Human embryo twinning with applications in reproductive medicine

Case report: Spontaneous abortion of monoamniotic twins at the third trimester of pregnancy in Camelus dromedarius

Monoamniotic twins develop when a blastocyst spontaneously splits its progenitor cells, and each group of progenitor cells independently grows to become an individual. It is the rarest type of twin pregnancy and usually has significant developmental or congenital abnormalities, a higher rate of abortion, perinatal morbidity, and mortality. There is no information regarding monoamniotic twins in livestock species. Here, we reported a spontaneous abortion of monoamniotic twins in a dromedary camel at 278 days of gestation. Gonadorelin acetate (100 μg) was injected intramuscularly to induce ovulation in the recipient. A 7 days-old embryo produced by somatic cell nuclear transfer was transferred transcervically to the recipient. Early pregnancy was confirmed by an elevated level of serum progesterone followed by ultrasonography at 22 and 44 days after embryo transfer. A single sac was observed on 22 days while twins were evident 44 days after embryo transfer. Pregnancy was periodically monitored by the tail-up phenomenon. A ruptured fetal sac was observed on the ground having two fetuses. On autopsy, full-grown fetuses were found. Their bodies were separated. There was no congenital anomaly or any malformation in the fetuses. According to the reported chronology in human twins, we hypothesized that the blastocyst splitted before 13 days as it was monoamniotic and not conjoined. If the embryo splits within 4 to 8 days, it develops two amniotic sacs, and splitting after 13 days develops conjoined fetuses. To the authors' knowledge, this is the first reported case of monoamniotic twin abortion in dromedary camels. This report will increase awareness among practicing veterinarians and camel breeders about twin abortions.

Lab partners: oocytes, embryos and company. A personal view on aspects of oocyte maturation and the development of monozygotic twins

The present review addresses the oocyte and the preimplantation embryo, and is intended to highlight the underlying principle of the "nature versus/and nurture" question. Given the diversity in mammalian oocyte maturation, this review will not be comprehensive but instead will focus on the porcine oocyte. Historically, oogenesis was seen as the development of a passive cell nursed and determined by its somatic compartment. Currently, the advanced analysis of the cross-talk between the maternal environment and the oocyte shows a more balanced relationship: Granulosa cells nurse the oocyte, whereas the latter secretes diffusible factors that regulate proliferation and differentiation of the granulosa cells. Signal molecules of the granulosa cells either prevent the precocious initiation of meiotic maturation or enable oocyte maturation following hormonal stimulation. A similar question emerges in research on monozygotic twins or multiples: In Greek and medieval times, twins were not seen as the result of the common course of nature but were classified as faults. This seems still valid today for the rare and until now mainly unknown genesis of facultative monozygotic twins in mammals. Monozygotic twins are unique subjects for studies of the conceptus-maternal dialogue, the intra-pair similarity and dissimilarity, and the elucidation of the interplay between nature and nurture. In the course of in vivo collections of preimplantation sheep embryos and experiments on embryo splitting and other microsurgical interventions we recorded observations on double blastocysts within a single zona pellucida, double inner cell masses in zona-enclosed blastocysts and double germinal discs in elongating embryos. On the basis of these observations we add some pieces to the puzzle of the post-zygotic genesis of monozygotic twins and on maternal influences on the developing conceptus.

Zona pellucida removal by acid Tyrode's solution affects pre- and post-implantation development and gene expression in mouse embryos

The zona pellucida (ZP) plays a crucial role in the process of fertilization to early embryonic development, including cellular arrangement and communication between blastomeres. However, little is known regarding the role of the ZP in pre- and post-implantation embryonic development associated with gene expression. We investigated the effect of zona pellucida removal (ZPR) on pre- and post-implantation development of mouse embryos. After ZPR of 2-cell stage embryos was performed by acid Tyrode's solution, which is commonly used for ZP treatment, compaction occurred earlier in ZP-free (ZF) than ZP-intact (ZI) embryos. In addition, the expression of differentiation-related genes in the inner cell mass (ICM) and trophectoderm (TE) was significantly altered in ZF blastocyst compared with ZI embryos. After embryo transfer, the rate of implantation and live fetuses was lower in ZF embryos than in control embryos, whereas the fetal weight at E17.5 was not different. However, placental weight significantly increased in ZF embryos. RNA-seq analysis of the placenta showed that a total of 473 differentially expressed genes (DEGs) significantly influenced the biological process. The present study suggests that ZPR by acid Tyrode's solution at the 2-cell stage not only disturbs the expression pattern of ICM/TE-related genes but affects the post-implantation development of mouse embryos. Overall, this study provides deeper insight into the role of the ZP during early embryonic development and the viability of post-implantation development.

