Timing of early developmental events in embryos of a tropical sea urchin Echinometra mathaei

Egg volume of a tropical sea urchin Echinometra mathaei is about one half that of other well-known species. We asked whether such a small size of eggs affected the timings of early developmental events or not. Cleavages became asynchronous from the 7th cleavage onward, and embryos hatched out before completion of the 9th cleavage. These timings were one cell cycle earlier than those in well-known sea urchins, raising the possibility that much earlier events, such as the increase in adhesiveness of blastomeres or the specification of dorso-ventral axis (DV-axis), would also occur earlier by one cell cycle. By examining the pseudopodia formation in dissociated blastomeres, it was elucidated that blastomeres in meso- and macromere lineages became adhesive after the 4th and 5th cleavages, respectively. From cell trace experiments, it was found that the first or second cleavage plane was preferentially employed as the median plane of embryo; the DV-axis was specified mainly at the 16-cell stage. Timings of these events were also one cell cycle earlier than those in Hemicentrotus pulcherrimus. The obtained results suggest that most of the early developmental events in sea urchin embryos do not depend on cleavage cycles, but on other factors, such as the nucleo-cytoplasmic ratio.

Expression of microinjected reporter gene lacZ during first cleavages of rabbit embryos

The growing use of reporter genes in a model transgenic system has been a fundamental approach of biology, but the strategy of transgenic embryo selection prior to transfer to foster mothers may greately increase the efficiency of transgenic livestock production. This study was conducted to assess the possibility of beta-galactosidase (beta-gal)-labeled transgenic rabbit embryo production. Rabbit zygotes were obtained from superovulated females after mating. Zygotes were microinjected into male pronuclei with pCMV-lacZ or SV40-lacZ constructs; while some embryos were co-injected with the scaffold attachment sequences--SAR. Embryos from control non-injected and microinjected groups were cultured in vitro. After 24, 48, 72, or 96 h of culture the embryos were stained with X-gal for beta-galactosidase. Transgenic embryos produced by pronuclear injection showed a discrete pattern of beta-galactosidase expression. The percentage of transgenesis with pCMV-lacZalone was 1.5, but with SAR sequences it increased to 4.2. In the case of SV40-lacZ construct, the efficiency of transgenesis was 2.3% and 4.1%, respectively. The mosaicism was 66.7% for all embryos injected with both constructs with or without SAR. The highest numbers of 100%-transgenic (non-mosaic) embryos were found in the group co-injected with SV40-lacZ and SAR. Transgenesis was seen as early as 24 h after injection, in four-cell embryos. Most of the microinjected embryos showed delayed development as compared with control. It was concluded that lacZ may serve as a reliable reporter for early transgenic embryo selection in order to produce transgenic animals.

Effect of the number of passages of fetal and adult fibroblasts on nuclear remodelling and first embryonic division in reconstructed horse oocytes after nuclear transfer

The effects of repeated passage in vitro of fetal fibroblast cells (FFC) and adult fibroblast cells (AFC) on nuclear remodelling and first embryonic division when used to reconstruct horse oocytes, and the reasons for the developmental block in progression to the two-cell stage were investigated. A total of 463 metaphase II oocytes produced 427 fibroblast-cytoplasm couplets after nuclear transfer, which finally resulted in 319 reconstructed oocytes. With increasing numbers of passages, the rates of nuclear remodelling decreased in both types of donor cell; about half of the fused donor cell nuclei showed the S-G2-prometaphase stages of the first embryonic division 18-20 h after cell-fusion treatment, irrespective of the number of donor cell passages (FFC: 49%; AFC: 53%). The rates of first embryonic division in the reconstructed oocytes fell with increasing age of the donor cells (FFC: 32%-26%-23%; AFC: 27%-23%-24%) and these rates were significantly lower than those obtained from metaphase II oocytes activated parthenogenetically (79%, P < 0.05). Microscopic analysis of the organization of the first embryonic division in the developmentally blocked oocytes reconstructed with either FFC or AFC showed that most of these (FFC: 78%; AFC: 92%) could not form the mitotic spindle and the metaphase plate of chromosomes. These findings indicate that either fetal or adult fibroblasts that have undergone relatively few passages in vitro are most suitable as donors. However, both types of cell have lower potential to restart first embryonic development after nuclear transfer than do the equivalent cells in other species. Improvement in the rate of donor cell nuclear progression from S-G2-prometaphase to beyond the metaphase stage, and the normal organization of first embryonic development in reconstructed horse oocytes, would seem to be the key to the production of cloned embryos in this species.

