High reliability of morphokinetic annotations among embryologists

STUDY QUESTION

Are morphokinetic measurements of time lapse-videos of human embryos comparable among operators?

SUMMARY ANSWER

There is little variation among morphokinetic measurements taken by different operators when analyzing the same time lapse-videos of human embryos.

WHAT IS KNOWN ALREADY

Morphokinetic analysis of preimplantation embryo development is a complementary method of embryo assessment increasingly used in IVF laboratories. Time-lapse videos of embryo development are normally viewed by trained embryologists and annotated with the times when specific developmental events occur. Such annotations form the basis of embryo selection algorithms, used to rank the embryos for transfer. It is unknown whether the reliability of morphokinetic annotations is related to the morphological characteristics of the analyzed embryo or to the ability of the embryologists performing the annotation. One study so far reported the reliability of morphokinetic annotations among three embryologists using the time-lapse system (TLS), but larger studies with different setups are needed to address this issue further.

STUDY DESIGN SIZE DURATION

A prospective study was carried out between October 2015 and June 2016. Six embryologists with various degrees of experience in static, morphology-based evaluation, individually annotated the same 93 videos of preimplantation development, corresponding to 18 IVF/ICSI cycles, recorded with a TLS.

PARTICIPANTS/MATERIALS SETTING METHODS

Times of second polar body extrusion, appearance and disappearance of pronuclei, and embryo cleavages (times from 2-cell to 5-cell stage: t2, t3, t4, t5) were annotated. Each embryologist was blinded to the annotations of the others. Intra- and inter-observer agreement was evaluated by computing intra-class correlation coefficients (ICCs).

MAIN RESULTS AND THE ROLE OF CHANCE

In the inter-observer analysis, most ICCs obtained were higher than 0.80, indicating a high level of agreement: t2: 0.93; t3: 0.80; t4: 0.89; t5: 0.89; disappearance of two pronuclei: 0.98. However, the ICCs obtained for second polar body extrusion and the appearance of two pronuclei annotations was lower: 0.51 and 0.63, respectively, indicating an average level of agreement. The ICCs obtained from the intra-observer analysis were also higher than 0.80 (t2: 0.96; t3: 0.89; t4: 0.88; t5: 0.86; disappearance of two pronuclei: 0.96). The ICCs obtained from second polar body extrusion and the appearance of two pronuclei annotations were 0.77 and 0.66, respectively. These results indicate that developmental timings, annotated in time-lapse videos, are highly reliable both within and among observers.

LIMITATIONS REASONS FOR CAUTION

The events at the developmental stages from 6-cells to blastocyst were not evaluated; since some morphokinetic algorithms use times past the 6-cell stage in their calculations, further studies should be carried out to understand the variations among observers in these cases.

WIDER IMPLICATIONS OF THE FINDINGS

Time-lapse measurement should be as objective as possible, especially for the first embryo cleavages, because they are often measured to define algorithms to assess the embryonic implantation potential. Our results show that measurements using this particular TLS are consistent and reliable both within and among operators.

STUDY FUNDING/COMPETING INTERESTS

None.

TRIAL REGISTRATION NUMBER

Not applicable.

27 PSAMMAPLIN A INCREASES DEVELOPMENT AND QUALITY OF MOUSE SOMATIC CELL NUCLEAR TRANSFER EMBRYOS

Among the many biological and technical factors affecting the success rate of mouse somatic cell nuclear transfer (SCNT), faulty reprogramming of the differentiated donor nucleus to a totipotent embryonic state by the recipient oocyte seems key. Accordingly, treatment of SCNT embryos with epigenetic modifiers such as valproic acid (VPA), a histone deacetylase inhibitor (HDACi), enhances cloning efficiency. Psammaplin A (PsA) is a natural and potent DNA methyltransferase inhibitor and HDACi that has never been used in nuclear reprogramming studies. The purpose of our study was to determine the effect of PsA on the development and quality of mouse SCNT embryos, and to compare it to that of VPA. To this aim, mechanically enucleated oocytes from B6CBAF1 female mice were reconstructed with cumulus cell nuclei, activated, and cultured in the presence of the epigenetic modifier. Embryos that reached the blastocyst stage were differentially stained for counting inner cell mass (ICM) and trophectoderm cells. Alternatively, 2-cell embryos were transferred to CD1 recipient females to assess full-term development. In a first set of experiments, embryos were exposed to different concentrations of PsA (5, 10, and 20 µM) or VPA (2 and 4 mM) for 1 to 2 h after reconstruction and 6 h of activation (total 8–9 h). We found that 10 µM PsA and 2 mM VPA significantly increased blastocyst rates (37.3 and 31 v. 23.3% for the control group), although no differences were found in blastocyst quality (10.4–13.6 ICM cells). In a second set of experiments, we studied the effect of treatment duration by incubating the embryos in 10 µM PsA or 2 mM VPA for 8 to 9, 16, or 24 h after reconstruction. With PsA, all treatments showed equivalent blastocyst rates (35.2–43.3%), which were significantly higher than in the control group (20%), but only treatments for 16 and 24 h yielded blastocysts with significantly higher numbers of ICM cells (16.3 and 18.5 v. 10 for the control group). With VPA, treatments for 8 to 9 h and 16 h were equivalent in terms of blastocyst rates (34.0 and 32.5%) and significantly higher than the control group, but only VPA 16 h yielded blastocysts with a significantly higher number of ICM cells (15.6). In a third set of experiments, we studied the full-term development of embryos treated with 10 µM PsA or 2 mM VPA for 16 h and we found that both treatments, but especially the PsA treatment, resulted in higher birth rates than those obtained in the control group, although the differences were not statistically significant (1.79 and 0.86 v. 0.46%). Finally, when the actin polymerization inhibitor latrunculin A was used instead of cytochalasin B in the SCNT protocol during oocyte micromanipulation and activation, we obtained a 3-fold increase in the birth rate of embryos treated with PsA (5.29%). In conclusion, PsA enhances development and quality of mouse SCNT embryos, to a greater extent than VPA, and when combined with the use of latrunculin A instead of cytochalasin B, it results in an 11.5-fold increase in full-term development. Support from MEC AGL-2011-23784, 2009-SGR-282, and PIF-UAB Fellowships is acknowledged.

