Gene expression profiling of human oocytes developed and matured in vivo or in vitro

Energy metabolism disorders during in vitro maturation of bovine cumulus-oocyte complexes interfere with blastocyst quality and metabolism

Glucose and fatty acids (FA) metabolism disturbances during oocyte in vitro maturation (IVM) affect their metabolism and surrounding cumulus cells, but only inhibition of glucose metabolism decreases embryo culture efficiency. Therefore, the present experiment aimed to reveal if glucose or FA metabolism inhibition leads to the disruption of embryo developmental potential, and to characterize the metabolic landscape of embryos reaching the blastocyst stage. Inhibitors of glucose (IO + DHEA) or FA (ETOMOXIR) metabolism were applied during IVM, and the control group was matured under standard conditions. Blastocysts obtained from experimental and control groups were analyzed with regard to lipidome and metabolome (mass spectrometry), transcriptome (RNA-Seq) and fluorescence lipid droplets staining (BODIPY). We showed that inhibition of glucose and fatty acid metabolism leads to cellular stress response compromising the quality of preimplantation embryos. The inhibition of energy metabolism affects membrane fluidity as well as downregulates fatty acids biosynthesis and gene expression of trophectoderm cell line markers. Therefore, we conclude that oocyte maturation environment exerts a substantial effect on preimplantation development programming at cellular and molecular levels.

Differential transcript usage across mammalian oocytes at the germinal vesicle and metaphase II stages

Ongoing progress in mRNA-Sequencing technologies has significantly contributed to the refinement of assisted reproductive technologies. However, the prior investigations have predominantly concentrated on alterations in overall gene expression levels, thereby leaving a considerable gap in our understanding of the influence of transcript isoform expression on fundamental cellular mechanisms of oocytes. Given the efficacy of differential transcript usage (DTU) analysis to address such knowledge, we conducted comprehensive DTU analysis utilizing mRNA-Seq datasets of germinal vesicle (GV) and metaphase II (MII) oocytes across six mammalian species from the SRA database, including cow, donkey, horse, human, mouse, and pig. To further illuminate the roles of these genes, we also conducted a rigorous Gene Ontology (GO) term enrichment analysis. While the DTU analysis of each species exhibited several genes with alterations in their transcript isoform usage, referred to as DTU genes, this study focused on only ten cross-species DTU genes sharing among a minimum of five distinct species (FDR≤0.05). These cross-species DTU genes were as follows: ABCF1, CDC6, CFAP36, CNOT10, DNM3, IWS1, NBN, NDEL1, RAD50 and ZCCHC17. GO term enrichment analysis unveiled the alignment of these cross-species DTU gene functions with RNA and cell-cycle control mechanisms across diverse mammalian species, thereby suggesting their vital roles during oocyte maturation. Further exploration of the transcript isoforms of these genes hence bore the potential to uncover novel transcript isoform markers for future reproductive technologies in both human and animal contexts.

Transcriptomic integrity of human oocytes used in ARTs: technical and intrinsic factor effects

BACKGROUND

Millions of children have been born throughout the world thanks to ARTs, the harmlessness of which has not yet been fully demonstrated. For years, efforts to evaluate the specific effects of ART have focused on the embryo; however, it is the oocyte quality that mainly dictates first and foremost the developmental potential of the future embryo. Ovarian stimulation, cryopreservation, and IVM are sometimes necessary steps to obtain a mature oocyte, but they could alter the appropriate expression of the oocyte genome. Additionally, it is likely that female infertility, environmental factors, and lifestyle have a significant influence on oocyte transcriptomic quality, which may interfere with the outcome of an ART attempt.

OBJECTIVE AND RATIONALE

The objective of this review is to identify transcriptomic changes in the human oocyte caused by interventions specific to ART but also intrinsic factors such as age, reproductive health issues, and lifestyle. We also provide recommendations for future good practices to be conducted when attempting ART.

SEARCH METHODS

An in-depth literature search was performed on PubMed to identify studies assessing the human oocyte transcriptome following ART interventions, or in the context of maternal aging, suboptimal lifestyle, or reproductive health issues.

OUTCOMES

ART success is susceptible to external factors, maternal aging, lifestyle factors (smoking, BMI), and infertility due to endometriosis or polycystic ovary syndrome. Indeed, all of these are likely to increase oxidative stress and alter mitochondrial processes in the foreground. Concerning ART techniques themselves, there is evidence that different ovarian stimulation regimens shape the oocyte transcriptome. The perturbation of processes related to the mitochondrion, oxidative phosphorylation, and metabolism is observed with IVM. Cryopreservation might dysregulate genes belonging to transcriptional regulation, ubiquitination, cell cycle, and oocyte growth pathways. For other ART laboratory factors such as temperature, oxygen tension, air pollution, and light, the evidence remains scarce. Focusing on genes involved in chromatin-based processes such as DNA methylation, heterochromatin modulation, histone modification, and chromatin remodeling complexes, but also genomic imprinting, we observed systematic dysregulation of such genes either after ART intervention or lifestyle exposure, as well as due to internal factors such as maternal aging and reproductive diseases. Alteration in the expression of such epigenetic regulators may be a common mechanism linked to adverse oocyte environments, explaining global transcriptomic modifications.

WIDER IMPLICATIONS

Many IVF factors and additional external factors have the potential to impair oocyte transcriptomic integrity, which might not be innocuous for the developing embryo. Fortunately, it is likely that such dysregulations can be minimized by adapting ART protocols or reducing adverse exposure.

Maternal patterns of inheritance alter transcript expression in eggs

BACKGROUND

Modifications to early development can lead to evolutionary diversification. The early stages of development are under maternal control, as mothers produce eggs loaded with nutrients, proteins and mRNAs that direct early embryogenesis. Maternally provided mRNAs are the only expressed genes in initial stages of development and are tightly regulated. Differences in maternal mRNA provisioning could lead to phenotypic changes in embryogenesis and ultimately evolutionary changes in development. However, the extent that maternal mRNA expression in eggs can vary is unknown for most developmental models. Here, we use a species with dimorphic development- where females make eggs and larvae of different sizes and life-history modes-to investigate the extent of variation in maternal mRNA provisioning to the egg.

