Genetic regulation of egg and embryo survival

Vitrification yields higher cryo-survival rate than slow freezing in biopsied bovine in vitro produced blastocysts

Vitrification and slow freezing are the two commonly used embryo cryopreservation methods. In most studies, vitrification of intact embryos has proven superior in several respects, including cell and embryo survival and pregnancy rate. However, there is a lack of data for comparing these two methods in in vitro produced (IVP) bovine blastocysts, which have been subjected to the retrieval of trophectoderm (TE) biopsy. Day 7 IVP blastocysts were pooled and randomized into four groups: 1) non-biopsy (NB), 2) biopsy (B), 3) biopsy-vitrification (BV), 4) biopsy-slow freeze (BSF). The blastocysts in the B, BV, and BSF groups were subjected to TE biopsy. For the B group, this was followed by 5 hours (h) incubation and subsequent scoring of the biopsy-survival (re-expansion) rate before processing for further analyses. For the BV and BSF groups, the biopsy procedure was followed by 2 h incubation, allowing for a quick re-expansion, after which the blastocysts were subjected to vitrification and slow freezing, respectively. After warming and thawing, respectively, they were then incubated for 5 h followed by scoring the cryo-survival (re-expansion) rates before processing for further analyses. These included quantification of ICM and TE cells, cleaved caspase-3- and TUNEL-positive cells, quantitative PCR on cellular stress markers (SOD1 and PRDX1), and ultrastructural analysis. The biopsy-survival rate in the B group was 94% (307/326). The cryo-survival rate in BV (86%, 138/161) was higher than that in BSF (57%, 81/142; P < 0.001). No differences were noted between the average ICM, TE, and total cell numbers of the groups. The percentages of cleaved caspase-3-positive cells were higher in BV vs. NB (P < 0.05), in BSF vs. NB (P < 0.001), and in BSF vs. B (P < 0.001). The percentages of TUNEL-positive cells were higher in BV vs. NB (P < 0.05) and in BSF vs. NB (P < 0.001). The levels of mRNA abundance for SOD1 and PRDX1 in B, BV, and BSF were not different from that in NB. The ultrastructural analysis of blastocysts in the BV and BSF groups showed distension of extracellular spaces and appearance of intracellular vacuoles in the ICM, distension of mitochondria, and disorganization of mitochondrial cristae in both ICM and TE, and weakened tight junctions between adjacent TE cells. In summary, our findings demonstrate that vitrification yields a higher cryo-survival rate than slow freezing in biopsied bovine IVP blastocysts. However, biopsy-vitrification and biopsy-slow-freeze values are comparable in terms of ICM, TE, and total blastocyst cell numbers, as well as cleaved caspase-3- and TUNEL-positive cell rates. Moreover, biopsy and cryopreservation performed alone had no effect on ICM, TE, total blastocyst cell numbers, or TUNEL-positive cell rates. Biopsy and vitrification performed alone had no effect on the cleaved caspase-3 positive cell rates, whereas slow freezing resulted in an increased rate. Furthermore, double traumatization with a combination of biopsy and cryopreservation, either vitrification or slow freezing, resulted in increased rates of cleaved caspase-3- and TUNEL-positive cells.

Effect of caspase inhibitor Z-VAD-FMK on bovine sperm cryotolerance

The aim of this study was to evaluate the treatment of bovine semen with the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK), before or after freezing on semen quality. After the initial assessment, sperm from 4 bulls were pooled (Experiment 1) and cryopreserved in BioXcell containing 0, 20 and 100 μM Z-VAD-FMK. After thawing semen viability, motility, membrane integrity, as well as DNA fragmentation and ΔΨm were evaluated. In Experiment 2, bovine frozen/thawed sperm were incubated for 1 hr with 0, 20 and 100 µM Z-VAD-FMK before assessing the semen quality. The treatment with Z -VAD-FMK before cryopreservation improved post-thawing sperm motility compared to the control group (p < .05), while no differences were recorded in sperm viability and membrane integrity among groups (on average 86.8 ± 1.5 and 69.1 ± 1.4, respectively). Interestingly, at the highest concentration, DNA fragmentation decreased (p < .05), while the percentage of spermatozoa with high ΔΨm increased (p < .05). The results of Experiment 2 showed that 1-hr treatment with Z-VAD-FMK did not affect sperm motility and viability (on average 63.4 ± 5.8 and 83.7.1 ± 1.2, respectively). However, Z-VAD-FMK improved sperm membrane integrity (p < .05) and at the highest concentration tested decreased the proportion of sperm showing DNA fragmentation (p < .05). No differences were recorded in the percentage of spermatozoa with high ΔΨm (on average 57.0 ± 11.4). In conclusion, the treatment with 100 µM of the caspase inhibitor Z-VAD-FMK before freezing increased bovine sperm mass motility and ΔΨm, while decreasing sperm DNA fragmentation. Treatment of semen after thawing with 100 µM Z-VAD-FMK improved sperm membrane integrity and reduced DNA fragmentation.

Using Time Lapse Monitoring for Determination of Morphological Defect Frequency in Feline Embryos after In Vitro Fertilization (IVF)

Simple Summary

This study was conducted with the aim of determining the frequency of morphological defects in feline embryos, their competence to reach the blastocyst stage, and their ability to hatch. Embryonic morphological disorders affect development potential, and the use of time lapse monitoring (TLM) guarantees the precise observation of any changes that occur during in vitro embryo development.

Abstract

Some human, bovine, and mouse in vitro fertilized (IVF) embryos with morphokinetic abnormalities such as fragmentation, direct cleavage, and cytoplasmic vacuoles have the potential to reach the blastocyst stage, which is related to a high potential for implantation. The latest techniques of embryo development observation to enable the evaluation and selection of embryos are based on time lapse monitoring (TLM). The aim of this study was to determine the frequency of morphological defects in feline embryos, their competence to reach the blastocyst stage, and their ability to hatch. Oocyte-cumulus complexes were isolated after the scarification of ovaries and matured in vitro. Matured oocytes were fertilized in vitro by capacitated spermatozoa. Randomly selected oocytes were observed by TLM for seven-to-eight days. Out of 76 developed embryos, 41 were morphologically normal, of which 15 reached the blastocyst stage. Of 35 abnormally developed embryos, 17 reached the blastocyst stage, of which six had single aberrations and 11 had multiple aberrations. The hatching rate (%) was 15.6% in normally cleaving embryos, 6.25% in embryos with single aberrations, and 3.33% in those with multiple aberrations. The present study reports the first results, found by using TLM, about the frequency of the morphological defects of feline embryos, their competence to reach the blastocyst stage, and their ability to hatch.

Is there any correlation between apoptotic genes expression in cumulus cells with embryo morphokinetics?

The aim was to assess the correlation between apoptotic genes of cumulus cells (CCs) with embryo morphokinetics as non invasive methods for embryo selection. Evaluation of cleavage activity among in vitro-fertilized embryos was dependent on determining not only expression profiles of pro- and anti-apoptotic genes in CCs surrounding ovulated oocytes but also morphokinetic parameters such as time of second PB extrusion (tPB2), pronuclei appearance (tPN), pronuclei fading (tPNf), formation of two to eight cells (t2-t8) and cleavage pattern [uneven at two cells stage, cell fusion (Fu) and trichomonas mitoses (TM)]. A total of 269 embryos from 90 intracytoplasmic sperm injection (ICSI) cycles were assessed. The data showed that t2 was associated with CCs expression of Bax, Caspase3 Bcl2 and bax/bcl2 (p = 0.000, p = 0.000, p = 0.04, p = 0.00, respectively). Uneven blastomeres embryo associated with Bax and Caspase3 (p = 0.007, p = 0.000 respectively) as well as Fu and TM embryo significantly correlated to CCs expression of Bax, Caspase3 Bcl2 and bax/bcl2 (p = 0.000, p = 0.000, p = 0.00, p = 0.00, respectively) (p = 0.006, p = 0.000, p = 0.009, p = 0.0340, respectively). Embryo morphokinetics and cleavage pattern associated with CCs apoptotic gene expression. It seems that embryo selection by morphokinetics assessment using TLM with conjunction in CCs gene expression can improve ART outcome.

