Fate of fertilized human oocytes

Cathepsin L regulates oocyte meiosis and preimplantation embryo development

Early embryonic loss, caused by reduced embryo developmental competence, is the major cause of subfertility in humans and animals. This embryo developmental competence is determined during oocyte maturation and the first embryo divisions. Therefore, it is essential to identify the underlying molecules regulating these critical developmental stages. Cathepsin L (CTSL), a lysosomal cysteine protease, is involved in regulating cell cycle progression, proliferation and invasion of different cell types. However, CTSL role in mammalian embryo development is unknown. Using bovine in vitro maturation and culture systems, we show that CTSL is a key regulator for embryo developmental competence. We employed a specific CTSL detection assay in live cells to show that CTSL activity correlates with meiotic progression and early embryo development. Inhibiting CTSL activity during oocyte maturation or early embryo development significantly impaired oocyte and embryo developmental competence as evidenced by lower cleavage, blastocyst and hatched blastocyst rates. Moreover, enhancing CTSL activity, using recombinant CTSL (rCTSL), during oocyte maturation or early embryo development significantly improved oocyte and embryo developmental competence. Importantly, rCTSL supplementation during oocyte maturation and early embryo development significantly improved the developmental competence of heat-shocked oocytes/embryos which are notoriously known for reduced quality. Altogether, these results provide novel evidence that CTSL plays a pivotal role in regulating oocyte meiosis and early embryonic development.

Events Leading to the Establishment of Pregnancy and Placental Formation: The Need to Fine-Tune the Nomenclature on Pregnancy and Gestation

Today, there is strong and diversified evidence that in humans at least 50% of early embryos do not proceed beyond the pre-implantation period. This evidence comes from clinical investigations, demography, epidemiology, embryology, immunology, and molecular biology. The purpose of this article is to highlight the steps leading to the establishment of pregnancy and placenta formation. These early events document the existence of a clear distinction between embryonic losses during the first two weeks after conception and those occurring during the subsequent months. This review attempts to highlight the nature of the maternal-embryonic dialogue and the major mechanisms active during the pre-implantation period aimed at "selecting" embryos with the ability to proceed to the formation of the placenta and therefore to the completion of pregnancy. This intense molecular cross-talk between the early embryo and the endometrium starts even before the blastocyst reaches the uterine cavity, substantially initiating and conditioning the process of implantation and the formation of the placenta. Today, several factors involved in this dialogue have been identified, although the best-known and overall, the most important, still remains Chorionic Gonadotrophin, indispensable during the first 8 to 10 weeks after fertilization. In addition, there are other substances acting during the first days following fertilization, the Early Pregnancy Factor, believed to be involved in the suppression of the maternal response, thereby allowing the continued viability of the early embryo. The Pre-Implantation Factor, secreted between 2 and 4 days after fertilization. This linear peptide molecule exhibits a self-protective and antitoxic action, is present in maternal blood as early as 7 days after conception, and is absent in the presence of non-viable embryos. The Embryo-Derived Platelet-activating Factor, produced and released by embryos of all mammalian species studied seems to have a role in the ligand-mediated trophic support of the early embryo. The implantation process is also guided by signals from cells in the decidualized endometrium. Various types of cells are involved, among them epithelial, stromal, and trophoblastic, producing a number of cellular molecules, such as cytokines, chemokines, growth factors, and adhesion molecules. Immune cells are also involved, mainly uterine natural killer cells, macrophages, and T cells. In conclusion, events taking place during the first two weeks after fertilization determine whether pregnancy can proceed and therefore whether placenta's formation can proceed. These events represent the scientific basis for a clear distinction between the first two weeks following fertilization and the rest of gestation. For this reason, we propose that a new nomenclature be adopted specifically separating the two periods. In other words, the period from fertilization and birth should be named "gestation", whereas that from the completion of the process of implantation leading to the formation of the placenta, and birth should be named "pregnancy".

