Lineage tracing demonstrates that blastomeres of early cleavage-stage human pre-embryos contribute to both trophectoderm and inner cell mass

Epigenetic manipulation to improve mouse SCNT embryonic development

Cloned mammals can be achieved through somatic cell nuclear transfer (SCNT), which involves reprogramming of differentiated somatic cells into a totipotent state. However, low cloning efficiency hampers its application severely. Cloned embryos have the same DNA as donor somatic cells. Therefore, incomplete epigenetic reprogramming accounts for low development of cloned embryos. In this review, we describe recent epigenetic barriers in SCNT embryos and strategies to correct these epigenetic defects and avoid the occurrence of abnormalities in cloned animals.

Hypothesis: human trophectoderm biopsy downregulates the expression of the placental growth factor gene

Preeclampsia (PE) and intrauterine growth retardation (IUGR) are the results of defective placentation associated with the downregulation of different genes in the human trophoblast including the Placental Growth Factor (PGF). TrophEctoderm (TE) biopsy is increasingly performed for Pre-implantation Genetic Testing of Aneuploidies and it involves the traumatical removal of an unpredictable number of mural TE cells from the human blastocyst. We observed strikingly similar obstetrical and neonatal complications in pregnancies where the placenta bears PGF downmodulation or a TE biopsy has been done. In both groups, the risk of PE, IUGR, congenital cardiac ventricular septal defects, caesarean section, sex ratio in favour of males and preterm birth is significantly increased compared to controls. Given the high degree of correlation, the observation may not be a casual one. We postulate herein that the TE biopsy may induce persistent dysregulation of different genes in the placenta including PGF. The mechanism proposed is the disruption of tight junctions caused by the TE biopsy.

A model for postzygotic mosaicisms quantifies the allele fraction drift, mutation rate, and contribution to de novo mutations

The allele fraction (AF) distribution, occurrence rate, and evolutionary contribution of postzygotic single-nucleotide mosaicisms (pSNMs) remain largely unknown. In this study, we developed a mathematical model to describe the accumulation and AF drift of pSNMs during the development of multicellular organisms. By applying the model, we quantitatively analyzed two large-scale data sets of pSNMs identified from human genomes. We found that the postzygotic mutation rate per cell division during early embryogenesis, especially during the first cell division, was higher than the average mutation rate in either male or female gametes. We estimated that the stochastic cell death rate per cell cleavage during human embryogenesis was ∼5%, and parental pSNMs occurring during the first three cell divisions contributed to ∼10% of the de novo mutations observed in children. We further demonstrated that the genomic profiles of pSNMs could be used to measure the divergence distance between tissues. Our results highlight the importance of pSNMs in estimating recurrence risk and clarified the quantitative relationship between postzygotic and de novo mutations.

Implications for a Stem Cell Regenerative Medicine Based Approach to Human Intervertebral Disk Degeneration

The human body develops from a single cell, the zygote, the product of the maternal oocyte and the paternal spermatozoon. That 1-cell zygote embryo will divide and eventually grow into an adult human which is comprised of ~3.7 × 10¹³ cells. The tens of trillions of cells in the adult human can be classified into approximately 200 different highly specialized cell types that make up all of the different tissues and organs of the human body. Regenerative medicine aims to replace or restore dysfunctional cells, tissues and organs with fully functional ones. One area receiving attention is regeneration of the intervertebral discs (IVDs), which are located between the vertebrae and function to give flexibility and support load to the spine. Degenerated discs are a major cause of lower back pain. Different stem cell based regenerative medicine approaches to cure disc degeneration are now available, including using autologous mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs) and even attempts at direct transdifferentiation of somatic cells. Here we discuss some of the recent advances, successes, drawbacks, and the failures of the above-mentioned approaches.

When Family History Matters: The Importance of Lineage Analyses and Fate Maps for Explaining Animal Development

Initial interest in understanding how the fertilized egg becomes a multicellular animal suggested two possible answers: either the embryo came from preformed components or it arose through epigenetic processes. Extensive research during the past few decades has identified aspects of development that depend on preformed elements, such as cytoplasmic components and a cell's lineage; it also has identified aspects that depend on epigenetic processes, such as cell interactions and morphogen gradients. These advances have depended on understanding embryonic cell lineage and cell fate. This essay explains how lineage analysis and fate mapping have contributed to our current understanding of embryonic development.

