Role of Filia, a maternal effect gene, in maintaining euploidy during cleavage-stage mouse embryogenesis

Anchoring cortical granules in the cortex ensures trafficking to the plasma membrane for post-fertilization exocytosis

Following fertilization, cortical granules exocytose ovastacin, a metalloendopeptidase that cleaves ZP2 in the zona pellucida surrounding mouse eggs to prevent additional sperm binding. Using high- and super-resolution imaging with ovastacinmCherry as a fluorescent marker, we characterize cortical granule dynamics at single granule resolution in transgenic mouse eggs. Newly-developed imaging protocols provide an unprecedented view of vesicular dynamics near the plasma membrane in mouse eggs. We discover that cortical granule anchoring in the cortex is dependent on maternal MATER and document that myosin IIA is required for biphasic trafficking to the plasma membrane. We observe local clearance of cortical actin during exocytosis and determine that pharmacologic or genetic disruption of trafficking to the plasma membrane impairs secretion of cortical granules and results in polyspermy. Thus, the regulation of cortical granule dynamics at the cortex-plasma membrane interface is critical for exocytosis and the post-fertilization block to sperm binding that ensures monospermic fertilization.

Genetic diagnosis of subfertility: the impact of meiosis and maternal effects

During reproductive age, approximately one in seven couples are confronted with fertility problems. While the aetiology is diverse, including infections, metabolic diseases, hormonal imbalances and iatrogenic effects, it is becoming increasingly clear that genetic factors have a significant contribution. Due to the complex nature of infertility that often hints at a multifactorial cause, the search for potentially causal gene mutations in idiopathic infertile couples has remained difficult. Idiopathic infertility patients with a suspicion of an underlying genetic cause can be expected to have mutations in genes that do not readily affect general health but are only essential in certain processes connected to fertility. In this review, we specifically focus on genes involved in meiosis and maternal-effect processes, which are of critical importance for reproduction and initial embryonic development. We give an overview of genes that have already been linked to infertility in human, as well as good candidates which have been described in other organisms. Finally, we propose a phenotypic range in which we expect an optimal diagnostic yield of a meiotic/maternal-effect gene panel.

Mutations in NLRP2 and NLRP5 cause female infertility characterised by early embryonic arrest

BACKGROUND

Successful human reproduction requires normal spermatogenesis, oogenesis, fertilisation and early embryonic development, and abnormalities in any of these processes will result in infertility. Early embryonic arrest is commonly observed in infertile patients with recurrent failure of assisted reproductive technology (ART). However, the genetic basis for early embryonic arrest is largely unknown.

OBJECTIVE

We aim to identify genetic causes of infertile patients characterised by early embryonic arrest.

METHODS

We pursued exome sequencing in a proband with embryonic arrest from the consanguineous family. We further screened candidate genes in a cohort of 496 individuals diagnosed with early embryonic arrest by Sanger sequencing. Effects of mutations were investigated in HeLa cells, oocytes and embryos.

RESULTS

We identified five independent individuals carrying biallelic mutations in NLRP2. We also found three individuals from two families carrying biallelic mutations in NLRP5. These mutations in NLRP2 and NLRP5 caused decreased protein expression in vitro and in oocytes and embryos.

CONCLUSIONS

NLRP2 and NLRP5 are novel mutant genes responsible for human early embryonic arrest. This finding provides additional potential diagnostic markers for patients with recurrent failure of ART and helps us to better understand the genetic basis of female infertility characterised by early embryonic arrest.

The subcortical maternal complex protein Nlrp4f is involved in cytoplasmic lattice formation and organelle distribution

In mammalian oocytes and embryos, the subcortical maternal complex (SCMC) and cytoplasmic lattices (CPLs) are two closely related structures. Their detailed compositions and functions remain largely unclear. Here, we characterized Nlrp4f as a novel component associated with the SCMC and CPLs. Disruption of maternal Nlrp4f leads to decreased fecundity and delayed preimplantation development in the mouse. Lack of Nlrp4f affects organelle distribution in mouse oocytes and early embryos. Depletion of Nlrp4f disrupts CPL formation but does not affect the interactions of other SCMC proteins. Interestingly, the loss of Filia or Tle6, two other SCMC proteins, also disrupts CPL formation in mouse oocytes. Thus, the absence of CPLs and aberrant distribution of organelles in the oocytes disrupted the examined SCMC genes, including previously reported Zbed3, Mater, Floped and Padi6, indicate that the SCMC is required for CPL formation and organelle distribution. Consistent with the SCMC's role in CPL formation, the SCMC forms before CPLs during oogenesis. Together, our results suggest that SCMC protein Nlrp4f is involved in CPL formation and organelle distribution in mouse oocytes.

Maternal gene Ooep may participate in homologous recombination-mediated DNA double-strand break repair in mouse oocytes

DNA damage in oocytes can cause infertility and birth defects. DNA double-strand breaks (DSBs) are highly deleterious and can substantially impair genome integrity. Homologous recombination (HR)-mediated DNA DSB repair plays dominant roles in safeguarding oocyte quantity and quality. However, little is known regarding the key players of the HR repair pathway in oocytes. Here, we identified oocyte-specific gene Ooep as a novel key component of the HR repair pathway in mouse oocytes. OOEP was required for efficient ataxia telangiectasia mutated (ATM) kinase activation and Rad51 recombinase (RAD51) focal accumulation at DNA DSBs. Ooep null oocytes were defective in DNA DSB repair and prone to apoptosis upon exogenous DNA damage insults. Moreover, Ooep null oocytes exhibited delayed meiotic maturation. Therefore, OOEP played roles in preserving oocyte quantity and quality by maintaining genome stability. Ooep expression decreased with the advance of maternal age, suggesting its involvement in maternal aging.

Maternal variants in NLRP and other maternal effect proteins are associated with multilocus imprinting disturbance in offspring

Background

Genomic imprinting results from the resistance of germline epigenetic marks to reprogramming in the early embryo for a small number of mammalian genes. Genetic, epigenetic or environmental insults that prevent imprints from evading reprogramming may result in imprinting disorders, which impact growth, development, behaviour and metabolism. We aimed to identify genetic defects causing imprinting disorders by whole-exome sequencing in families with one or more members affected by multilocus imprinting disturbance.

Methods

Whole-exome sequencing was performed in 38 pedigrees where probands had multilocus imprinting disturbance, in five of whom maternal variants in NLRP5 have previously been found.

Results

We now report 15 further pedigrees in which offspring had disturbance of imprinting, while their mothers had rare, predicted-deleterious variants in maternal effect genes, including NLRP2, NLRP7 and PADI6. As well as clinical features of well-recognised imprinting disorders, some offspring had additional features including developmental delay, behavioural problems and discordant monozygotic twinning, while some mothers had reproductive problems including pregnancy loss.

Conclusion

The identification of 20 putative maternal effect variants in 38 families affected by multilocus imprinting disorders adds to the evidence that maternal genetic factors affect oocyte fitness and thus offspring development. Testing for maternal-effect genetic variants should be considered in families affected by atypical imprinting disorders.

Protein profile of mouse ovarian follicles grown in vitro

STUDY QUESTION

Could the follicle proteome be mapped by identifying specific proteins that are common or differ between three developmental stages from the secondary follicle (SF) to the antrum-like stage?