RESULTS

We find that there is significant variation in gene expression across eggs of different development modes, and that there are both qualitative and quantitative differences in mRNA expression. We separate parental effects from allelic effects, and find that both mechanisms contribute to mRNA expression differences. We also find that offspring of intraspecific crosses differentially provision their eggs based on the parental cross direction (a parental effect), which has not been previously demonstrated in reproductive traits like oogenesis.

CONCLUSION

We find that maternally controlled initiation of development is functionally distinct between eggs of different sizes and maternal genotypes. Both allele-specific effects and parent-of-origin effects contribute to gene expression differences in eggs. The latter indicates an intergenerational effect where a parent's genotype can affect gene expression in an egg made by the next generation.

Distinct patterns of gene expression during regeneration and asexual reproduction in the annelid Pristina leidyi

Regeneration, the ability to replace lost body parts, is a widespread phenomenon in the animal kingdom often connected to asexual reproduction or fission, since the only difference between the two appears to be the stimulus that triggers them. Both developmental processes have largely been characterized; however, the molecular toolkit and genetic mechanisms underlying these events remain poorly unexplored. Annelids, in particular the oligochaete Pristina leidyi, provide a good model system to investigate these processes as they show diverse ways to regenerate, and can reproduce asexually through fission under laboratory conditions. Here, we used a comparative transcriptomics approach based on RNA-sequencing and differential gene expression analyses to understand the molecular mechanisms involved in anterior regeneration and asexual reproduction. We found 291 genes upregulated during anterior regeneration, including several regeneration-related genes previously reported in other annelids such as frizzled, paics, and vdra. On the other hand, during asexual reproduction, 130 genes were found upregulated, and unexpectedly, many of them were related to germline development during sexual reproduction. We also found important differences between anterior regeneration and asexual reproduction, with the latter showing a gene expression profile more similar to that of control individuals. Nevertheless, we identified 35 genes that were upregulated in both conditions, many of them related to cell pluripotency, stem cells, and cell proliferation. Overall, our results shed light on the molecular mechanisms that control anterior regeneration and asexual reproduction in annelids and reveal similarities with other animals, suggesting that the genetic machinery controlling these processes is conserved across metazoans.

Detection of histamine receptors on mouse oocytes and their involvement in fertilization potential

Histamine widely involves in local immune responses, physiological function in the gut, and acting as a neurotransmitter in the brain. Scientist also found the importance of histamine in the reproductive systems. The present study aimed to determine the existence of histamine receptor subtypes; H1R, H2R, H3R, and H4R on mouse oocytes through immunofluorescence (IF) staining and reverse transcription- polymerase chain reaction (RT-PCR). These further confirmed by the involvement of histamine receptor antagonists in in vitro fertilization (IVF). In IF staining, mouse oocytes were incubated with primary antibody against histamine receptor, followed by incubation with fluorescence conjugated secondary antibody. Then RT-PCR analysis was carried out for the undetected receptors during IF for confirmation. The RT-PCR used RNA extracted from mice COCs and cumulus free oocytes. In IVF, sperm was cultured in a group of treated histamine receptor antagonists oocytes. This investigation revealed the existance of H1R, H2R, and H3R on mouse oocytes in IF and RT-PCR analyses. The treatment of IVF with histamine receptor antagonists (H1R: pyrilamine; H2R: cimetidine; H3R: thioperamide) led to a significant reduction quantity of 2-cell embryos (4.61 ± 2.44%; 5.83 ± 4.65%; 3.83 ± 1.82%, respectively) as compared with the control group (22.50 ± 6.44%). Therefore, according to the results of this study, the presence of H1R, H2R, and H3R on mouse oocytes possibly will suggest the involvement of histamine in fertilization.

Identifying genetic variants and pathways influencing daughter averages for twinning in North American Holstein cattle and evaluating the potential for genomic selection

Multiple birth in dairy cattle is a detrimental trait both economically for producers and for animal health. Genetics of twinning is complex and has led to several quantitative trait loci regions being associated with increased twinning. To identify variants associated with this trait, calving records from 2 time periods were used to estimate daughter averages for twinning for Holstein bulls. Multiple analyses were conducted and compared including GWAS, genomic prediction, and gene set enrichment analysis for pathway detection. Although pathway analysis did not yield many congruent pathways of interest between data sets, it did indicate two of interest. Both pathways have ties to the strong candidate region on BTA11 from the genome-wide association analysis across data sets. This region does not overlap with previously identified quantitative trait loci regions for twinning or ovulation rate in cattle. The strongest associated SNPs were upstream from 2 candidate genes LHCGR and FSHR, which are involved in folliculogenesis. Genomic prediction showed a moderate correlation accuracy (0.43) when predicting genomic breeding values for bulls with estimates from calving records from 2010 to 2016. Future analysis of the region on BTA11 and the relation of the candidate genes could improve this accuracy.

Role of bone morphogenetic protein signaling in bovine early embryonic development and stage specific embryotropic actions of follistatin†

Characterization of the molecular factors regulating early embryonic development and their functional mechanisms is critical for understanding the causes of early pregnancy loss in monotocous species (cattle, human). We previously characterized a stage specific functional role of follistatin, a TGF-beta superfamily binding protein, in promoting early embryonic development in cattle. The mechanism by which follistatin mediates this embryotropic effect is not precisely known as follistatin actions in cattle embryos are independent of its classically known activin inhibition activity. Apart from activin, follistatin is known to bind and modulate the activity of the bone morphogenetic proteins (BMPs), which signal through SMAD1/5 pathway and regulate several aspects of early embryogenesis in other mammalian species. Present study was designed to characterize the activity and functional requirement of BMP signaling during bovine early embryonic development and to investigate if follistatin involves BMP signaling for its stage specific embryotropic actions. Immunostaining and western blot analysis demonstrated that SMAD1/5 signaling is activated after embryonic genome activation in bovine embryos. However, days 1-3 follistatin treatment reduced the abundance of phosphorylated SMAD1/5 in cultured embryos. Inhibition of active SMAD1/5 signaling (8-16 cell to blastocyst) using pharmacological inhibitors and/or lentiviral-mediated inhibitory SMAD6 overexpression showed that SMAD1/5 signaling is required for blastocyst production, first cell lineage determination as well as mRNA and protein regulation of TE (CDX2) cell markers. SMAD1/5 signaling was also found to be essential for embryotropic actions of follistatin during days 4-7 but not days 1-3 of embryo development suggesting a role for follistatin in regulation of SMAD1/5 signaling in bovine embryos.