Embryonic development of in vitro matured and in vitro fertilized dog oocytes

In several studies, early cleavage stage canine embryos have been derived from in vitro fertilized oocytes cultured under various conditions. Despite these results, IVF protocols for canine oocytes have yielded low fertilization rates. In this study, Experiment I compared the effects of tissue culture medium (TCM)-199 supplemented with either (A) 1 microg/ml estradiol or (B) 20 microg/ml estradiol + 1 microg/ml human somatotropin (hST) on the in vitro nuclear maturation rate of canine oocytes. Meiotic progression to the metaphase I and II (MI/MII) stages at 72 hr of in vitro culture (IVC) was 10.2% (11/108) in medium A versus 14.1% (30/142) in medium B (P = 0.802). In Experiment II, cleavage rate was determined among oocytes recovered from ovaries of bitches at different reproductive stages. Oocytes (n = 888) were retrieved from bitches at the follicular, anestrous, and luteal stages and selected for high morphological quality. Oocytes were matured for 48 hr in TCM-199 supplemented with 1 microg/ml hST + 20 microg/ml estradiol. Oocytes were in vitro fertilized with fresh canine spermatozoa that had been isolated on a Percoll gradient, and were cultured in synthetic oviduct fluid (SOF) medium with bovine serum albumin (BSA; 4 mg/ml) up to 5 days in 5% CO(2) in air at 37 degrees C. A proportion of oocytes (30.6%) with identifiable nuclear material had cytoplasm penetrated or fertilized by sperm. The percentage of oocytes developing into early stage embryos was 10.1% (27/267). Although pronuclear development was observed to be higher for oocytes recovered at the follicular phase, the cleavage rate was similar among oocytes recovered from bitches at the follicular, anestrus, and luteal stages. There was no correlation between the proportion of capacitated or acrosome reacted spermatozoa and pronuclei formation and/or percent cleavage. It was concluded that TCM-199 supplemented with 1 microg/ml hST and estradiol (20 microg/ml) supports nuclear and cytoplasmic maturation of canine oocytes. In this study, meiotic competence was verified by the in vitro production (IVP) and development of embryos up to the 8 cell-stage. Furthermore, the results indicate that, under the described conditions and despite the influence of reproductive status of the bitch on the developmental competence of in vitro fertilized oocytes to the pronuclei stage, cleavage was independent of donor's reproductive estrous cycle stage.

Simple and efficient in vitro fertilization with cryopreserved C57BL/6J mouse sperm

Archiving of mouse stocks by cryopreservation of sperm has great potential, because it is simple, rapid, and cheap. However, for some of the most commonly used inbred strains, including C57BL/6J, the postthaw fertility of the sperm (0%-12%) is too low to be useful without recourse to zona nicking or intracytoplasmic sperm injection to aid penetration of the zona pellucida. In the present study, nonmotile sperm and cell debris were removed from thawed suspensions of C57BL/6J mouse sperm, and the remaining, largely progressively motile sperm were used for in vitro fertilization. These sperm fertilized 38%-88% of denuded, zona-intact eggs, and when 2-cell embryos were transferred to pseudopregnant recipient mice, 40%-63% produced live-born young. The production of 2-cell embryos and the birth of live pups at these rates indicate that cryopreservation of sperm is a practical way to archive the haploid genome of genetically altered C57BL/6J mice.