25 COMPARISON BETWEEN CHEMICALLY ASSISTED, CHEMICALLY INDUCED AND MECHANICAL ENUCLEATION OF MOUSE OOCYTES

Chemically-assisted (AE) and chemically induced (IE) enucleation using demecolcine (DEM) or nocodazole (NOC) have proven to be technically simple procedures to prepare developmentally competent cytoplasts for nuclear transfer (NT) in different species. In this study, we analyzed AE and IE in mouse oocytes in terms of enucleation efficiency, amount of cytoplasmic volume removed and distribution of spindle-associated γ-tubulin after enucleation, and spindle morphology after cytoplast reconstruction by NT. Results were compared to the standard mechanical enucleation (ME) method. Outbred CD-1 and hybrid B6CBAF1 oocytes were collected at 13 to 16 h post-hCG. In AE experiments, oocytes were treated with either 0.4 μg mL–1 DEM or 0.3 μg mL–1 NOC in KSOM for 30 min. Protrusions induced in CD-1 (92.2%, n = 695) and B6CBAF1 (83.3%, n = 370) oocytes were aspirated by piezo-actuated micromanipulation, in H-KSOM with 2.5 μg mL–1 cytochalasin B and 0.05 m sucrose. In IE experiments, oocytes were preactivated with 7% ethanol for 5 min and treated with DEM or NOC in calcium-free KSOM containing 10 mm strontium. At 90 min postactivation (p.a.), completely- and partially-extruded second polar bodies (PBs) were mechanically aspirated. Enucleation efficiencies were higher than 90% both for AE (90.8%, n = 509 CD-1; 90.4%, n = 260 B6CBAF1) and IE methods (90.3%, n = 167 CD-1; 92.9%, n = 197 B6CBAF1), though they were significantly lower than those obtained for ME in nontreated CD-1 (98.4%; n = 126) or B6CBAF1 (100%, n = 498) oocytes. The amount of cytoplasmic volume removed in CD-1 oocytes was smaller in AE than in ME (2.1%, n = 35 and 3.9%, n = 30, respectively). In B6CBAF1 oocytes, used to compare IE (5.4%, n = 60) and ME (4.9%, n = 41), no differences were found. Volumes were calculated using the CellA software on images of cytoplasts and karyoplasts taken after enucleation. Even though both AE and IE methods avoided the removal of the oocyte spindle microtubules, spindle-associated γ-tubulin was eliminated from the cytoplasts generated by all 3 enucleation procedures, as confirmed by immunofluorescence analysis of the cytoplasts and the complementary karyoplasts produced. Finally, spindle morphology was examined in enucleated oocytes reconstructed by NT with a cumulus cell nucleus. Cytoplasts prepared by NOC-AE or NOC-IE displayed morphologically normal bipolar spindles by 2 h post-NT or 18 to 20 h post-activation (hpa), respectively, similar to cytoplasts prepared by ME. However, when DEM was used, microtubule repolymerization was slower and bipolar spindles could not be observed until 4 h post-NT (AE) or 22 to 24 hpa (IE). In conclusion, although enucleation rates are slightly higher for ME, AE and IE protocols allow oocyte enucleation without removal of the meiotic spindle, and a very small cytoplasm volume is eliminated during AE. Treatments with NOC and DEM are reversible, and cytoplasts produced by AE and IE can form morphologically normal spindles after NT, similar to those of cytoplasts produced by ME. MEC BIO 2006-11792; 2005-SGR00437; Portuguese FCT.