Relationship between chromatin configuration and in vitro maturation ability in guinea pig oocytes

Background

Germinal vesicle (GV) chromatin configurations of oocytes are proposed to be related to oocyte competence and may reflect the quality of oocyte. Currently, a limited number of published studies investigated the GV chromatin configurations of guinea pig oocytes.

Objective

In this study on the in vitro maturation (IVM) of guinea pig oocytes, we examined the changes in their GV chromatin configurations during meiotic progression.

Methods

Based on the degree of chromatin compaction, the GV chromatin configurations of guinea pig oocytes could be divided into three categories depending on whether the nucleolus‐like body (NLB) was surrounded or partly surrounded by compacted chromatin, namely the uncondensed (NSN), the intermediate type (SN‐1) and the compacted type (SN‐2).

Results

The percentage of cells displaying the SN‐2 configuration increased with the growth of guinea pig oocytes, suggesting that this configuration presents the potential for maturation in oocytes. Oocytes derived from larger follicle exhibited increased meiotic potential. Serum starvation affected the GV chromatin configurations of guinea pig oocytes.

Conclusions

Collectively, these results suggest that the SN‐2 type might be a more mature form of configuration in guinea pig oocyte, whose proportion was associated with the follicle size and susceptible to the environment (e.g. serum concentration).

Human oocyte meiotic maturation is associated with a specific profile of alternatively spliced transcript isoforms

The transition from a transcriptionally active state (GV) to a transcriptionally inactive state (mature MII oocytes) is required for the acquisition of oocyte developmental competence. We hypothesize that the expression of specific genes at the in vivo matured (MII) stage could be modulated by posttranscriptional mechanisms, particularly regulation of alternative splicing (AS). In this study, we examined the transcriptional activity of GV oocytes after ovarian stimulation followed by oocyte pick-up and the landscape of alternatively spliced isoforms in human MII oocytes. Individual oocytes were processed and analyzed for transcriptional activity (GV), gene expression (GV and MII), and AS signatures (GV and MII) on HTA 2.0 microarrays. Samples were grouped according to maturation stage, and then subgrouped according to women's age and antral follicular count (AFC); array results were validated by quantitative polymerase chain reaction. Differentially expressed genes between GV and MII oocytes clustered mainly in biological processes related to mitochondrial metabolism. Interestingly, 16 genes that were related to the regulation of transcription and mitochondrial translation showed differences in alternatively spliced isoform profiles despite not being differentially expressed between groups. Altogether, our results contribute to our understanding of the role of AS in oocyte developmental competence acquisition.

Maternal preconception PFOS exposure of Drosophila melanogaster alters reproductive capacity, development, morphology and nutrient regulation

Perfluorooctanesulfonic acid (PFOS) is a persistent synthetic surfactant widely detected in the environment. Developmental PFOS exposures are associated with low birth weight and chronic exposures increase risk for obesity and type 2 diabetes. As an obesogen, PFOS poses a major public health exposure risk and much remains to be understood about the critical windows of exposure and mechanisms impacted, especially during preconception. Here, we leverage evolutionarily conserved pathways and processes in the fruit fly Drosophila melanogaster (wild-type Canton-S and megalin-UAS RNAi transgenic fly lines) to investigate the window of maternal preconception exposure to PFOS on reproductive and developmental toxicity, and examine receptor (megalin)-mediated endocytosis of nutrients and PFOS into the oocyte as a potential mechanism. Preconception exposure to 2 ng PFOS/female resulted in an internal concentration of 0.081 ng/fly over two days post exposure, no mortality and reduced megalin transcription. The number of eggs laid 1-3 days post exposure was reduced and contained 0.018 ng PFOS/egg. Following heat shock, PFOS was significantly reduced in eggs from megalin-knockdown transgenic females. Cholesterol and triglycerides were increased in eggs laid immediately following PFOS exposure by non-heat shocked transgenic females whereas decreased cholesterol and increased protein levels were found in eggs laid by heat shocked transgenic females. Preconception exposure likewise increased cholesterol in early emerging wildtype F1 adults and also resulted in progeny with a substantial developmental delay, a reduction in adult weights, and altered transcription of Drosophila insulin-like peptide genes. These findings support an interaction between PFOS and megalin that interferes with normal nutrient transport during oocyte maturation and embryogenesis, which may be associated with later in life developmental delay and reduced weight.

Human pericentromeric tandemly repeated DNA is transcribed at the end of oocyte maturation and is associated with membraneless mitochondria-associated structures

Most of the human genome is non-coding. However, some of the non-coding part is transcriptionally active. In humans, the tandemly repeated (TR) pericentromeric non-coding DNA-human satellites 2 and 3 (HS2, HS3)-are transcribed in somatic cells. These transcripts are also found in pre- and post-implantation embryos. The aim of this study was to analyze HS2/HS3 transcription and cellular localization of transcripts in human maturating oocytes. The maternal HS2/HS3 TR transcripts transcribed from both strands were accumulated in the ooplasm in GV-MI oocytes as shown by DNA-RNA FISH (fluorescence in-situ hybridization). The transcripts' content was higher in GV oocytes than in somatic cumulus cells according to real-time PCR. Using bioinformatics analysis, we demonstrated the presence of polyadenylated HS2 and HS3 RNAs in datasets of GV and MII oocyte transcriptomes. The transcripts shared a high degree of homology with HS2, HS3 transcripts previously observed in cancer cells. The HS2/HS3 transcripts were revealed by a combination of FISH and immunocytochemical staining within membraneless RNP structures that contained DEAD-box helicases DDX5 and DDX4. The RNP structures were closely associated with mitochondria, and are therefore similar to membraneless bodies described previously only in oogonia. These membraneless structures may be a site for spatial sequestration of RNAs and proteins in both maturating oocytes and cancer cells.