SUMMARY ANSWER

From a total of 1401 proteins identified in the follicles, 609 were common to the three developmental stages investigated and 444 were found uniquely at one of the stages.

WHAT IS KNOWN ALREADY

The importance of the follicle as a functional structure has been recognized; however, up-to-date the proteome of the whole follicle has not been described. A few studies using proteomics have previously reported on either isolated fully-grown oocytes before or after meiosis resumption or cumulus cells.

STUDY DESIGN, SIZE, DURATION

The experimental design included a validated mice model for isolation and individual culture of SFs. The system was chosen as it allows continuous evaluation of follicle growth and selection of follicles for analysis at pre-determined developmental stages: SF, complete Slavjanski membrane rupture (SMR) and antrum-like cavity (AF). The experiments were repeated 13 times independently to acquire the material that was analyzed by proteomics.

PARTICIPANTS/MATERIALS, SETTING, METHODS

SFs (n = 2166) were isolated from B6CBA/F1 female mice (n = 42), 12 days old, from 15 l. About half of the follicles isolated as SF were analyzed as such (n = 1143) and pooled to obtain 139 μg of extracted protein. Both SMR (n = 359) and AF (n = 124) were obtained after individual culture of 1023 follicles in a microdrop system under oil, selected for analysis and pooled, to obtain 339 μg and 170 μg of protein, respectively. The follicle proteome was analyzed combining isoelectric focusing (IEF) fractionation with 1D and 2D LC-MS/MS analysis to enhance protein identification. The three protein lists were submitted to the 'Compare gene list' tool in the PANTHER website to gain insights on the Gene Ontology Biological processes present and to Ingenuity Pathway Analysis to highlight protein networks. A label-free quantification was performed with 1D LC-MS/MS analyses to emphasize proteins with different expression profiles between the three follicular stages. Supplementary western blot analysis (using new biological replicates) was performed to confirm the expression variations of three proteins during follicle development in vitro.

MAIN RESULTS AND THE ROLE OF CHANCE

It was found that 609 out of 1401 identified proteins were common to the three follicle developmental stages investigated. Some proteins were identified uniquely at one stage: 71 of the 775 identified proteins in SF, 181 of 1092 in SMR and 192 of 1100 in AF. Additional qualitative and quantitative analysis highlighted 44 biological processes over-represented in our samples compared to the Mus musculus gene database. In particular, it was possible to identify proteins implicated in the cell cycle, calcium ion binding and glycolysis, with specific expressions and abundance, throughout in vitro follicle development.

LARGE SCALE DATA

Data are available via ProteomeXchange with identifier PXD006227.

LIMITATIONS, REASONS FOR CAUTION

The proteome analyses described in this study were performed after in vitro development. Despite fractionation of the samples before LC-MS/MS, proteomic approaches are not exhaustive, thus proteins that are not identified in a group are not necessarily absent from that group, although they are likely to be less abundant.

WIDER IMPLICATIONS OF THE FINDINGS

This study allowed a general view of proteins implicated in follicle development in vitro and it represents the most complete catalog of the whole follicle proteome available so far. Not only were well known proteins of the oocyte identified but also proteins that are probably expressed only in granulosa cells.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Portuguese Foundation for Science and Technology, FCT (PhD fellowship SFRH/BD/65299/2009 to A.A.), the Swedish Childhood Cancer Foundation (PR 2014-0144 to K.A.R-.W.) and Stockholm County Council to K.A.R-.W. The authors of the study have no conflict of interest to report.

Mouse embryonic stem cells have increased capacity for replication fork restart driven by the specific Filia-Floped protein complex

Pluripotent stem cells (PSCs) harbor constitutive DNA replication stress during their rapid proliferation and the consequent genome instability hampers their applications in regenerative medicine. It is therefore important to understand the regulatory mechanisms of replication stress response in PSCs. Here, we report that mouse embryonic stem cells (ESCs) are superior to differentiated cells in resolving replication stress. Specifically, ESCs utilize a unique Filia-Floped protein complex-dependent mechanism to efficiently promote the restart of stalled replication forks, therefore maintaining genomic stability. The ESC-specific Filia-Floped complex resides on replication forks under normal conditions. Replication stress stimulates their recruitment to stalling forks and the serine 151 residue of Filia is phosphorylated in an ATR-dependent manner. This modification enables the Filia-Floped complex to act as a functional scaffold, which then promotes the stalling fork restart through a dual mechanism: both enhancing recruitment of the replication fork restart protein, Blm, and stimulating ATR kinase activation. In the Blm pathway, the scaffolds recruit the E3 ubiquitin ligase, Trim25, to the stalled replication forks, and in turn Trim25 tethers and concentrates Blm at stalled replication forks through ubiquitination. In differentiated cells, the recruitment of the Trim25-Blm complex to replication forks and the activation of ATR signaling are much less robust due to lack of the ESC-specific Filia-Floped scaffold. Thus, our study reveals that ESCs utilize an additional and unique regulatory layer to efficiently promote the stalled fork restart and maintain genomic stability.

The Role of Maternal-Effect Genes in Mammalian Development: Are Mammalian Embryos Really an Exception?

The essential contribution of multiple maternal factors to early mammalian development is rapidly altering the view that mammals have a unique pattern of development compared to other species. Currently, over 60 maternal-effect mutations have been described in mammalian systems, including critical determinants of pluripotency. This data, combined with the evidence for lineage bias and differential gene expression in early blastomeres, strongly suggests that mammalian development is to some extent mosaic from the four-cell stage onward.

NLRPs, the subcortical maternal complex and genomic imprinting

Before activation of the embryonic genome, the oocyte provides many of the RNAs and proteins required for the epigenetic reprogramming and the transition to a totipotent state. Targeted disruption of a subset of oocyte-derived transcripts in mice results in early embryonic lethality and cleavage-stage embryonic arrest as highlighted by the members of the subcortical maternal complex (SCMC). Maternal-effect recessive mutations of NLRP7, KHDC3L and NLRP5 in humans are associated with variable reproductive outcomes, biparental hydatidiform moles (BiHM) and widespread multi-locus imprinting disturbances. The precise mechanism of action of these genes is unknown, but the maternal-effect phenomenon suggests a function during early pre-implantation development, while biochemical and genetic studies implement them as SCMC members or interacting partners. In this review article, we discuss the role of the NLRP family members and the SCMC proteins in the establishment of genomic imprints and post-zygotic methylation maintenance, the recent advances made in the understanding of the biology involved in BiHM formation and the wider roles of the SCMC in mammalian reproduction.

Maternal control of early embryogenesis in mammals

Oocyte quality is a critical factor limiting the efficiency of assisted reproductive technologies (ART) and pregnancy success in farm animals and humans. ART success is diminished with increased maternal age, suggesting a close link between poor oocyte quality and ovarian aging. However, the regulation of oocyte quality remains poorly understood. Oocyte quality is functionally linked to ART success because the maternal-to-embryonic transition (MET) is dependent on stored maternal factors, which are accumulated in oocytes during oocyte development and growth. The MET consists of critical developmental processes, including maternal RNA depletion and embryonic genome activation. In recent years, key maternal proteins encoded by maternal-effect genes have been determined, primarily using genetically modified mouse models. These proteins are implicated in various aspects of early embryonic development, including maternal mRNA degradation, epigenetic reprogramming, signal transduction, protein translation and initiation of embryonic genome activation. Species differences exist in the number of cell divisions encompassing the MET and maternal-effect genes controlling this developmental window. Perturbations of maternal control, some of which are associated with ovarian aging, result in decreased oocyte quality.