Inhibition of apoptosis by caspase inhibitor Z-VAD-FMK improves cryotolerance of in vitro derived bovine embryos

The aim of this work was to evaluate whether the treatment with the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK) during cryopreservation and post-warming in vitro culture improves cryotolerance of bovine in vitro produced (IVP) embryos. Abattoir derived bovine oocytes were in vitro matured, fertilized and cultured according to standard procedure. On Day 7, embryo yields were assessed and blastocysts randomly divided in 2 groups: vitrification and post-warming culture in the absence (n = 184) or presence (n = 156) of 20 μM Z-VAD-FMK. Resistance to cryopreservation was evaluated post-warming culture by assessing the survival rate and hatching rate. Differential staining combined with in situ terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL) technique was performed to evaluate total cells number, cell allocation into inner cell mass (ICM) and trophectoderm (TE) lineages, as well as the DNA fragmentation rate of vitrified blastocysts, while immunohystochemical staining was used to assess the level of cleaved-caspase 3. It was demonstrated that inhibition of caspase activity by Z-VAD-FMK increases embryo cryotolerance, as indicated by higher survival (76.1 vs 51.1%; P < 0.01) and hatching rates (26.5 vs 17.6%; P < 0.05) after 48 h of post-warming culture. Furthermore, Z-VAD-FMK decreased both the average number (4.7 ± 0.3 vs 7.7 ± 0.5; P < 0.01) and the percentage (3.4 ± 0.2 vs 6.1 ± 0.5; P < 0.01) of DNA fragmented cells in blastocysts compared to the control. No differences were recorded in the average number of ICM, TE and total cells between groups. The level of cleaved-caspase-3, the downstream effector of apoptosis, and its relative percentage on total area of blastocysts was reduced (P < 0.01) in the presence of Z-VAD-FMK both at thawing (1.29 ± 0.17 vs 3.24 ± 0.46) and after 48 h post-warming culture (1.46 ± 0.17 vs 5.06 ± 0.41). In conclusion, the addition of 20 μM Z-VAD-FMK during vitrification/warming and post-warming culture partially inhibits cryopreservation-induced apoptosis by reducing the level of active caspase 3, suggesting a potential use as an additive to ameliorate the efficiency of embryo cryopreservation in cattle, critical for a further diffusion of IVEP technology in the field. Further studies are though needed to evaluate the effect of Z-VAD-FMK on post-transfer embryo development before considering a commercial application.

Developmental competence and apoptotic gene expression patterns of mature and immature human oocytes retrieved from controlled ovarian stimulation cycles

The purpose was to assess the developmental competence of the in vitro or in vivo matured human oocytes as well as the apoptotic genes expression of cumulus cells (CCs) regarding nuclear maturity status of associated oocytes retrieved from stimulated ICSI cycles. A total of 590 oocytes and the associated CCs were retrieved and divided into groups of test and control according to the nuclear maturity status in order to the developmental evaluation as well as expression patterns of apoptosis-related genes using real time PCR. The fertilization and embryo formation rates were 60.3% and 87.5% vs.69.1% and 92.8% in test and control groups, respectively. Good quality embryos on day 3 were 62.2% in test and 69.1% in control groups. There were significant differences in the rates of normal fertilized as well as unfertilized oocytes between the groups. Also, mRNA levels of some apoptotic genes were significantly higher in the CCs obtained from immature oocytes among patients with premature ovarian factors (POF) rather than other infertility etiologies (p < 0.001). The data demonstrated the developmental competence of in vitro matured oocytes -even to good quality cleavage embryos- is not completely consistent with molecular integrity and well-mannered gene expression patterns resulting to ICSI success. It seems that using immature oocytes could be helpful for patients at risk of ovarian hyperstimulation syndrome (OHSS) as the same as patients with diminished ovarian reserve.

Aromatase Inhibition Reduces the Dose of Gonadotropin Required for Controlled Ovarian Hyperstimulation

OBJECTIVE

To compare the use of the aromatase inhibitor, letrozole, in conjunction with follicle-stimulating hormone (FSH) injection, and FSH alone for controlled ovarian hyperstimulation (COH) in patients with polycystic ovarian syndrome (PCOS) or ovulatory infertility.

METHODS

This nonrandomized study included two study groups: 26 patients with PCOS and 63 with ovulatory infertility (unexplained infertility [41 patients], male factor infertility [17 patients], and endometriosis [5 patients]), who received letrozole in addition to FSH; and two control groups: 46 PCOS patients and 308 with ovulatory infertility (unexplained infertility [250 patients], male factor infertility [42 patients], and endometriosis [16 patients], who received FSH only. All patients had intrauterine insemination (IUI). Main outcome measures included dose of FSH used per cycle, number of preovulatory follicles greater than 16 mm in diameter, cancellation rate, and pregnancy rate.

RESULTS

The FSH dose required for ovarian stimulation was significantly lower when letrozole was used in both study groups compared to the control groups without a significant difference in number of follicles greater than 16 mm. IUI cancellation rate was significantly lower with letrozole treatment in PCOS patients. In women with PCOS, clinical pregnancy rate per completed IUI cycle was 26.5% in the letrozole plus FSH group versus 18.5% in the FSH-only group. In ovulatory infertility patients, the pregnancy rate was similar in both study and control groups (11%).

CONCLUSION

We believe that inhibition of estrogen synthesis by aromatase inhibition will release the estrogenic negative feedback, resulting in an increase in endogenous FSH secretion. Moreover, by inhibiting conversion of androgens into estrogens, accumulating androgens may increase follicular sensitivity to FSH. Such a protocol has the potential to lower FSH treatment cost and may improve response for low responders who require high FSH doses during ovarian stimulation.

Does sperm DNA fragmentation affect the developmental potential and the incidence of apoptosis following blastomere biopsy?

Common methods employed in assisted reproduction technology (ART) include intracytoplasmic sperm injection (ICSI) with an unspecified level of sperm DNA fragmentation (SDF) and preimplantation genetic diagnosis (PGD). The aim of this study was to investigate the impact of SDF on human preimplantation embryo development and the incidence of apoptosis following a single blastomere biopsy. Using sperm chromatin dispersion (SCD) to assess SDF, a total of 20 processed semen samples were categorized into two groups; group I: SDF ≤30% and group II: SDF >30%. After ICSI, fertilization, cleavage, and embryo quality score were assessed. A single blastomere was biopsied from day 3 embryos and development was monitored on day 4. The frequency of apoptosis in biopsied embryos was assayed by TUNEL and the level of BCL-2, BAX, hsa-mir-15a, and hsa-mir-16-1 were assessed by quantitative real-time polymerase chain reaction (qRT-PCR). SCD was found to be negatively correlated with sperm motility and normal form spermatozoa (p < 0.05). The rate of fertilization, cleavage, and embryo quality score were not significantly different between the two groups (all p > 0.05). SDF >30% had no negative effect on potential development and did not increase the proportion of apoptotic cells and the level of apoptosis-related genes and microRNAs (miRNAs) in group II vs. group I (p > 0.05). It appears that at the levels assessed paternal genome damage had little if any negative effect on preimplantaton embryo development and apoptosis following single blastomere biopsy. This may reflect the selection of morphologically normal sperm for ICSI and the repair capacity of the oocyte.