Single-cell analysis of transcriptome and DNA methylome in human oocyte maturation

Oocyte maturation is a coordinated process that is tightly linked to reproductive potential. A better understanding of gene regulation during human oocyte maturation will not only answer an important question in biology, but also facilitate the development of in vitro maturation technology as a fertility treatment. We generated single-cell transcriptome and used our previously published single-cell methylome data from human oocytes at different maturation stages to investigate how genes are regulated during oocyte maturation, focusing on the potential regulatory role of non-CpG methylation. DNMT3B, a gene encoding a key non-CpG methylation enzyme, is one of the 1,077 genes upregulated in mature oocytes, which may be at least partially responsible for the increased non-CpG methylation as oocytes mature. Non-CpG differentially methylated regions (DMRs) between mature and immature oocytes have multiple binding motifs for transcription factors, some of which bind with DNMT3B and may be important regulators of oocyte maturation through non-CpG methylation. Over 98% of non-CpG DMRs locate in transposable elements, and these DMRs are correlated with expression changes of the nearby genes. Taken together, this data indicates that global non-CpG hypermethylation during oocyte maturation may play an active role in gene expression regulation, potentially through the interaction with transcription factors.

Features of DNA Repair in the Early Stages of Mammalian Embryonic Development

Cell repair machinery is responsible for protecting the genome from endogenous and exogenous effects that induce DNA damage. Mutations that occur in somatic cells lead to dysfunction in certain tissues or organs, while a violation of genomic integrity during the embryonic period often leads to death. A mammalian embryo’s ability to respond to damaged DNA and repair it, as well as its sensitivity to specific lesions, is still not well understood. In this review, we combine disparate data on repair processes in the early stages of preimplantation development in mammalian embryos.

The challenge of getting a high quality of RNA from oocyte for gene expression study

The extraction of intact RNA from oocyte is quite challenging and time-consuming. A standard protocol using commercial RNA extraction kit, yields a low quantity of RNA in oocytes. In the past, several attempts in getting RNA for gene expression study ended up with a few different modified methods. Extraction of high-quality RNA from oocyte is important before further downstream analyses such as reverse transcription-polymerase chain reaction, quantitative polymerase chain reaction, or northern blot analysis. In this review, the efficiency of RNA extraction methods from all species oocytes was compared between published articles and our research to gather all possible methods of RNA extraction. Two different methods of RNA extraction that were proposed from various experiments were reviewed to determine the best method of RNA extraction from the oocyte. Modified TRIzol method can be concluded as an efficient RNA extraction method especially for good RNA from oocytes. Meanwhile, comparing RNA extraction kits to extract the RNA from oocytes or pre-implantation embryos, the micro RNA extraction kit type is the best. Therefore, an appropriate RNA extraction method is important to obtain high quality of total RNA for gene expression profiling analysis.

MiRNA-155 regulates cumulus cells function, oocyte maturation, and blastocyst formation

Numerous oocytes are retrieved during in vitro fertilization from patients with polycystic ovary syndrome (PCOS). The poor quality of these oocytes leads to lower fertilization and decreases in cleavage and implantation. MiR-155 is one of the microRNA (miRNA) that is increased in serum and granulosa cells of PCOS patients. In this study, we investigate the effects of miR-155 expression and its target genes on oocyte maturation and embryo development. We used the calcium phosphate protocol to transfect vectors that contained miR-155 or miR-off 155 and alone eGFP into cumulus oophorus complex (COCs) of B6D2F1 female mice for in vitro maturation. Cumulus expansion, nuclear, and cytoplasmic maturation, as well as cleavage rates were determined in groups transfected and compared with the control groups. Quantitative real-time polymerase chain reaction was performed to analyze expression levels of miR-155 and the target genes in the cumulus cells, oocytes, and blastocysts. MiR-155 overexpression in COCs suppressed cumulus expansion, oocyte maturation, and inhibition of endogenous miR-155 by miR-off 155 improved cumulus expansion and oocyte maturation by downregulation and expression increase of the Smad2 and Bcl2 genes. On the other hand, overexpression and downregulation of miR-155 in the COCs led to increase and decrease in cleavage rates by changes in expressions of the Mecp2, Jarid2, and Notch1 genes, respectively (P < 0.05). These results suggested that miR-155 overexpression in granulosa cells of PCOS patients can negatively affect nuclear and cytoplasmic maturation, but this miRNA expression has a positive impact on embryo development.

Expression of genes involved in neurogenesis, and neuronal precursor cell proliferation and development: Novel pathways of human ovarian granulosa cell differentiation and transdifferentiation capability in vitro

The process of neural tissue formation is associated primarily with the course of neurogenesis during embryonic life. The source of neural-like cells is stem cells, which, under the influence of appropriate differentiating factors, may differentiate/transdifferentiate towards a neural-like lineage. The present study suggested that, under long-term in vitro culture conditions, human ovarian granulosa cells (GCs), obtained from granulosa-rich follicular fluid, acquired new properties and expressed genes characteristic of the ontological groups ‘neurogenesis’ (GO:0022008), ‘neuronal precursor cell proliferation’ (GO:0061351) and ‘nervous system development’ (GO:0007399), which are closely related to the formation of neurons. The present study collected GCs from 20 women referred for the procedure of in vitro fertilization. Cells were maintained in long-term in vitro culture for 30 days, and RNA was isolated after 1, 7, 15 and 30 days of culture. The expression profile of individual genes was determined using the Affymetrix microarray method. The 131 genes with the highest expression change in relation to day 1 of culture were then selected; the 10 most affected genes found to be primarily involved in nerve cell formation processes were chosen for consideration in this study: CLDN11, OXTR, DFNA5, ATP8B1, ITGA3, CD9, FRY, NANOS1, CRIM1 and NTN4. The results of the present study revealed that these genes may be considered potential markers of the uninduced differentiation potential of GCs. In addition, it was suggested that GCs may be used to develop a cell line showing neuronal characteristics after 30 days of cultivation. In addition, due to their potential, these cells could possibly be used in the treatment of neurodegenerative diseases, not only in the form of ‘cultured neurons’ but also as producers of factors involved in the regeneration of the nervous system.