Comparison of slow- and rapid-cooling protocols for early-cleavage-stage Macaca fascicularis embryos

Cryostorage of nonhuman primate embryos by time-consuming slow-cooling methods is often limited to early cleavage stages. Effective rapid-cooling methods have been developed for many species and represent valuable tools for laboratory- and field-based studies of nonhuman primate reproductive biology. However, few rapid-cooling protocols have been applied to nonhuman primate embryos in terms of comparing various developmental stages. Here we compare slow cooling vs. two- and three-step rapid cooling of two-, four-, and eight-cell Macaca fascicularis (Mf) embryos. Rapid cooling was conducted in open pulled straws (OPS) using cooling solutions containing reduced quantities of ethylene glycol (EG) and supplemented with either of two high-molecular-weight polymers, ficoll and dextran. The survival of the slow-cooled embryos, but not the rapid-cooled embryos, was independent of embryonic stage at cryostorage. Slow cooling was associated with greater cell survival (82%) post thaw compared to warming following rapid cooling (18-29%). Slow cooling resulted in a high proportion of embryo survival (18/20; 90%) and cleavage (15/18; 83%) post thaw. Rapid cooling resulted in significantly reduced percentages of embryo survival (26-32%) and embryo cleavage in culture (29-38%) after warming. Conventional slow cooling was more effective than the rapid-cooling protocols employed in this study for cryopreservation of early-cleavage-stage Mf embryos.

The origin of monozygotic twinning

The incidence of monozygotic twinning appears to be increasing within the field of assisted human reproduction. Many theories have been put forward as to how and when this occurs. Whatever the cause, the normal events of embryo development, which necessarily involve axis formation, patterning and polarization, need to be adhered to in order to obtain a viable offspring. This paper describes the course of development in terms of axis formation and polarity and offers suggestions as to how either a disruption of this or duplication events in the course of the formation of these parameters could prevent or contribute to a twinning event. The likelihood of twinning occurring at any point is discussed in terms of the establishment of polarity and axes.

Fundamentals of human embryonic growth in vitro and the selection of high-quality embryos for transfer

Knowledge of the nature of embryo growth, and the handling and scoring of quality in human embryos are significant aspects for embryologists in IVF clinics. This review describes the formation, growth and maturation of human oocytes, many aspects of fertilization in vitro, embryonic transcription during preimplantation stages, and the formation of polarities, timing controls, role of mitochondria and functions of endocrine and paracrine systems. Modern concepts are fully discussed, together with their significance in the practice of IVF. This knowledge is essential for the correct clinical care of human embryos growing in vitro, especially in view of their uncharacteristic tendency to vary widely in implantation potential. Underlying causes of such variation have not been identified. Stringent tests must be enforced to ensure human embryos develop under optimal conditions, and are scored for quality using the most advanced techniques. Optimal methods of culture are described, including methods such as co-culture introduced to improve embryo quality but less important today. Detailed attention is given to quality as assessed from embryonic characteristics determined by timers, polarities, disturbed embryo growth and anomalous cell cycles. Methods for classification are described. Approaches to single embryo transfers are described, including the use of sequential media to produce high-quality blastocysts. These approaches, and others involved in surgical methods to remove fragments, transfer ooplasm or utilize newer approaches such as preimplantation diagnosis of chromosomal complements in embryos are covered. New outlooks in this field are summarized.

Ultrastructure of oocyte maturation, fertilization, and early embryo development in vitro in the Siberian tiger (Panthera tigris altaica)

The application of assisted reproduction techniques to wild cats has been stalled by a lack of basic knowledge of the reproductive biology in these species. In this study, the ultrastructure of Siberian tiger (Panthera tigris altaica) cumulus-oocyte-complexes (COCs), as well as in vitro produced (IVP) zygotes and embryos were investigated, to estimate the normality of the manipulated reproduction processes. Adult female tigers were subjected to a purified porcine pFSH/pLH stimulation treatment followed by oocyte aspiration. According to morphological appearance at the stereomicroscopical level, COCs were classified as mature, immature, or degenerated, and then allocated into the following groups: presumptively immature COCs, which were in vitro matured (IVM-group) before fixation; presumptively mature COCs, which were either fixed after retrieval (pre-IVF-group), following in vitro insemination (IVF-group) or following in vitro insemination and subsequent in vitro culture (IVC-group). All specimens were processed for light and transmission electron microscopy (TEM). Both the IVM- and pre-IVF-group included oocytes in meiotic stages ranging from prophase I to metaphase II, and some prophase I oocytes in the IVM-group were apparently in their growth phase. The IVF-group presented features of presumptive normal fertilization, but aberrations such as polynucleation were also noted. The IVC-group included cleavage stage embryos of which, however, many were polynucleated. In conclusion, the procedures used for stimulation, aspiration, and classification of COCs resulted in retrieval of a heterogeneous population of oocytes which, following IVF and IVC, displayed a high rate of developmental deviations.

