Exome sequencing in genuine empty follicle syndrome: Novel candidate genes

OBJECTIVE(S)

Empty follicle syndrome (EFS) is a condition in which no oocytes are retrieved in an IVF cycle despite apparently normal follicular development and meticulous follicular aspiration following ovulation induction. The EFS is called genuine (gEFS) when the trigger administration is correct. The existence of gEFS is a subject of controversy, and it is quite rare with an undetermined etiology. Genetic defects in specific genes have been demonstrated to be responsible for this condition in some patients. Our objective was to identify novel genetic variants associated with gEFS.

STUDY DESIGN

We conducted a prospective observational study including 1,689 egg donors from July 2017 to February 2023. WES were performed in patients suffering gEFS.

RESULTS

Only 7 patients (0.41 %) exhibited gEFS after two ovarian stimulation cycles and we subsequently performed whole exome sequencing (WES) on these patients. Following stringent filtering, we identified 6 variants in 5 affected patients as pathogenic in new candidate genes which have not been previously associated with gEFS before, but which are involved in important biological processes related to folliculogenesis. These genetic variants included c.603_618del in HMMR, c.1025_1028del in LMNB1, c.1091-1G > A in TDG, c.607C > T in HABP2, c.100 + 2 T > C in HAPLN1 and c.3592_3593del in JAG2.

CONCLUSION

As a conclusion, we identified new candidate genes related to gEFS that expand the mutational spectrum of genes related to gEFS.This study show that WES might be an efficient tool to identify the genetic etiology of gEFS and provide further understanding of the pathogenic mechanism of gEFS.

Ferulic acid ameliorates the quality of in vitro-aged bovine oocytes by suppressing oxidative stress and apoptosis

Ferulic acid (FA) is a well-known natural antioxidant that scavenges oxygen free radicals and alleviates oxidative stress. This study investigated the chemopreventive potential of FA against bovine oocyte quality decline during in vitro aging. The results showed that 5 μM FA supplementation decreased the abnormality rate of in vitro-aged bovine oocytes. In addition, FA supplementation effectively improved antioxidant capacity by removing excessive ROS and maintaining intracellular GSH levels and antioxidant enzyme activity. The mitochondrial activity, mitochondrial membrane potential and intracellular ATP levels in aged bovine oocytes were obviously enhanced by FA supplementation. Furthermore, FA supplementation reduced in vitro aging-induced DNA damage and maintained DNA stability in bovine oocytes. Moreover, sperm binding assay showed the number of sperm that bound to the zona pellucida on aged bovine oocytes was significantly higher in the FA supplemented group than in the Aged group. Therefore, FA is beneficial for maintaining in vitro-aged bovine oocyte quality and could become a potential antioxidant for preventing bovine oocyte in vitro aging during in vitro maturation.

Morphokinetic parameters of mouse oocyte meiotic maturation and cumulus expansion are not affected by reproductive age or ploidy status

INTRODUCTION

Morphokinetic analysis using a closed time-lapse monitoring system (EmbryoScope + ™) provides quantitative metrics of meiotic progression and cumulus expansion. The goal of this study was to use a physiologic aging mouse model, in which egg aneuploidy levels increase, to determine whether there are age-dependent differences in morphokinetic parameters of oocyte maturation.

METHODS

Denuded oocytes and intact cumulus-oocyte complexes (COCs) were isolated from reproductively young and old mice and in vitro matured in the EmbryoScope + ™. Morphokinetic parameters of meiotic progression and cumulus expansion were evaluated, compared between reproductively young and old mice, and correlated with egg ploidy status.