Systematic analysis of the factors that adversely affect the rate of cell accumulation in mouse embryos during their culture in vitro

BACKGROUND

Retarded embryo growth is a pervasive effect of culture in vitro.

METHODS

A systematic analysis of the interactions between media design, embryo culture density, oxygen tension, amino acids, trophic ligands and the genetic background of the mouse on embryo growth rates in vitro was performed.

RESULTS

Growth retardation of mouse zygotes was greater in 20% O2 than 5%, a sequential media design was superior to static simple media designs, but the supplementation of simple media with mixed amino acids mitigated this difference. There was a beneficial effect of communal culture in small volumes, and supplementation with a trophic ligand (Paf) further enhanced growth rates. For hybrid strain zygotes (B6CBF1) communal culture in KSOM media supplemented with amino acids, albumin and Paf under 5% O₂ resulted in complete rescue of their rate of accumulation of cells and blastocyst formation. Inbred strain (C57BL6/J) zygotes, however, still showed some retardation of development under these conditions. The additional supplementation of media with another trophic ligand (IGF1) showed a further additive beneficial effect on development of inbred strain embryos but they still showed a growth deficit of ~ 23% cell number. The results show that optimising the interactions between a range of culture conditions and media design can rescue hybrid strain embryos from a retarded rate of cell proliferation caused by culture in vitro, but this was incomplete for the B6 strain.

CONCLUSIONS

The results indicate that the growth requirement of embryos in vitro varies depending upon their genetic background and provide models for the further genetic analysis of embryo growth.

Intracellular glutathione content, developmental competence and expression of apoptosis-related genes associated with G6PDH-activity in goat oocyte

PURPOSE

To associate glucose-6-phosphate dehydrogenase (G6PDH) activity in goat oocytes with intracellular glutathione (GSH) content, meiotic competence, developmental potential, and relative abundance of Bax and Bcl-2 genes transcripts.

METHODS

Goat oocytes were exposed to brilliant cresyl blue (BCB) staining test and categorized into BCB(+) (blue-cytoplasm), and BCB(-) (colorless-cytoplasm) groups. A group of oocytes were not exposed to BCB test and was considered as a control group. After maturation in vitro, a group of oocytes were used for determination of nuclear status and intracellular GSH content while another group was subjected to parthenogenetic activation followed by in vitro embryo culture.

RESULTS

We found that BCB(+) oocytes not only yielded higher rate of maturation, but also showed an increased level of intracellular GSH content than BCB(-) and control oocytes. Furthermore, BCB(+) oocytes produced more blastocysts than BCB(-) and control oocytes. Our data revealed that the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes were interacted with G6PDH-activity in mature oocyte, their surrounding cumulus cells, and blastocyst-stage embryos.

CONCLUSIONS

The results of this study demonstrate that selection of goat oocytes based on G6PDH-activity through the BCB test improves their developmental competence, increases intracellular GSH content, and affects the expression of the apoptosis-related genes.

Developmental potential and kinetics of pig embryos with different cytoplasmic volume

The effects of cytoplasmic volumes on development and developmental kinetics of in vitro produced porcine embryos were investigated. During hand-made cloning (HMC), selected cytoplasts were separated into two groups according to their size in relation to the initial oocyte: ~75% or ~50%. Following two fusion steps and activation (day 0), reconstructed embryos were cultured in vitro for 6 days. Cleavage rates on day 2 as well as blastocyst rates and cell numbers on day 6 were recorded. Results showed that embryo development was no different for ~50% versus ~75% cytoplasm at first fusion. This result was used in the following experiments, where the effect of varying cytoplasm volume in second fusion to obtain a final cytoplasm volume of ~75% to ~200% was tested. The results showed that the lowest quality was obtained when the final cytoplasm volume was ~75% and the highest quality at ~200% of the original oocyte. Similar results were observed in parthenogenetic (PA) embryos activated with different cytoplasmic volumes. A common pattern for the developmental kinetics of HMC and PA embryos was observed: the smaller group tended to have a longer time for the first two cell cycles, but subsequently a shorter time to form morula and blastocyst. In conclusion, the developmental kinetics of in vitro produced embryos was affected by the cytoplasm volume of the initial oocyte, and this further accounted for the developmental ability of the reconstructed embryos.

Early cleaved bovine embryos show reduced incidence of chromosomal aberrations and higher developmental potential on day 4.5 post-insemination

The present study aimed to investigate whether the timing of the first zygotic cleavage (FZC) influences the speed of embryo development expressed by the total cell count and the rate of chromosomally aberrant embryos. Bovine embryos were produced in vitro and divided into two categories according to the timing of FZC: early cleavers (at 30 hpi; EC) and non-early cleavers (at 48 hpi; NEC). On day 4.5 pi, embryos were grouped into three classes depending on the number of blastomeres: delayed (<8 BL), normal (8-16 BL) and advanced (>16 BL). We applied fluorescence in situ hybridization (FISH) with probes for bovine chromosomes 6 and X. The only form of chromosomal imbalance observed was mixoploidy [(2n/3n; 2n/4n); 19.9%, 54/271]. Early cleavers were less often chromosomally unbalanced (13.9%, 20/144) than their NEC counterparts (26.7%, 34/127). Among embryos developing at a normal speed, the NEC embryos were more often abnormal (NEC 20/80; EC 10/79; p < 0.05). The advanced embryos were not observed among the NEC category, whereas such embryos from EC category displayed no chromosomal aberrations. The majority of embryos arrested at the 8 BL stage were of NEC category and were carriers of chromosomally abnormal blastomeres. With regard to embryonic sex, we demonstrated that although males dominate among bovine embryos developing in vitro, the incidence of mixoploidy was equal for both sexes. It can be suggested that a good-quality bovine embryo is usually an early cleaver that develops at higher speed and contains less aberrant cells. The present study also confirmed the usefulness of the FZC as a marker of embryo quality by demonstrating a significantly lower incidence of aberrations in early embryos.

Histological development of human testicular cords from 70 to 90 days of gestation

The development of the testicular cord structure was investigated in 4 human fetuses between 70 and 90 days of gestation, in which the testicular cords are differentiating into the seminiferous tubules. Histological examinations were performed using stains with haematoxylin-eosin (HE), Masson's trichrome (MT), periodic acid schiff (PAS), anti-proliferating cell nuclear antigen (PCNA) monoclonal antibodies, and TUNEL methods. It was found that the testicular cords structures were indefinitely observed in HE-stained sections of four fetuses. However, the basement membranes of the testicular cord were clearly stained with MT, showing the tubular structure. Furthermore, cells in the testicular cords were positive with PAS, but the interstitial tissues outside the testicular cords were negative. PCNA-positive cells were detected not only inside but also outside the testicular cords, however, TUNEL positive cells are not detected throughout all testicular tissues.