Chromosomal instability in mammalian pre-implantation embryos: potential causes, detection methods, and clinical consequences

Formation of a totipotent blastocyst capable of implantation is one of the first major milestones in early mammalian embryogenesis, but less than half of in vitro fertilized embryos from most mammals will progress to this stage of development. Whole chromosomal abnormalities, or aneuploidy, are key determinants of whether human embryos will arrest or reach the blastocyst stage. Depending on the type of chromosomal abnormality, however, certain embryos still form blastocysts and may be morphologically indistinguishable from chromosomally normal embryos. Despite the implementation of pre-implantation genetic screening and other advanced in vitro fertilization (IVF) techniques, the identification of aneuploid embryos remains complicated by high rates of mosaicism, atypical cell division, cellular fragmentation, sub-chromosomal instability, and micro-/multi-nucleation. Moreover, several of these processes occur in vivo following natural human conception, suggesting that they are not simply a consequence of culture conditions. Recent technological achievements in genetic, epigenetic, chromosomal, and non-invasive imaging have provided additional embryo assessment approaches, particularly at the single-cell level, and clinical trials investigating their efficacy are continuing to emerge. In this review, we summarize the potential mechanisms by which aneuploidy may arise, the various detection methods, and the technical advances (such as time-lapse imaging, "-omic" profiling, and next-generation sequencing) that have assisted in obtaining this data. We also discuss the possibility of aneuploidy resolution in embryos via various corrective mechanisms, including multi-polar divisions, fragment resorption, endoreduplication, and blastomere exclusion, and conclude by examining the potential implications of these findings for IVF success and human fecundity.

A comparison of pregnancy outcomes between day 3 and day 5/6 embryo transfers: does day of embryo transfer really make a difference?

PURPOSE

To determine if day of embryo transfer (ET) affects gestational age (GA) and/or birth weight (BW) at a single university fertility center that primarily performs day 5/6 ET.

METHODS

Retrospective cohort study of 2392 singleton live births resulting from IVF/ICSI at a single large university fertility center from 2003 to 2012. Patients were stratified by day 3 or day 5/6 ET. Outcome variables included patient age, gravidity, prior miscarriages, prior assisted reproduction technology cycles, number of embryos transferred, number of single ET, infertility diagnosis, neonatal sex, GA at birth, and BW. Subanalyses were performed on subgroups of preterm infants. A comparison was made between the study data and the Society of Assisted Reproductive Technologies (SART) published data.

RESULTS

There was no difference in GA at birth (39 ± 2.1 weeks for day 3 ET, 39 ± 1.9 weeks for day 5/6 ET) or BW between ET groups (3308 ± 568 g for day 3 ET, 3268 ± 543 g for day 5/6 ET). There was also no difference in the number of preterm deliveries (8.5 % for day 3 ET vs. 10.8 % for day 5/6 ET). The day 5/6 ET study data had significantly fewer pre-term deliveries than the SART day 5/6 ET data.

CONCLUSION

In contrast to published SART data, GA and BW were not influenced by day of ET. Data may be more uniform at a single institution. Day 5/6 ET continues to offer improved pregnancy rates without compromising birth outcomes.

Embryonic aneuploidy: overcoming molecular genetics challenges improves outcomes and changes practice patterns

Since its inception, in vitro fertilization (IVF) has pursued molecular technology to improve patient outcomes, leading to enhanced methods of embryo selection. Comprehensive chromosomal screening (CCS) is a powerful tool that decreases maternal and neonatal morbidity due to multiple gestations by allowing the transfer of fewer embryos while maintaining success rates. To optimize this genetic test, physiological principles limiting the timing and type of cells to be removed had to be realized. Molecular barriers involved in genome amplification and ensuring the accuracy and validity of the CCS platform required a multistep approach to ensure that this technology was not used prematurely. Only after ensuring that the potential for harm was minimized and benefit maximized could clinicians use this technology to improve patient care.

