development. This is a controversial issue that brings back the idea of prepatterning and is explored further by Plusa et al., who claim it is the first cleavage of the mouse zygote that predicts the blastocyst axis, rather than the animal pole or sperm entry point, as previously suggested. However, other evidence indicates that the blasotcyst axis is not predetermined and there is no prepatterning in the mouse egg. Here we investigate the origin of these different views and conclude that they arise from differences in the data themselves and in their interpretation.

Effects of BSA and fetal bovine serum in culture medium on development of rat embryos

Rat 1-cell embryos, recovered from naturally mated females, were cultured in a chemically defined medium (mR1ECM) or in mR1ECM supplemented with BSA (4 mg/ml; mR1ECM-BSA) or fetal bovine serum (FBS; 10%, v:v; mR1ECM-FBS) instead of polyvinylalcohol. There was no difference in percentages of embryos that developed to the 2-cell to blastocyst stages between mR1ECM and mR1ECM-BSA, but in mR1ECM-FBS, no development beyond the 2-cell stage was observed. When embryos were transferred to mR1ECM-FBS from mR1ECM after 24 to 64 h of culture, development of embryos to and beyond the 4-cell stage was inhibited. However, when transferred after 80 h of culture, more embryos developed to blastocysts and hatching or hatched blastocysts than in embryos cultured in mR1ECM. When 8-cell embryos and early morulae obtained after 72 and 80 h of culture in mR1ECM, respectively, were cultured in mR1ECM-FBS, a higher proportion of early morulae developed to the blastocyst stage than did 8-cell embryos. When morulae obtained after culture in mR1ECM or mR1ECM-BSA were transferred to recipient females, there was no difference in proportions of fetuses obtained. However, a higher proportion of blastocysts cultured in mR1ECM-FBS developed to fetuses compared with those obtained in mR1ECM. These results indicate that BSA has neither deleterious nor beneficial effects on development of rat 1-cell embryos. In contrast, FBS has deleterious effects on early cleavage of embryos but it promotes more rapid development of morulae to blastocysts, resulting in better quality blastocysts.

Reorganization of cytoplasm in the zebrafish oocyte and egg during early steps of ooplasmic segregation

The aim of this work is to determine when and how ooplasmic segregation is initiated in the zebrafish egg. To this end, the organization of the ooplasm and vitelloplasm were examined in oocytes and eggs shortly after activation. Ooplasmic segregation, initiated in the stage V oocyte, led to the formation of ooplasmic domains rich in organelles, and ribonucleoproteins. A linear array of closely arranged peripheral yolk globules separated an outer domain of ectoplasm from an inner domain of interconnected endoplasmic lacunae. The structure of this yolk array and the distribution of microinjected labeled tracers suggests that it may provide a barrier limiting ooplasm transit. Loosely arranged yolk globules at the animal hemisphere allow wide connections between the endoplasm and a preblastodisc domain. Activation caused further segregation of ooplasm, reorganization of endoplasmic lacunae, and blastodisc growth. The presence of an endoplasmic cytoskeleton suggests that these changes may be driven by microtubules and microfilaments.

A quantitative approach to the study of cell shapes and interactions during early chordate embryogenesis

BACKGROUND

The prospects of deciphering the genetic program underlying embryonic development were recently boosted by the generation of large sets of precisely organized quantitative molecular data. In contrast, although the precise arrangement, interactions, and shapes of cells are crucial for the fulfilment of this program, their description remains coarse and qualitative. To bridge this gap, we developed a generic software, 3D Virtual Embryo, to quantify the geometry and interactions of cells in interactive three-dimensional embryo models. We applied this approach to early ascidian embryos, chosen because of their simplicity and their phylogenetic proximity to vertebrates.

RESULTS

We generated a collection of 19 interactive ascidian embryos between the 2- and 44-cell stages. We characterized the evolution with time, and in different cell lineages, of the volume of cells and of eight mathematical descriptors of their geometry, and we measured the surface of contact between neighboring blastomeres. These analyses first revealed that early embryonic blastomeres adopt a surprising variety of shapes, which appeared to be under strict and dynamic developmental control. Second, we found novel asymmetric cell divisions in the posterior vegetal lineages, which gave birth to sister cells with different fates. Third, during neural induction, differences in the area of contact between individual competent animal cells and inducing vegetal blastomeres appeared important to select the induced cells.