Maternally expressed NLRP2 links the subcortical maternal complex (SCMC) to fertility, embryogenesis and epigenetic reprogramming

Mammalian parental genomes contribute differently to early embryonic development. Before activation of the zygotic genome, the maternal genome provides all transcripts and proteins required for the transition from a highly specialized oocyte to a pluripotent embryo. Depletion of these maternally-encoded transcripts frequently results in failure of preimplantation embryonic development, but their functions in this process are incompletely understood. We found that female mice lacking NLRP2 are subfertile because of early embryonic loss and the production of fewer offspring that have a wide array of developmental phenotypes and abnormal DNA methylation at imprinted loci. By demonstrating that NLRP2 is a member of the subcortical maternal complex (SCMC), an essential cytoplasmic complex in oocytes and preimplantation embryos with poorly understood function, we identified imprinted postzygotic DNA methylation maintenance, likely by directing subcellular localization of proteins involved in this process, such as DNMT1, as a new crucial role of the SCMC for mammalian reproduction.

Genetic mosaics and time-lapse imaging identify functions of histone H3.3 residues in mouse oocytes and embryos

During development from oocyte to embryo, genetic programs in mouse germ cells are reshaped by chromatin remodeling to orchestrate the onset of development. Epigenetic modifications of specific amino acid residues of core histones and their isoforms can dramatically alter activation and suppression of gene expression. H3.3 is a histone H3 variant that plays essential roles in mouse oocytes and early embryos, but the functional role of individual amino acid residues has been unclear because of technical hurdles. Here, we describe two strategies that successfully investigated the functions of three individual H3.3 residues in oogenesis, cleavage-stage embryogenesis and early development. We first generated genetic mosaic ovaries and blastocysts with stochastic expression of wild-type or mutant H3.3 alleles and showed dominant negative effects of H3.3R26 and H3.3K27 in modulating oogenesis and partitioning cells to the inner cell mass of the early embryo. Time-lapse imaging assays also revealed the essential roles of H3.3K56 in efficient H2B incorporation and paternal pronuclei formation. Application of these strategies can be extended to investigate roles of additional H3.3 residues and has implications for use in other developmental systems.

Maternal expression of the JMJD2A/KDM4A histone demethylase is critical for pre-implantation development

Regulation of chromatin composition through post-translational modifications of histones contributes to transcriptional regulation and is essential for many cellular processes, including differentiation and development. JMJD2A/KDM4A is a lysine demethylase with specificity towards di- and tri-methylated lysine 9 and lysine 36 of histone H3 (H3K9me2/me3 and H3K36me2/me3). Here, we report that Kdm4a as a maternal factor plays a key role in embryo survival and is vital for female fertility. Kdm4a−/- female mice ovulate normally with comparable fertilization but poor implantation rates, and cannot support healthy transplanted embryos to term. This is due to a role for Kdm4a in uterine function, where its loss causes reduced expression of key genes involved in ion transport, nutrient supply and cytokine signalling, that impact embryo survival. In addition, a significant proportion of Kdm4a deficient oocytes displays a poor intrinsic ability to develop into blastocysts. These embryos cannot compete with healthy embryos for implantation in vivo, highlighting Kdm4a as a maternal effect gene. Thus, our study dissects an important dual role for maternal Kdm4a in determining faithful early embryonic development and the implantation process.

ECAT1 is essential for human oocyte maturation and pre-implantation development of the resulting embryos

ECAT1 is a subunit of the subcortical maternal complex that is required for cell cycle progression during pre-implantation embryonic development; however, its exact function remains to be elucidated. Here we investigated the expression of ECAT1 in human ovarian tissue, oocytes and pre-implantation embryos and assessed its function by using RNA interference (RNAi) in oocytes. ECAT1 mRNA was highly expressed in human oocytes and zygotes, as well as in two-cell, four-cell and eight-cell embryos, but declined significantly in morulae and blastocysts. ECAT1 was expressed in the cytoplasm of oocytes and pre-implantation embryos and was localized more specifically in the cortical region than in the inner cytoplasm. RNAi experiments demonstrated that down-regulation of ECAT1 expression not only impaired spindle assembly and reduced maturation and fertilization rates of human oocytes but also decreased the cleavage rate of the resulting zygotes. In conclusion, our study indicates that ECAT1 may play a role in meiotic progression by maintaining the accuracy of spindle assembly in human oocytes, thus promoting oocyte maturation and subsequent development of the embryo.

Mutations in PADI6 Cause Female Infertility Characterized by Early Embryonic Arrest

Early embryonic arrest is one of the major causes of female infertility. However, because of difficulties in phenotypic evaluation, genetic determinants of human early embryonic arrest are largely unknown. With the development of assisted reproductive technology, the phenotype of early human embryonic arrest can now be carefully evaluated. Here, we describe a consanguineous family with a recessive inheritance pattern of female infertility characterized by recurrent early embryonic arrest in cycles of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). We have identified a homozygous PADI6 nonsense mutation (c.1141C>T [p.Gln381(∗)]) that is responsible for the phenotype. Mutational analysis of PADI6 in a cohort of 36 individuals whose embryos displayed developmental arrest identified two affected individuals with compound-heterozygous mutations (c.2009_2010del [p.Glu670Glyfs(∗)48] and c.633T>A [p.His211Gln]; c.1618G>A [p.Gly540Arg] and c.970C>T [p.Gln324(∗)]). Immunostaining indicated a lack of PADI6 in affected individuals' oocytes. In addition, the amount of phosphorylated RNA polymerase II and expression levels of seven genes involved in zygotic genome activation were reduced in the affected individuals' embryos. This phenotype is consistent with Padi6 knockout mice. These findings deepen our understanding of the genetic basis of human early embryonic arrest, which has been a largely ignored Mendelian phenotype. Our findings lay the foundation for uncovering other genetic causes of infertility resulting from early embryonic arrest.

The subcortical maternal complex: multiple functions for one biological structure?

The subcortical maternal complex (SCMC) is a multiprotein complex uniquely expressed in mammalian oocytes and early embryos, essential for zygote progression beyond the first embryonic cell divisions. Similiar to other factors encoded by maternal effect genes, the physiological role of SCMC remains unclear, although recent evidence has provided important molecular insights into different possible functions. Its potential involvement in human fertility is attracting increasing attention; however, the complete story is far from being told. The present mini review provides an overview of recent findings related to the SCMC and discusses its potential physiological role/s with the aim of inspiring new directions for future research.