DNA damage and repair in human oocytes and embryos: a review

The genome of all cells is protected at all times by mechanisms collectively known as DNA repair activity (DRA). Such activity is particularly important at the beginning of human life, i.e. at fertilization, immediately after and at the very onset of embryonic development. DRA in early development is, by definition, of maternal origin: the transcripts stored during maturation, need to control the integrity of chromatin, at least until the maternal/zygotic transition at the 4- to 8-cell stage in the human embryo. Tolerance towards DNA damage must be low during this critical stage of development. The majority of DNA damage is due to either apoptosis or reactive oxygen species (ROS). Apoptosis, abortive or not, is a common feature in human sperm, especially in oligoasthenospermic patients and FAS ligand has been reported on the surface of human spermatozoa. The susceptibility of human sperm to DNA damage is well documented, particularly the negative effect of ROS (Kodama et al., 1997; Lopes et al., 1998a, b) and DNA modifying agents (Zenzes et al., 1999; Badouard et al., 2007). DNA damage in sperm is one of the major causes of male infertility and is of much concern in relation to the paternal transmission of mutations and cancer (Zenzes, 2000; Aitken et al., 2003; Fernández-Gonzalez, 2008). It is now clear that DNA damaged spermatozoa are able to reach the fertilization site in vivo (Zenzes et al., 1999), fertilize oocytes and generate early embryos both in vivo and in vitro. The effect of ROS on human oocytes is not as easy to study or quantify. It is a common consensus that the maternal genome is relatively well protected while in the maturing follicle; however damage may occur during the long quiescent period before meiotic re-activation (Zenzes et al., 1998). In fact, during the final stages of follicular growth, the oocyte may be susceptible to damage by ROS. With regards to the embryo there is active protection against ROS in the surrounding environment i.e. in follicular and tubal fluid (El Mouatassim et al., 2000; Guerin et al., 2001). DNA repair activity in the zygote is mandatory in order to avoid mutation in the germ line (Derijck et al., 2008). In this review we focus on the expression of mRNAs that regulate DNA repair capacity in the human oocyte and the mechanisms that protect the embryo against de novo damage.

Clomiphene citrate or aromatase inhibitors combined with gonadotropins for superovulation in women undergoing intrauterine insemination: a prospective randomised trial

The objective of this study was to test the use of letrozole in combination with follicle-stimulating hormone (FSH) vs clomiphene citrate (CC) with FSH for ovarian hyperstimulation prior to intrauterine insemination (IUI). A prospective randomised trial in which 280 women with unexplained infertility were randomised to 100 mg of CC (141 patients, 219 cycles) or 5 mg of letrozole daily (139 patients, 215 cycles) for 5 days starting on day 3 of menses both combined with gonadotropins for ovarian stimulation prior to IUI. The primary outcome measures were the number of growing and mature follicles, the concentrations of serum E2 (pg/ml) and progesterone (ng/ml), and the endometrial thickness (mm). The secondary outcome measure was the occurrence of pregnancy and miscarriage. The total number of follicles was significantly greater in the CC group (4.1 +/- 0.46 vs 2.6 +/- 0.43). There was no significant difference in endometrial thickness between the two groups. Pregnancy occurred in 33 out of 139 patients (215 cycles) in the letrozole group (23.7% and 15.3%, respectively) and 37 out of 141 patients (219 cycles) (26.2% and 16.8%, respectively) in the CC group; the differences were not statistically significant. The allied use of either CC or letrozole, during ovarian stimulation to reduce the dose of gonadotropins prior to IUI is justified. This approach will reduce the cost of stimulation protocols without effect on the treatment outcome and letrozole has no advantage over CC in this respect.

Pertinence of apoptosis markers for the improvement of in vitro fertilization (IVF)

In assisted reproductive technology (ART), the pregnancy and birth rates following in vitro fertilization (IVF) attempts are still low. Recently, apoptotic markers have been suggested as new criteria for oocyte and embryo quality selection. Many studies have provided evidence that poor oocyte and embryo quality can be associated with apoptosis. The aim of this review is to summarize our current knowledge on the apoptotic process in oocytes and embryos, and focus on the possibility for using apoptotic markers as a reliable and predictive marker to select competent oocytes and embryos during IVF. Moreover, it is currently accepted that IVF failures, linked to poor embryo quality, are, in part, associated with suboptimal in vitro culture conditions. Here, we also review the current state of knowledge concerning how the genetic control of apoptosis during folliculogenesis and pre-implantation embryonic development is affected by in vitro culture conditions during IVF. In the future, identification of apoptotic markers in ART for oocyte and embryo selection should result in the development of new agonistic or antagonistic molecules of apoptosis by medicinal chemistry.

Gene expression in mouse preimplantation embryos affected by apoptotic inductor actinomycin D

The aim of this study was to test the effect of actinomycin D on the expression of selected genes and to elucidate possible components of its apoptotic pathway in mouse embryos. Selected mRNAs and Trp53 protein were examined in blastocysts cultured for 24 h in vitro with or without the presence of a high concentration of actinomycin D. In all tested genes, the relative quantities of mRNA were significantly lower in treated blastocysts than in controls. The mRNA quantities of H2afz, Actb, Bax, Bad and Bcl2 were reduced at a similar rate, but the decreases in Bcl2l2 and Trp53 mRNA were significantly greater. Treatment with actinomycin D also changed the ratio between the mRNA levels of some pro-apoptotic and anti-apoptotic genes: the Bad/Bcl2l2 and the Bax/Bcl2l2 ratios were on average 4.39 and 2.66 times higher in the treated embryos than in the controls, respectively. Generally, treatment led to developmental arrest and significant increase in the incidence of cells with typical apoptotic features. However, its effect on Trp53 protein expression was not significant. The results suggest that mechanisms beyond the apoptotic effect of actinomycin D might include specific changes in the expression of pro-apoptotic and anti-apoptotic genes, shifting the expression ratio in favor of the pro-apoptotic ones. The results also show that the role of Trp53 is probably not crucial in this apoptotic pathway.

Active caspase-3 and ultrastructural evidence of apoptosis in spontaneous and induced cell death in bovine in vitro produced pre-implantation embryos

In this study we investigated chronological onset and involvement of active caspase-3, apoptotic nuclear morphology, and TUNEL-labeling, as well as ultrastructural evidence of apoptosis, in both spontaneous and induced cell death during pre-implantation development of bovine in vitro produced embryos. Pre-implantation embryos (2-cell to Day 8 blastocysts) were cultured with either no supplementation (untreated) or with 10 microM staurosporine for 24 hr (treated). Embryos were subjected to immunohistochemical staining of active caspase-3, TUNEL-reaction for detection of DNA degradation and DAPI staining for detection of apoptotic nuclear morphology, and subjected to fluorescence microscopy. Additionally, treated and untreated blastocysts were fixed and processed for ultrastructural identification of apoptosis. Untreated embryos revealed no apoptotic features at 2- and 4-cell stages. However, active caspase-3 and apoptotic nuclear morphology were observed in an untreated 8-cell stage, and TUNEL-labeling was observed from the 16-cell stage. Blastomeres concurrently displaying all apoptotic features were present in a few embryos at 16-cell and morula stages and in all blastocysts. All three features were observed from the 8-cell stage in treated embryos, and blastomeres with apoptotic features appeared more numerous in treated than in untreated embryos. Ultrastructural evidence of apoptosis occurred with a comparable distribution pattern as apoptotic features detected by fluorescence microscopy in both treated and untreated blastocysts. Activation of caspase-3 is likely involved in both spontaneous and induced apoptosis in bovine pre-implantation embryos, and immunohistochemical staining of active caspase-3 may be used in combination with other markers to identify apoptosis in pre-implantation embryos.