33 ENUCLEATION OF PRE-ACTIVATED MOUSE OOCYTES INDUCED BY DEMECOLCINE, NOCODAZOLE, AND VINBLASTINE

Demecolcine-induced enucleation has been previously used to prepare developmentally competent enucleated mouse and bovine cytoplasts for nuclear transfer (Gasparrini et al. 2003 Biol. Reprod. 68, 1259–1266; Fischer-Russell et al. 2005 Mol. Reprod. Dev. 72, 161–170). The approach is technically simple, but the proportion of pre-activated oocytes that extrude all of the chromatin within the second polar body (PB) after exposure to demecolcine is relatively low, especially in the mouse (20%). This study was designed to explore the potential of other antimitotic drugs (nocodazole and vinblastine), besides demecolcine, to induce enucleation of mouse oocytes and to characterize the morphological progression of the treated oocytes after drug removal. Metaphase II (MII) oocytes were collected from cytochalasin D-1 (CD-1) females (6–12 weeks old) at 16 h post-hCG, activated in 7% ethanol (for a fast release from MII arrest) for 5 min and immediately treated for 15, 30, or 60 min with demecolcine (DEM, 0.4 �g mL-1), nocodazole (NOC, 0.3 �g mL-1), or vinblastine (VIN, 0.1 �g mL-1), prepared in calcium-free KSOM containing 10 mM strontium. Then, the oocytes were cultured in drug-free medium for up to 2 h, 6 h, or 20 h post-activation (p.a.) and fixed in a microtubule stabilization buffer-extraction fixative. A triple-labelling protocol for microtubules, microfilaments, and chromatin was used to analyze oocytes (approximately 60 per treatment) by fluorescence microscopy. Results were statistically analyzed by chi-square. At 2 h p.a., the highest rates of enucleation were achieved when pre-activated oocytes were treated with VIN (63.8%) or NOC (41.9%) for 15 min or with DEM (66.1%) for 30 min. Although antimitotic treatments did not affect activation rates (91.8–100%), a significant proportion of DEM- (19.6%) and of VIN-treated (15.5%) oocytes failed to complete second PB extrusion when compared to control (0%) or NOC-treated (4.8%) oocytes. From the total of the enucleated oocytes, 11.5%, 24.3%, and 29.7% had an incomplete second PB extrusion in NOC, VIN, and DEM groups, respectively, and therefore were classified as partially enucleated. Further culture of oocytes after drug withdrawal resulted in 100% of activated oocytes having a completely extruded second PB in all groups by 6 h p.a. and resulted in a significant and similar decrease in enucleation rates for all treatments by 6 h (20.3–34.9%) and 20 h p.a. (10.2–16.1%). This decrease might be caused by the reintegration of the chromosomes into the oocyte after incomplete second PB extrusion, or by re-fusion of second PBs to enucleated oocytes. Thus, our results show that both VIN and NOC, in addition to DEM, can be successfully applied to produce enucleated mouse cytoplasts, omitting the potentially harmful step (staining and ultraviolet illumination) of the traditional enucleation method. However, removal of the second PB at 2 h p.a. is recommended in order to achieve an irreversible oocyte enucleation. It remains to be demonstrated if the cytoplasts prepared with VIN or NOC are as competent as those prepared by DEM to support embryo development to term after being reconstructed by nuclear transfer.

Preimplantation genetic diagnosis in patients with male meiotic abnormalities

Indications and candidates for preimplantation genetic diagnosis (PGD) have increased in recent years. This study evaluates whether IVF-intracytoplasmic sperm injection (ICSI) results could be improved by selecting embryos through PGD-AS (aneuploidy screening) in couples in whom the male partner presents meiotic abnormalities. Two hundred and fifty-six embryos were biopsied and 183 were suitable for analysis (73.2%). Ninety-two embryos showed normal chromosomal analysis (50.3% of the analysed embryos and 57.5% of the diagnosed embryos). Pregnancy, abortion and implantation rates were compared with 66 IVF-ICSI cycles performed in 44 patients with meiotic abnormalities without PGD (control group). No statistically significant differences in the pregnancy rate (52 versus 43.9%), implantation rate (32.1 versus 23.5%) and miscarriage rate (15.4 versus 10.3%) were observed between the groups. Although the embryos obtained from men with meiotic abnormalities showed a high frequency of chromosome abnormalities, no improvements in pregnancy and implantation rates were obtained after PGD-AS in the series analysed.

Preimplantation genetic screening and human implantation

In recent years, preimplantation genetic screening (PGS) has been used and recommended to increase the implantation rate in older women or in couples with previous assisted reproduction (ART) failures, to try to increase pregnancy rates in couples with recurrent abortions, to prevent the transmission of chromosome anomalies to the offspring of carriers of balanced chromosomal rearrangements, or even to try to decrease the incidence of trisomic births in older women. So far, PGS has contributed to increase the implantation rate in older women; however, the rate of clinical pregnancies has not increased, either in older women or in couples with previous ART failures. In couples with recurrent abortions, the pregnancy rate seems to increase, but only when the woman is young (< or =35). In carriers of balanced reorganizations, the prognosis is poor. Attempts to decrease the birth of trisomic children to older women are difficult to evaluate. This absence of relevant results is not related to the technique itself, which is quite safe, but to other still largely unknown factors.