Characterization and quantification of proteins secreted by single human embryos prior to implantation

The use of in vitro fertilization (IVF) has revolutionized the treatment of infertility and is now responsible for 1–5% of all births in industrialized countries. During IVF, it is typical for patients to generate multiple embryos. However, only a small proportion of them possess the genetic and metabolic requirements needed in order to produce a healthy pregnancy. The identification of the embryo with the greatest developmental capacity represents a major challenge for fertility clinics. Current methods for the assessment of embryo competence are proven inefficient, and the inadvertent transfer of non-viable embryos is the principal reason why most IVF treatments (approximately two-thirds) end in failure. In this study, we investigate how the application of proteomic measurements could improve success rates in clinical embryology. We describe a procedure that allows the identification and quantification of proteins of embryonic origin, present in attomole concentrations in the blastocoel, the enclosed fluid-filled cavity that forms within 5-day-old human embryos. By using targeted proteomics, we demonstrate the feasibility of quantifying multiple proteins in samples derived from single blastocoels and that such measurements correlate with aspects of embryo viability, such as chromosomal (ploidy) status. This study illustrates the potential of high-sensitivity proteomics to measure clinically relevant biomarkers in minute samples and, more specifically, suggests that key aspects of embryo competence could be measured using a proteomic-based strategy, with negligible risk of harm to the living embryo. Our work paves the way for the development of “next-generation” embryo competence assessment strategies, based on functional proteomics.

Expressional and Bioinformatic Analysis of Bovine Filia/Ecat1/Khdc3l Gene: A Comparison with Ovine Species

Maternal effect genes have highly impressive effects on pre-implantation development. Filia/Ecat1/Khdc3l is a maternal effect gene found in mouse oocytes and embryos, loss of which causes a 50% decrease in fertility. In the present study, we investigated Filia mRNA expression in bovine oviduct, 30- to 40-day fetus, liver, heart, lung, and oocytes (as a positive control), by RT-PCR and detected it only in oocytes. A 443 bp fragment was amplified only in oocytes and was sequenced as a part of bovine predicted Filia mRNA. We analyzed bovine and ovine Filia N-terminal peptide sequence in PHYRE2, and a KH domain was predicted. Protein alignment using ClustalW indicated a highly identical N-terminal extention between the 2 species. Immunohistochemical analysis using anti-bovine Filia antibody showed the expression of Filia protein in the zone surrounding the nuclear membrane, and in the subcortex of ovine oocytes of primary and antral follicles. However, in the bovine, Filia has been found through the oocyte cytoplasm of antral follicles, and here it is further confirmed in the primary follicles. Our data suggests a difference in Filia expression pattern between cow and sheep, although the sequence is highly conserved.

Cloning of Porcine Pituitary Tumor Transforming Gene 1 and Its Expression in Porcine Oocytes and Embryos

The maternal-to-embryonic transition (MET) is a complex process that occurs during early mammalian embryogenesis and is characterized by activation of the zygotic genome, initiation of embryonic transcription, and replacement of maternal mRNA with embryonic mRNA. The objective of this study was to reveal the temporal expression and localization patterns of PTTG1 during early porcine embryonic development and to establish a relationship between PTTG1 and the MET. To achieve this goal, reverse transcription-polymerase chain reaction (RT-PCR) was performed to clone porcine PTTG1. Subsequently, germinal vesicle (GV)- and metaphase II (MII)-stage oocytes, zygotes, 2-, 4-, and 8-cell-stage embryos, morulas, and blastocysts were produced in vitro and their gene expression was analyzed. The results revealed that the coding sequence of porcine PTTG1 is 609-bp in length and that it encodes a 202-aa polypeptide. Using qRT-PCR, PTTG1 mRNA expression was observed to be maintained at high levels in GV- and MII-stage oocytes. The transcript levels in oocytes were also significantly higher than those in embryos from the zygote to blastocyst stages. Immunohistochemical analyses revealed that porcine PTTG1 was primarily localized to the cytoplasm and partially localized to the nucleus. Furthermore, the PTTG1 protein levels in MII-stage oocytes and zygotes were significantly higher than those in embryos from the 2-cell to blastocyst stage. After fertilization, the level of this protein began to decrease gradually until the blastocyst stage. The results of our study suggest that porcine PTTG1 is a new candidate maternal effect gene (MEG) that may participate in the processes of oocyte maturation and zygotic genome activation during porcine embryogenesis.

Decrease in expression of maternal effect gene Mater is associated with maternal ageing in mice

STUDY HYPOTHESIS

What factors in mouse oocytes are involved in the ageing-related decline in oocyte quality?

STUDY FINDING

The maternal effect gene Mater is involved in ageing-related oocyte quality decline in mice.

WHAT IS KNOWN ALREADY

Premature loss of centromere cohesion is a hallmark of ageing-related oocyte quality decline; the maternal effect gene Mater (maternal antigen that embryos require, also known as Nlrp5) is required for preimplantation embryo development beyond the 2-cell stage, and mRNA expression of Mater decreases with maternal ageing.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Mater protein expression level in mature oocytes from 7 young (5-8 weeks old) to 7 old mice (41-68 weeks old) was compared by immunoblotting analysis. Wild-type and Mater-null mice were used to examine whether Mater is necessary for maintaining normal centromere cohesion by means of cytogenetic karyotyping, time-lapse confocal microscopy and immunofluorescence staining.

MAIN RESULTS AND THE ROLE OF CHANCE

Mater protein is decreased in mature oocytes from old versus young mice (P = 0.0022). Depletion of Mater from oocytes leads to a reduction in centromere cohesion, manifested by precocious sister chromatid separation, enlargement of sister centromere distance and misalignment of chromosomes in the metaphase plate during meiosis I and II.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted in mice. Whether or not the results are applicable to human remains further elucidation. In addition, we were unable to confirm if the strain of mice (C57BL/6XSv129) at the age of 41-68 weeks old has the 'cohesin-loss' phenotype.

WIDER IMPLICATIONS OF THE FINDINGS

Investigating Mater's functional mechanisms could provide fresh insights into understanding how the ageing-related oocyte quality decline occurs.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by the research grant from Chinese NSFC to P.Z. (31071274). We have no conflict of interests to declare.

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.

Oviductal estrogen receptor α signaling prevents protease-mediated embryo death

Development of uterine endometrial receptivity for implantation is orchestrated by cyclic steroid hormone-mediated signals. It is unknown if these signals are necessary for oviduct function in supporting fertilization and preimplantation development. Here we show that conditional knockout (cKO) mice lacking estrogen receptor α (ERα) in oviduct and uterine epithelial cells have impaired fertilization due to a dramatic reduction in sperm migration. In addition, all successfully fertilized eggs die before the 2-cell stage due to persistence of secreted innate immune mediators including proteases. Elevated protease activity in cKO oviducts causes premature degradation of the zona pellucida and embryo lysis, and wild-type embryos transferred into cKO oviducts fail to develop normally unless rescued by concomitant transfer of protease inhibitors. Thus, suppression of oviductal protease activity mediated by estrogen-epithelial ERα signaling is required for fertilization and preimplantation embryo development. These findings have implications for human infertility and post-coital contraception.

DOI:http://dx.doi.org/10.7554/eLife.10453.001

In female mammals, eggs made in the ovaries travel to the uterus via tubes called oviducts (or Fallopian tubes). If sperm fertilize these eggs on the way, they complete this journey as early embryos and then implant into the wall of the uterus. As sperm and then newly fertilized embryos travel down these tubes, they encounter fluid inside the oviduct, which is generated by the cells that line the tube.

The hormonal changes that occur with the menstrual cycle alter the complexity and cellular composition of the uterus. When an egg is fertilized, further changes in the levels of the hormones, estrogen and progesterone, ensure the uterus becomes receptive to the embryo. However, it remains unknown whether such hormone-mediated signals also regulate the oviduct to support fertilization and early embryo development.