Determination and synchronisation of G1-phase of the cell cycle in 2- and 4-cell mouse embryos

Incorporation of [3H]thymidine at different concentrations into mouse embryos at early developmental stages was determined by autoradiography. Methods to synchronise the G1-phase of mouse 2- and 4-cell embryos were also investigated. The results showed that the ability of embryos to incorporate [3H]thymidine increased with development. Embryos at the 4-cell stage were not labelled when the concentration of [3H]thymidine was lower than 5 microCi/ml, whereas the nuclei of embryos at morula and blastocyst stages began to show silver grains at a concentration of 0.1 microCi/ml of [3H]thymidine. After 2- and 4-cell mouse embryos were synchronised at the onset of G1-phase by treatment with low temperature or nocodazole, and DNA synthesis was detected by autoradiography, the duration of G1-phase was estimated. The result showed that 43% of the 2-cell embryos had a G1-phase of < or = 1 h, 22% had a G1-phase of < or = 2 h, 22% had a G1-phase of < or = 3 h and 13% had a G1-phase of < or = 4 h. The G1-phase in 85% of the 4-cell embryos was < or = 3 h, that in 8% of embryos was < or = 4 h and that in 7% of embryos was < or = 5 h. The toxicity of nocodazole on mouse embryo development was assessed based on both blastocyst formation and the number of blastomeres, and the results indicated that the effect of nocodazole on embryo development and cell cycle block was dose-dependent. The minimum concentration of nocodazole for metaphase block of mouse late 2-cell embryos was 0.05 microM, and the appropriate concentrations which did not impair development were 0.05-0.5 microM.

Chromosome mosaicism in cleavage-stage human embryos: evidence of a maternal age effect

The present study evaluated mosaicism in a large series of cleavage-stage human embryos analysed by fluorescence in-situ hybridization. Only embryos with at least three cells analysed were included (n = 1235), of which 556 were mosaics. The most common types of mosaicism were chaotic (48%), diploid/polyploid (26%), and those caused by mitotic non-disjunction (25%). The number of abnormal cells per embryo ranged from 44% in diploid/polyploid to 84% in chaotic mosaics. Chromosome 16 was most commonly involved in mitotic non-disjunction mosaics. While overall mosaicism did not increase with maternal age, the average maternal age of the embryos that had mosaics caused by mitotic non-disjunction was significantly higher than that for normal or other mosaic embryos (P < 0.001). During the cleavage stage, the embryonic genome is not yet fully activated and consequently the mRNA and protein pools are still similar to those found in the oocyte. We therefore propose that the malfunctioning of the meiosis apparatus, which is similar to the mitotic one, may cause either meiotic errors or mitotic non-disjunction at cleavage-stage embryo development.

Heat shock-induced apoptosis in preimplantation bovine embryos is a developmentally regulated phenomenon