Cloning and Embryo Splitting in Mammalians: Brief History, Methods, and Achievements

Embryo splitting is one of the newest developed methods in reproductive biotechnology. In this method, after splitting embryos in 2-, 4-, and even 8-cell stages, every single blastomere can be developed separately, but the embryos are genetically identical. Embryo splitting, as an approach in reproductive cloning, is extensively employed in reproductive medicine studies, such as investigating human diseases, treating sterility, embryo donation, and gene therapy. In the present study, cloning in mammalians and cloning approaches are briefly reviewed. In addition, embryo splitting and the methods commonly used in embryo splitting and recent achievements in this field, as well as the applications of embryo splitting into livestock species, primate animals, and humans, are outlined. Finally, a perspective of embryo splitting is provided as the conclusion.

Efficacy of the in vitro splitting of human preimplantation embryos from ART programs

Background/aim

The aim of this study was to evaluate the efficiency of in vitro embryo splitting (IES) procedures. We also assessed the quality of the blastocysts developed from embryos obtained from different sources.

Materials and methods

Good quality embryos at 6–8-cell stages were categorized according to their fertilization sources: 1) frozen-warmed donated embryos, 2) chromosomally abnormal embryos, 3) parthenogenetic embryos, and 4) embryos derived from fertilization of in vitro matured oocytes (rescue IVM). After IES, splitting and developmental efficiency was assessed. Furthermore, the quality of the developed blastocysts was evaluated by Hoechst and propidium iodide (PI) staining.

Results

The data showed a high rate of both splitting and developmental efficiency in the frozen-warmed embryos after IES (140% and 71.7%, respectively), followed by chromosomally abnormal embryos (96.8% and 52.5%, respectively). Results of the Hoechst and PI staining showed that the mean ± SD cell numbers of the control group were higher (113.11 ± 16.01) than that of twins A (donor blastomeres embryos, 58 ± 12.2) and B (recipient blastomeres embryos, 50.4 ± 8.5), respectively.

Conclusion

Chromosomally normal embryos enrolled in IES are more potent to develop into viable blastocysts. For research purposes, 1PN and 3PN embryos are the best options for splitting procedures, regardless of the poor quality of developed blastocysts.

Quality of Blastocysts Created by Embryo Splitting: A Time-Lapse Monitoring and Chromosomal Aneuploidy Study

Objective

The aim of this study was to screen the potential of human embryos to develop into expanding blastocysts following in vitro embryo splitting and then assess the quality of the generated blastocysts based on chromosomal characteristics and using morphokinetics.

Materials and Methods

In this experimental study, a total of 82 good quality cleavage-stage donated embryos (8- 14 cells) were used (24 embryos were cultured to the blastocyst stage as controls and 58 embryos underwent in vitro splitting). After in vitro splitting, the blastomere donor and blastomere recipient embryos were named twin A and twin B, respectively. Morphokinetics and morphological parameters were evaluated using a time-lapse system in the blastocysts developed from twin embryos. Aneuploidy of chromosomes 13, 15, 16, 18, 21, 22, X and Y were analyzed in the twin blastocysts.

Results

Following in vitro splitting, of the 116 resulting twin embryos, 80 (69%) developed to the expanded blastocyst (EBL) stage compared to 21 (87.5%) embryos in the control group (P>0.05). The morphokinetics analysis suggested that the developmental time-points were influenced by the in vitro splitting. Moreover, the blastocysts developed from A and B twins had impaired morphology compared to controls. Regarding chromosome abnormalities, there was no significant difference in the rate of aneuploidy or mosaicism between the different groups.

Conclusion

This study showed that while no chromosomal abnormalities were seen, in vitro embryo splitting may affect the embryo morphokinetics.

Attempts for Generation of Embryonic Stem Cells from Human Embryos Following In Vitro Embryo Twinning

In vitro embryo twinning can be used to increase the number of the human embryos available for production of human embryonic stem cell (hESC) lines. The aim of this study was to generate hESCs following the production of the twin embryos by in vitro embryo splitting procedures. In total 21 chromosomally abnormal (three pronuclei) embryos underwent in vitro embryo twinning and were allowed to develop to the blastocyst stage. As a result, 42 twin embryos were obtained, of which 24 developed to blastocyst stage. Using micromanipulation technique, the zona-free blastocysts were recovered and plated onto mitotically inactivated Yazd human foreskin fibroblast (Batch18; YhFF#18) feeder layers in microdrops. After 3 to 5 days of blastocyst culture onto human foreskin fibroblast feeder layers, the hESC-like outgrowths were passaged onto new feeders in microdrops. The initial outgrowths of hESC-like cells were generated, and cells were proliferated, passaged, and some of them expressed hESC and trophoblastic markers; however, no cell lines were established. This might be due to the low cell number and poor quality of inner cell mass within these twin blastocysts. In vitro embryo twinning by increasing the number of the human embryos could be useful in the future for the generation of new pluripotent stem cell lines. However, the challenge remains to optimize the methods.