To investigate this question, Winuthayanon et al. studied female mice that lack an important estrogen receptor in the cells that line their oviducts and uterus. These mice are infertile. This is partly because most sperm become stuck in the uterus and fail to reach the eggs in the oviduct in order to fertilize them. The oviduct also becomes a hostile environment for both eggs and embryos, as reflected in damaged eggs and the complete loss of all new embryos by two days after fertilization. These embryos die, not because their development fails, but because their outer membrane becomes damaged and breaks apart. Winuthayanon et al. showed that this is due to the persistence of enzymes that form part of the immune system inside the oviduct. These enzymes can degrade proteins and damage cell membranes.

The presence of this estrogen receptor on the inner lining of the oviduct thus appears to be crucially important for reproduction (these effects were not seen when it is removed from other cells of the oviduct). The loss of this receptor also reveals the vital role that estrogen plays in suppressing parts of the immune response to ensure the oviduct provides a supportive environment for fertilization and embryo development. These findings could also have future application in the development of new contraceptives and might also shed light on the causes of human infertility.

DOI:http://dx.doi.org/10.7554/eLife.10453.002

TLE6 mutation causes the earliest known human embryonic lethality

BACKGROUND

Embryonic lethality is a recognized phenotypic expression of individual gene mutations in model organisms. However, identifying embryonic lethal genes in humans is challenging, especially when the phenotype is manifested at the preimplantation stage.

RESULTS

In an ongoing effort to exploit the highly consanguineous nature of the Saudi population to catalog recessively acting embryonic lethal genes in humans, we have identified two families with a female-limited infertility phenotype. Using autozygosity mapping and whole exome sequencing, we map this phenotype to a single mutation in TLE6, a maternal effect gene that encodes a member of the subcortical maternal complex in mammalian oocytes. Consistent with the published phenotype of mouse Tle6 mutants, embryos from female patients who are homozygous for the TLE6 mutation fail to undergo early cleavage, with resulting sterility. The human mutation abrogates TLE6 phosphorylation, a step that is reported to be critical for the PKA-mediated progression of oocyte meiosis II. Furthermore, the TLE6 mutation impairs its binding to components of the subcortical maternal complex.

CONCLUSION

In this first report of a human defect in a member of the subcortical maternal subcritical maternal complex, we show that the TLE6 mutation is gender-specific and leads to the earliest known human embryonic lethality phenotype.

NLRP9B protein is dispensable for oocyte maturation and early embryonic development in the mouse

Nlrp9a, Nlrp9b and Nlrp9c are preferentially expressed in oocytes and early embryos in the mouse. Simultaneous genetic ablation of Nlrp9a and Nlrp9c does not affect early embryonic development, but the function of Nlrp9b in the process of oocyte maturation and embryonic development has not been elucidated. Here we show that both Nlrp9b mRNA and its protein are expressed in ovaries and the small intestine. Moreover, the NLRP9B protein was restricted to oocytes in the ovary and declined with oocyte aging. After ovulation and fertilization, NLRP9B protein was found in preimplantation embryos. Confocal microscopy demonstrated that it was mainly localized in the cytoplasm in the oocytes and blastomeres. Thus, this protein might play a role in oocyte maturation and early embryonic development. However, knockdown of Nlrp9b expression in GV-stage oocytes using RNA interference did not affect oocyte maturation or subsequent parthenogenetic development after Nlrp9b-deficient oocytes were activated. Furthermore, Nlrp9b knockdown zygotes could reach the blastocyst stage after being cultured for 3.5 days in vitro. These results provide the first evidence that the NLRP9B protein is dispensable for oocyte maturation and early embryonic development in the mouse.

Mammalian pre-implantation chromosomal instability: species comparison, evolutionary considerations, and pathological correlations

Pre-implantation embryo development in mammals begins at fertilization with the migration and fusion of the maternal and paternal pro-nuclei, followed by the degradation of inherited factors involved in germ cell specification and the activation of embryonic genes required for subsequent cell divisions, compaction, and blastulation. The majority of studies on early embryogenesis have been conducted in the mouse or non-mammalian species, often requiring extrapolation of the findings to human development. Given both conserved similarities and species-specific differences, however, even comparison between closely related mammalian species may be challenging as certain aspects, including susceptibility to chromosomal aberrations, varies considerably across mammals. Moreover, most human embryo studies are limited to patient samples obtained from in vitro fertilization (IVF) clinics and donated for research, which are generally of poorer quality and produced with germ cells that may be sub-optimal. Recent technical advances in genetic, epigenetic, chromosomal, and time-lapse imaging analyses of high quality whole human embryos have greatly improved our understanding of early human embryogenesis, particularly at the single embryo and cell level. This review summarizes the major characteristics of mammalian pre-implantation development from a chromosomal perspective, in addition to discussing the technological achievements that have recently been developed to obtain this data. We also discuss potential translation to clinical applications in reproductive medicine and conclude by examining the broader implications of these findings for the evolution of mammalian species and cancer pathology in somatic cells.

Filia Is an ESC-Specific Regulator of DNA Damage Response and Safeguards Genomic Stability

Pluripotent stem cells (PSCs) hold great promise in cell-based therapy, but the genomic instability seen in culture hampers their full application. A greater understanding of the factors that regulate genomic stability in PSCs could help address this issue. Here we describe the identification of Filia as a specific regulator of genomic stability in mouse embryonic stem cells (ESCs). Filia expression is induced by genotoxic stress. Filia promotes centrosome integrity and regulates the DNA damage response (DDR) through multiple pathways, including DDR signaling, cell-cycle checkpoints and damage repair, ESC differentiation, and apoptosis. Filia depletion causes ESC genomic instability, induces resistance to apoptosis, and promotes malignant transformation. As part of its role in DDR, Filia interacts with PARP1 and stimulates its enzymatic activity. Filia also constitutively resides on centrosomes and translocates to DNA damage sites and mitochondria, consistent with its multifaceted roles in regulating centrosome integrity, damage repair, and apoptosis.

Age-related increase in aneuploidy and alteration of gene expression in mouse first polar bodies

PURPOSE

To confirm that aneuploidy candidate genes are detectable in the first polar body (PB(1)) of MII oocytes and to investigate the age-dependent molecular changes in PB(1).

METHODS

Aged (12-to 15-mo-old) and young (2-mo-old) mice were administered pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotrophin (hCG). MII oocytes were obtained and the first PB was removed. mRNA from each PB and its sibling oocyte was reverse transcribed. Real-time PCR was performed to quantify the expression of six genes (BUB1, CDC20, Filia, MCAK, SGOL1, SMC1A) in single PB.

RESULTS

We first demonstrated that detection and quantification of transcripts associated with aneuploidy in single mouse oocyte and sibling PB(1) is possible and the relative abundance of mRNA transcripts in a single PB faithfully reflects the relative abundance of that transcript in its sibling oocyte. We further found that transcript levels were significantly lower in aged PBs compared with young PBs (P<0.05).

CONCLUSIONS

Our results suggest that the detection and analysis of polar body mRNA may provide insight in age-related aneuploidy in oocyte. This analysis is a novel concept to investigate the genesis of chromosome abnormality and could potentially assist in the characterization of mechanisms underlying key molecular origin of female meiotic aneuploidy, which would be of great scientific and clinical value.