RESULTS

Oocytes from reproductively old mice were smaller than young counterparts in terms of GV area (446.42 ± 4.15 vs. 416.79 ± 5.24 µm2, p < 0.0001) and oocyte area (4195.71 ± 33.10 vs. 4081.62 ± 41.04 µm2, p < 0.05). In addition, the aneuploidy incidence was higher in eggs with advanced reproductive age (24-27% vs. 8-9%, p < 0.05). There were no differences in the morphokinetic parameters of oocyte maturation between oocytes from reproductively young and old mice with respect to time to germinal vesicle breakdown (GVBD) (1.03 ± 0.03 vs. 1.01 ± 0.04 h), polar body extrusion (PBE) (8.56 ± 0.11 vs. 8.52 ± 0.15 h), duration of meiosis I (7.58 ± 0.10 vs. 7.48 ± 0.11 h), and kinetics of cumulus expansion (0.093 ± 0.002 vs. 0.089 ± 0.003 µm/min). All morphokinetic parameters of oocyte maturation were similar between euploid and aneuploid eggs irrespective of age.

CONCLUSION

There is no association between age or ploidy and the morphokinetics of mouse oocyte in vitro maturation (IVM). Future studies are needed to evaluate whether there is an association between morphokinetic dynamics of mouse IVM and embryo developmental competence.

Quantitative morphokinetic parameters identify novel dynamics of oocyte meiotic maturation and cumulus expansion†

Meiotic maturation and cumulus expansion are essential for the generation of a developmentally competent gamete, and both processes can be recapitulated in vitro. We used a closed time-lapse incubator (EmbryoScope+™) to establish morphokinetic parameters of meiotic progression and cumulus expansion in mice and correlated these outcomes with egg ploidy. The average time to germinal vesicle breakdown (GVBD), time to first polar body extrusion (PBE), and duration of meiosis I were 0.91 ± 0.01, 8.82 ± 0.06, and 7.93 ± 0.06 h, respectively. The overall rate of cumulus layer expansion was 0.091 ± 0.002 μm/min, and the velocity of expansion peaked during the first 8 h of in vitro maturation (IVM) and then slowed. IVM of oocytes exposed to Nocodazole, a microtubule disrupting agent, and cumulus oocyte complexes (COCs) to 4-methylumbelliferone, a hyaluronan synthesis inhibitor, resulted in a dose-dependent perturbation of morphokinetics, thereby validating the system. The incidence of euploidy following IVM was >90% for both denuded oocytes and intact COCs. No differences were observed between euploid and aneuploid eggs with respect to time to GVBD (0.90 ± 0.22 vs. 0.97 ± 0.19 h), time to PBE (8.89 ± 0.98 vs. 9.10 ± 1.42 h), duration of meiosis I (8.01 ± 0.91 vs. 8.13 ± 1.38 h), and overall rate and kinetics of cumulus expansion (0.089 ± 0.02 vs 0.088 ± 0.03 μm/min) (P > 0.05). These morphokinetic parameters provide novel quantitative and non-invasive metrics for the evaluation of meiotic maturation and cumulus expansion and will enable screening compounds that modulate these processes.

Absorption, distribution, metabolism and excretion of hyaluronic acid during pregnancy: a matter of molecular weight

INTRODUCTION

For many years hyaluronic acid (HA) was mainly used for its hydrating properties. However, new applications have recently arisen, considering the biological properties of HA and its molecular weight. Clinical application of low molecular weight HA (LMW-HA) initially was supported by specific absorption data. The identification of high molecular weight HA (HMW-HA) absorption pathways and the knowledge of its physiological role allowed to evaluate its clinical application. Based on the immunomodulatory properties of HMW-HA and its physiological involvement as signaling molecule, pregnancy represents an interesting context of application.

AREA COVERED

This expert opinion includes in-vitro, in-vivo, ex-vivo and clinical studies on gestational models. It provides an overview of the physiological and the therapeutic role of HMW-HA in pregnancy starting from its metabolism. Indeed, HMW-HA is widely involved in several physiological processes as implantation, immune response, uterine quiescence and cervical remodeling, and therefore is an essential molecule for a successful pregnancy.