Assessment of the proportion of transgene-bearing sperm by fluorescence in situ hybridization: a novel approach for the detection of germline mosaicism in transgenic male founders

Genetic mosaicism is frequent among transgenic animals produced by pronuclear microinjection. A successful method for the screening of founder animals for germline mosaicism prior to mating would greatly reduce the costs associated with the propagation of the transgenic lines, and improve the efficiency of transgenic livestock production. With this aim, we have devised a simple method to detect integrated transgenes in individual spermatozoa using fluorescence in situ hybridization (FISH). The experiments reported here were undertaken to investigate the efficiency of this FISH-based approach to accurately evaluate the proportion of transgene-bearing sperm and to be applied for the detection of potential germline mosaics. Sperm samples from mice homozygous and hemizygous for a beta-lactoglobulin transgene were analyzed in a first set of experiments. A high hybridization efficiency was achieved, and the proportions of transgene-positive sperm cells in both homozygous (94.8-98.2%) and hemizygous (49.8-51.9%) animals were close to the expected frequencies (100 and 50%, respectively). To evaluate the sensitivity of the assay more directly, simulated mosaic samples with 5, 10, 15, 20 and 40% of transgene-bearing spermatozoa were then prepared and analyzed by FISH. Significant differences in the frequency of transgene-positive sperm were observed between all mosaic samples, indicating that even small deviations (5%) from the expected 50% transgene transmission rate in a founder animal could be reliably detected with our assay. Therefore, the method proposed represents a novel approach for the identification of germline mosaic founder males in livestock transgenic projects and a much more economic and faster alternative to breeding.

Preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) includes a variety of techniques that have been developed to detect the transmission to the offspring of genetic diseases or of chromosome abnormalities by couples at risk before a pregnancy is established, to avoid these couples the risk of recurrent abortions and/or of repeated terminations of pregnancy. Candidate couples are carriers of gene mutations or of structural chromosome rearrangements, or with recurrent spontaneous abortions of unknown origin. Diagnostic procedures include different modalities of gene amplification using the polymerase chain reaction (PCR) or of fluorescent in situ hybridization (FISH). Embryo biopsies are carried out at the 6-8 cell stage. Healthy embryos are transferred on day 4 or at the blastocyst stage. By now, several hundred healthy children have been born using PGD, and only one diagnostic error has been reported.

Is there a place for preimplantation genetic diagnosis screening in recurrent miscarriage patients?

Chromosomal abnormalities are one of the factors known to interfere with normal embryo development; thus preimplantation genetic diagnosis (PGD) for chromosome anomalies may be a new tool for improving the pregnancy rate in selected groups of patients. Embryos from three groups of patients (control, aged and recurrent miscarriage patients) were screened by PGD using specific DNA probes for chromosomes 13, 16, 18, 21, 22, X and Y. The control and aged groups were included in the PGD study because the women carried sex-linked genetic disease. The frequencies of chromosome anomalies observed in older women (46.3%) and in recurrent miscarriage patients (53%) were significantly higher (P < 0.05) than the frequency in the control group (19.3%). After PGD screening and transfer of normal embryos, pregnancies were obtained in women who had undergone repeated abortions (approximate 25% pregnancy rate per transfer) but not in older women. On the basis of these data, it seems that PGD screening of embryos can help some women undergoing repeated abortions, as these techniques allow successful pregnancies to be obtained or, if no pregnancy can be obtained, the results may help the couple to decide whether to enter an embryo or gamete donation programme.

The decision to cancel a preimplantation genetic diagnosis cycle

It has been suggested that a minimum number (six) of cumulus-oocyte complexes (COCs) should be retrieved for fertilization to offer enough chances to ensure a pregnancy after a preimplantation genetic diagnosis (PGD) procedure. Therefore a decision to cancel a PGD cycle should be adequately weighted to offer the patients the highest chances to obtain a pregnancy. We describe a case where, after retrieving only three COCs suitable for fertilization, a triplet pregnancy was obtained. This case suggests that, although low numbers of COCs can reduce the effectiveness of the PGD procedure, other factors are involved in its final result. Thus, the opportunity of routinely cancelling such cycles should be reconsidered. In addition, this is, to our knowledge, the first case where sex selection was carried out to prevent the birth of carriers of the abnormal gene, and not of affected offspring.