Apoptosis is a form of cell death that can function to eliminate cells damaged by environmental stress. One stress that can compromise embryonic development is elevated temperature (i.e., heat shock). For the current studies, we hypothesized that heat shock induces apoptosis in bovine embryos in a developmentally regulated manner. Studies were performed to 1) determine whether heat shock can induce apoptosis in preimplantation embryos, 2) test whether heat-induced apoptosis is developmentally regulated, 3) evaluate whether heat shock-induced changes in caspase activity parallel patterns of apoptosis, and 4) ascertain whether exposure to a mild heat shock can protect embryos from heat-induced apoptosis. As determined by TUNEL reaction, exposure of bovine embryos > or =16 cells on Day 5 after insemination to 41 or 42 degrees C for 9 h increased the percentage of cells undergoing apoptosis. In addition, there was a duration-dependent increase in the proportion of blastomeres that were apoptotic when embryos were exposed to temperatures of 40 or 41 degrees C, which are more characteristic of temperatures experienced by heat-stressed cows. Heat shock also increased caspase activity in Day 5 embryos. However, heat shock did not induce apoptosis in 2- or 4-cell embryos, nor did it increase caspase activity in 2-cell embryos. The apoptotic response of 8- to 16-cell-stage bovine embryos to heat shock depended upon the day after insemination that heat shock occurred. When 8- to 16-cell embryos were collected on Day 3 after insemination, heat shock of 41 degrees C for 9 h did not induce apoptosis. In contrast, when 8- to 16-cell embryos were collected on Day 4 after insemination and exposed to heat shock, there was an increase in the percentage of cells undergoing apoptosis. Exposure of 8- to 16-cell embryos at Day 4 to a mild heat shock of 40 degrees C for 80 min blocked the apoptotic response to a subsequent, more-severe heat shock of 41 degrees C for 9 h. In conclusion, apoptosis is a developmentally acquired phenomenon that occurs in embryos exposed to elevated temperature, and it can be prevented by induced thermotolerance.

Processes that occur before second cleavage determine third cleavage orientation in Xenopus

As in many organisms, the first three cleavage planes of Xenopus laevis eggs form in a well-described mutually orthogonal geometry. The factors dictating this simple pattern have not been unambiguously identified. Here, we describe experiments, using static magnetic fields as a novel approach to perturb normal cleavage geometry, that provide new insight into these factors. We show that a magnetic field applied during either or both of the first two cell cycles can induce the third cell cycle mitotic apparatus (MA) at metaphase and the third cleavage plane to align nearly perpendicular to their nominal orientations without changing cell shape. These results indicate that processes occurring during the first two cell cycles primarily dictate the third cleavage plane and mitotic apparatus orientation. We discuss how mechanisms that can align the MA after it has formed are likely to be of secondary importance in determining cleavage geometry in this system.

Cyclin B1 levels in the porcine 4-cell stage embryo

The relative quantity of cyclin B1 was determined during the development of in vitro and in vivo derived porcine 4-cell embryos by western blotting and immunolocalised during the 4-cell stage. After cleavage to the 4-cell stage cyclin B1 localised to the cytoplasm at the 5, 10, 18 and 25 time points and localised to the nucleus 33 h post 4-cell cleavage (P4CC). The relative abundance of cyclin B1 was not significantly different in in vivo or in vitro derived 4-cell stage embryos cultured in the absence of the RNA polymerase inhibitor alpha-amanitin. Cyclin B1 protein was not detectable in embryos cultured in medium without alpha-amanitin for 5, 10, 18 or 25 h P4CC followed by culture in medium with alpha-amanitin to 33 P4CC. These results suggest that the maternal to zygotic transition of mRNA production that occurs at the 4-cell stage of the pig embryo does not result in an increase in cyclin B1 production. In addition, cyclin B1 protein levels remained constant in the absence of embryonic genome activation at the 4-cell stage.

Improved development of very-poor-quality human preembryos by coculture with human fallopian ampullary cells

PURPOSE

To determine whether a confluent culture of fallopian ampullary epithelial cells, taken from women at the end of their reproductive life, is capable of rescuing very-poor-quality preembryos from cleavage arrest and/or degeneration.

METHODS

Human preembryos. rejected for transfer or freezing because of very poor quality, and arrested within 24 h of cleavage, were cultured for 5 days in medium alone or over a confluent culture of fallopian ampullary epithelia] cells. Morphological criteria were utilized to assess preembryo degeneration and stage of development.

RESULTS

The described coculture rescued preembryos from degeneration, enhancing development to the blastocyst stage 2.2-fold, compared with cultures in medium alone. Furthermore, fully expanded and hatching blastocysts were observed only under coculture conditions.

CONCLUSIONS

Very-poor-quality human preembryos may be rescued from degeneration, and their growth and development dramatically improved, when cocultured with a confluent culture of fallopian ampullary epithelial cells.