Polygenic signals of sex differences in selection in humans from the UK Biobank

Sex differences in the fitness effects of genetic variants can influence the rate of adaptation and the maintenance of genetic variation. For example, "sexually antagonistic" (SA) variants, which are beneficial for one sex and harmful for the other, can both constrain adaptation and increase genetic variability for fitness components such as survival, fertility, and disease susceptibility. However, detecting variants with sex-differential fitness effects is difficult, requiring genome sequences and fitness measurements from large numbers of individuals. Here, we develop new theory for studying sex-differential selection across a complete life cycle and test our models with genotypic and reproductive success data from approximately 250,000 UK Biobank individuals. We uncover polygenic signals of sex-differential selection affecting survival, reproductive success, and overall fitness, with signals of sex-differential reproductive selection reflecting a combination of SA polymorphisms and sexually concordant polymorphisms in which the strength of selection differs between the sexes. Moreover, these signals hold up to rigorous controls that minimise the contributions of potential confounders, including sequence mapping errors, population structure, and ascertainment bias. Functional analyses reveal that sex-differentiated sites are enriched in phenotype-altering genomic regions, including coding regions and loci affecting a range of quantitative traits. Population genetic analyses show that sex-differentiated sites exhibit evolutionary histories dominated by genetic drift and/or transient balancing selection, but not long-term balancing selection, which is consistent with theoretical predictions of effectively weak SA balancing selection in historically small populations. Overall, our results are consistent with polygenic sex-differential-including SA-selection in humans. Evidence for sex-differential selection is particularly strong for variants affecting reproductive success, in which the potential contributions of nonrandom sampling to signals of sex differentiation can be excluded.

Detection of sexually antagonistic transmission distortions in trio datasets

Sexual dimorphisms are widespread in animals and plants, for morphological as well as physiological traits. Understanding the genetic basis of sexual dimorphism and its evolution is crucial for understanding biological differences between the sexes. Genetic variants with sex‐antagonistic effects on fitness are expected to segregate in populations at the early phases of sexual dimorphism emergence. Detecting such variants is notoriously difficult, and the few genome‐scan methods employed so far have limited power and little specificity. Here, we propose a new framework to detect a signature of sexually antagonistic (SA) selection. We rely on trio datasets where sex‐biased transmission distortions can be directly tracked from parents to offspring, and identify signals of SA transmission distortions in genomic regions. We report the genomic location of six candidate regions detected in human populations as potentially under sexually antagonist selection. We find an enrichment of genes associated with embryonic development within these regions. Last, we highlight two candidate regions for SA selection in humans.

Foetal loss and feminine sex ratios at birth in sub-Saharan Africa

A wealth of demographic research has explored the determinants of sex ratios at birth, but few studies have considered the role of foetal loss (spontaneous abortion), in producing feminine sex ratios. One challenge is measuring the occurrence of foetal loss, which is difficult to recognize and report in survey research. This study uses the length of the birth interval as a proxy for foetal loss; foetal loss restarts the clock on time to conception and lengthens the birth interval. We use Demographic and Health Survey data on second births to women in 17 sub-Saharan African countries. Results show that longer second birth intervals are significantly related to lower odds of a male second birth and to feminine sex ratios at birth. These findings suggest that high levels of foetal loss, which could signal underlying poor maternal health in a population, have dramatic effects on the sex ratio at birth.

Bovine eggs release zinc in response to parthenogenetic and sperm-induced egg activation

Upon fertilization or parthenogenesis, zinc is released into the extracellular space through a series of exocytic events termed zinc sparks, which are tightly coordinated with intracellular calcium transients. The zinc spark reduces the total amount of intracellular zinc, and this reduction is necessary and sufficient to induce egg activation even in the absence of calcium transients. In addition, this zinc release contributes to the block to polyspermy through modification of the zona pellucida. The zinc spark has been documented in all organisms examined to date including the mouse, two species of nonhuman primates, and human. Here we determined whether zinc sparks occur in the bovine, an important model of gamete development in mono-ovulatory mammalian species. We obtained metaphase II-arrested (MII) bovine eggs following in vitro maturation. Total zinc, assessed in single cells using X-Ray Fluorescence Microscopy, was significantly more abundant in the bovine egg compared to iron and copper. Studies with intracellular fluorescent probes revealed that labile zinc pools are localized to discrete cytoplasmic punctae enriched at the cortex. To determine whether zinc undergoes dynamic fluxes during egg activation, we parthenogenetically activated bovine eggs using two approaches: ionomycin or bovine phospholipase C zeta (bPlcζ). Both these methods induced zinc sparks coordinately with intracellular calcium transients. The zinc spark was also observed in bovine eggs following intracytoplasmic sperm injection. These results establish that zinc is the most abundant transition metal in the bovine egg, and zinc flux during egg activation - induced by chemical activation or sperm - is a highly conserved event across mammalian species.