EXPERT OPINION

Available evidence suggests that HMW-HA administration can support physiological pregnancy, favoring blastocyst adhesion and development, preventing miscarriage and pre-term birth. For this reason, supplementation in pregnancy should be evaluated.

Effects of glucuronic acid and N-acetyl-D-glucosamine supplementation on the perivitelline space during the IVM of pig oocytes

The objective of this study was to minimise polyspermic penetration by increasing the perivitelline space (PVS) thickness through supplementation of the hyaluronic acid components glucuronic acid and N-acetyl-d-glucosamine (GlcNAc). Oocytes (n=4690) were supplemented during the first 24h and/or the remainder of maturation (final 16-18h) with 0.01mM glucuronic acid and 0.01mM GlcNAc and then evaluated for PVS thickness, hyaluronic acid, glutathione and glutathione peroxidase concentrations. Fertilised oocytes were evaluated for polyspermic penetration and embryo development. The PVS thickness and amount of hyaluronic acid was significantly (P<0.05) greater in oocytes supplemented with 0.01mM glucuronic acid and 0.01mM GlcNAc during the second part or all of maturation compared with the other treatments. In addition, polyspermic penetration was significantly (P<0.05) less in oocytes supplemented with 0.01mM glucuronic acid and 0.01mM GlcNAc during the second part or all of maturation compared with the other treatments. Supplementing 0.01mM glucuronic acid and GlcNAc during maturation significantly (P<0.05) increased the percentage of cleaved embryos by 48h after IVF and blastocysts formed by 144h after IVF compared those not supplemented. These results indicate that supplementing PVS components during maturation decreases polyspermic penetration by increasing PVS thickness.

Regulation and roles of the hyaluronan system in mammalian reproduction

Hyaluronan (HA) is a non-sulphated glycosaminoglycan polymer naturally occurring in many tissues and fluids of mammals, including the reproductive system. Its biosynthesis by HA synthase (HAS1–3) and catabolism by hyaluronidases (HYALs) are affected by ovarian steroid hormones. Depending upon its molecular size, HA functions both as a structural component of tissues in the form of high-molecular-weight HA or as a signalling molecule in the form of small HA molecules or HA fragments with effects mediated through interaction with its specific cell-membrane receptors. HA is produced by oocytes and embryos and in various segments of the reproductive system. This review provides information about the expression and function of members of the HA system, including HAS, HYALs and HA receptors. We examine their role in various processes from folliculogenesis through oocyte maturation, fertilisation and early embryo development, to pregnancy and cervical dilation, as well as its application in assisted reproduction technologies. Particular emphasis has been placed upon the role of the HA system in pre-implantation embryo development and embryo implantation, for which we propose a hypothetical sequential model.

RHAMM deficiency disrupts folliculogenesis resulting in female hypofertility

The postnatal mammalian ovary contains the primary follicles, each comprising an immature oocyte surrounded by a layer of somatic granulosa cells. Oocytes reach meiotic and developmental competence via folliculogenesis. During this process, the granulosa cells proliferate massively around the oocyte, form an extensive extracellular matrix (ECM) and differentiate into cumulus cells. As the ECM component hyaluronic acid (HA) is thought to form the backbone of the oocyte-granulosa cell complex, we deleted the relevant domain of the Receptor for HA Mediated Motility (RHAMM) gene in the mouse. This resulted in folliculogenesis defects and female hypofertility, although HA-induced signalling was not affected. We report that wild-type RHAMM localises at the mitotic spindle of granulosa cells, surrounding the oocyte. Deletion of the RHAMM C-terminus in vivo abolishes its spindle association, resulting in impaired spindle orientation in the dividing granulosa cells, folliculogenesis defects and subsequent female hypofertility. These data reveal the first identified physiological function for RHAMM, during oogenesis, and the importance of this spindle-associated function for female fertility.