Reprogramming the genome to totipotency in mouse embryos

Despite investigative interest, the artificial derivation of pluripotent stem cells remains inefficient and incomplete reprogramming hinders its potential as a reliable tool in regenerative medicine. By contrast, fusion of terminally differentiated gametes at fertilization activates efficient epigenetic reprogramming to ensure totipotency of early embryos. Understanding the epigenetic mechanisms required for the transition from the fertilized egg to the embryo can improve efforts to reprogram differentiated cells to pluripotent/totipotent cells for therapeutic use. We review recent discoveries that are providing insight into the molecular mechanisms required for epigenetic reprogramming to totipotency in vivo.

Identification of a human subcortical maternal complex

Maternal effect genes play essential roles in early embryonic development. However, the mechanisms by which maternal effect genes regulate mammalian early embryonic development remain largely unknown. Recently, we identified a subcortical maternal complex (SCMC) that is composed of at least four proteins encoded by Mater, Floped, Tle6 and Filia and is critical for mouse preimplantation development. The present study demonstrates that human SCMC homologous genes (NLRP5, OOEP, TLE6 and KHDC3L) are specifically expressed in the oocytes of human fetal ovaries. The proteins of this complex co-localize in the subcortex of human oocytes and early embryos. Furthermore, the SCMC proteins physically interact with each other when they are co-expressed in cell lines. These results indicate that human NLRP5, OOEP, TLE6 and KHDC3L function as a complex in the oocytes and early embryos of Homo sapiens. Considering the important roles of the SCMC in mouse early embryogenesis, the characterization of the human SCMC will provide a basis for investigating human early embryonic development and will have clinical implications in human female infertility or recurrent spontaneous abortion.

Expression of maternally derived KHDC3, NLRP5, OOEP and TLE6 is associated with oocyte developmental competence in the ovine species

BACKGROUND

The sub-cortical maternal complex (SCMC), located in the subcortex of mouse oocytes and preimplantation embryos, is composed of at least four proteins encoded by maternal effect genes: OOEP, NLRP5/MATER, TLE6 and KHDC3/FILIA. The SCMC assembles during oocyte growth and was seen to be essential for murine zygote progression beyond the first embryonic cell divisions; although roles in chromatin reprogramming and embryonic genome activation were hypothesized, the full range of functions of the complex in preimplantation development remains largely unknown.

RESULTS

Here we report the expression of the SCMC genes in ovine oocytes and pre-implantation embryos, describing for the first time its expression in a large mammalian species. We report sheep-specific patterns of expression and a relationship with the oocyte developmental potential in terms of delayed degradation of maternal SCMC transcripts in pre-implantation embryos derived from developmentally incompetent oocytes. In addition, by determining OOEP full length cDNA by Rapid Amplification of cDNA Ends (RACE) we identified two different transcript variants (OOEP1 and OOEP2), both expressed in oocytes and early embryos, but with different somatic tissue distributions. In silico translation showed that 140 aminoacid peptide OOEP1 shares an identity with orthologous proteins ranging from 95% with the bovine to 45% with mouse. Conversely, OOEP2 contains a premature termination codon, thus representing an alternative noncoding transcript and supporting the existence of aberrant splicing during ovine oogenesis.

CONCLUSIONS

These findings confirm the existence of the SCMC in sheep and its key role for the oocyte developmental potential, deepening our understanding on the molecular differences underlying cytoplasmic vs nuclear maturation of the oocytes. Describing differences and overlaps in transcriptome composition between model organisms advance our comprehension of the diversity/uniformity between mammalian species during early embryonic development and provide information on genes that play important regulatory roles in fertility in nonmurine models, including the human.

Expression and localization of Nlrp4g in mouse preimplantation embryo

The Nlrp gene family contains 20 members and plays a pivotal role in the innate immune and reproductive systems in the mouse. During evolution, seven Nlrp4 gene copies (named from Nlrp4a to Nlrp4g). Nlrp4a-Nlrp4g have arisen that display specific or preferential ovarian expression patterns. However, the expression pattern and localization of Nlrp4g in mouse preimplantation embryo development are unknown. Here we report that Nlrp4g was highly expressed in mature oocytes and zygotes, then downregulated and not detected after the 2-cell embryo stage. NLRP4G protein remained present through the blastocyst stage and was mainly localized in the cytoplasm. Furthermore, overexpression of Nlrp4g in zygotes did not affect normal development in terms of the rate of blastocyst formation. These results provide the first evidence that NLRP4G is a maternal factor that may play essential role during zygotic genome activation in the mouse.

Expression of bovine Ecat1 gene in immature and in vitro matured oocytes as well as during early embryonic development

Ecat1 is a maternal effect gene that is exclusively expressed in oocytes and embryonic stem cells, and has an important role in pre-implantation development. This study was designed to investigate the expression of bovine Ecat1 gene in immature and in vitro matured oocytes as well as during early embryonic development, and also Ecat1 protein localization. Samples were obtained from slaughtered animals. RNA extractions were carried out from ovary, immature and in vitro matured oocytes and also different stages of embryonic development (2-, 4-, 8- to 16-cell stages and blastocysts). RT-PCR analysis revealed the expression of Ecat1 in ovary, oocytes and embryos. Analysis in FGENESH online tool predicted three exons and one transcription start site (TSS) in Ecat1 gene, and the 3' RACE-PCR result showed that just one splice variant was amplified. By quantitative real-time PCR technique, we showed that Ecat1 transcript increased at 8- to 16-cell-stage embryos and decreased in blastocyst stage (p < 0.05). Immunofluorescence analysis showed cytoplasmic localization of Ecat1 protein in bovine oocytes. Results demonstrated bovine Ecat1 expression at protein level and also indicated that Ecat1 has a significant higher embryonic expression at 8- to 16-cell stage. This embryonic expression is probably required for further developmental stages.

NLRP7 and KHDC3L, the two maternal-effect proteins responsible for recurrent hydatidiform moles, co-localize to the oocyte cytoskeleton

STUDY QUESTION

What is the subcellular localization in human oocytes and preimplantation embryos, of the two maternal-effect proteins, NLRP7 and KHDC3L, responsible for recurrent hydatidiform moles (RHMs)?

SUMMARY ANSWER

NLRP7 and KHDC3L localize to the oocyte cytoskeleton and are polar and absent from the cell-to-cell contact region in early preimplantation embryos.

WHAT IS KNOWN ALREADY

NLRP7 and KHDC3L expression has been described at the RNA level in some stages of human oocytes and preimplantation embryos and at the protein level by immunohistochemistry in human and bovine ovaries. NLRP7 and KHDC3L co-localize to the microtubule organizing center and/or the Golgi apparatus in human hematopoietic cells.

STUDY DESIGN, SIZE, DURATION

A total of 164 spare human oocytes and embryos from patients undergoing in vitro fertilization were used.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oocytes and early cleavage-stage embryos were fixed, immunostained with NLRP7 and/or KHDC3L antibodies, and analyzed using high-resolution confocal immunofluorescence and electron microscopies.

MAIN RESULTS AND THE ROLE OF CHANCE

NLRP7 and KHDC3L localize to the cytoskeleton and are predominant at the cortical region in growing oocytes. After the first cellular division, these two maternal-effect proteins become asymmetrically confined to the outer cortical region and excluded from the cell-to-cell contact region until the blastocyst stage where NLRP7 and KHDC3L homogeneously redistribute to the cytoplasm and the nucleus, respectively.