Effect of 6 beta-methylprednisolone on mouse pregnancy rate

The aim of this study was to evaluate the effect of methyl-prednisolone on the pregnancy rate in mice. For this reason, zona pellucida-intact and zona pellucida-free embryos at the blastocyst stage were transferred to recipient mice at day 2.5 of pseudopregnancy. Embryo transfer was performed into non-immunodepressed and immunodepressed groups of recipient mice using 0.3 or 0.6 microgram/g of 6 beta-methylprednisolone. A higher implantation and developmental rate of zona-free embryos transferred to the immunodepressed group of recipients was observed after using the higher dose of methylprednisolone.

Distribution of alpha3, alpha5 and alpha(v) integrin subunits in mature and immature human oocytes

The distribution of three integrin subunits, alpha3, alpha5 and alpha(v), in immature and mature human oocytes has been examined using immunofluorescence and confocal microscopy. The results demonstrate that both alpha5 and alpha(v) are present at the germinal vesicle stage, while alpha3 was only detected in oocytes after germinal vesicle breakdown, in metaphase I and II stage oocytes. The cortical concentration of integrin subunits alpha3 and alpha5 is consistent with their localization in the oolemma. In contrast, the homogeneous distribution of alpha(v) throughout the oocyte suggests the existence of cytoplasmic reservoirs of this protein in the oocyte.

FISH preimplantation diagnosis of chromosome aneuploidy in recurrent pregnancy wastage

PURPOSE

Our purpose was to detect aneuploidy for chromosomes 13, 16, 18, 21, 22, X, and Y in preimplantation embryos from patients with a history of unexplained recurrent miscarriage.

METHODS

Three patients with a history of unexplained recurrent spontaneous abortion were included in this study. Embryos were biopsied at the eight-cell stage, individually fixed on slides, and processed for fluorescent in situ hybridization (FISH). A multiple FISH protocol for seven chromosomes pairs (13, 16, 18, 21, 22, X, and Y) has been developed.

RESULTS

A total of 39 embryos was studied with the multiple FISH protocol developed. Successful analysis of the biopsied embryos was achieved within the time limits usually allowed in a preimplantation diagnosis program. Analysis of the blastomeres showed that 17 embryos were chromosomally normal for the probes used, 16 embryos were aneuploid, and in 6 embryos no informative results were obtained.

CONCLUSIONS

In the patients studied, a large proportion of embryos (41%) exhibited chromosomal abnormalities for the probes used. Preimplantation diagnosis to screen for chromosome abnormalities could be a feasible approach to improve the possibility of successful pregnancy in these couples.

Recurrent in vitro fertilization failure evaluated by fluorescence in situ hybridization: a case report

OBJECTIVE

To present a case of IVF failure evaluated by fluorescence in situ hybridization (FISH).

DESIGN

Case report.

SETTING

Research university laboratory and clinical IVF laboratory.

PATIENT(S)

An infertile couple with recurrent IVF failure.

INTERVENTION(S)

Fluorescence in situ hybridization study of the complete cohort of "zygotes" obtained at the third IVF attempt.

MAIN OUTCOME MEASURE(S)

Fluorescence in situ hybridization studies of chromosomes X, Y, 13, 18, and 21.

RESULT(S)

All the recovered putative zygotes were abnormal for the expected ploidy, presumably as a result of abnormal oocytes.

CONCLUSION(S)

Fluorescence in situ hybridization techniques represent a promising approach to analyze zygotes that fail to divide normally in vitro and eggs that fail to become fertilized. In cases of recurrent IVF failure, the results of FISH could be used to counsel couples and thus to help them choose among methods other than IVF for assisted reproduction.

Plasma membrane and cytocortex alterations in frozen/thawed mouse embryos deprived of the zona pellucida

We analyzed the morphological and ultrastructural abnormalities present in two-cell mouse embryos frozen/thawed without the zona pellucida (ZP). Transmission electron microscopy revealed that these embryos had plasma membrane abnormalities that were not observed in the embryos frozen/thawed with an intact ZP. The most frequent anomalies were a decreased number of microvilli with a nonhomogeneous distribution and showing an abnormal morphology and the presence of an increased number of vesicles in the periphery of the cell. The distribution of actin filaments, studied by fluorescence microscopy revealed alterations in both embryos, frozen/ thawed with ZP and embryos frozen/thawed without ZP: an increased staining in some regions of the peripheral actin band, discontinuities or gaps in the band, or the presence of a second actin band connected to the peripheral one.

Origin of tripronucleate zygotes after intracytoplasmic sperm injection

Zygotes morphologically classified as tripronuclear (3PN) after intracytoplasmic sperm injection (ICSI), which are thought to be digynic in their origin, were studied by fluorescent in-situ hybridization (FISH). FISH results allowed us to assess the suspected ploidy after morphological evaluation of the zygote and to determine the origin of the third pronuclei. Our results show that, firstly, 36% of those zygotes classified as 3PN following their morphological evaluation were, in fact, diploid, and secondly, the main cause for triploidy after ICSI is the non-extrusion of the second polar body.