A prostaglandin E2 receptor antagonist prevents pregnancies during a preclinical contraceptive trial with female macaques

STUDY QUESTION

Can administration of a prostaglandin (PG) E2 receptor 2 (PTGER2) antagonist prevent pregnancy in adult female monkeys by blocking periovulatory events in the follicle without altering menstrual cyclicity or general health?

SUMMARY ANSWER

This is the first study to demonstrate that a PTGER2 antagonist can serve as an effective non-hormonal contraceptive in primates.

WHAT IS KNOWN ALREADY

The requirement for PGE2 in ovulation and the release of an oocyte surrounded by expanded cumulus cells (cumulus-oocyte expansion; C-OE) was established through the generation of PTGS2 and PTGER2 null-mutant mice. A critical role for PGE2 in primate ovulation is supported by evidence that intrafollicular injection of indomethacin in rhesus monkeys suppressed follicle rupture, whereas co-injection of PGE2 with indomethacin resulted in ovulation.

STUDY DESIGN, SIZE, DURATION

First, controlled ovulation protocols were performed in adult, female rhesus monkeys to analyze the mRNA levels for genes encoding PGE2 synthesis and signaling components in the naturally selected pre-ovulatory follicle at different times after the ovulatory hCG stimulus (0, 12, 24, 36 h pre-ovulation; 36 h post-ovulation, n = 3-4/time point). Second, controlled ovarian stimulation cycles were utilized to obtain multiple cumulus-oocyte complexes (COCs) from rhesus monkeys to evaluate the role of PGE2 in C-OE in vitro (n = 3-4 animals/treatment; ≥3 COCs/animal/treatment). Third, adult cycling female cynomolgus macaques were randomly assigned (n = 10/group) to vehicle (control) or PTGER2 antagonist (BAY06) groups to perform a contraceptive trial. After the first treatment cycle, a male of proven fertility was introduced into each group and they remained housed together for the duration of the 5-month contraceptive trial that was followed by a post-treatment reversibility trial.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative real-time PCR, COC culture and expansion, immunofluorescence/confocal microscopy, enzyme immunoassay, contraceptive trial, ultrasonography, complete blood counts, serum biochemistry tests and blood lipid profiles.

MAIN RESULTS AND THE ROLE OF CHANCE

Several mRNAs encoding proteins involved in PGE2 synthesis, metabolism and signaling increase (P < 0.05) in the periovulatory follicle after administration of an ovulatory hCG bolus. PGE2 signaling through PTGER2 induces cumulus cell expansion and production of hyaluronic acid, which are critical events for fertilization. Moreover, chronic administration of a selective PTGER2 antagonist resulted in a significant (P < 0.05 versus vehicle-treated controls) contraceptive effect without altering steroid hormone patterns or menstrual cyclicity during a 5-months contraceptive trial. Fertility recovered as early as 1 month after ending treatment.

LIMITATIONS, REASONS FOR CAUTION

This is a proof-of-concept study in a non-human primate model. Further investigations are warranted to elucidate the mechanism(s) of PTGER2 antagonist action in the primate ovary. Although PTGER2 antagonist treatment did not produce any obvious undesirable effects, improvements in the mode of administration, as well as the efficacy of these compounds, are necessary to consider such a contraceptive for women.

WIDER IMPLICATIONS OF THE FINDINGS

Monitoring as well as improving the efficacy and safety of female contraceptives is an important public health activity. Even though hormonal contraceptives are effective for women, concerns remain regarding their side-effects and long-term use because of the widespread actions of such steroidal products in many tissues. Moreover, some women cannot take hormones for medical reasons. Thus, development of non-hormonal contraceptives for women is warranted.

STUDY FUNDING/COMPETING INTEREST(S)

Supported by Bayer HealthCare Pharmaceuticals, The Eunice Kennedy Shriver NICHD Contraceptive Development and Research Center (U54 HD055744), NIH Office of the Director (Oregon National Primate Research Center P51 OD011092), and a Lalor Foundation Postdoctoral Basic Research Fellowship (MCP). The use of the Leica confocal was supported by grant number S10RR024585. Some of the authors (N.B., A.R., K.-H.F., U.F., B.B. and B.L.) are employees of Bayer Healthcare Pharma.