Luteinizing Hormone Action in Human Oocyte Maturation and Quality: Signaling Pathways, Regulation, and Clinical Impact

The ovarian follicle luteinizing hormone (LH) signaling molecules that regulate oocyte meiotic maturation have recently been identified. The LH signal reduces preovulatory follicle cyclic nucleotide levels which releases oocytes from the first meiotic arrest. In the ovarian follicle, the LH signal reduces cyclic nucleotide levels via the CNP/NPR2 system, the EGF/EGF receptor network, and follicle/oocyte gap junctions. In the oocyte, reduced cyclic nucleotide levels activate the maturation promoting factor (MPF). The activated MPF induces chromosome segregation and completion of the first and second meiotic divisions. The purpose of this paper is to present an overview of the current understanding of human LH signaling regulation of oocyte meiotic maturation by identifying and integrating the human studies on this topic. We found 89 human studies in the literature that identified 24 LH follicle/oocyte signaling proteins. These studies show that human oocyte meiotic maturation is regulated by the same proteins that regulate animal oocyte meiotic maturation. We also found that these LH signaling pathway molecules regulate human oocyte quality and subsequent embryo quality. Remarkably, in vitro maturation (IVM) prematuration culture (PMC) protocols that manipulate the LH signaling pathway improve human oocyte quality of cultured human oocytes. This knowledge has improved clinical human IVM efficiency which may become a routine alternative ART for some infertile patients.

The phenotypic variations of multi-locus imprinting disturbances associated with maternal-effect variants of NLRP5 range from overt imprinting disorder to apparently healthy phenotype

BACKGROUND

A subset of individuals affected by imprinting disorders displays multi-locus imprinting disturbances (MLID). MLID has been associated with maternal-effect variants that alter the maintenance of methylation at germline-derived differentially methylated regions (gDMRs) in early embryogenesis. Pedigrees of individuals with MLID also include siblings with healthy phenotype. However, it is unknown if these healthy individuals have MLID themselves or if their methylation patterns differ from those associated with imprinting disorders, and in general, if MLID affects the clinical phenotype.

METHODS

We have investigated gDMR methylation by locus-specific and whole-genome analyses in a family with multiple pregnancy losses, a child with Beckwith-Wiedemann syndrome (BWS) and a further child with no clinical diagnosis of imprinting disorder or other pathologies.

RESULTS

We detected MLID with different methylation profiles in the BWS-affected and healthy siblings. Whole-exome sequencing demonstrated the presence of novel loss-of-function variants of NLRP5 in compound heterozygosity in the mother. The methylation profiles of the two siblings were compared with those of other cases with MLID and control groups by principal component analysis and unsupervised hierarchical clustering, but while their patterns were clearly separated from those of controls, we were unable to cluster those associated with specific clinical phenotypes among the MLID cases.

CONCLUSION

The identification of two novel maternal-effect variants of NLRP5 associated with poly-abortivity and MLID adds further evidence to the role of this gene in the maintenance of genomic imprinting in early embryos. Furthermore, our results demonstrate that within these pedigrees, MLID can also be present in the progeny with healthy phenotype, indicating that some sort of compensation occurs between altered imprinted loci in these individuals. The analysis of larger cohorts of patients with MLID is needed to formulate more accurate epigenotype-phenotype correlations.

Multiplexed detection and the establishment of a novel high-throughput method for human germ cell quality screening based on aggregation-induced emission

We report a rapid, sensitive, and high-throughput method for quality control of human sperm cells and oocytes staining based on the aggregation-induced emission feature of the tetraphenylethylene-based luminogen (TPE-Ph-In), which is mitochondria-specific. Germ cells are evaluated to assess fertility and to facilitate assisted reproduction. In regular clinical practice, sperm quality is determined on the basis of visual examination and mathematical models of the sperm cell number, motility, and morphology. The maturation of the oocyte is crucial for the developmental competence of the resulting embryo. Human in vitro fertilization (IVF) have indicated that delaying insemination improves fertilization rates, presumably by allowing the completion of cytoplasmic maturation for those oocytes that have not completely matured at the time. Therefore, a more reliable method to determine germ cell quality is needed. The mitochondrial membrane potential (MMP) of spermatozoa reflects the function and status of those cells. In oocytes, the distribution of mitochondria indicates the readiness of the cell for fertilization. Aggregation-induced emission luminogens (AIEgens) have good biocompatibility and photostability and produce low levels of background signal. There are about 100,000 mitochondria per fully-grown human oocyte. Mitochondria in mammalian oocytes are spherical with little cristae, supplying large scale of ATP for embryo development. Here, we expanded the use of TPE-Ph-Into determine germ cell quality on the basis of the MMP and the intracellular distribution of mitochondria. We stained clinical sperm samples from 36 patients with infertility, as well as four oocytes, with TPE-Ph-In and examined the cells by confocal microscopy and cell sorting analysis. Our results showed a positive correlation between the MMP and sperm cell motility, as well as the different distribution of mitochondria in oocyte. Thus, staining with TPE-Ph-In could be used to quickly determine germ cell quality in vivo, bringing new possibilities for applications of AIEgens in biomedical research and clinical trials.