Enhanced development of mouse single blastomeres into blastocysts via the simultaneous inhibition of TGF-β and ERK pathways in microdroplet culture

Optimization of an in vitro culture that supports blastocyst (BL) development from single blastomeres (SBs) is essential to generate additional embryos for farm animals and humans and unravel the mechanisms that underlie totipotency. In this study, we have examined BL development from SBs that were derived from 2-cell and 4-cell mouse embryos in different media. Moreover, BLs were assessed for inner cell mass (ICM) by staining with Oct4. We found that BL development was improved in a lower volume of medium (1 µL) compared with a higher volume (5 µL). Furthermore, the supplementation of medium with the inhibitors of ERK1/2 and TGFβ (R2i) signaling pathways in 1 µL droplets of T6 medium improved BL development. The co-culture of SBs with intact embryos in the presence of R2i showed more BL development and ICM to trophectoderm cell number ratio in comparison with SB culture and SB group culture. We also observed reduced total cell number, ICM, and trophectoderm cell numbers in all of the SB culture conditions versus intact embryo development. These findings might facilitate the successful generation of additional embryos for biomedical applications and elucidate the mechanisms that underlie totipotency.

Cleavage-stage embryo micromanipulation in the clinical setting

Embryo micromanipulation was developed after introduction of microinjection to overcome infertility. Embryo micromanipulation may be performed at any embryo stage from pronuclear to blastocyst. The technique started out as basic and turned out to be increasingly more complex. Embryo micromanipulation at the cleavage-stage includes a wide range of techniques, from opening the zona pellucida in order to improve the chance of implantation, to removing detrimental components from the embryo to enhance embryo development or blastomeres for preimplantation genetic diagnosis and embryo splitting. Evaluating the impact(s) of different micromanipulation techniques on epigenetics of the embryo and considering quality control during these techniques are important issues in this regard. This review aims to discuss the micromanipulation of cleavage-stage embryos in clinical assisted reproductive technology (ART).

ABBREVIATIONS

ART: assisted reproductive technology; ICSI: intracytoplasmic sperm injection; IVF: in vitro fertilization; PGD: preimplantation genetic diagnosis; PZD: partial zona dissection; ZP: zona pellucida; SUZI: subzonal insemination; PVS: perivitelline space; AH: assisted hatching; LAH: laserassisted hatching; ZT: zona thinning; UV: ultraviolet; IR: infrared; PCR: polymerase chain reaction; FISH: fluorescent in situ hybridization; NGS: next generation sequencing; QC: quality control; QA: quality assurance.

Potential of human twin embryos generated by embryo splitting in assisted reproduction and research

BACKGROUND

Embryo splitting or twinning has been widely used in veterinary medicine over 20 years to generate monozygotic twins with desirable genetic characteristics. The first human embryo splitting, reported in 1993, triggered fierce ethical debate on human embryo cloning. Since Dolly the sheep was born in 1997, the international community has acknowledged the complexity of the moral arguments related to this research and has expressed concerns about the potential for reproductive cloning in humans. A number of countries have formulated bans either through laws, decrees or official statements. However, in general, these laws specifically define cloning as an embryo that is generated via nuclear transfer (NT) and do not mention embryo splitting. Only the UK includes under cloning both embryo splitting and NT in the same legislation. On the contrary, the Ethics Committee of the American Society for Reproductive Medicine does not have a major ethical objection to transferring two or more artificially created embryos with the same genome with the aim of producing a single pregnancy, stating that 'since embryo splitting has the potential to improve the efficacy of IVF treatments for infertility, research to investigate the technique is ethically acceptable'.

OBJECTIVE AND RATIONALE

Embryo splitting has been introduced successfully to the veterinary medicine several decades ago and today is a part of standard practice. We present here an overview of embryo splitting experiments in humans and non-human primates and discuss the potential of this technology in assisted reproduction and research.