Sericin accelerates the production of hyaluronan and decreases the incidence of polyspermy fertilization in bovine oocytes during in vitro maturation

Fetal bovine serum (FBS) has been widely used as a supplement in the maturation medium of bovine oocytes in vitro. However, serum contains many undefined factors and is potentially infectious to humans and animals. As a serum replacement, we evaluated the feasibility of using the silk protein, sericin, derived from the cocoons of silkworm. To examine the rates of oocyte maturation and fertilization, cumulus-oocyte complexes were cultured in TCM-199 supplemented with 0.01%, 0.05%, 0.1% or 0.15% sericin or 5% FBS. The sizes of the perivitelline space that might relate to polyspermy, the expressions of Has2 and CD44 mRNA, the amount of hyaluronan (hyaluronic acid: HA) contained in the oocytes and the rates of blastocyst formation following insemination were then compared between the oocytes cultured with 0.05% sericin and 5% FBS, because the polyspermy rates in oocytes cultured with 0.05% sericin were significantly lower than in those cultured with 5% FBS. After in vitro maturation (IVM), the mean size of the perivitelline space was significantly greater in oocytes cultured with sericin than in those cultured with FBS, although the rates of nuclear maturation, fertilization and blastocyst formation of oocytes under both IVM conditions were not significantly different. The expression of HAS2 and CD44 mRNA and the amount of HA in the denuded oocytes cultured with 0.05% sericin were significantly greater than in those cultured with FBS. These results indicate the feasibility of sericin as an alternative protein supplement for IVM in bovine oocytes.

Age-associated changes in gene expression of goat oocytes

Oocyte aging severely decreases the quality of oocytes, which hampers fertilization and subsequent embryo development. In the present study, age-dependent molecular changes in goat oocytes were investigated. First, the quality of goat oocytes with various in vitro culture times (24, 30, 36, 48, and 60 hours) was evaluated on the basis of developmental rates of parthenogenetically activated embryos and apoptosis of cumulus cells (CCs). Second, relative gene expression of six genes (mitochondrial genes: PGC-1α and NRF-1; epigenetic modification genes: SNRPN and HAT1; mitotic spindle checkpoint protein: SMAD2; and hyaluronan synthase gene: HAS3) were analyzed during oocyte aging. Third, we further studied the changes of seven genes (PGC-1α and NRF-1; apoptotic-related genes: BAX and BCL2; hyaluronan synthase gene: HAS2; metabolism-related gene: STAR; and superoxide dismutase gene: SOD1) in CCs during oocyte aging. In these studies, the blastocyst rate gradually decreased and the number of apoptotic cells significantly increased as the culture time increased (P < 0.05). Moreover, relative gene expressions of PGC-1α, NRF-1 and SMAD2 significantly decreased from 24 to 36 hours (P < 0.05), whereas the levels of HAT1 and HAS3 slowly increased as culture was prolonged. Furthermore, the levels of PGC-1α, BCL2, HAS2 and SOD1 quickly reduced, and BAX significantly increased from 24 to 36 hours in aged CCs (P < 0.05). In conclusion, goat oocytes started to age at 30 hours in vitro culture, and gene expression patterns of oocytes and CCs significantly changed as the oocytes aged. Gene expression pattern changes in CCs may provide a convenient and effective way to detect oocyte aging without compromising oocyte integrity.