Impact of sperm DNA fragmentation on ICSI outcome and incidence of apoptosis of human pre-implantation embryos obtained from in vitro matured MII oocytes

BACKGROUND

Sperm DNA integrity and oocyte quality significantly affect embryo development and survival. The current study evaluated embryo development and quality, as well as the expression level of apoptosis-related genes and microRNAs in embryo derived from in vitro matured MII oocytes according to sperm DNA fragmentation (SDF) level.

METHODS

The semen and immature oocytes were collected from 50 ICSI cycles with any recognizable female factor infertility. After ovarian stimulation, germinal vesicle stage (GV) oocytes were collected and incubated in in vitro maturation (IVM) medium for 24 h. Next, reactive oxygen species (ROS) level of media culture was determined. Using by sperm chromatin dispersion (SCD) test, the SDF levels of processed semen were assessed and categorized into SDF ≤ 30% and SDF>30%. Seventy two hours after intracytoplasmic injection, the embryo development and quality score were recorded in the groups I (GV-MII + SDF≤ 30%) and II (GV-MII + SDF> 30%). Also, the apoptosis incidence of embryos at morula stage was evaluated at molecular and cellular levels by quantitative real time PCR and TUNEL staining, respectively.

RESULTS

Cleavage rate did not differ between two groups. The quality score of embryos obtained from IVM matured oocytes and high level of SDF was significantly lower than that of low level of SDF (P < 0.05). The embryos from group II had a significant reduction of the expression of BCL-2 compared to group I (P < 0.05). Also, they showed an increase in relative transcription of pro-apoptotic microRNAs; miR 15a and miR 16-1 versus group I (P < 0.05). A rise of TUNEL positive blastomers of embryo was observed at group II versus group I, but it did not reach to significantly level.

CONCLUSION

The IVM oocytes, probably, did not suffice to recover the high level of paternal genomic damage and inhibition of apoptosis pathway beginning.

Genes Involved in Drosophila melanogaster Ovarian Function Are Highly Conserved Throughout Evolution

This work presents a systematic approach to study the conservation of genes between fruit flies and mammals. We have listed 971 Drosophila genes involved in female reproduction at the ovarian level and systematically looked for orthologs in the Ciona, zebrafish, coelacanth, lizard, chicken, and mouse. Depending on the species, the percentage of these Drosophila genes with at least one ortholog varies between 69% and 78%. In comparison, only 42% of all the Drosophila genes have an ortholog in the mouse genome (P < 0.0001), suggesting a dramatically higher evolutionary conservation of ovarian genes. The 177 Drosophila genes that have no ortholog in mice and other vertebrates correspond to genes that are involved in mechanisms of oogenesis that are specific to the fruit fly or the insects. Among 759 genes with at least one ortholog in the zebrafish, 73 have an expression enriched in the ovary in this species (RNA-seq data). Among 760 genes that have at least one ortholog in the mouse; 76 and 11 orthologs are reported to be preferentially and exclusively expressed in the mouse ovary, respectively (based on the UniGene expressed sequence tag database). Several of them are already known to play a key role in murine oogenesis and/or to be enriched in the mouse/zebrafish oocyte, whereas others have remained unreported. We have investigated, by RNA-seq and real-time quantitative PCR, the exclusive ovarian expression of 10 genes in fish and mammals. Overall, we have found several novel candidates potentially involved in mammalian oogenesis by an evolutionary approach and using the fruit fly as an animal model.

Defective sperm head decondensation undermines the success of ICSI in the bovine

The efficiency of intracytoplasmic sperm injection (ICSI) in the bovine is low compared to other species. It is unknown whether defective oocyte activation and/or sperm head decondensation limit the success of this technique in this species. To elucidate where the main obstacle lies, we used homologous and heterologous ICSI and parthenogenetic activation procedures. We also evaluated whether in vitro maturation negatively impacted the early stages of activation after ICSI. Here we showed that injected bovine sperm are resistant to nuclear decondensation by bovine oocytes and this is only partly overcome by exogenous activation. Remarkably, when we used heterologous ICSI, in vivo-matured mouse eggs were capable of mounting calcium oscillations and displaying normal PN formation following injection of bovine sperm, although in vitro-matured mouse oocytes were unable to do so. Together, our data demonstrate that bovine sperm are especially resistant to nuclear decondensation by in vitro-matured oocytes and this deficiency cannot be simply overcome by exogenous activation protocols, even by inducing physiological calcium oscillations. Therefore, the inability of a suboptimal ooplasmic environment to induce sperm head decondensation limits the success of ICSI in the bovine. Studies aimed to improve the cytoplasmic milieu of in vitro-matured oocytes and to replicate the molecular changes associated with in vivo capacitation and acrosome reaction will deepen our understanding of the mechanism of fertilization and improve the success of ICSI in this species.

The histone codes for meiosis

Meiosis is a specialized process that produces haploid gametes from diploid cells by a single round of DNA replication followed by two successive cell divisions. It contains many special events, such as programmed DNA double-strand break (DSB) formation, homologous recombination, crossover formation and resolution. These events are associated with dynamically regulated chromosomal structures, the dynamic transcriptional regulation and chromatin remodeling are mainly modulated by histone modifications, termed 'histone codes'. The purpose of this review is to summarize the histone codes that are required for meiosis during spermatogenesis and oogenesis, involving meiosis resumption, meiotic asymmetric division and other cellular processes. We not only systematically review the functional roles of histone codes in meiosis but also discuss future trends and perspectives in this field.