Laser blastocyst biopsy for preimplantation diagnosis in the human

A new methodology for blastocyst biopsy that uses a 1.48 microm diode laser is described. Trophectoderm cells are biopsied after laster zona drilling and culture, fixed and processed for fluorescent in situ hybridisation (FISH) analysis. Preliminary results on the efficiency of the procedure and blastocyst recovery rate are promising. Blastocyst laser biopsy is a useful tool in preimplantation genetic diagnosis (PGD) as it allows a more reliable diagnosis and widens the diagnostic possibilities on account of the higher number of cells obtained in the biopsy.

Cryopreservation of caprine beta-lactoglobulin transgenic mouse embryos

As an economical and safer alternative to the maintenance of transgenic animals as live stocks, transgenic embryo cryobanks can be generated and maintained indefinitely. Two-cell embryos obtained from four lines of caprine beta-lactoglobulin transgenic mice homozygous for the transgene were cryopreserved, and their response to cryopreservation-related stress was investigated. Significant differences between transgenic lines were found in the viability of frozen/thawed transgenic embryos and also in two-cell embryo production after superovulatory treatment of transgenic females. The results of this study suggest that cryopreservation protocols should be assessed on each transgenic line before the generation of transgenic embryo banks.

Characteristics of actin fibers and ultrastructure of the contact regions involved in the separation of blastomeres of two-cell mouse embryos, frozen-thawed without the zona pellucida

Freezing of embryos deprived of the zona pellucida (ZP) decreases their survival rate immediately after thawing, and gives rise to the separation of their blastomeres in a high percentage of cases. We have studied the ultrastructure and the characteristics of actin fibers in the cell-to-cell contact region in mouse embryos frozen-thawed without the ZP at the two-cell stage. Our results indicate that most of the embryos that retain their blastomeres united after freezing and thawing show either the presence of a midbody, or a contact region with a close apposition of the plasma membranes but without an organized actin cortex in their contact region. Only a small percentage of embryos that retain their blastomeres united after freezing and thawing show a contact region with widely separated plasma membranes and an organized actin cytocortex.

Expression of caprine beta-lactoglobulin in the milk of transgenic mice

A 14.5 kb-long transgene containing the complete caprine beta-lactoglobulin gene transcription unit as well as 6.1 kb and 3.7 kb of the 5'- and 3'-flanking regions, respectively, was microinjected into pronuclear stage mouse embryos. Four lines of transgenic mice were obtained, three of them expressing the transgene in their mammary glands during lactation. Western blot analysis of caprine beta-lactoglobulin in the milk of hemizygous transgenic animals demonstrated the presence of the exogenous protein at concentrations up to 0.5 mg ml-1 of mouse milk.

Does Ca2+/Mg(2+)-free medium have an effect on the survival of the preimplantation mouse embryo after biopsy?

The way in which the different technical aspects of clinical preimplantation genetic diagnosis affect the survival of the biopsied embryo is not well understood. One of these aspects is the influence of Ca2+/Mg(2+)-free medium on the developmental capacity of the biopsied embryo and the biopsied cell itself. Therefore, we used an experimental design involving 4-cell mouse embryos to evaluate the effect of performing the biopsy procedure under such conditions. Our results indicate that the use of Ca2+/Mg(2+)-free medium has no detrimental effect (at least in mouse embryos) on the viability of the biopsied embryos and their biopsied cells when used during relatively short times of exposure.

Evaluation of cytogenetic analysis for clinical preimplantation diagnosis

OBJECTIVE

To evaluate the feasibility of using cytogenetic analysis in preimplantation diagnosis.

DESIGN

Two different biopsy protocols (chemical drilling and zona cutting) and two fixation methods were tested in a mouse model. Afterwards, the efficiency of obtaining chromosome preparations from untransferable human embryos depending on the method used to obtain the blastomeres (embryos biopsy or removal of the zona pellucida and blastomere disaggregation) was determined. The chances of obtaining chromosome preparations depending on the type of embryo (haploid, diploid, triploid, and apparently unfertilized) were also evaluated.

RESULTS

Results from the mouse model showed that chemical drilling yields better results than cutting in terms of metaphases per biopsied embryo and surviving rate after biopsy. In human embryos, biopsy of diploid embryos produced 46.6% chromosome preparations, while 29% were obtained after blastomere disaggregation and 20.4% when biopsying triploid embryos.

CONCLUSIONS

These results suggest that the disaggregating procedure and triploid embryos cannot be considered as good models to assess the feasibility of cytogenetic analysis in preimplantation diagnosis. Poor chromosome quality and loss during fixation are the main problems to use cytogenetics in preimplantation diagnosis; a combination of cytogenetics and other techniques is suggested in cases of balanced translocations.

Twin pregnancy after preimplantation diagnosis for sex selection

A twin female pregnancy was obtained in a haemophilia carrier after two preimplantation diagnosis cycles. The embryonic sex of biopsied blastomeres was determined with the use of dual fluorescence in-situ hybridization with directly labelled DNA probes specific for the X and Y chromosome. A twin female pregnancy was confirmed by means of ultrasonography and amniocentesis at the 14th week of amenorrhoea. The patient delivered two healthy females by Caesarian section at the 37th week of pregnancy.