Heat stress-induced apoptosis in porcine in vitro fertilized and parthenogenetic preimplantation-stage embryos

Decades worth of research have consistently shown the adverse effects of elevated temperatures on reproductive parameters of livestock species. The objective of this study was to evaluate the developmental and apoptotic responses of porcine in vitro fertilized (IVF) and parthenogenetically activated (PA) embryos heat stressed at the late 1-cell stage. Embryos were heat stressed (HS) at 42 degrees C for 9 hr starting 22 hr after insemination or artificial activation stimulus. Non heat-stressed (NHS) control embryos were maintained at 39 degrees C for the duration of the experiments. TUNEL staining on Day 5 of development demonstrated that heat stress elicited a significant apoptotic response in IVF embryos (45.6% of HS embryos and 26.7% of NHS embryos were apoptotic; P<0.05), but not in PA embryos (51.1% and 39.9% for HS and NHS embryos, respectively; P>0.1). And, while IVF embryos were highly susceptible to heat-induced developmental perturbations (20.6% and 8.8% development to blastocyst for NHS and HS embryos, respectively; P<0.05), elevated temperatures did not affect blastocyst rates in PA embryos (22.2% for NHS PA embryos and 21.2% for HS PA embryos; P>0.1). These findings indicate that, as in other systems studied, IVF pig embryos are directly affected adversely by heat stress conditions. Parthenogenetic embryos, though, appear to be surprisingly tolerant of the elevated temperatures. The differences between IVF and PA embryos in their response to heat stress warrants further investigation.

Effect of fragment removal on blastocyst formation and quality of human embryos

Blastomere fragmentation is one of the most significant defects in cleaving embryos. Scientists believed that removing the fragments was a possible way to reduce their unwanted effects. This hypothesis has been tested in some studies in which the development of human fragmented embryos was followed in vivo after all fragments were removed, but little is known about the potential for in-vitro development of such embryos, which is the subject of the present study. For this purpose, 4-6 cell surplus human embryos were scored according to the degree and pattern of fragmentation into four grades, allocated into two groups of control and fragmentation removal (experimental) and cultured sequentially. At the end of day 6 of culture, in the experimental group especially in grade IV blastocyst rate, size and number of blastomeres in each blastocyst were all improved compared with those of the control group (42.3 versus 20.0%; 19,205.7 +/- 1060.3 versus 15,825.9 +/- 448.7 microm(2) and 100.14 +/- 13.48 versus 63.75 +/- 19.79 respectively, P < 0.05). In the grade IV embryos, apoptotic index was also significantly reduced after embryo fragmentation removal (3.40 +/- 0.88 versus 22.99 +/- 4.45, P < 0.05). In conclusion, fragmentation removal had a positive effect on human fragmented embryos and produced the best quality blastocysts.

Predictive factors for embryo implantation potential

In spite of recent improvements in IVF, pregnancy rates have not increased significantly and one of the major problems remains the high multiple pregnancy rate. Better criteria are therefore necessary to establish the viability of a transferable embryo. Early prognosis of the developmental fate of the oocyte would help in selecting the best embryos to transfer, but non-invasive selection at the oocyte stage (extracytoplasmic and intracytoplasmic morphology) has proved to be of little prognostic value. Recently, it has been shown that follicular vascularization appears to be predictive of oocyte developmental fate, making it a good first-step approach for selection. Observation of pronuclei patterns at the zygote stage appears to offer an additional prognostic tool, correlating well with IVF outcome. Morphological evaluation of the embryo at days 2-3 remains the most used and valid method of selection, even though it is not sufficient to select embryos with the higher implantation potential. Blastocyst culture is another possible strategy for selecting the best embryos with reduced risk of aneuploidies, though not all major chromosomal aberrations are excluded by prolonged in-vitro culture. In summary, selecting the best embryo for transfer is a decision that should be based on choices made during the different stages of assisted reproductive technologies.

Preliminary experience with low concentration of granulocyte-macrophage colony-stimulating factor: a potential regulator in preimplantation mouse embryo development and apoptosis

PURPOSE

To investigate the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the development of preimplantation mouse embryos.

METHODS

Mouse 2-cell embryos were collected and cultured in P-1 medium supplemented with GM-CSF at different concentrations. Using reverse transcription-polymerase chain reaction, expression Bcl-2 and Bax mRNA in blastocyst were evaluated in the GM-CSF group and control group. Apoptosis detection was performed using the in situ apoptosis detection kit in mouse blastocysts. The statistical significance of the data was analyzed using t-test and chi-square test.

RESULTS

The development of blastocyst increased to 89% in the addition of GM-CSF (0.125 ng/mL), compared to controlled group (80%). The number of cells staining for apoptosis was lower in GM-CSF group than that in the control group. Bcl-2 expression was found to be upregulated in blastocysts in the GM-CSF supplemented group compared to the control group.

CONCLUSION

These results suggest that GM-CSF might be an important regulator in embryo development.

The aromatase inhibitor anastrozole is associated with favorable embryo development and implantation markers in mice ovarian stimulation cycles

OBJECTIVE

To investigate the embryonic and endometrial effects of anastrozole in preimplantation and implantation phases in FSH-induced cycles in mice.

DESIGN

Blind randomized study.

SETTING

University research laboratory.

ANIMAL(S)

Twenty-seven mature female mice.

INTERVENTION(S)

Single-dose anastrozole (25 mg/kg [0.75 mg]), recombinant FSH (5 IU/mL), and hCG (5 IU/mL) (n = 9); recombinant FSH (5 IU/mL) and hCG (5 IU/mL) (n = 9); or sterile saline (1 mL) (n = 9). The morning of finding the vaginal plug was designated as day 1 of embryonic development (E1). Three mice from each group were sacrificed on E1 and embryos aspirated from uterine tubes. The rest of the mice were sacrificed on E2.5-3 and uteruses removed.

MAIN OUTCOME MEASURE(S)

Embryo quality, endometrial histologic evaluation, and immunohistochemical analysis of tumor necrosis factor-alpha, leukemia inhibitory factor, laminin, and collagen IV staining.

RESULT(S)

Anastrozole use in FSH-induced cycles not only caused an increase in preimplantation receptivity and implantation but also supported release of implantation markers. The enhanced embryo development seen in this study would explain the higher implantation because embryo development is synchronized with endometrial development.

CONCLUSION(S)

In mice, the use of anastrozole in FSH-induced cycles has a positive effect on embryo quality and implantation. This effect might be species dependent, and human studies are needed.

Cytoplasmic fragmentation in activated eggs occurs in the cytokinetic phase of the cell cycle, in lieu of normal cytokinesis, and in response to cytoskeletal disorder

The timing of cytoplasmic fragmentation in relation to the cell cycle was studied in mature oocytes and early cleavage stages using mouse oocytes and embryos as experimental models. The central approach was to remove the nuclear apparatus, in whole or in part, from non-activated and activated oocytes and early embryos, and follow their response during subsequent culture in vitro. Oocytes arrested in metaphase of the second meiotic division did not fragment following complete removal of the meiotic apparatus, provided they were not subsequently activated. Exposure of spindle-chromosome-complex-depleted oocytes to activation conditions immediately after enucleation led to fragmentation, although not until control embryos entered first mitosis. Delaying activation until 24 h post-enucleation led to earlier fragmentation. Enucleation of normally fertilized or artificially activated oocytes after emission of the second polar body also led to fragmentation coinciding with the first mitosis in nucleated control embryos. However, if artificially activated oocytes were prevented from completing second meiosis, by exposure to cytochalasin, and then enucleated, this universal wave of fragmentation was preceded in some cytoplasts by limited fragmentation after just a few hours in culture, and coinciding with completion of meiosis II in nucleated oocytes. Fragmentation also occurred in the second mitotic cell cycle, but it was limited to blastomeres of fertilized oocytes that were enucleated in late interphase. These results indicate that fragmentation in oocytes and early embryos, though seemingly uncoordinated, is a precisely timed event that occurs only in mitotically active cells, during the cytokinetic phase of the cell cycle, in lieu of normal cytokinesis, and in response to altered cytoskeletal organization.