The development of a malignant tumor is due to a desperate asexual self-cloning process in which cancer stem cells develop the ability to mimic the genetic program of germline cells

To date there is no explanation why the development of almost all types of solid tumors occurs sharing a similar scenario: (1) creation of a cancer stem cell (CSC), (2) CSC multiplication and formation of a multicellular tumor spheroid (TS), (3) vascularization of the TS and its transformation into a vascularized primary tumor, (4) metastatic spreading of CSCs, (5) formation of a metastatic TSs and its transformation into metastatic tumors, and (6) potentially endless repetition of this cycle of events. The above gaps in our knowledge are related to the biology of cancer and specifically to tumorigenesis, which covers the process from the creation of a CSC to the formation of a malignant tumor and the development of metastases. My Oncogerminative Theory of Tumorigenesis considers tumor formation as a dynamic self-organizing process that mimics a self-organizing process of early embryo development. In the initial step in that process, gene mutations combined with epigenetic dysregulation cause somatic cells to be reprogrammed into CSCs, which are immortal pseudo-germline cells. Mimicking the behavior of fertilized germline cells, the CSC achieves immortality by passing through the stages of its life-cycle and developing into a pseudo-blastula-stage embryo, which manifests in the body as a malignant tumor. In this view, the development of a malignant tumor from a CSC is a phenomenon of developmental biology, which we named a desperate asexual self-cloning event. The theory explains seven core characteristics of malignant tumors: (1) CSC immortality, (2) multistep development of a malignant tumor from a single CSC, (3) heterogeneity of malignant tumor cell populations, (4) metastatic spread of CSCs, (5) invasive growth, (6) malignant progression, and (7) selective immune tolerance toward cancer cells. The Oncogerminative Theory of Tumorigenesis suggests new avenues for discovery of revolutionary therapies to treat, prevent, and eradicate cancer.

Developmental capacity and pregnancy rate of tetrahedral- versus non-tetrahedral-shaped 4-cell stage human embryos

PURPOSE

The arrangement of the blastomeres within the 4-cell stage embryo reflects the orientation of the cleavage planes during the second division. To examine their relevance, the developmental capacity and the pregnancy rate were compared between tetrahedral-shaped and non-tetrahedral-shaped 4-cell stage human embryos.

METHODS

The study included 3,546 4-cell stage embryos. The arrangement of the blastomeres at the 4-cell stage was annotated as being tetrahedral or non-tetrahedral on day 2 of preimplantation development. Embryo quality was compared on day 3 and day 5. Pregnancy rates were calculated per single embryo transfer on day 3 or day 5.

RESULTS

In total, 2,803 4-cell stage embryos (79 %) displayed a tetrahedral arrangement and 743 (21 %) displayed a non-tetrahedral arrangement. Tetrahedral-shaped embryos developed more into high-quality embryos on day 3 (p < 0.001) and day 5 (p = 0.036) and had a higher blastulation rate (p = 0.009). Though, the number of high-quality embryos selected for transfer did not differ between both groups on day 3 (p = 0.167) and day 5 (p ~ 1). Three hundred thirty single embryo transfers were analysed. No significant difference in clinical pregnancy was found between both groups after transfer on day 3 (p = 0.209) and day 5 (p = 0.653).

CONCLUSIONS

The arrangement of the blastomeres according to their previous cleavage planes was correlated to the developmental potential of the 4-cell stage embryo up to the blastocyst stage. If embryo transfers are performed on day 3 and day 5 of development using embryos of adequate quality, the blastomere arrangement at the 4-cell stage had no predictable value regarding pregnancy success.

Single thawed euploid embryo transfer improves IVF pregnancy, miscarriage, and multiple gestation outcomes and has similar implantation rates as egg donation

PURPOSE

The objective of our study was to determine if trophectoderm biopsy, vitrification, array-comparative genomic hybridization and single thawed euploid embryo transfer (STEET) can reduce multiple gestations and yield high pregnancy and low miscarriage rates.