Effect of anti-human sperm monoclonal antibodies on mouse in vitro fertilization

We employed anti-human sperm monoclonal antibodies to investigate how sperm membrane antigens are involved in gamete interactions. We have produced seven monoclonal antibodies specific for human sperm antigens, that showed reaction with mouse sperm by ELISA and by immunofluorescence. These antibodies did not react with zona pellucida or any other somatic human tissue. Some degree of toxicity was detected for oocytes at high antibody concentration and this was correlated with their inhibitory effect on fertilization. Unrelated to the degree of antigen expression or localization on sperm membrane, the antibodies showed several degrees of inhibition. The participation in sperm-zona pellucida interaction for every antigen could be evidenced by the impaired penetration of sperm caused by the presence of several concentrations of antibody. Thus, DAN-2, MOU-8 and VAC-4 inhibit mouse in vitro fertilization.

Sephadex filtration and human serum albumin gradients do not select spermatozoa by sex chromosome: a fluorescent in-situ hybridization study

Fluorescent in-situ hybridization (FISH) of decondensed sperm nuclei has been used directly to evaluate the enrichment efficiency of human sperm separation using Sephadex gel filtration and human serum albumin (HSA) gradients. Control and processed spermatozoa were fixed and their nuclei decondensed. In-situ hybridization was carried out with a Y-specific DNA probe (DYZ1). Sephadex filtration yielded 52.5% Y-chromosome-bearing spermatozoa, HSA separation resulted in 49.4% Y-chromosome-bearing spermatozoa and in the untreated control sample the percentage of Y spermatozoa was 49.3%. Statistical analysis revealed no significant differences between the selection methods employed and the controls, and no real enrichment for X- or Y-bearing spermatozoa was detected for any of the selection methods assayed. The usefulness of the protocols reported for selection of spermatozoa by sex chromosome in couples at risk for X-linked diseases is discussed.

The genetic risks of in vitro fertilization techniques: the use of an animal model

PURPOSE

The influence of some technical and biological parameters on the genetic characteristics of embryos derived from in vitro fertilization (IVF) techniques was studied.

METHOD

Using a murine model, we assessed the effect of gamete manipulation, gamete maturation stage, and maternal age on the chromosome complements of first-cleavage embryos.

RESULTS AND CONCLUSIONS

We found a positive correlation between some of these parameters and the incidence of the different chromosome abnormalities studied. Regarding aneuploidy, we observed an influence of maternal age, using both prepubertal and old females. Polyspermy showed a positive correlation with in vitro fertilization, the immaturity and overmaturity of the oocytes employed, and the use of prepubertal females. The appearance of diploid female complements was related to oocyte immaturity and prepubertal females, while diploid male complements were directly related to in vitro fertilization. Premature chromosome condensation (PCC) had a direct relationship with oocyte immaturity and in vitro maturation of the oocyte. Finally, structural abnormalities were associated with the process of sperm aging in vitro.

Zona pellucida surface of immature and in vitro matured mouse oocytes: analysis by scanning electron microscopy

PURPOSE

The aim of this work was to determine the morphology of the zona pellucida surface of immature and in vitro matured mouse oocytes by scanning electron microscopy. For this purpose two groups of immature oocytes (germinal vesicle group and metaphase I group) were studied either before or after in vitro maturation.

RESULTS

Before in vitro maturation, the germinal vesicle immature group showed mainly an unstructured zona pellucida surface with smooth cumulus cells. The metaphase I immature group showed a more structured zona pellucida with smooth or blebbing cumulus cells. After in vitro maturation, development of the zona pellucida toward a mature surface, related to the initial degree of oocyte maturity, was observed in both groups.

CONCLUSIONS

These observations show a correlation between the morphology of the zona pellucida surface and the degree of oocyte maturity; the in vitro maturation process can give rise to a proper development of this endowment when immature oocytes are used.

Premature chromosome condensation as a sign of oocyte immaturity

In this work we report the possibility that oocyte immaturity is associated with premature chromosome condensation (PCC) after in-vitro fertilization (IVF). Using a murine model, we have related PCC and endoreduplicated-like oocytes to oocyte immaturity as a basis for a prognosis in oocyte immaturity problems. The cytogenetic analysis was performed in 511 embryos obtained from immature oocytes that were directly fertilized in vitro and in 1363 embryos obtained from immature oocytes that were matured in vitro with different concentrations of human chorionic gonadotrophin (HCG) added to the culture medium. As a control we used 507 embryos obtained from freshly ovulated oocytes. PCC at the G1-phase-(G1-PCC) was observed only when immature oocytes were immediately fertilized in vitro (45.4%) and PCC at the S-phase (S-PCC) only when using in-vitro matured oocytes with the highest HCG concentration (3.3%). Neither G1-PCC nor S-PCC were found in the control group. Endoreduplicated-like oocytes appeared in a significant percentage (27.3%) only in the immature group. Immature oocytes yielded a low fertilization rate (16.6%) while in-vitro maturation seemed to confer a higher fertilization capacity compared to the control group (90.1% versus 78.2%). The possible correlation between PCC and oocyte immaturity provides new prospects in the determination of human IVF failures of unknown origin. Thus, when a problem of oocyte immaturity is diagnosed through the presence of PCC, a special programme of in vitro oocyte maturation, such as a longer preincubation time or addition of hormones to the media, would be recommended.