Miscarriages in families with an offspring that have classic congenital adrenal hyperplasia and 21-hydroxylase deficiency

BACKGROUND

The most common form of congenital adrenal hyperplasia is 21-hydroxylase deficiency (CAH). Both men and women with classic CAH have lower fertility rates than the general population, and an increased rate of miscarriages has been reported in affected women. There are no data on the incidence rate of miscarriages in families with an offspring that have classic CAH.

METHODS

We studied families with a history of classic CAH. The families came from different parts of Germany and attended the annual meeting of the German CAH support group for parents and patients which was held in Hamburg in September 2014. The data was collected anonymously by a paper-based questionnaire which was completed by the families at home. The families also accepted the responsibility to address this question to their siblings. In all, the data of 50 families with at least one child with classic CAH, and the data of 164 parental siblings were available for evaluation. Miscarriage rates were calculated in relation to the reported pregnancies.

RESULTS

Twenty-two miscarriages were reported from 19 families. At least one miscarriage occurred in 38% of the families, three families experienced two miscarriages and 16 families had one miscarriage each. The mean miscarriage rate was 15.8%. The heterozygous mothers had a total of 90 siblings (41 m, 49 f), while 74 siblings (33 m, 41 f) were reported from the heterozygous fathers. The miscarriage rate was 10.1% in the families of the mothers` siblings, and 11.4% in the families of the fathers` siblings. The genotype was known in all parents that have an offspring with classic CAH, but not defined in 82% of the maternal siblings, and in 86% of the paternal siblings. No child with classic CAH has been diagnosed in any of the sibling's families to date.

CONCLUSION

Our data show that the miscarriage rate in German families with a child with classic CAH is not elevated.

Early embryo mortality in natural human reproduction: What the data say

How many human embryos die between fertilisation and birth under natural conditions? It is widely accepted that natural human embryo mortality is high, particularly during the first weeks after fertilisation, with total prenatal losses of 70% and higher frequently claimed. However, the first external sign of pregnancy occurs two weeks after fertilisation with a missed menstrual period, and establishing the fate of embryos before this is challenging. Calculations are additionally hampered by a lack of data on the efficiency of fertilisation under natural conditions. Four distinct sources are used to justify quantitative claims regarding embryo loss: (i) a hypothesis published by Roberts & Lowe in TheLancet  is widely cited but has no practical quantitative value; (ii) life table analyses give consistent assessments of clinical pregnancy loss, but cannot illuminate losses at earlier stages of development; (iii) studies that measure human chorionic gonadotrophin (hCG) reveal losses in the second week of development and beyond, but not before; and (iv) the classic studies of Hertig and Rock offer the only direct insight into the fate of human embryos from fertilisation under natural conditions. Re-examination of Hertig's data demonstrates that his estimates for fertilisation rate and early embryo loss are highly imprecise and casts doubt on the validity of his numerical analysis. A recent re-analysis of hCG study data concluded that approximately 40-60% of embryos may be lost between fertilisation and birth, although this will vary substantially between individual women. In conclusion, natural human embryo mortality is lower than often claimed and widely accepted. Estimates for total prenatal mortality of 70% or higher are exaggerated and not supported by the available data.