Exploring timing activation of functional pathway based on differential co-expression analysis in preimplantation embryogenesis

Recent genome-wide omics studies have confirmed the early embryogenesis strictly dependent on the rigorous spatiotemporal activation and multilevel regulation. However, the full effect of functional pathway was not considered. To obtain complete understanding of the gene activation during early development, we performed systematic comparisons based on differential co-expression analysis for bovine preimplantation embryo development (PED). The results confirmed that the functional pathways actively transcribes as early as the 2-cell and 4-cell waves, which Basal transcription factor, Endocytosis and Spliceosome pathway can represent first signs of embryonic activity. Endocytosis act as one of master activators for uncovering a series of successive waves of maternal pioneer signal regulator with the help of Spliceosome complex. Furthermore, the results showed that pattern recognition receptors began to perform its essential function at 4-cell stage, which might be needed to coordinate the later major activation. And finally, our work presented a probable dynamic landscape of key functional pathways for embryogenesis. A clearer understanding of early embryo development will be helpful for Assisted Reproductive Technology (ART) and Regenerative Medicine (RM).

Oviduct: roles in fertilization and early embryo development

Animal oviducts and human Fallopian tubes are a part of the female reproductive tract that hosts fertilization and pre-implantation development of the embryo. With an increasing understanding of roles of the oviduct at the cellular and molecular levels, current research signifies the importance of the oviduct on naturally conceived fertilization and pre-implantation embryo development. This review highlights the physiological conditions within the oviduct during fertilization, environmental regulation, oviductal fluid composition and its role in protecting embryos and supplying nutrients. Finally, the review compares different aspects of naturally occurring fertilization and assisted reproductive technology (ART)-achieved fertilization and embryo development, giving insight into potential areas for improvement in this technology.

Comparison of Gene Expression Profiles in Human Germinal Vesicle Before and After Cytoplasmic Transfer From Mature Oocytes in Iranian Infertile Couples

OBJECTIVE

To evaluate the effect of cytoplasm transfer from mature oocytes to germinal vesicle(GV)s on promoting the maturation of cytoplasm of GV at the mRNA level.

MATERIALS AND METHODS

Sixty six in vitro fertilization (IVF) operations between June 2012 and November 2013 were included in this study. Totally 120 GVs were obtained. Normal GVs were categorized into 3 groups (n = 40) randomly: the first comprised oocytes that did not receive the cytoplasm of mature oocytes; the second group comprised oocytes that did not receive the cytoplasm of mature oocytes but were incubated for 24 h; and the third group comprised oocytes that received 10-15% the cytoplasm of mature oocytes and were then incubated for 24 h. Each group was separately analyzed by quantitative polymerase chain reaction (qPCR) and the expression levels of selected genes were assessed.

RESULTS

The expression levels of genes involved in the cytoplasmic maturity, and energy-producing mitochondria were significantly higher in the pooled oocytes of 2(nd) control group than those of the 1(st) control and intervention groups (p < 0.001). The genes involved in the meiosis, spindle check point, DNA repairing and cell cycle checkpoint did not have any expression in the 1(st) and intervention groups; however, these genes were expressed in the 2(nd) group, significantly. In the 2(nd) group, the highest expression level was observed for genes involved in the DNA repairing and cell cycle checkpoint. In the intervention group, none of the genes were expressed except for energy-producing mitochondria gene; even in this case, the expression level of this gene in this group of oocytes was significantly lower than that in other groups (p < 0.001). After 24 h meiosis assumption was significantly higher in the third group than in the second group (95% vs. 68%, p < 0.001).

CONCLUSION

The cytoplasm transfer technique is not effective in cytoplasmic maturity of the recipient GV oocytes. In contrast, 24-hr in-vitro culture is associated with increased expression of studied genes in GVs.

Identification of Maturation-Specific Proteins by Single-Cell Proteomics of Human Oocytes

Oocytes undergo a range of complex processes via oogenesis, maturation, fertilization, and early embryonic development, eventually giving rise to a fully functioning organism. To understand proteome composition and diversity during maturation of human oocytes, here we have addressed crucial aspects of oocyte collection and proteome analysis, resulting in the first proteome and secretome maps of human oocytes. Starting from 100 oocytes collected via a novel serum-free hanging drop culture system, we identified 2,154 proteins, whose function indicate that oocytes are largely resting cells with a proteome that is tailored for homeostasis, cellular attachment, and interaction with its environment via secretory factors. In addition, we have identified 158 oocyte-enriched proteins (such as ECAT1, PIWIL3, NLRP7)(1) not observed in high-coverage proteomics studies of other human cell lines or tissues. Exploiting SP3, a novel technology for proteomic sample preparation using magnetic beads, we scaled down proteome analysis to single cells. Despite the low protein content of only ∼100 ng per cell, we consistently identified ∼450 proteins from individual oocytes. When comparing individual oocytes at the germinal vesicle (GV) and metaphase II (MII) stage, we found that the Tudor and KH domain-containing protein (TDRKH) is preferentially expressed in immature oocytes, while Wee2, PCNA, and DNMT1 were enriched in mature cells, collectively indicating that maintenance of genome integrity is crucial during oocyte maturation. This study demonstrates that an innovative proteomics workflow facilitates analysis of single human oocytes to investigate human oocyte biology and preimplantation development. The approach presented here paves the way for quantitative proteomics in other quantity-limited tissues and cell types. Data associated with this study are available via ProteomeXchange with identifier PXD004142.

A stereological study on organelle distribution in human oocytes at prophase I

The ultrastructural analysis of human oocytes at different maturation stages has only been descriptive. The aim of this study was to use a stereological approach to quantify the distribution of organelles in oocytes at prophase I (GV). Seven immature GV oocytes were processed for transmission electron microscopy and a classical manual stereological technique based on point-counting with an adequate stereological grid was used. The Kruskal–Wallis test and Mann–Whitney U-test with Bonferroni correction were used to compare the means of the relative volumes occupied by organelles in oocyte regions: cortex (C), subcortex (SC) and inner cytoplasm (IC). Here we first describe in GV oocytes very large vesicles of the smooth endoplasmic reticulum (SER), vesicles containing zona pellucida-like materials and coated vesicles. The most abundant organelles were the very large vesicles of the SER (6.9%), mitochondria (6.3%) and other SER vesicles (6.1%). Significant differences in organelle distribution were observed between ooplasm regions: cortical vesicles (C: 1.3% versus SC: 0.1%, IC: 0.1%, P = 0.001) and medium-sized vesicles containing zona pellucida-like materials (C: 0.2% versus SC: 0.02%, IC: 0%, P = 0.004) were mostly observed at the oocyte cortex, whereas mitochondria (C: 3.6% versus SC: 6.0%, IC: 7.2%, P = 0.005) were preferentially located in the subcortex and inner cytoplasm, and SER very large vesicles (IC: 10.1% versus C: 0.9%, SC: 1.67%, P = 0.001) in the oocyte inner cytoplasm. Further quantitative studies are needed in immature metaphase-I and mature metaphase-II oocytes, as well as analysis of correlations between ultrastructural and molecular data, to better understand human oocyte in vitro maturation.