Dynamic expression and essential functions of Hes7 in somite segmentation

The basic helix-loop-helix (bHLH) gene Hes7, a putative Notch effector, encodes a transcriptional repressor. Here, we found that Hes7 expression oscillates in 2-h cycles in the presomitic mesoderm (PSM). In Hes7-null mice, somites are not properly segmented and their anterior-posterior polarity is disrupted. As a result, the somite derivatives such as vertebrae and ribs are severely disorganized. Although expression of Notch and its ligands is not affected significantly, the oscillator and Notch modulator lunatic fringe is expressed continuously throughout the mutant PSM. These results indicate that Hes7 controls the cyclic expression of lunatic fringe and is essential for coordinated somite segmentation.

Births of kittens produced by intracytoplasmic sperm injection of domestic cat oocytes matured in vitro

In Experiment 1, cleavage frequency and in vitro development of domestic cat embryos produced after in vitro maturation of oocytes obtained from ovaries after ovariohysterectomy (in vitro) with that of oocytes retrieved from follicle-stimulating hormone-treated donors at 24 h after administration of luteinizing hormone (in vivo) and fertilization by intracytoplasmic sperm injection (ICSI) or IVF were compared. In each group presumptive zygotes were assessed for cleavage on IVC Days 1 and 4 and for development to blastocysts on IVC Day 7. In vitro matured oocytes had lower frequencies of meiotic maturation (59.2% v. 66.5%), cleavage at Day 1 (41.4% v. 64.9%) and development to the morula stage at Day 4 (65.8% v. 87.9%) than did in vivo matured oocytes, after ICSI and IVF. Development to the blastocyst stage was lower in in vitro matured oocytes (19.0%) than in vivo matured oocytes (29.5%) after ICSI. In Experiment 2, we evaluated the capacity of sperm injected oocytes without a visible polar body to undergo cleavage and in vitro development. More in vivo matured than in vitro matured oocytes underwent cleavage at Day 1 (46.6% v. 12.6%) and developed to the morula stage by Day 4 (66.7% v. 46.1%), but no blastocysts were obtained at Day 7 in either group. In Experiment 3, we evaluated the in vivo viability of domestic cat embryos derived from ICSI of in vitro matured oocytes. Morula stage embryos were transferred to 18 domestic cat recipients either on Day 4 or 5 after oocyte recovery. A total of 3 domestic cat recipients were pregnant after transfer to recipients on Day 5. Two pregnant cats delivered two normal and healthy live male kittens on Day 68 of gestation and the remaining cat delivered a male kitten on Day 62 that died during the last two days of gestation. These results demonstrate that: (1) inadequate cytoplasmic maturation of in vitro matured domestic cat oocytes is the main cause of deficient oocyte activation; (2) the injection of oocytes without a visible polar body is a useful technique to evaluate oocyte cytoplasmic maturation; and (3) blastocysts obtained after ICSI of in vitro matured oocytes are viable and not a result of parthenogenesis.

How many blastomeres of the 4-cell embryo contribute cells to the mouse body?

The aim of this study was to estimate how many blastomeres of the 4-cell mouse embryo contribute cells to the embryo proper and finally to the animal. To this end, 4-cell embryos of pigmented and albino genotypes were disaggregated and single blastomeres (henceforth called '1/4' or 'quarter' blastomeres) were reaggregated in the following combinations: one 'pigmented' blastomere + three 'albino' blastomeres or vice versa (henceforth called '1+3') and two pigmented blastomeres + two albino blastomeres (henceforth called '2+2'). The aggregations were cultured in vitro and transferred as blastocysts either to the oviduct or uterus of pseudopregnant females. Recipients were allowed to litter naturally, or the foetuses were removed by Caesarian section and raised by lactating foster mothers. Chimaerism was assessed on the basis of coat (adults) or eye pigmentation (dead neonates). Among 28 '1+3' animals, there were 13 chimaeric and 15 non-chimaeric individuals. The pigmentation of non-chimaeras was always concordant with the genotype of the three 1/4 blastomeres and not with the genotype of the single blastomere in the given aggregation. These results make rather unlikely the possibility that the mouse is built of cells derived either from one or all four 1/4 blastomeres. Both two remaining options (2 or 3 1/4 blastomeres) are conceivable but the observed ratio of chimaeras to non-chimaeras among '1+3' animals (13:15) fits better the assumption of two 1/4 blastomeres contributing cells to the animal body. This assumption finds additional support in the observation that among '2+2' animals there were non-chimaeras (5 out of 7) and these would not have been expected should three 1/4 blastomeres contribute cells to the mouse body.