Early embryo mortality in natural human reproduction: What the data say

It is generally accepted that natural human embryo mortality during pregnancy is high - losses of 70% and higher from fertilisation to birth are frequently claimed. The first external sign of pregnancy occurs two weeks after fertilisation with a missed menstrual period. Establishing the fate of embryos before this is challenging, and hampered by a lack of data on the efficiency of fertilisation under natural conditions. Four distinct sources are cited to justify quantitative claims regarding embryo loss: (i) a hypothesis published by Roberts & Lowe in TheLancet  is widely cited but has no quantitative value; (ii) life table analyses give consistent assessments of clinical pregnancy loss, but cannot illuminate losses at earlier stages of development; (iii) studies that measure human chorionic gonadotrophin (hCG) reveal losses in the second week of development and beyond, but not before; and (iv) the classic studies of Hertig and Rock offer the only direct insight into the fate of human embryos from fertilisation under natural conditions. Re-examination of Hertig's data demonstrates that his estimates for fertilisation rate and early embryo loss are highly imprecise and casts doubt on the validity of his numerical analysis. A recent re-analysis of hCG study data suggests that approximately 40-60% of embryos may be lost between fertilisation and birth, although this will vary substantially between individual women. In conclusion, it is clear that some published estimates of natural embryo mortality are exaggerated. Although available data do not provide a precise estimate, natural human embryo mortality is lower than is often claimed.

Estimating limits for natural human embryo mortality

Natural human embryonic mortality is generally considered to be high. Values of 70% and higher are widely cited. However, it is difficult to determine accurately owing to an absence of direct data quantifying embryo loss between fertilisation and implantation. The best available data for quantifying pregnancy loss come from three published prospective studies (Wilcox, Zinaman and Wang) with daily cycle by cycle monitoring of human chorionic gonadotrophin (hCG) in women attempting to conceive. Declining conception rates cycle by cycle in these studies indicate that a proportion of the study participants were sub-fertile. Hence, estimates of fecundability and pre-implantation embryo mortality obtained from the whole study cohort will inevitably be biased. This new re-analysis of aggregate data from these studies confirms the impression that discrete fertile and sub-fertile sub-cohorts were present. The proportion of sub-fertile women in the three studies was estimated as 28.1% (Wilcox), 22.8% (Zinaman) and 6.0% (Wang). The probability of conceiving an hCG pregnancy (indicating embryo implantation) was, respectively, 43.2%, 38.1% and 46.2% among normally fertile women, and 7.6%, 2.5% and 4.7% among sub-fertile women. Pre-implantation loss is impossible to calculate directly from available data although plausible limits can be estimated. Based on this new analysis and a model for evaluating reproductive success and failure it is proposed that a plausible range for normal human embryo and fetal mortality from fertilisation to birth is 40-60%.

Detection of Allelic Frequency Differences between the Sexes in Humans: A Signature of Sexually Antagonistic Selection

Sexually antagonistic (SA) selection, a form of selection that can occur when both sexes have different fitness optima for a trait, is a major force shaping the evolution of organisms. A seminal model developed by Rice (Rice WR. 1984. Sex chromosomes and the evolution of sexual dimorphism. Evolution 38:735-742.) predicts that the X chromosome should be a hotspot for the accumulation of loci under SA selection as compared with the autosomes. Here, we propose a methodological framework designed to detect a specific signature of SA selection on viability, differences in allelic frequencies between the sexes. Applying this method on genome-wide single nucleotide polymorphism (SNP) data in human populations where no sex-specific population stratification could be detected, we show that there are overall significantly more SNPs exhibiting differences in allelic frequencies between the sexes on the X chromosome as compared with autosomes, supporting the predictions of Rice's model. This pattern is consistent across populations and is robust to correction for potential biases such as differences in linkage disequilibrium, sample size, and genotyping errors between chromosomes. Although SA selection is not the only factor resulting in allelic frequency differences between the sexes, we further show that at least part of the identified X-linked loci is caused by such a sex-specific processes.

The Effect of Prolonged Culture of Chromosomally Abnormal Human Embryos on The Rate of Diploid Cells

Background

A decrease in aneuploidy rate following a prolonged co-culture of human blastocysts has been reported. As co-culture is not routinely used in assisted reproductive technology, the present study aimed to evaluate the effect of the prolonged single culture on the rate of diploid cells in human embryos with aneuploidies.

Materials and Methods

In this cohort study, we used fluorescence in situ hybridi- zation (FISH) to reanalyze surplus blastocysts undergoing preimplantation genetic diagnosis (PGD) on day 3 postfertilization. They were randomly studied on days 6 or 7 following fertilization.