Expression of 11 members of the BCL-2 family of apoptosis regulatory molecules during human preimplantation embryo development and fragmentation

Apoptosis during preimplantation development has received much interest because of its potential role in eliminating defective cells. Although development in humans is characterised by a high degree of genetic abnormality, little is known of the regulation of apoptosis in embryos. By PolyA PCR we analysed expression of 11 BCL-2 genes in individual human embryos representative of normal development and in severely fragmented embryos. We demonstrate constitutive expression of BAX in virtually all embryos at all stages of development, and variable expression of BCL2, BCL-XL, BCL-W, MCL-1 BAK, BAD, BOKL, BID, BIK, and BCL-XS. The frequency of expression of pro- and anti-apoptotic BCL-2 members was similar throughout development, except at the two-cell stage where pro-apoptotic genes predominated. Protein expression was confirmed for BCL-2, MCL-1, BCL-X, BAX, BAD, and activated caspase 3. BCL-2 protein was associated with mitochondria but expressed inconsistently in the blastocyst inner cell mass. Consistent differences between morphologically intact and fragmented embryos included the expression of BAK in fragmented but not intact four-cell embryos. Our study addresses the importance of examining single human embryos representative of the viable population for a large number of genes, in order to establish meaningful expression profiles and provide information on overlapping function in a large gene family.

Expression of Smac/DIABLO in mouse preimplantation embryos and its correlation to apoptosis and fragmentation

Regulation of early embryonal development during fertilization and implantation is crucial for mammalian reproduction. Several studies have described cell death during preimplantation embryogenesis in a range of mammalian species, both in vivo and in vitro. Therefore, apoptosis may be involved in early embryonic arrest and the characteristic cytoplasmic fragments are the equivalents of apoptotic bodies, the end-product of apoptosis. Although apoptosis is expected to associate with fragmentation in early preimplantation embryos, the mechanism through which this fragmentation occurs has not been elucidated. Recently, second mitochondria-derived activator of caspase/Direct IAP Binding Protein with Low pI (Smac/DIABLO) was identified as a mitochondrial protein that is released into the cytosol during apoptosis. Once released, the Smac/DIABLO blocks the anti-apoptotic activity of inhibitor of apoptosis proteins (IAPs). We hypothesized that the Smac/DIABLO may be involved in the fragmentation of mouse preimplantation embryos. Therefore, we investigated the expression of Smac/DIABLO mRNA and protein and its localization in mouse oocytes and preimplantation embryos. Smac/DIABLO mRNA was detected by RT-PCR in the oocytes and the preimplantation embryos. Immunohistochemistry studies showed that the Smac/DIABLO protein localized in mitochondria and was released into the cytosol in both fragmented embryos and embryos in which apoptosis was induced by staurosporine. These observations indicate that the Smac/DIABLO is involved in the fragmentation and apoptosis of preimplantation embryos.

Search for the Bovine Homolog of the Murine Ped Gene and Characterization of Its Messenger RNA Expression During Bovine Preimplantation Development1

In mice, a gene (Ped: preimplantation embryo development) that regulates preimplantation embryonic growth, including cleavage rate and embryo survivability, has been described. The objective of the current study was to identify the bovine homolog of the Ped gene and to characterize the mRNA expression pattern of this gene during bovine preimplantation embryo development. The NCBI GenBank/EBI expressed sequence tags (EST) databases were searched for bovine ESTs that were homologous to the murine Ped gene, and the resulting ESTs were aligned and assembled into a contiguous sequence. The homology of the sequence to the murine Ped gene was confirmed. Primers were designed for the sequence, and the mRNA expression pattern was characterized during bovine preimplantation embryo development in vivo and in vitro. In vitro-produced bovine zygotes were cultured either in vitro, in synthetic oviduct fluid, or in vivo in the ewe oviduct for 1-7 days and processed for quantitative real-time polymerase chain reaction (PCR). Transcript abundance increased at each stage of development. However, the expression levels were consistently higher in in vivo-cultured embryos at all stages, with in vivo-cultured embryos showing a 9-fold increase in relative transcript abundance during culture from the zygote to the blastocyst stage in contrast to just under a 4-fold increase during the same culture period in vitro. The mRNA expression pattern of the gene was investigated in early- and late-cleaving two-cell embryos collected at 25, 28, 32, and >or=36 h postinsemination (pi). Transcript relative abundance was highest in those embryos that had cleaved by 28 hpi and decreased almost 3-fold thereafter. In conclusion, we have identified a potential bovine homolog of the murine Ped gene. We have characterized the mRNA expression pattern of this gene during preimplantation embryo development in cattle and shown that a greater relative abundance of the gene transcript is associated with embryos of higher quality (in vivo cultured) and greater developmental potential (early cleaving).

Consequences of in vivo development and subsequent culture on apoptosis, cell number, and blastocyst formation in bovine embryos

Bovine embryos produced in vitro differ considerably in quality from embryos developed in vivo. The in vitro production system profoundly affects the competence to form blastocysts, the number of cells of the total embryo and of the inner cell mass (ICM), and the incidence of apoptosis. To our knowledge, the effects of different postfertilization regimens before and after completion of the fourth embryonic cell cycle on these aspects have not yet been investigated. In the present study, we assessed the blastulation rate by stereomicroscopy and the cell number of the total embryo, of the ICM, and of the cells with apoptotic changes by confocal laser-scanning microscopy after staining with propidium iodide and TUNEL. Two groups of embryos were developed in heifers, after superovulation, until 45 or 100 h postovulation (po) and, after collection on slaughter, were further cultured in vitro until Day 7 po. A third and fourth group comprised embryos that were produced entirely in vitro or in vivo. The results indicate that passage in vivo of the fourth cell cycle does not prevent acceleration of the formation of the blastocoele in vitro but may be the critical factor contributing to a higher cell number in the total blastocyst and its ICM. The lower quality of in vitro-produced embryos can be attributed to the ICM having less viable cells because of a lower number of cells and a higher incidence of apoptosis that appears to be determined before completion of the fourth cell cycle.

Chronology of apoptosis in bovine embryos produced in vivo and in vitro

The postimplantation developmental potential of embryos can be affected by various forms of cell death, such as apoptosis, at preimplantation stages. However, correct assessment of apoptosis is needed for adequate inference of the developmental significance of this process. This study is the first to investigate the independent chronological occurrence of apoptotic changes in nuclear morphology and DNA degradation (detected by the TUNEL reaction) and incidences of nuclei displaying these features at various preimplantation stages of bovine embryos produced both in vivo and in vitro. Different elements of apoptosis were observed at various developmental stages and appeared to be differentially affected by in vitro production. Nuclear condensation was observed from the 6-cell stage in vitro and the 8-cell stage in vivo, whereas the TUNEL reaction was first observed at the 6-cell stage in vitro and the 21-cell stage in vivo. Morphological signs of other forms of cell death were also observed in normally developing embryos produced both in vivo and in vitro. The onset of apoptosis seems to be developmentally regulated in a stage-specific manner, but discrete features of the apoptotic process may be differentially regulated and independently modulated by the mode of embryo production. Significant differences in indices of various apoptotic features were not evident between in vivo- and in vitro-produced embryos at the morula stage, but such differences could be observed at the blastocyst stage, where in vitro production was associated with a higher degree of apoptosis in the inner cell mass.