Genome-wide identification, phylogeny, and gonadal expression of fox genes in Nile tilapia, Oreochromis niloticus

The fox genes play important roles in various biological processes, including sexual development. In the present study, we isolated 65 fox genes, belonging to 18 subfamilies named A-R, from Nile tilapia through genome-wide screening. Twenty-four of them have two or three (foxm1) copies. Furthermore, 16, 25, 68, and 45 fox members were isolated from nematodes, protochordates, teleosts, and tetrapods, respectively. Phylogenetic analyses indicated fox gene family had undergone three expansions parallel to the three rounds of genome duplication during evolution. We also analyzed the clustered fox genes and found that apparent linkage duplication existed in teleosts, which further supported fish-specific genome duplication hypothesis. In addition, species- and lineage-specific duplication is another reason for fox gene family expansion. Based on the four pairs of XX and XY gonadal transcriptome data from four critical developmental stages, we analyzed the expression profile of all fox genes and identified sexually dimorphic fox genes at each stage. All fox genes were detected in gonads, with 15 of them at the background expression level (total read per kb per million reads, RPKM < 10), 29 at moderate expression level (10 < total RPKM < 100), and 21 at high expression level (total RPKM > 100). There are 27, 24, 28, and 9 sexually dimorphic fox genes at 5, 30, 90, and 180 days after hatching (dah), respectively. foxq1a, foxf1, foxr1, and foxr1 were identified as the most differentially expressed genes at each stage. foxl2 was characterized as XX-dominant gene, while foxd5, foxi3, foxn3, foxj1a, foxj3b, and foxo6b were characterized as XY-dominant genes. qPCR and in situ hybridization of foxh1 and foxj1a were performed to confirm the expression profiles and to validate the transcriptome data. Our results suggest that fox genes might play important roles in sex determination and gonadal development in teleosts.

Effects of heat shock during the early stage of oocyte maturation on the meiotic progression, subsequent embryonic development and gene expression in ovine

Heat shock may affect different aspects of oocyte maturation and its subsequent development to the blastocyst stage. A series of in vitro experiments was performed to determine whether physiologically heat shock (41°C) disrupts the progression of the ovine oocytes through meiosis, activation and blastocyst formation. Cumulus–oocyte complexes (COCs) were aspirated from 2–6-mm follicles and cultured at 38.5°C (control) or 41°C (heat shock) for the first 12 h of maturation. The oocytes were incubated at 38.5°C during the last 10 h of maturation and 8 days after activation. Results showed that most of the oocytes matured under heat-shock conditions remained at the germinal vesicle breakdown (GVBD) stage and they showed an aberrant chromatin configuration. After heat shock, oocyte diameter and time spent for zona pellucida dissolution increased (P < 0.05). The heat-shocked group had a higher percentage of oocytes with incomplete migration of cortical granules (P < 0.05). The heat-shock condition decreased (P < 0.05) cleavage rates (56.19 versus 89.28%) and morula formation (26.85 versus 37.81%). However, there was no significant difference in blastocyst formation and percentage of hatched blastocysts. At 12 h, heat shock had an adverse effect on embryo quality and reduced inner cell mass number (P < 0.05). Quantitative gene expression analysis showed greater transcripts (P < 0.05) for Na/K-ATPase mRNA in heat-shocked oocytes. To sum up, heat shock has disruptive effects on ovine oocyte maturation and can impair cellular and molecular factors that are important for embryo development.

Digital multiplexed mRNA analysis of functionally important genes in single human oocytes and correlation of changes in transcript levels with oocyte protein expression

OBJECTIVE

To investigate functionally important transcripts in single human oocytes with the use of NanoString technology and determine whether observed differences are biologically meaningful.

DESIGN

Analysis of human oocytes with the use of NanoString and immunoblotting.

SETTING

University-affiliated reproductive medicine unit.

PATIENTS

Women undergoing in vitro fertilization.

INTERVENTION

Human oocytes were analyzed with the use of NanoString or immunoblotting.

MAIN OUTCOME MEASURES

The abundance of transcripts for ten functionally important genes-AURKA, AURKC, BUB1, BUB1B (encoding BubR1), CDK1, CHEK1, FYN, MOS, MAP2K1, and WEE2-and six functionally dispensable genes were analyzed with the use of NanoString. BubR1 protein levels in oocytes from younger and older women were compared with the use of immunoblotting.

RESULT(S)

All ten functional genes but none of the six dispensable genes were detectable with the use of NanoString in single oocytes. There was 3- to 5-fold variation in BUB1, BUB1B, and CDK1 transcript abundance among individual oocytes from a single patient. Transcripts for these three genes-all players within the spindle assembly checkpoint surveillance mechanism for preventing aneuploidy-were reduced in the same oocyte from an older patient. Mean BUB1B transcripts were reduced by 1.5-fold with aging and associated with marked reductions in BubR1 protein levels.

CONCLUSION(S)

The abundance of functionally important transcripts exhibit marked oocyte-to-oocyte heterogeneity to a degree that is sufficient to affect protein expression. Observed variations in transcript abundance are therefore likely to be biologically meaningful, especially if multiple genes within the same pathway are simultaneously affected.