Paternal influence on the time of first embryonic cleavage post insemination and the implications for subsequent bovine embryo development in vitro and fertility in vivo

The objectives of this study were: (1) to evaluate the effect of sire on the time from insemination to first cleavage following insemination in vitro and the relationship of this parameter to field fertility and (2) to establish the relationship between the kinetics of cleavage in vitro and oocyte developmental competence for bulls of known field fertility. Frozen semen from six bulls with 150-day non-return rates ranging from 57-78% was used. In experiment 1, after insemination with semen from one of the six bulls, presumptive zygotes were transferred to IVC in droplets of synthetic oviduct fluid. Droplets were examined at 24, 27, 30, 33, 36, 42, and 48 hr after insemination and the number of cleaved oocytes was recorded. Blastocyst yield was recorded on Days 6-, 7-, and 8-post insemination. In experiment 2, culture droplets were examined at 30, 36, and 48 hr after insemination. At each time point, the number of cleaved embryos was recorded and these embryos were transferred into new droplets and were cultured separately for the duration of the experiment. The proportion of embryos developing to the blastocyst stage was recorded for each of the groups for each bull. The best predictor of field fertility was a model containing 33-hpi-cleavage percentage only (r = 0.689, P < 0.0001). There was also a significant correlation between blastocyst yield and non-return rate, with Day 7 blastocyst yield having the highest correlation (r = 0.356), although this was relatively low in comparison. In experiment 2, irrespective of sire, a significantly higher proportion of those early-cleaving oocytes (before 30 hpi) developed to blastocysts than those cleaving later. In most cases, a higher proportion of blastocysts derived from early-cleaving oocytes hatched from the zona pellucida suggesting that such blastocysts are of superior quality to those derived from late-cleaving oocytes. In conclusion these data confirm our earlier observations that earliest cleaving zygotes are more competent in terms of development to the blastocyst stage than those that cleave later. This phenomenon is independent of the sire used. However, we have demonstrated that the kinetics of early embryonic development as measured by the timing of the first cleavage division post insemination vary between different bulls and that these differences can be used to discriminate between bulls of high and low bull field fertility.

Embryo selection by the first cleavage parameter between 25 and 27 hours after ICSI

PURPOSE

The objective of this study was to assess first embryo cleavage (FEC) 25-27 h after intracytoplasmic sperm injection (ICSI) as a parameter for the embryo selection process.

METHODS

From January 1998 to December 1999, a total of 670 patients were subjected to the ICSI programme at the Centre for Human Reproduction, Sinhá Junqueira Maternity Foundation, and the FEC parameter was evaluated in three situations.

RESULTS

In the first, a total of 300 zygotes were analyzed on the basis of a score (16-18 h after ICSI) and observed for the presence or absence of FEC (25-27 h after ICSI). A significant (p < 0.02) presence of FEC was observed in zygotes with a score of 15 (ideal score). In the second, a total of 200 patients were selected and divided into two groups matched for age and laboratory performance. Group I (n = 100) was subjected to transfer of embryos with the absence of FEC only (since in this cycle no embryos with FEC were detected within 25-27 h after ICSI) and Group II (n = 100) was subjected to transfer of embryos with the presence of FEC only. The age of Group I patients (33.8 +/- 4.2 years) did not differ significantly (p = 0.50) from that of Group II patients (33.5 +/- 4.3 years). The number of embryos transferred was similar (p = 0.07) for Group I (2.7 +/- 1.1) and Group II (2.9 +/- 0.88). In Group II, the 17.5% implantation rate was significantly higher (p < 0.01) than the 5.9% rate obtained for Group I. The pregnancy rate for Group II was significantly higher (p < 0.01) (33%) than that for Group I (12%). The incidence of abortion was 16.6% in Group I as compared with 6% in Group II. In the third situation, we observed the frequency of embryos with FEC in 36 patients whose implantation rate was 100% (ideal result) and obtained a value of 82%.