Results

Of the 30 analyzed blastocysts, mosaicism was observed in 26(86.6%), while 2(6.7%) were diploid, and 2(6.7%) were triploid. Of those with mosaicism, 23(88.5%) were determined to be diploid-aneuploid and 3(11.5%) were aneuploid mosaic. The total frequency of embryos with more than 50% diploid cells was 33.3% that was lower on day 7 in comparison with the related value on day 6 (P<0.05); however, there were no differences when the embryos were classified according to maternal age, blastocyst developmental stage, total cell number on day 3, and embryo quality.

Conclusion

Although mosaicism is frequently observed in blastocysts, the prolonged single culture of blastocysts does not seem to increase the rate of normal cells.

Italian Constitutional Court removes the prohibition on gamete donation in Italy

In 2004, The Italian Constitutional Court prohibited treatments involving gamate donation, embryo donation, embryo cryopreservation (except under exceptional circumstances), and the transfer of more than three embryos. Basically three statements were made by the Court: the ban violates a couple's fundamental right to health, to self-determination and to have a child. Here, the consequences of such a decision and the legal challenges that ensued are discussed.

Do daughters really cause divorce? Stress, pregnancy, and family composition

Provocative studies have reported that in the United States, marriages producing firstborn daughters are more likely to divorce than those producing firstborn sons. The findings have been interpreted as contemporary evidence of fathers' son preference. Our study explores the potential role of another set of dynamics that may drive these patterns: namely, selection into live birth. Epidemiological evidence indicates that the characteristic female survival advantage may begin before birth. If stress accompanying unstable marriages has biological effects on fecundity, a female survival advantage could generate an association between stability and the sex composition of offspring. Combining regression and simulation techniques to analyze real-world data, we ask, How much of the observed association between sex of the firstborn child and risk of divorce could plausibly be accounted for by the joint effects of female survival advantage and reduced fecundity associated with unstable marriage? Using data from the National Longitudinal Survey of Youth (NLSY79), we find that relationship conflict predicts the sex of children born after conflict was measured; conflict also predicts subsequent divorce. Conservative specification of parameters linking pregnancy characteristics, selection into live birth, and divorce are sufficient to generate a selection-driven association between offspring sex and divorce, which is consequential in magnitude. Our findings illustrate the value of demographic accounting of processes which occur before birth-a period when many outcomes of central interest in the population sciences begin to take shape.

Double-effect reasoning and the conception of human embryos

Some commentators argue that conception signals the onset of human personhood and that moral responsibilities toward zygotic or embryonic persons begin at this point, not the least of which is to protect them from exposure to death. Critics of the conception threshold of personhood ask how it can be morally consistent to object to the embryo loss that occurs in fertility medicine and research but not object to the significant embryo loss that occurs through conception in vivo. Using that apparent inconsistency as a starting point, they argue that if that embryo loss is tolerable as a way of conceiving children, it should be tolerable in fertility medicine and human embryonic research. Double-effect reasoning shows, by contrast, that conception in vivo is justified even if it involves the death of persons because the motives for wanting children are not inherently objectionable, because the embryo loss that occurs in unassisted conception is not the means by which successful conception occurs, and because the effect of having children is proportionate to the loss involved. A similar outcome holds true for in vitro fertilisation in fertility medicine but not for in vitro fertilisation for research involving human embryos.

"After birth" abortion: a biomedical and conceptual nonsense

Recently, two authors suggested that killing a healthy newborn might be morally permissible, subsuming it under the heading of 'after birth abortion'. Their proposed new definition implies that infanticide should be permitted whenever II trimester abortion for social reasons is. The suggestion stirred public outcry; nonetheless it needs to be analyzed since some 20% of countries allow II trimester abortion for social reasons and 5% do this on demand. A proper delimitation of the definition of "abortion" is thus very important to ensure careful application; for this reason we have attempted a critical analysis of their arguments. In the area of pregnancy termination different moral standards are apparently applied in different countries, but many reasons exist why the equation between II trimester abortion for social reasons and the killing of healthy neonates is to be morally rejected in all cases. The "inversed reification" of the concept of infanticide as a more abstract, euphemistic 'after birth abortion' blurs the fundamental difference between a non-viable fetus and a viable neonate. The best-known and most widely utilized (although illegal) "social reason" for "late abortion" and "infanticide" is a pregnancy with a female fetus or neonate. If infanticide for neonates were to be considered morally permissible, specifically it is this practice that would be applied. And this should be rejected on two levels: conceptual, through a critique of the exclusive use of one specific notion of personhood, and pragmatic through refusal of gender-discriminatory forms of infanticide (the killing of female neonates). In conclusion, having investigated the new concept we have concluded that the term "after birth abortion" is biologically and conceptually nonsensical.