METHODS

We performed a retrospective observational study comparing single thawed euploid embryo to routine age matched in vitro fertilization (IVF) patients that underwent blastocyst transfer from 2008 to 2011 and to our best prognosis group donor oocyte recipients (Donor). Our main outcome measures were implantation rate, clinical pregnancy rate, spontaneous abortion rate and multiple gestation rate.

RESULTS

The STEET group had a significantly higher implantation rate (58 %, 53/91) than the routine IVF group (39 %, 237/613) while the Donor group (57 %, 387/684) had a similar implantation rate. The clinical pregnancy rates were not statistically different between the STEET and IVF groups. However, the multiple gestation rate was significantly lower in the STEET group (STEET 2 % versus IVF 34 %, Donor 47 %).

CONCLUSIONS

STEET results in a high pregnancy rate, low multiple gestation rate and miscarriage rates. Despite the older age of STEET patients and transfer of twice as many embryos, the implantation rate for STEET was indistinguishable from that for egg donation. STEET offers an improvement to IVF, lowering risks without compromising pregnancy rate.

Aberrant behavior of mouse embryo development after blastomere biopsy as observed through time-lapse cinematography

OBJECTIVE

To analyze whether blastomere biopsy affects early embryonal growth as observed through time-lapse cinematography.

DESIGN

Comparative prospective study between embryos in which a blastomere was removed and embryos in which a blastomere was not removed.

SETTING

An experimental laboratory of the university.

MAIN OUTCOME MEASURE(S)

We calculated the time between blastocele formation and the end of hatching, the time between the start and end of hatching, the number of contractions and expansions between blastocyst formation and the end of hatching, and the maximum diameter of the expanded blastocyst.

RESULT(S)

In blastomere removal embryos, compaction began at the six-cell stage instead of at the eight-cell stage. We also found that hatching was delayed in these embryos as compared with matched controls. Moreover, the frequency of contraction and expansion movements after blastocyst formation was significantly higher in the blastomere removal group as compared with the control group. Finally, the maximum diameter of the expanded blastocyst just before hatching was not significantly different between both groups.

CONCLUSION(S)

These findings suggested that blastomere removal has an adverse effect on embryonic development around the time of hatching. Thus, future developments in preimplantation genetic diagnosis and screening should involve further consideration and caution in light of the influence of blastomere biopsy on embryonal growth.

Insights on blastomere nuclearity

PURPOSE

To analyze the results of our transferred embryos, especially those that "changed" their blastomere nuclearity from Multinucleated (MN) to Mono-nucleated during development.

METHODS

Pregnancies where at least one MN embryo was transferred were retrospectively evaluated and categorized in order to record and follow-up on the ones that were implanted. Embryos were classified as normal (when all blastomeres were mono-nucleated on day one and two of development), corrected (multinucleated embryos on day one that became mono-nucleated on day two) and non-corrected (multinucleated either on day one, on day two or both days).

RESULTS

There were 633 transfer cycles analyzed. Thirty-three percent (206) had at least one embryo with a MN blastomere at a given stage of development. Pregnancy and implantation rates were 29.0% and 19.0% for the group of exclusively mono-nucleated embryo transfers, and 28.6% and 15.8% for the group with at least one MN embryo transferred. The pregnancy outcome for "corrected" and "non-corrected" embryos could be corroborated unequivocally in only 9 cases, with an outcome of 8 and 4 normal babies, respectively.

CONCLUSIONS

Because the amount of data analyzed is not satisfactorily large, differences were not significantly different; however, a trend may exist showing that normal at term pregnancies obtained from corrected embryos are more likely to occur than those from non-corrected embryos. Nuclear observation on a daily basis should be one of the strategies used to select the best embryos for transferring, to improve implantation rates and avoid multiple pregnancies.

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.