CONCLUSIONS

In addition to novel insight into both cell-autonomous and inductive processes controlling early ascidian development, we establish a generic conceptual framework for the quantitative analysis of embryo geometry that can be applied to other model organisms.

[Embryo quality evaluation according to the speed of the first cleavage after IntraCytoplasmic Sperm Injection (ICSI)]

OBJECTIVE

To evaluate morphological parameters of embryos obtained in the process of ICSI.

DESIGN

A prospective study.

SETTING

Centre of Assisted Reproduction, Dept. of Obstetrics and Gynecology, Palacký University Medical School, Olomouc.

METHODS

In the present study 1116 embryos developing after ICSI (IntraCytoplasmic Sperm Injection) procedure in the period of 2001-2004 were evaluated. The beginning of the mitotic cleavage was assessed within the interval of 22-27 hours after insemination. The embryos were divided into three groups according to the speed of their division as Early Cleavage (EC) embryos, where two blastomeres were present at the time of assessment, Break Down ProNuclei stage (BDPN) where the pronuclei had already disappeared, and ProNuclei (PN) embryos, where both pronuclei were still present. In these groups the degree of fragmentation was evaluated on day two of cultivation and embryos were divided into four categories as: A--regular blastomeres, without fragmentation, B--irregular blastomeres or fragmentation below 30%, C--fragmentation 30-50%, D--fragmentation above 50%. The speed of further cleavage and average number of blastomeres were evaluated on day two and three of cultivation. Statistical analysis was preformed at the Palacky University Computer Centre. The chi2 test and t-test for independent samples were used.

RESULTS

EC embryos were found in 37.4%, BDPN in 33.1% and PN in 29.5%. The degree of fragmentation between evaluated groups of embryos were statistically significant (p = 0.000). EC embryos were less fragmented (p = 0.000), had more blastomeres at the time of evaluation (p = 0.000) and their speed of cleavage was faster (p = 0.000). The cleavage of EC embryos was faster in comparison with the PN group (p = 0.000), but there were no significant differences between the EC and BDPN groups on day two of cultivation. On day three significant differences were found also between the EC and BDPN groups (p = 0.000). The embryonic developmental arrest was found only in PN embryos.

CONCLUSION

The speed of the first cell cleavage is a useful additional criterion for the embryo selection for embryotransfer. EC embryos usually have better morphology and more blastomeres than the BPDN and PN ones.

Assessment of sperm quality parameters of six bulls showing different abilities to promote embryo development in vitro

Experiments were conducted to investigate the possible origins of variation between six bulls showing various blastocyst rates after in vitro fertilisation. No significant difference was observed for the rates of cleavage and 5-8 cell stages, whereas blastocyst yields at Day 6, 7 and 8 post insemination were significantly different between bulls (P < 0.05). Fertilisation rates ranged from 59.5 to 79.3% (P < 0.05), with no difference in the incidence of polyspermy. The proportions of motile and progressive spermatozoa before and after Percoll separation were analysed. A positive effect of Percoll was noted on both parameters (P < 0.05), leading to the absence of difference between bulls after the separation process. Sperm viability and spontaneous acrosome reaction were assessed during 18 h incubation in fertilisation medium. A sharp decrease in sperm viability was observed for all bulls after 2 h incubation, with only 12.6-21.7% of spermatozoa still viable at 18 h. In contrast, the proportion of reacted acrosomes was low in five out of six bulls (<15% at 18 h). In conclusion, the fertilisation rate was the only parameter to show some correlation with blastocyst rate for all bulls.