Effect of the degree of maturation of mouse oocytes at fertilization: a source of chromosome imbalance

It has been suggested that the abnormal maturation of the human oocyte during fertilization in vitro may result in chromosome imbalance and induce embryonic loss. Using a mouse model, we have studied the influence of the degree of oocyte maturation (either immaturity or overmaturity) on the chromosome characteristics of embryos at the first-cleavage division. Immature oocytes were obtained 2-3 h or 3-4 h before the expected ovulation time (b.o.). Overmaturation was induced by aging the newly ovulated oocytes in vitro for 3, 6, and 12 h. Our results show a significant decrease in the fertilization rate in the immature groups (65.53% at 2-3 h b.o. and 16.59% at 3-4 h b.o. vs. 78.22% at control) and after 12 h of in vitro aging (69.39%), while a significant increase of this parameter was found at 3 h of aging (82.59%) as compared to the other groups. No significant differences were found in the occurrence of aneuploidy or hyperhaploidy in embryos obtained from immature, newly ovulated, and overmature oocytes. Finally, an increased incidence of polyploidy was detected in immature, 2-3 h b.o. (31.20%), and overmature, 3 h (23.04%) and 6 h (31.61%), groups as compared to the control group (14.59%).

The genotoxic effect of beta-propiolactone on mammalian oocytes

beta-Propiolactone (beta PL) has been tested on preimplantation mouse embryos for possible genotoxic effects. Tests were performed at different stages of meiosis (late prophase I, diakinesis/metaphase I, anaphase I, telophase I/prophase II and metaphase II) by injecting females at various times after the induction of superovulation. Male and female derived chromosome complements from first-cleavage embryos were analysed before syngamy for cytogenetic abnormalities. A higher proportion of diploid oocytes, produced by the non-extrusion of the first or second polar body, was found after fertilization when the compound was administered immediately before metaphase I or II. No obvious effect was detected at any other time of beta PL exposure. Based on these results, several possible modes of action for beta PL are postulated.

Chromosomes of mouse embryos in vivo and in vitro: effect of manipulation, maternal age and gamete ageing

The use of human material does not allow the determination of the influence of different parameters on the genetic characteristics of the embryos derived from in-vitro fertilization (IVF) techniques. Using a murine model we assessed the effect of gamete manipulation, maternal age and oocyte ageing on the chromosome complements of the embryos. We have found a positive correlation between all these parameters and the incidence of chromosome abnormalities in first-cleavage mouse embryos obtained by IVF.

Chromosome studies in oocytes and zygotes from an IVF programme

Chromosome studies have been carried out in 117 oocytes, 17 one-cell zygotes and four, two- to four-cell zygotes in our IVF programme. Three apparently unfertilized oocytes were, in fact, diploid zygotes. Two of 14 apparently polyspermic zygotes were also diploid. One zygote with four pronuclei was pentaploid. This indicates that pronuclei can either be confused with other cytoplasmic structures, like vacuoles, or be eliminated. Endoreduplication was observed in one tetraploid, apparently polyspermic zygote, and in one two-cell degenerated zygote. The incidence of aneuploidy in unfertilized oocytes, taken as twice the level of hyperhaploidy, was 15.4%. Five oocytes showed fragmented metaphase II chromosomes (4.3%). The incidence of unreduced oocytes, due to a lack of extrusion of the first polar body, was 6.8%. Thus the total number of potentially aneuploid, polyploid or non-viable zygotes due to chromosome aberrations in the oocyte was 26.5%.

The chromosome complement of first-cleavage mouse embryos after in vitro fertilization

A comparison of the first cleavage-stage chromosome complements of 1022 in vivo fertilized mouse embryos and 1033 in vitro fertilized mouse embryos is reported. The chromosome analysis of first-cleavage embryos allows us to study directly the chromosome complement of the sperm and oocyte that contribute to the embryo, since both chromosome clusters remain separate when an antimitotic agent is used to prevent syngamy. In this paper we show that the sex ratio and the incidence of aneuploidy are similar, irrespective of the fertilization system used. Male and female gametes have the same levels of aneuploidy. Triploidy is more frequent in the in vitro fertilized embryos and the difference can be ascribed to a higher incidence of polyspermy and diploid spermatozoa.