SEARCH METHODS

A comprehensive literature search was carried out using PUBMED and Google Scholar databases to identify studies on embryo splitting in humans and non-human primates. 'Embryo splitting' and 'embryo twinning' were used as the keywords, alone or in combination with other search phrases relevant to the topics of biology of preimplantation embryos.

OUTCOMES

A very limited number of studies have been conducted in humans and non-human primates. The published material, especially the studies with human embryos, is controversial. Some reports suggest that twinning technology will find clinical use in reproductive medicine in the future, whereas others conclude the opposite that human twin embryos created in vitro are unsuitable not only for clinical, but also for research, purposes.

WIDER IMPLICATIONS

The blastomere biopsy technique of embryo splitting seems to be unsuitable for either clinical or research purposes; however, embryo bisection, a preferable method of cloning in veterinary medicine, has not yet been tested on human embryos.

Human Embryos Created by Embryo Splitting Secrete Significantly Lower Levels of miRNA-30c

Studies reporting term pregnancy and the production of genetically identical offspring from isolated blastomeres of early stage embryos have been carried out in small and large animals. However, very little is known about the effects of embryo splitting on the development and reproductive competency of human embryos. In this study, we investigated the effects of embryo splitting on profile of microRNAs (miRNAs) detected in their spent blastocyst medium (SBM) by comparative analysis of miRNA profiles in SBM of human twin embryos created by blastomere biopsy and SBM of blastocysts that resulted in a healthy pregnancy and live birth following embryo transfer. The profile of miRNA secretion in in vitro culture media consistently distinguishes twin from control embryos. We found that six miRNAs are significantly more abundant in SBM from twin embryos, while nine are significantly more abundant in SBM from euploid implanted blastocysts. These nine include miRNA-30c, a previously reported marker of blastocyst implantation potential. Furthermore, 22.9% of miRNAs secreted by twin embryos were never detected in SBM from normal reproductively competent blastocysts, or from trophectoderm (TE) samples from normal blastocysts donated for the research. The miRNA profile, unique to twin blastocysts, might be a result of differential lineage commitment in these embryos.

Developmental clock compromises human twin model created by embryo splitting

STUDY QUESTION

Is the quality of the human embryos generated by twinning in vitro comparable to the quality of the embryos created by fertilization?

SUMMARY ANSWER

Our data suggest that the human twin embryos created in vitro are unsuitable not only for clinical use but also for research purposes.

WHAT IS KNOWN ALREADY

Pregnancy from in vitro generated monozygotic twins by embryo splitting or twinning leads to live birth of healthy animals. Similar strategies, however, have been less successful in primates. Recent reports suggest that the splitting of human embryos might result in viable, morphologically adequate blastocysts, although the qualitative analyses of the embryos created in such a way have been very limited.

STUDY DESIGN, SIZE, DURATION

This study was a comparative analysis of embryos generated by twinning in vitro and the embryos created by in vitro fertilization.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We analysed morphokinetics and developmental competence of 176 twin embryos created by splitting of 88 human embryos from either early (2-5 blastomeres, n = 43) or late (6-10 blastomeres, n = 45) cleavage stages. We compared the data with morphometrics of embryos created by in vitro fertilization and resulting in pregnancy and live birth upon single blastocyst transfer (n = 42).

MAIN RESULTS AND THE ROLE OF CHANCE

The morphokinetic data suggested that the human preimplantation development is subjected to a strict temporal control. Due to a 'developmental clock', the size of twin embryos was proportionate to the number of cells used for their creation. Furthermore, the first fate decision was somewhat delayed; the inner cell mass (ICM) became distinguishable later in the twin than in the normal blastocysts obtained through fertilization. If an ICM was present at all, it was small and of poor quality. The majority of the cells in the twin embryos expressed ICM and trophectoderm markers simultaneously.

LIMITATIONS, REASONS FOR CAUTION

We created monozygotic twins by blastomere separation from cleavage stage embryos. Embryo twinning by blastocyst bisection may circumvent limitations set by the developmental clock.

WIDER IMPLICATIONS OF THE FINDINGS

Taken together, our data suggest that the human twin embryos created in vitro are unsuitable not only for clinical use but also for research purposes.

Double trouble: should double embryo transfer be banned?