Amplification of representative cDNA pools from single human oocytes and pronucleate embryos

In the human embryo, gene expression studies have been hindered by the scarcity of material and the fact that in vitro fertilisation (IVF) embryos available for research are usually of poor quality and are, therefore, not representative of normal development. This has led most authors to study individual human embryos, using conventional RT-PCR strategies, which permit analysis of only a few genes. Variability in the expression of genes between individual embryos is characteristic of these studies. In this study, a global RT-PCR strategy has been used, allowing the analysis of an almost infinite number of genes from a single embryo. We have used oocytes, which failed to fertilise and representative pronucleate embryos donated from cycles in which the patient conceived, to investigate possible variability in transcript abundance between individual embryos. We have screened oocytes and embryos for a panel of genes including beta-actin (expressed in 24/28 oocytes, 6/6 pronuclear embryos), the integrins beta1 (17/28 oocytes, 6/6 pronuclear embryos) and beta5 (8/28 oocytes, 5/6 pronuclear embryos), and the apoptotic regulators BCL-2 (20/28 oocytes, 2/6 pronuclear embryos) and BAX (21/28 oocytes, 5/6 pronuclear embryos). The expression of the pro-apoptotic regulator BAX increased in human oocytes following prolonged periods of culture. Overall, patterns of gene transcript presence showed variation between embryos and this was independent of either zona removal or lysis conditions. Pronucleate embryos showed less variation, however, even sibling embryos from the patient did not express an identical subset of genes.

Apoptosis in normal rat embryo tissues during early organogenesis: the possible involvement of Bax and Bcl-2

Apoptosis commonly occurs in a variety of developmental processes in mammals. In this study, we investigated the relationship between apoptosis and the expression of both Bax and Bcl-2 during the early organogenesis period (9.5-11.5 days of gestation) of rat embryos. Apoptotic cells detected by the terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) method were extremely abundant in the foregut diverticulum at 9.5 days of gestation, while they largely disappeared at 10.5 and 11.5 days of gestation, although they were detected in newly formed mid- and hindgut diverticulum at these times. Real-time RT-PCR analysis of whole embryos revealed that the expression of bax mRNA was constant at days 9.5 to 11.5, while the expression of bcl-2 mRNA gradually increased. Immunohistochemical studies of Bax and Bcl-2 expression revealed that these apoptotic cells were exactly positive to Bax in mirror sections, while their expression of Bcl-2 was generally too low to be detected. A disappearance of apoptotic cells was associated with strong Bcl-2 expression in the foregut diverticulum at 10.5 and 11.5 days of gestation. It was similarly observed that apoptotic cells detected in the cardiogenic area at 9.5 days of gestation disappeared with the formation of the primitive heart tube--accompanied by a strong expression of both Bcl-2 and Bax--in the developmental process of the primitive heart. Apoptotic cells were also observed in the primitive brain vesicle, optic vesicle, otic vesicle, and thyroid primordium at 10.5 and 11.5 days of gestation during the developmental process, with a strong expression of Bax. These results indicate that the Bax and Bcl-2 may be important in regulating the induction of embryonic cell apoptosis during early organogenesis.

Intracellular calcium oscillations signal apoptosis rather than activation in in vitro aged mouse eggs

We have previously demonstrated that initiation of intracellular calcium ([Ca2+]i) oscillations in mouse eggs signals activation or apoptotic death depending on the age of the eggs in which the oscillations are induced. To extend these studies, mouse eggs were aged in vitro to 24, 32, and 40 h post-hCG and injected with sperm cytosolic factor (SF), adenophostin A, or sperm (intracytoplasmic sperm injection), and the times at which signs of apoptosis first appeared were examined. These treatments, which induced [Ca2+]i oscillations, caused fragmentation and other signs of programmed cell death in eggs as early as 32 h post-hCG. The susceptibility of aged eggs to apoptosis appeared to be due to cytoplasmic deficiencies, because fusion of recently ovulated eggs with aged, SF-injected eggs prevented fragmentation. Evaluation of mRNA and protein levels of the apoptotic regulatory proteins Bcl-2 and Bax showed a prominent decrease in the amounts of Bcl-2 mRNA and protein in aged eggs, whereas Bax mRNA levels did not appear to be changed. Lastly, the Ca2+ responses induced by the aforementioned Ca2+ agonists ceased in advance in aged eggs. Together, these results suggest that one or several critical cytosolic molecules involved in the regulation of Ca2+ homeostasis, and in maintaining the equilibrium between anti- and proapoptotic proteins, is either lost or inactivated during postovulatory egg aging, rendering the fertilizing Ca2+ signal into an apoptosis-inducing signal.

Genetic regulation of preimplantation embryo survival

Mammalian embryonic death is the most common outcome of fertilization. This review focuses on the recent advances concerning genetic regulation of preimplantation embryo survival. The predominant role of the Ped(preimplantation embryo development) gene, which regulates fast or slow cleavage of preimplantation mouse embryos, and its implication on embryo survival are discussed. Recent morphological and biochemical observations suggested that programmed cell death was an essential mechanism in preimplantation embryo fragmentation and survival, thus leading to original investigations on apoptosis and apoptosis-related genes. Other genes, transcripts, or proteins seem to be involved in embryo development and control of survival. In particular, the role of heat shock proteins (HSP), telomerase activity (human telomerase catalytic subunit hTCS), and the developmental significance of regulatory protein polarization (leptin, STAT 3) in preimplantation embryos are discussed.

Apoptosis in mammalian preimplantation embryos: regulation by survival factors

The formation of a developmentally competent mammalian blastocyst requires the transition from a unicellular state, the fertilized zygote, to a differentiated multicellular structure. In common with other developing organisms, generation of the required cell population involves the processes of cell division, differentiation and cell death, all of which can be regulated by peptide growth factors. Cell death in the preimplantation embryo occurs by apoptosis and, by analogy with other systems, may serve to eliminate unwanted cells during the critical developmental transitions that take place during this period. Cells may be eliminated because they are abnormal or possess defects, including damaged DNA or chromosomal abnormalities. At the early cleavage stages, apoptosis may be associated with activation of the embryonic genome and may contribute to the blastomere fragmentation commonly observed in human IVF embryos. The major wave of apoptosis occurs in a number of species in the inner cell mass of the blastocyst, as identified using nuclear labelling including terminal transferase-mediated dUTP nick end labelling (TUNEL) and fluorescence and confocal microscopy. Apoptosis may protect the integrity and cellular composition of the inner cell mass, by eliminating damaged cells or possibly those with an inappropriate phenotype. Preimplantation embryos express genes involved in the regulation and execution of apoptosis and their cells can undergo this default pathway in the absence of exogenous survival signals. Evidence is now accumulating from several species that apoptosis in the embryo is regulated by soluble peptide growth factors acting as survival factors in an autocrine or paracrine manner. To date, these include transforming growth factor alpha and members of the insulin-like growth factor family. Apoptosis may also be affected by environmental factors, including culture conditions and the composition of media. The regulation of apoptosis in the preimplantation embryo is likely to be of critical importance for both embryo viability and for later development, since the cells of the inner cell mass give rise to the fetus and carry the germ line.