LIMITATIONS, REASONS FOR CAUTION

We could not analyze fresh human oocytes and embryos. The analyzed materials were donated by patients undergoing assisted reproductive technologies and released for research 1-3 days after their collection and the transfer of embryos to the patients.

WIDER IMPLICATIONS OF THE FINDINGS

Our study is the first comprehensive and high-resolution localization of the only two known maternal-effect proteins, NLRP7 and KHDC3L, in human oocytes and preimplantation embryos. Our data contribute to a better understanding of the roles of these two proteins in the integrity of the oocytes, post-zygotic divisions, and cell-lineage differentiation.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the Canadian Institute of Health Research (86546 to R.S.); E.A. was supported by fellowships from the Research Institute of the McGill University Health Centre and a CREATE award from the Réseau Québécois en Reproduction. All authors declare no conflict of interest.

NOD-like receptors interfacing the immune and reproductive systems

Nucleotide-binding oligomerization domain receptors (NOD-like receptors, NLRs) are intracellular proteins that are chiefly known for their critical functions in inflammatory responses and host defense against microbial pathogens. Several NLRs have been demonstrated to assemble inflammasomes or to engage transcriptional signaling cascades that result in the production of pro-inflammatory cytokines and bactericidal factors. In recent years, NLRs have also emerged as key regulators of early mammalian embryogenesis and reproduction. A subset of phylogenetically related NLRs represents a new class of maternal effect genes that are highly expressed in maturing oocytes and pre-implantation embryos. Mutations in several of these NLRs have been linked to hereditary reproductive defects and imprinting diseases. In this review, we discuss the expression profiles, the emerging functions and molecular mode of action of these NLRs with newly recognized roles at the interfaces of the immune and reproductive systems. In addition, we provide an overview of coding mutations in NLRs that have been associated with human reproductive diseases, and outline crucial outstanding questions in this emerging research field.

The subcortical maternal complex controls symmetric division of mouse zygotes by regulating F-actin dynamics

Maternal effect genes play critical roles in early embryogenesis of model organisms where they have been intensively investigated. However, their molecular function in mammals remains largely unknown. Recently, we identified a subcortical maternal complex (SCMC) that contains four proteins encoded by maternal effect genes (Mater, Filia, Floped and Tle6). Here we report that TLE6, similar to FLOPED and MATER, stabilizes the SCMC and is necessary for cleavage beyond the two-cell stage of development. We document that the SCMC is required for formation of the cytoplasmic F-actin meshwork that controls the central position of the spindle and ensures symmetric division of mouse zygotes. We further demonstrate that the SCMC controls formation of the actin cytoskeleton specifically via Cofilin, a key regulator of F-actin assembly. Our results provide molecular insight into the physiological function of TLE6, its interaction with the SCMC and their roles in the symmetric division of the zygote in early mouse development.

Embryotropic actions of follistatin: paracrine and autocrine mediators of oocyte competence and embryo developmental progression

Despite several decades since the birth of the first test tube baby and the first calf derived from an in vitro-fertilised embryo, the efficiency of assisted reproductive technologies remains less than ideal. Poor oocyte competence is a major factor limiting the efficiency of in vitro embryo production. Developmental competence obtained during oocyte growth and maturation establishes the foundation for successful fertilisation and preimplantation embryonic development. Regulation of molecular and cellular events during fertilisation and embryo development is mediated, in part, by oocyte-derived factors acquired during oocyte growth and maturation and programmed by factors of follicular somatic cell origin. The available evidence supports an important intrinsic role for oocyte-derived follistatin and JY-1 proteins in mediating embryo developmental progression after fertilisation, and suggests that the paracrine and autocrine actions of oocyte-derived growth differentiation factor 9, bone morphogenetic protein 15 and follicular somatic cell-derived members of the fibroblast growth factor family impact oocyte competence and subsequent embryo developmental progression after fertilisation. An increased understanding of the molecular mechanisms mediating oocyte competence and stage-specific developmental events during early embryogenesis is crucial for further improvements in assisted reproductive technologies.

Evidence supporting a functional requirement of SMAD4 for bovine preimplantation embryonic development: a potential link to embryotrophic actions of follistatin

Transforming growth factor beta (TGFbeta) superfamily signaling controls various aspects of female fertility. However, the functional roles of the TGFbeta-superfamily cognate signal transduction pathway components (e.g., SMAD2/3, SMAD4, SMAD1/5/8) in early embryonic development are not completely understood. We have previously demonstrated pronounced embryotrophic actions of the TGFbeta superfamily member-binding protein, follistatin, on oocyte competence in cattle. Given that SMAD4 is a common SMAD required for both SMAD2/3- and SMAD1/5/8-signaling pathways, the objectives of the present studies were to determine the temporal expression and functional role of SMAD4 in bovine early embryogenesis and whether embryotrophic actions of follistatin are SMAD4 dependent. SMAD4 mRNA is increased in bovine oocytes during meiotic maturation, is maximal in 2-cell stage embryos, remains elevated through the 8-cell stage, and is decreased and remains low through the blastocyst stage. Ablation of SMAD4 via small interfering RNA microinjection of zygotes reduced proportions of embryos cleaving early and development to the 8- to 16-cell and blastocyst stages. Stimulatory effects of follistatin on early cleavage, but not on development to 8- to 16-cell and blastocyst stages, were observed in SMAD4-depleted embryos. Therefore, results suggest SMAD4 is obligatory for early embryonic development in cattle, and embryotrophic actions of follistatin on development to 8- to 16-cell and blastocyst stages are SMAD4 dependent.

Maternal effect genes: Findings and effects on mouse embryo development

Stored maternal factors in oocytes regulate oocyte differentiation into embryos during early embryonic development. Before zygotic gene activation (ZGA), these early embryos are mainly dependent on maternal factors for survival, such as macromolecules and subcellular organelles in oocytes. The genes encoding these essential maternal products are referred to as maternal effect genes (MEGs). MEGs accumulate maternal factors during oogenesis and enable ZGA, progression of early embryo development, and the initial establishment of embryonic cell lineages. Disruption of MEGs results in defective embryogenesis. Despite their important functions, only a few mammalian MEGs have been identified. In this review we summarize the roles of known MEGs in mouse fertility, with a particular emphasis on oocytes and early embryonic development. An increased knowledge of the working mechanism of MEGs could ultimately provide a means to regulate oocyte maturation and subsequent early embryonic development.

The effect of hormonal estrus induction on maternal effect and apoptosis-related genes expression in porcine cumulus-oocyte complexes

BACKGROUND

The effect of hormonal estrus induction on maternal effect (MATER - maternal antigen that embryo requires, ZAR-1 - zygote arrest 1, and BMP15 - bone morphogenetic protein 15) and apoptosis-related genes expression (BCL-2 and BAX) in porcine cumulus-oocyte complexes (COCs) and selected follicular parameters was investigated in this study.

METHODS

Gilts were divided into three groups: (I) with natural estrus; (II) stimulated with PMSG/hCG; and (III) with PMSG/hCG + PGF2alpha. Analysis of maternal effect and apoptosis-related transcripts expression in COCs, and progesterone synthesis pathway genes expression (P450scc and 3betaHSD) in granulosa cells was performed by qPCR. BMP15 protein expression in follicular fluid (FF) was analyzed by western blot. Oocyte nuclear maturation was assessed by aceto-orcein staining. Progesterone (P4) and estradiol (E2) concentrations in FF and serum were measured by ELISA. Data were analyzed with the one-way ANOVA and Bonferroni post-test or Kruskal-Wallis test and Dunns post-test.