Factors controlling embryo viability

Many diverse factors affect embryo viability. The morphological measures routinely used to grade human embryos are of limited use as many of the factors influencing the longterm viability of embryos are genetic or molecular and are undetectable or inconclusive from visualization of living embryos by microscopy. This article presents examples of factors that are known to affect embryo viability, including gamete formation, embryonic genome activation, and im-printing. Aspects of both gamete and embryo development are addressed, and the possibility that various anomalies remain hidden for extended periods before impacting upon a later aspect of development is hypothesized. In future, more detailed and informative assessments of embryo viability before embryo transfer may require invasive approaches to study the composition of embryos at various stages of preimplantation development; however, indirect, non-invasive measures would be preferable.

Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage-stage or some extra-embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrode's solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+-free medium for decompaction, and removal of one or two cells from cleavage-stage embryos.

Embryo implantation after biopsy of one or two cells from cleavage-stage embryos with a view to preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) can be offered as an alternative to prenatal diagnosis (PND) to couples at risk of having a child with a genetic disease. The affected embryos are detected before implantation by fluorescent in situ hybridisation (FISH) for sexing (X-linked diseases) and chromosomal disorders (numerical and structural) or by polymerase chain reaction (PCR) for monogenic disorders (including some X-linked diseases). The accuracy and reliability of the diagnosis is increased by analysing two blastomeres of the embryo. However, the removal of two blastomeres might have an effect on the implantation capacity of the embryo. We have evaluated the implantation of embryos after the removal of one, two or three cells in 188 PGD cycles where a transfer was done. The patients were divided into five groups: a first group which received only embryos from which one cell had been removed, a second group which received only embryos from which two cells had been removed, a third group which received a mixture of embryos from which one and two cells had been taken, a fourth group where two and three cells had been removed, and a fifth group where three cells had been removed. The overall ongoing pregnancy rate per transfer was 26.1%, the overall implantation rate per transfer was 15.2% and the overall birth rate was 14.2%. Although pregnancy rates between the groups cannot be compared because the second group (two cells removed) contains more rapidly developing and therefore 'better quality' embryos, an ongoing pregnancy rate of 29.1% and an implantation rate of 18.6% per transferred embryo in this group is acceptable, and we therefore advise analysing two cells from a > or =7-cell stage embryo in order to render the diagnosis more accurate and reliable.

Positive outcome after preimplantation diagnosis of aneuploidy in human embryos

usromosomal abnormalities are responsible for a great deal of embryo wastage, which is reflected, at least partially, in decreased implantation and increased miscarriage in older women. To address this problem the transfer of only chromosomally normal embryos previously selected by preimplantation genetic diagnosis (PGD) has been proposed. We designed a multi-centre in-vitro fertilization (IVF) study to compare controls and a test group that underwent embryo biopsy and PGD for aneuploidy. Patients were matched retrospectively, but blindly, for average maternal age, number of previous IVF cycles, duration of stimulation, oestradiol concentrations on day +1, and average mature follicles. All these parameters were similar in test and control groups. Only embryos classified as normal for those chromosomes were transferred after PGD. The results showed that the rates of fetal heart beat (FHB)/embryo transferred between the control and test groups were similar. However, spontaneous abortions, measured as FHB aborted/FHB detected, decreased after PGD (P < 0.05), and ongoing pregnancies and delivered babies increased (P < 0.05) in the PGD group of patients. Two conclusions were obtained: (i) PGD of aneuploidy reduced embryo loss after implantation; (ii) implantation rates were not significantly improved, but the proportion of ongoing and delivered babies was increased.

Laser scanning confocal imaging of abnormal or arrested human preimplantation embryos

PURPOSE

The improved resolution and optical sectioning of a confocal microscope make it an ideal instrument for extracting three-dimensional information, especially from extended biological specimens such as human embryos. The staining of actin together with chromatin allowed us to specify the architecture of the embryo and the appearance of the nucleus.

METHODS

F-Actin and chromatin distributions were visualized using laser scanning confocal microscopy in "fresh" and "cryopreserved" human preimplantation embryos obtained by in vitro fertilization.

RESULTS

The current study revealed a high rate of multinucleation in arrested or poor-quality embryos (89%, in grade IV embryos).

CONCLUSIONS

Confocal microscopy revealed high levels of multinucleated blastomeres, suggesting that the probable cause of arrested development in these embryos was due to multinucleation of blastomeres.