What role should legislation or policy play in avoiding the complications of in-vitro fertilization? In this article, we focus on single versus double embryo transfer, and assess three arguments in favour of mandatory single embryo transfer: risks to the mother, risks to resultant children, and costs to society. We highlight significant ethical concerns about each of these. Reproductive autonomy and non-paternalism are strong enough to outweigh the health concerns for the woman. Complications due to non-identity cast doubt on the extent to which children are harmed. Twinning may offer an overall benefit rather than burden to society. Finally, including the future health costs for children (not yet born) in reproductive policy is inconsistent with other decisions. We conclude that mandatory single embryo transfer is not justified and that a number of countries should reconsider their current embryo transfer policy.

Splitting of IVP bovine blastocyst affects morphology and gene expression of resulting demi-embryos during in vitro culture and in vivo elongation

Embryo splitting might be used to increase offspring yield and for molecular analysis of embryo competence. How splitting affects developmental potential of embryos is unknown. This research aimed to study the effect of bovine blastocyst splitting on morphological and gene expression homogeneity of demi-embryos and on embryo competence during elongation. Grade I bovine blastocyst produced in vitro were split into halves and distributed in nine groups (3 × 3 setting according to age and stage before splitting; age: days 7-9; stage: early, expanded and hatched blastocysts). Homogeneity and survival rate in vitro after splitting (12 h, days 10 and 13) and the effect of splitting on embryo development at elongation after embryo transfer (day 17) were assessed morphologically and by RT-qPCR. The genes analysed were OCT4, SOX2, NANOG, CDX2, TP1, TKDP1, EOMES, and BAX. Approximately 90% of split embryos had a well conserved defined inner cell mass (ICM), 70% of the halves had similar size with no differences in gene expression 12 h after splitting. Split embryos cultured further conserved normal and comparable morphology at day 10 of development; this situation changes at day 13 when embryo morphology and gene expression differed markedly among demi-embryos. Split and non-split blastocysts were transferred to recipient cows and were recovered at day 17. Fifty per cent of non-split embryos were larger than 100 mm (33% for split embryos). OCT4, SOX2, TP1 and EOMES levels were down-regulated in elongated embryos derived from split blastocysts. In conclusion, splitting day-8 blastocysts yields homogenous demi-embryos in terms of developmental capability and gene expression, but the initiation of the filamentous stage seems to be affected by the splitting.

An international view of surgically assisted conception and surrogacy tourism

Modern medicine, specifically assisted reproductive technology (ART), has overtaken the law in many jurisdictions around the world. New technologies and practices open a Pandora's Box of ethical, religious, social and legal questions, and may present a variety of significant legal problems to the courts and legislators. Surrogate motherhood and pregnancy through ART have both attracted controversy. Some groups condemn ART and want it banned while its supporters acknowledge there is a need for legislative guidelines and regulations. A proposed statute, the Assisted Reproductive Technique Services Act, aimed at regulating reproductive technologies, including surrogacy arrangements, will be introduced in the Malaysian parliament, probably in 2012, and the Assisted Reproductive Technology (Regulation) Bill 2010 is already before the Indian parliament. This paper will discuss several of the potential socio-legal issues surrounding ART in the light of the complex situation, with a comparative analysis of the Malaysian, USA, UK and Indian positions.

Development of monozygotic twin mouse embryos from the time of blastomere separation at the two-cell stage to blastocyst

The development of blastomeres separated from two-cell stage murine embryos has been compared. Blastomeres were removed from the zona pellucida (ZP) and cultured individually; the twin embryos were compared during their progression to blastocyst in terms of development rate, cell number, morphology, conformation at the four-cell stage, and CDX2 and POU5F1 (also known as OCT4) expression. In general, twin embryos, whether obtained from superovulated or normally bred dams, displayed comparable cell numbers as they advanced. They formed morulae and blastocysts more or less synchronously with each other and with control embryos, although possessing about half of the latter's cell number. Despite this apparent synchrony, the majority of twin blastocysts differed in terms of their relative complements of POU5F1+/CDX2- cells, which represent inner cell mass (ICM), and POU5F1+/CDX2+ cells, which identify trophectoderm (TE). Many, but not all, exhibited a disproportionately small ICM. By contrast, demiembryos retained within their ZP and created by randomly damaging one of the two blastomeres in two-cell stage embryos exhibited a more normal ratio of ICM to TE cells at blastocyst and significantly less variance in ICM cell number. One possible explanation is that ZP-free demiembryos only infrequently adopt the same conformation as their partners, including the favorable tetrahedral form, at the four-cell stage, suggesting that such embryos exhibit a high degree of plasticity with regard to the orientation of their first two cleavage planes and that a significant number likely deviate from paths that provide an optimal geometric progression to blastocyst. These data could explain the difficulty of creating monozygotic twins from two-cell stage embryos.