Differences in regulation of the first two M-phases in Xenopus laevis embryo cell-free extracts

The first embryonic M-phase is special, being the time when paternal and maternal chromosomes mix together for the first time. Reports from a variety of species suggest that the regulation of first M-phase has many particularities; however, no systematic comparative study of the biochemical aspects of first and the following M-phases has been previously undertaken. Here, we ask whether the regulation of the first embryonic M-phase is modified, using Xenopus cell-free extracts. We developed new types of extract specific for the first and the second M-phase obtained either from parthenogenetic or from in vitro fertilized embryos. Analyses of these extracts confirmed that the amplitude of histone H1 kinase activity reflecting CDK1/cyclin B (or MPF for M-phase Promoting Factor) activity is higher and persists longer than during the second M-phase, and that levels of cyclins B1 and B2 are correspondingly higher during the first than the second embryonic M-phase. Inhibition of protein synthesis shortly before M-phase entry reduced mitotic histone H1 kinase amplitude, shortened the period of mitotic phosphorylation of chosen marker proteins, and reduced cyclin B1 and B2 levels, suggesting a role of B-type cyclins in regulating the duration of mitotic events. Moreover, addition of exogenous cyclin B to the extract prior the second mitosis brought forward the activation of mitotic histone H1 kinase but prolonged the duration of this activity. We also confirmed that the inhibitory phosphorylation of CDK1 on tyrosine 15 oscillates between the first two embryonic M-phases, but is clearly more pronounced before the first than the second mitosis, while the MAP kinase ERK2 tended to show greater activation during the first embryonic M-phase but with a similar duration of activation. We conclude that discrete differences exist between the first two M-phases in Xenopus embryo and that higher CDK1/cyclin B activity and B-type cyclin levels could account for the different characteristics of these M-phases.

Asymmetrization of first cleavage by transient disassembly of one spindle pole aster in the leech Helobdella robusta

Unequal first cleavage is characteristic of a diverse group of protostome animals. In the nematode Caenorhabditis elegans, unequal first cleavage is achieved through the interaction of an apparently symmetric mitotic spindle apparatus with a clearly polarized cell cortex. In the clitellate annelid Tubifex tubifex, by contrast, the spindle is monastral and contains only one gamma-tubulin-reactive centrosome; this monastral spindle is inherently asymmetric throughout mitosis. Here, we have used immunostaining for beta- and gamma-tubulin to follow spindle dynamics during the unequal first cleavage in another clitellate annelid, the leech Helobdella robusta. We find that the mitotic spindle is diastral and symmetric through early metaphase, then becomes asymmetric following the transient down-regulation of one centrosome, as judged by gamma-tubulin immunofluorescence. Low levels of drugs that affect microtubule dynamics can symmetrize the first cleavage without affecting the gamma-tubulin dynamics. Our results provide a striking example of the evolvability of cellular mechanisms underlying an unambiguously homologous developmental process.

Cyclin A2-CDK2 regulates embryonic gene activation in 1-cell mouse embryos

Recruitment of maternal mRNA in mice appears essential for embryonic gene activation (EGA) that is initiated in the 1-cell stage. The identity of which recruited mRNAs is responsible, however, is not known. We report here that recruitment of cyclin A2 mRNA may be critical for EGA. Cyclin A2 protein accumulates in pronuclei between 6 and 12 h after fertilization, the time when EGA is initiated. This cyclin A2 may be generated from maternally recruited cyclin A2 mRNA because its accumulation was inhibited by 3'-deoxyadenosine, which inhibits mRNA polyadenylation. When CDK2 activity or pronuclear accumulation of cyclin A2 was inhibited with CDK2 inhibitors or by microinjected siRNAs, respectively, DNA replication was not inhibited but the increase of transcriptional activity was prevented. In addition, microinjection of recombinant cyclin A2-CDK2 protein increased transcriptional activity. Cyclin A2-CDK2 is activated following egg activation, because an increase in phosphorylation of retinoblastoma protein was observed using antibodies that recognize site-specific phosphorylation catalyzed by this kinase and treatment with a CDK2 inhibitor or microinjection with cyclin A2 siRNAs prevented the increase in retinoblastoma protein phosphorylation. These results suggest that recruitment of maternal cyclin A2 mRNA following egg activation is linked to EGA.