Genotyping: the HLA system and embryo development

The human major histocompatibility complex (MHC), in addition to its role in the regulation of cell-cell interactions in the immune response, also influences reproductive success. Human leukocyte antigen-G (HLA-G) is an MHC class I gene of particular interest in reproductive biology because of its specific expression on fetal cytotrophoblast cells, and its reported involvement both in protection of the developing fetus from destruction by the maternal immune response and in the prevention of maternal pre-eclampsia. HLA-G has 15 known alleles at the DNA level, and allelic frequency varies among ethnic groups. This study describes the results of an inaugural attempt to correlate an HLA-G genetic polymorphism with pregnancy outcome in a patient population undergoing IVF. The study group was composed of 102 Caucasian women. A maternal HLA-G genetic polymorphism was investigated by polymerase chain reaction (PCR) analysis of DNA collected from granulosa cells surrounding oocytes harvested for the IVF procedure. While no statistically significant correlation was identified in this initial study, larger studies examining DNA from trios of mother, father and offspring are planned.

Embryo fragmentation in vitro and its impact on treatment and pregnancy outcome

OBJECTIVE

To determine the impact of embryo fragmentation on pregnancy, obstetric, and perinatal outcome.

DESIGN

Retrospective analysis of embryo transfers that were homogeneous in regard to the degree of fragmentation.

SETTING

Fertility center.

PATIENT(S)

A cohort of 460 fresh embryo transfers.

INTERVENTION(S)

A total of 164 pregnancies were analyzed for the incidence of antepartum complications during gestation, obstetric (multiple pregnancy, preterm delivery, cesarean section), and perinatal outcome (sex, birth weight, admission to neonatal intensive care unit, malformations).

MAIN OUTCOME MEASURE(S)

Implantation and clinical pregnancy rate, obstetric and perinatal outcome.

RESULT(S)

Embryo fragmentation and number of embryos per transfer showed a significant influence on clinical pregnancy and implantation rate. No such relation was found concerning complications, multiple pregnancy rate, incidence of cesarean section, gestation week, birth weight, and average time at the neonatology. On the other hand, pregnancies derived from bad-quality embryos had a significantly higher rate of malformations.

CONCLUSION(S)

The higher percentage of malformations found in bad-quality embryos may be due to a higher percentage of apoptotic features and chromosomal disorders. For ethical reasons, the transfer of embryos with >50% fragmentation should be considered only after consultation with the patient.

Mitochondrial aggregation patterns and activity in human oocytes and preimplantation embryos

Mitochondria play a vital role in the metabolism of energy-containing compounds in the oocyte cytoplasm to provide adenosine trisphosphate for fertilization and preimplantation embryo development. In this study, ratiometric confocal microscopy with the mitochondrion-specific membrane potential-sensitive fluorescence dye JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide) was used to measure the activity of mitochondria in human oocytes and developing preimplantation embryos. Mitochondria in oocytes and embryos were characterized by distinct localized aggregation patterns. These patterns however did not determine localized regions of heterogeneity in mitochondrial activity. Mitochondrial activity was analysed during oocyte maturation and after fertilization. The activity of mitochondria in fresh metaphase II oocytes was negatively correlated with maternal age. This trend continued when the activity of developing embryos was analysed. Mitochondrial activity was strongly correlated with the rate of embryo development on day 3 after fertilization, but not on day 2. Partial regression analysis showed that the rate of cleavage of preimplantation embryos was more highly correlated with embryo mitochondrial activity than maternal age. These data suggest that the efficiency of mitochondrial respiration in oocytes and preimplantation embryos is closely correlated with the programmed rate of embryo development, and suggest that maternal age further influences this factor. The loss of mitochondrial activity in oocytes obtained from ageing couples may therefore contribute to lower embryo development and pregnancy rates observed during cycles of IVF.

Genetic regulation of embryo death and senescence

The survival of the preimplantation mammalian embryo depends not only on providing the proper conditions for normal development but also on acquiring the mechanisms by which embryos cope with adversity. The ability of the early conceptus to resist stress as development proceeds may be regulated by diverse factors such as the attainment of a cell death program and protective mechanisms involving stress-induced genes and/or cell cycle modulators. This paper reviews the recent research on the genetic regulation of early embryo cell death and senescence focussing on the bovine species where possible. The different modes of cell death will be explained, clarifying the confusing cell death terminology, by advocating the recommendations set forth by the Cell Death Nomenclature Committee to extend to the embryology research field. Specific pro-death and anti-death genes will be discussed with reference to their expression patterns during early mammalian embryogenesis.

Cleavage anomalies in early human embryos and survival after prolonged culture in-vitro

This study examines the relationship between common morphological anomalies of cleaving embryos and their ability to form apparently normal blastocysts in vitro. The impact of cleavage rate, fragmentation, and multinucleation on compaction, cavitation, along with inner cell mass and trophectoderm formation has been assessed. The study population consisted of 102 patients who elected or were selected to have a day 5 embryo transfer. Clinical pregnancy and implantation rates were 66.7 and 49% respectively. Slow and fast cleavage had a significant negative association with normal blastocyst formation. Only 13.8% (67/484) of embryos with <7 cells and 27.5% (25/91) of those with >9 cells on day 3 formed blastocysts with apparently normal morphology, compared to 41.9% (252/602) with 7-9 cells on day 3 (P < 0.001). Fragmentation had a negative impact on normal blastocyst formation. Embryos with >15% fragmentation formed normal blastocysts at a significantly lower rate (46/279; 16.5%) than embryos with 0-15% fragmentation (311/935; 33.3%) (P < 0. 001). Furthermore, the pattern of fragmentation was associated with blastocyst formation. Type IV fragmentation led to a significant reduction in blastocyst formation (25/170 or 14.7%), compared to types I, II and III which performed much better (38.6, 32.9 and 32.4% respectively). Only 15.9% (22/138) of embryos with one or more multinucleate cells on day 2 and/or 3 formed normal blastocysts compared with 31.9% (335/1051) (P < 0.001) of those without multinucleation. Collectively, the data suggest that cleavage anomalies, some of which do not preclude development after short-term culture, may reduce the developmental competence of embryos after prolonged culture.

Expression of apoptosis-related genes in human oocytes and embryos

PURPOSE

The objective was to study whether apoptosis occurs in human embryogenesis.

METHODS

Human viable, arrested, and nonviable embryos and immature, and nonfertilized oocytes donated by our patients were used to detect apoptosis by Tunel labeling, annexin staining, and single-cell reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

DNA fragmentation and phosphotidylserine translocation, the two markers for apoptosis, were detected frequently in fragmented human embryos derived from in vitro fertilization-embryo transfer (IVF-ET). Using RT-PCR, apoptotic genes also were detected in these embryos. The frequencies of gene expression in viable embryos, arrested embryos, nonviable embryos, immature oocytes, and non-fertilized oocytes were: 7/8, 5/5, 5/6, 0/6, 0/3, for Bax; 8/8, 5/5, 7/7, 0/4, 0/5 for Fas; 2/8, 0/2, 0/3, 0/5, 0/3 for BCL-2; 0/8, 1/3, 0/2, 0/3, 0/2 for Fas-ligand; and 8/8, 17/17, 21/21, 24/24, 15/15 for actin, respectively.

CONCLUSIONS

Our preliminary data did not show a significant difference in the expression frequency of all studied genes between viable embryos and nonviable or arrested embryos. However, the expression of Bax and Fas was noticeably higher in nonviable embryos than in viable embryos as judged by the intensities of amplicons visualized after ethidium bromide staining. In addition, BCL-2 was only detected in viable embryos. Whether embryos quality is related to the regulation of BCL-2, Bax, and Fas expressions requires further study.