CONCLUSIONS

The data suggest that the presence of the FEC parameter that was evaluated 25-27 h after ICSI could be used to select embryos with a higher implantation power. The data reported here may justify routine analysis of embryos with FEC for the process of embryo selection after ICSI.

Simulation of the mechanism of determining the position of the cleavage furrow in cytokinesis of sea urchin eggs

In cytokinesis of sea urchin eggs, the numerical density of astral microtubules extending close to the cell surface has been thought to determine the position of the cleavage furrow. In the present study, a new model was constructed to simulate the relationship between the microtubule density and the furrow formation. In the model, gradients of the microtubule density drive fluid membrane proteins whose accumulation triggers the formation of contractile-ring microfilaments. The model could explain the behavior of the cleavage furrow under various experimental conditions. These simulations revealed two aspects of furrow formation. One is that in some cases, the cleavage furrow appears in a surface region where the microtubule density has neither a minimum nor a maximum. In all furrow regions, however, the second derivative of the microtubule-density function has large positive values. Membrane proteins greatly slow down to accumulate in such a region. The other is that the cleavage furrow is mobile, not fixed in one position, because of the fluidity of membrane proteins. These results strongly suggested that the mitotic apparatus determines the position of the cleavage furrow by redistributing membrane proteins through gradients of the microtubule density at the cell surface.

Oral-aboral axis specification in the sea urchin embryo. I. Axis entrainment by respiratory asymmetry

In embryos of indirectly developing echinoids, the secondary (oral-aboral) larval axis is established after fertilization by an as yet undiscovered process. One of the earliest manifestations of this axis is an asymmetry in mitochondrial respiration, with the prospective oral side of the embryo exhibiting a higher rate of respiration than the prospective aboral side. We show here that respiratory asymmetry can be experimentally induced within embryos by immobilizing them in tight clusters of four ("rosettes"). Within such clusters a redox gradient is established from the inside to the outside of the rosette. Vital staining of clustered embryos demonstrates that the side of the embryo facing the outside of the rosette (i.e., the most oxidizing) tends to become the oral side, while the side facing the inside tends to become the aboral side. Effective entrainment of the oral-aboral axis requires that the embryos remain immobilized in rosettes until the hatching blastula stage. To begin to investigate the molecular mechanisms underlying this effect we made use of P3A2, a transcriptional regulatory protein whose activity is spatially modulated along the oral-aboral axis. When synthetic mRNA encoding P3A2 fused to the VP16 activation domain is injected into eggs, it activates embryonic expression of a green fluorescent protein reporter gene containing a basal promoter and a single strong P3A2 target site. In embryo rosettes, such activation occurs predominantly on the outside of the rosette, suggesting that the activity of the P3A2 protein is spatially regulated by the respiratory asymmetry established by clustering the embryos. These findings are discussed with reference to earlier work on both oral-aboral axis specification and P3A2 and used to develop a testable model of the mechanism of oral-aboral axis specification in the sea urchin embryo.

Analysis of Oct-4 expression and ploidy in individual human blastomeres

Oct-4, a decisive factor that maintains totipotency in murine embryonic and germ cells, is exclusively expressed in such cells. In mice, different levels of oct-4 expression in blastomeres predict development towards inner cell mass (ICM) (high oct-4) or trophectoderm (TE) (low oct-4). To address whether the mouse model also applies to human embryos, the cytoplasm of individual human blastomeres from normally and abnormally fertilized embryos was tested for Oct-4 expression by reverse transcription-polymerase chain reaction (RT-PCR). The nuclei of the same blastomeres were subjected to fluorescence in-situ hybridization (FISH) to determine ploidy. A significant difference in Oct-4 mRNA levels was revealed between blastomeres. The distribution of blastomeres with high Oct-4 levels varied according to the cleavage stage of the embryo: the more blastomeres, the lower the percentage with high Oct-4 levels. Aneuploid blastomeres did not exhibit lower Oct-4 mRNA levels than diploid ones. Thus, differential Oct-4 expression in individual human blastomeres appears to direct cells towards the ICM or TE lineages without regard to chromosomal status. Oct-4 might be used as a marker in preimplantation genetic diagnosis to identify embryogenic blastomeres.