Cleavage pattern and emerging asymmetry of the mouse embryo

Early mammalian development is regulative - it is flexible and responsive to experimental intervention. This flexibility could be explained if embryogenesis were originally completely unbiased and disordered; order and determination of cells only arising later. Alternatively, regulative behaviour could be consistent with the embryo having some order or bias from the very beginning, with inflexibility and cell determination increasing steadily over time. Recent evidence supports the second view and indicates that the sequence and the orientations of cell divisions help to build the first asymmetries.

Use of both early cleavage and day 2 mononucleation to predict embryos with high implantation potential in intracytoplasmic sperm injection cycles

OBJECTIVE

To evaluate the value of early cleavage and day 2 mononucleation as combined parameters in predicting the implantation potential of embryos.

DESIGN

Prospectively designed retrospective cohort analysis.

SETTING

Private IVF center.

PATIENT(S)

Two hundred eighty-seven ICSI cycles were evaluated in four groups according to the presence of early cleavage and mononucleation in all (ECM), some (pECM, ECpM), or none (noECnoM) of the transfer embryos.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Embryo quality and pregnancy and implantation rates.

RESULT(S)

The cycle characteristics, embryo quality, and pregnancy rates were similar when all (ECM) or some (pECM and ECpM) transfer embryos displayed these parameters. The poorest cycle characteristics and outcome were observed in the absence of both parameters (noECnoM). When early cleavage was present, a higher implantation rate was observed when all transfer embryos displayed mononucleation at day 2 (ECM) than when this was the case only in some (ECpM).

CONCLUSION(S)

Combination of early cleavage and day 2 mononucleation improves selection of embryos with high implantation potential in ICSI cycles with good prognosis.

Initial differentiation of blastomeres in 4-cell human embryos and its significance for early embryogenesis and implantation

This brief review is devoted to the nature of early blastomere differentiation in human 4-cell embryos and its consequences for embryonic development. Precursor cells of inner cell mass, germline, and trophectoderm may be formed at this stage, the clearest evidence being available for trophectoderm. The sites of these precursor cells in the embryo could be ascertained using markers for animal and vegetal poles, observing specific cleavage planes, and assessing gene and protein expression. This opens new opportunities for studying 4-cell embryos and removing or replacing specific cells. Knowledge of the properties of individual blastomeres should help in improving assisted human reproduction, performing preimplantation genetic diagnosis, and perhaps establishing specific stem cell lines. Special attention is paid to well-characterized trophectoderm, the trophectoderm stem cell, and possible new forms of clinical application.

An investigation of the origin and significance of bilateral symmetry of the pronuclear zygote in the mouse

BACKGROUND

Preliminary observations revealed that advanced zygotes of the PO strain mouse are often bilaterally symmetrical, and suggested that both the plane of first cleavage and features of the blastocyst bear a consistent relationship to the zygote's bilateral plane.

METHODS

Spaced oil drops were injected into the zona pellucida to delineate the bilateral plane in pronuclear zygotes, and a distinct cluster of drops then placed over the second polar body. Such non-invasive marking was combined with gelation of the perivitelline space to prevent rotation of the zygotes within the zona pellucida.

RESULTS

Nearly two-thirds of advanced pronuclear stage zygotes were bilaterally symmetrical and, regardless of whether first cleavage was meridional, it was almost invariably orthogonal to the bilateral plane. Moreover, both the axis of polarity and bilateral plane of the blastocyst bore a consistent relationship to the zygote's bilateral plane. Haploid parthenotes also exhibited bilateral symmetry, although in the absence of fertilization, first cleavage was less consistently orthogonal to the bilateral plane.

CONCLUSIONS

Bilateral symmetry may be an intrinsic property of the oocyte that is induced by its activation and, from the reproducible way it maps on both the 2-cell conceptus and blastocyst, seems to play a role in early patterning.