Impaired mitochondrial function in murine oocytes is associated with controlled ovarian hyperstimulation and in vitro maturation

The present study was designed to determine whether controlled ovarian hyperstimulation (COH) and in vitro maturation (IVM), two common clinical procedures in human IVF treatment, have an impact on mitochondrial DNA (mtDNA) copy number and mitochondrial function in oocytes. Matured mouse oocytes recovered following COH, IVM and natural cycles (NC), which simulated those treatments in human clinic IVF treatment. The copies of mtDNA, the activity of mitochondria as determined by inner mitochondrial membrane potential and oocyte adenosine trisphosphate (ATP) content, pattern of mitochondrial distribution, reactive oxygen species (ROS) levels and the integrity of the cytoskeleton were evaluated in oocytes. Significant differences were detected between COH and NC groups in all measures, except the pattern of mitochondrial distribution and ROS levels. There were also significant differences detected between IVM and NC treatment groups in the copies of mitochondrial DNA, the level of ROS and the integrity of the cytoskeleton in oocytes. In conclusion, the results of this investigation indicate that non-physiological COH and IVM treatments inhibit mtDNA replication, alter mitochondrial function and increase the percentage of abnormal cytoskeleton and ROS production. Damage related to the mitochondria may partly explain the low efficiency of IVF and high rate of embryonic loss associated with these clinical procedures.

Gastrulation in rabbit blastocysts depends on insulin and insulin-like-growth-factor 1

Insulin and insulin-like-growth-factor 1 (IGF1) are components of the uterine secretions. As potent growth factors they influence early embryo development. The underlying molecular mechanisms are largely unknown. Here we report on the effects of insulin and IGF1 on early gastrulation in rabbit blastocysts. We have studied blastocysts grown in vivo in metabolically healthy rabbits, in rabbits with type 1 diabetes and in vitro in the presence or absence of insulin or IGF1. Embryonic disc morphology and expression of Brachyury, Wnt3a and Wnt4 were analysed by qPCR and IHC. Pre-gastrulated blastocysts (stage 0/1) cultured with insulin or IGF1 showed a significantly higher capacity to form the posterior mesoderm and primitive streak (stage 2 and 3) than blastocysts cultured without growth factors. In gastrulating blastocysts the levels of the mesoderm-specific transcription factor Brachyury and the Wnt signalling molecules Wnt3a and Wnt4 showed a stage-specific expression pattern with Brachyury transcripts increasing from stage 0/1 to 3. Wnt4 protein was found spread over the whole embryoblast. Insulin induced Wnt3a, Wnt4 and Brachyury expression in a temporal- and stage-specific pattern. Only blastocysts cultured with insulin reached the Wnt3a, Wnt4 and Brachyury expression levels of stage 2 in vivo blastocysts, indicating that insulin is required for Wnt3a, Wnt4 and Brachyury expression during gastrulation. Insulin-induced Wnt3a and Wnt4 expression preceded Brachyury. Wnt3a-induced expression could be depleted by MEK1 inhibition (PD98059). Involvement of insulin in embryonic Wnt3a expression was further shown in vivo with Wnt3a expression being notably down regulated in stage 2 blastocysts from rabbits with type 1 diabetes. Blastocysts grown in diabetic rabbits are retarded in development, a finding which supports our current results that insulin is highly likely required for early mesoderm formation in rabbit blastocysts by inducing a distinct spatiotemporal expression profile of Wnt3a, Wnt4 and Brachyury.