RESULTS

The highest expression of MATER, ZAR-1, and BMP15 genes was found in COCs recovered from gilts treated with PMSG/hCG when compared to PMSG/hCG + PGF2alpha-stimulated or non-stimulated gilts. Hormonal treatment did not affect the BMP15 protein expression in FF, but increased the expression of genes participating in P4 synthesis in granulosa cells. The higher percentage of immature oocytes was found in PMSG/hCG-treated when compared to the non-stimulated gilts. The expression of BCL-2 and BAX mRNA, and BCL-2/BAX mRNA ratio was significantly higher in COCs derived from PMSG/hCG-treated when compared to PMSG/hCG + PGF2alpha-treated or non-stimulated subjects. The level of P4 in serum was similar in animals from all experimental groups, while its concentration in FF was greater in gilts subjected to PMSG/hCG treatment than in PMSG/hCG + PGF2alpha-stimulated and non-stimulated gilts. The concentration of E2 did not differ in the serum or FF between the control group and the hormonally stimulated groups.

CONCLUSIONS

Hormonal induction of estrus affected maternal effect gene transcripts levels in COCs and and oocyte nuclear maturation. The inclusion of PGF2alpha into the stimulation protocol enabled maintaining of physiological concentration of P4 in FF. Additionally, both hormonal treatments seem to be beneficial for apoptosis prevention through increasing BCL-2/BAX transcript ratio.

Totipotency: what it is and what it is not

There is surprising confusion surrounding the concept of biological totipotency, both within the scientific community and in society at large. Increasingly, ethical objections to scientific research have both practical and political implications. Ethical controversy surrounding an area of research can have a chilling effect on investors and industry, which in turn slows the development of novel medical therapies. In this context, clarifying precisely what is meant by "totipotency" and how it is experimentally determined will both avoid unnecessary controversy and potentially reduce inappropriate barriers to research. Here, the concept of totipotency is discussed, and the confusions surrounding this term in the scientific and nonscientific literature are considered. A new term, "plenipotent," is proposed to resolve this confusion. The requirement for specific, oocyte-derived cytoplasm as a component of totipotency is outlined. Finally, the implications of twinning for our understanding of totipotency are discussed.

Functional role of the bovine oocyte-specific protein JY-1 in meiotic maturation, cumulus expansion, and subsequent embryonic development

Oocyte-expressed genes regulate key aspects of ovarian follicular development and early embryogenesis. We previously demonstrated a requirement of the oocyte-specific protein JY-1 for bovine early embryogenesis. Given that JY-1 is present in oocytes throughout folliculogenesis, and oocyte-derived JY-1 mRNA is temporally regulated postfertilization, we hypothesized that JY-1 levels in oocytes impact nuclear maturation and subsequent early embryogenesis. A novel model system, whereby JY-1 small interfering RNA was microinjected into cumulus-enclosed germinal vesicle-stage oocytes and meiotic arrest maintained for 48 h prior to in vitro maturation (IVM), was validated and used to determine the effect of reduced oocyte JY-1 expression on nuclear maturation, cumulus expansion, and embryonic development after in vitro fertilization. Depletion of JY-1 protein during IVM effectively reduced cumulus expansion, percentage of oocytes progressing to metaphase II, proportion of embryos that cleaved early, total cleavage rates and development to 8- to 16-cell stage, and totally blocked development to the blastocyst stage relative to controls. Supplementation with JY-1 protein during oocyte culture rescued effects of JY-1 depletion on meiotic maturation, cumulus expansion, and early cleavage, but did not rescue development to 8- to 16-cell and blastocyst stages. However, effects of JY-1 depletion postfertilization on development to 8- to 16-cell and blastocyst stages were rescued by JY-1 supplementation during embryo culture. In conclusion, these results support an important functional role for oocyte-derived JY-1 protein during meiotic maturation in promoting progression to metaphase II, cumulus expansion, and subsequent embryonic development.

Nlrp4g is an oocyte-specific gene but is not required for oocyte maturation in the mouse

The Nlrp gene family contains 20 members and plays a pivotal role in the innate immune and reproductive systems in the mouse. The aim of the present study was to analyse the Nlrp4g gene expression pattern, protein distribution and function in mouse oocyte maturation. Quantitative real-time polymerase chain reaction and in situ hybridisation were performed on Nlrp4g mRNA. Western blotting, immunohistochemistry and immunofluorescence were used to assess expression at the protein level. Confocal and immunogold electron microscopy analyses and RNA interference approach were used to determine the location of the NLRP4G protein and inhibit Nlrp4g function specifically in mouse germinal vesicle oocytes, respectively. Nlrp4g transcripts and proteins (~85 kDa) are specifically expressed in mouse ovaries, restricted to the oocytes at various follicular stages and decline with oocyte aging. There is a marked decline in transcript levels in preimplantation embryos before zygotic genome activation, but the protein remains present through to the blastocyst stage. Confocal microscopy demonstrated that this protein is localised in the cytoplasm. Immunogold electron microscopy further confirmed that NLRP4G protein was present in the cytosol rather than in oocyte cytoplasmic organelles. Furthermore, knockdown of Nlrp4g in germinal vesicle oocytes did not affect oocyte maturation. These results provide the first evidence that Nlrp4g is an oocyte-specific gene but dispensable for oocyte maturation, suggesting that this gene may play roles in mouse oogenesis and/or preimplantation development.

Abnormality of maternal-to-embryonic transition contributes to MEHP-induced mouse 2-cell block

Mono (2-ethylhexyl) phthalate (MEHP), an environmental contaminant, is known to cause many serious diseases, especially in reproductive system. However, little is known about the effect of MEHP on preimplantation embryo development. In this study, we found that the development of mouse 2-cell embryo was blocked by 10(-3)  M MEHP. A significant increase in the level of reactive oxygen species (ROS) was observed in arrested 2-cell embryo following 10(-3)  M MEHP treatment for 24 h. However, antioxidants, catalase (CAT), and superoxide dismutase (SOD), reduced intracellular ROS and protected MEHP-exposed embryos from death but failed to return the arrested embryos. Further experiments demonstrated that the level of apoptosis was not altered in live arrested 2-cell embryo and increased in dead arrested 2-cell embryo after MEHP treatment, which implied that ROS and apoptosis were not related with 2-cell block. During analysis of the indicators of embryonic genome activation (EGA) initiation (Hsc70, MuERV-L, Hsp70.1, eIF-1A, and Zscan4) and maternal-effect genes (OCT4 and SOX2), we found that MEHP treatment could significantly decline Hsc70, MuERV-L mRNA level and SOX2 protein level, and markedly enhance Hsp70.1, eIF-1A, Zscan4 mRNA level, and OCT4 protein level at 2-cell to 4-cell stage. Supplementation of CAT and SOD did not reverse the expression tendency of EGA related genes. Collectively, this study demonstrates for the first time that MEHP-induced 2-cell block is mediated by the failure of EGA onset and maternal-effect genes, not oxidative stress and apoptosis.