Small GTPase RhoA is required for ooplasmic segregation and spindle rotation, but not for spindle organization and chromosome separation during mouse oocyte maturation, fertilization, and early cleavage

RhoA, a small GTPase, plays versatile roles in many aspects of cell function such as stress fiber formation, cytokinesis, and cell polarization. In this study, we investigated the subcellular localization of RhoA and its possible roles during oocyte maturation and fertilization. RhoA was localized in the cytoplasm of eggs from the germinal vesicle (GV) stage to 2-cell stage, especially concentrating in the midbody of telophase spindle when oocyte extruded PB1 and PB2. The RhoA kinases (ROCKs) specific inhibitor Y-27632 blocked GV breakdown (GVBD) and first polar body extrusion, but did not affect apparatus formation and anaphase/telophase I entry. Anti-RhoA antibody microinjection into the oocytes showed similar results. RhoA inhibitor caused abnormal organization of microfilaments, failure of spindle rotation, PB2 extrusion as well as cleavage furrow formation, while sister chromatid separation was not affected. Microinjection of RhoA antibody also blocked PB2 emission. Our findings indicate that RhoA, by regulating microfilament organization, regulates several important events including GVBD, polar body emission, spindle rotation, and cleavage.

Cell-cycle-dependent subcellular localization of cyclin B1, phosphorylated cyclin B1 and p34cdc2 during oocyte meiotic maturation and fertilization in mouse

M phase or maturation promoting factor (MPF), a kinase complex composed of the regulatory cyclin B and the catalytic p34cdc2 kinase, plays important roles in meiosis and mitosis. This study was designed to detect and compare the subcellular localization of cyclin B1, phosphorylated cyclin B1 and p34cdc2 during oocyte meiotic maturation and fertilization in mouse. We found that all these proteins were concentrated in the germinal vesicle of oocytes. Shortly after germinal vesicle breakdown, all these proteins were accumulated around the condensed chromosomes. With spindle formation at metaphase I, cyclin B1 and phosphorylated cyclin B1 were localized around the condensed chromosomes and concentrated at the spindle poles, while p34cdc2 was localized in the spindle region. At the anaphase/telophase transition, phosphorylated cyclin B1 was accumulated in the midbody between the separating chromosomes/chromatids, while p34cdc2 was accumulated in the entire spindle except for the midbody region. At metaphase II, both cyclin B1 and p34cdc2 were horizontally localized in the region with the aligned chromosomes and the two poles of the spindle, while phosphorylated cyclin B1 was localized in the two poles of spindle and the chromosomes. We could not detect a particular distribution of cyclin B1 in fertilized eggs when the pronuclei were initially formed, but in late pronuclei cyclin B1 was accumulated in the pronuclei. p34cdc2 and phosphorylated cyclin B1 were always concentrated in one pronucleus after parthenogenetic activation or in two pronuclei after fertilization. At metaphase of 1-cell embryos, cyclin B1 was accumulated around the condensed chromosomes. Cyclin B1 was accumulated in the nucleus of late 2-cell embryos but not in early 2-cell embryos. Furthermore, we also detected the accumulation of p34cdc2 in the nucleus of 2- and 4-cell embryos. All these results show that cyclin B1, phosphorylated cyclin B1 and p34cdc2 have similar distributions at some stages but different localizations at other stages during oocyte meiotic maturation and fertilization, suggesting that they may play a common role in some events but different roles in other events during oocyte maturation and fertilization.

Apoptosis in rabbit embryos produced by fertilization or nuclear transfer with fibroblasts and cumulus cells

In this study, we investigated the development, the cell number of the blastocyst, and apoptosis in rabbit nuclear transfer (NT) embryos derived from adult fibroblasts and cumulus cells as compared with embryos derived fromin vivofertilization andin vitroculture. The developmental rate and the total cell number of the blastocyst were significantly lower in NT embryos than in fertilized embryos (FEs). The type of donor cells did not affect the embryonic developmental rate and the total cell number of blastocysts in NT groups. The present study investigated the onset and the frequency of apoptosis in NT embryos and FEs by using a terminal deoxynucleotidyl transferase-mediated dUTP nick and labeling (TUNEL) assay. The earliest positive TUNEL signals were detected at the eight-cell stage in NT embryos and at the morula stage in FEs. The apoptotic index of the total blastocysts, the inner cell mass and the trophoderm was greatly higher in the NT embryos than in FEs. Moreover, the apoptotic index of the blastocyst from fibroblasts was significantly higher than that of the blastocyst from cumulus cells.