Glycosaminoglycans improves early development of zona-free 8-cell rat embryos to blastocysts in a chemically defined medium, but not the pregnancy rate following transfer of the blastocysts

The objective of the present study was to clarify the possible role of the zona pellucida (ZP) in early development of rat embryos and to determine the effect of glycosaminoglycans on the development of ZP-free 8-cell embryos before or after embryo transfer at the blastocyst stage. Eight-cell embryos were divided into three groups comprised of, 1) intact controls, 2) embryos with the ZP was removed with acidic solution and 3) pairs of ZP-free 8-cell embryos aggregated in a small hollow. These embryos were cultured in a chemically defined mR1ECM for 24 h. Developmental ability to the blastocyst stage and mean cell number in the blastocyst was lower in ZP-free embryos than in intact controls. When these blastocysts were transferred, the farrowing rate and efficiency of embryos developed to term were also lower in ZP-free embryos, but not in the aggregated ones. Supplementation with hyaluronan (HA; 63-250 µg/ml) or heparan sulfate proteoglycan (HS; 15 µg/ml) significantly improved blastocyst formation of ZP-free embryos and the cell number in the blastocyst by reducing the incidence of apoptosis. However, there were no beneficial effects of HA or HS on farrowing and newborn rates after transfer of the blastocysts. In conclusion, the ZP plays roles in maintaining successful development of early rat embryos at least from the 8-cell stage not only to the blastocyst stage but also to posttransfer stages. Glycosaminoglycans, such as HA or HS, appear to contribute to successful cleavage during early development to the blastocyst stage but may be insufficient to maintain the posttransfer survival of ZP-free embryos.

Genome integrity, stem cells and hyaluronan

Faithful preservation of genome integrity is the critical mission of stem cells as well as of germ cells. Reviewed are the following mechanisms involved in protecting DNA in these cells: (a) The efflux machinery that can pump out variety of genotoxins in ATP-dependent manner; (b) the mechanisms maintaining minimal metabolic activity which reduces generation of reactive oxidants, by-products of aerobic respiration; (c) the role of hypoxic niche of stem cells providing a gradient of variable oxygen tension; (d)(e) the presence of hyaluronan (HA) and HA receptors on stem cells and in the niche; (f) the role of role of HA in protecting DNA from oxidative damage; (g) the specific role of HA that may play a role protecting DNA in stem cells; (h) the interactions of HA with sperm cells and oocytes that also may shield their DNA from oxidative damage, and (e) mechanisms by which HA exerts the anti-oxidant activity. While HA has multitude of functions its anti-oxidant capabilities are often overlooked but may be of significance in preservation of integrity of stem and germ cells genome.

The eggshell in the C. elegans oocyte-to-embryo transition

In egg-laying animals, embryonic development takes place within the highly specialized environment provided by the eggshell and its underlying extracellular matrix. Far from being simply a passive physical support, the eggshell is a key player in many early developmental events. Herein, we review current understanding of eggshell structure, biosynthesis, and function in zygotic development of the nematode, C. elegans. Beginning at sperm contact or entry, eggshell layers are produced sequentially. The earlier outer layers are required for secretion or organization of inner layers, and layers differ in composition and function. Developmental events that depend on the eggshell include polyspermy barrier generation, high fidelity meiotic chromosome segregation, osmotic barrier synthesis, polar body extrusion, anterior-posterior polarization, and organization of membrane and cortical proteins. The C. elegans eggshell is proving to be an excellent, tractable system to study the molecular cues of the extracellular matrix that instruct cell polarity and early development.

Eggshell chitin and chitin-interacting proteins prevent polyspermy in C. elegans

Development requires fertilization by a single sperm. In Caenorhabditis elegans, fertilization occurs in a sperm-filled spermatheca, implying the barrier to polyspermy is generated in this compartment. Eggshell chitin synthesis is initiated at fertilization, and chitin is deposited before the zygote exits the spermatheca. Whereas polyspermy is very rare in wild-type, here we report an incidence of 14%-51% in zygotes made chitin deficient by loss of chitin synthase-1 (CHS-1), the CHS-1 substrate UDP-N-acetylglucosamine, the CHS-1-interacting protein EGG-3, or the sperm-provided protein SPE-11. The spe-11(hc90) mutant deposits chitin at the male end but fails to complete a continuous layer. The polyspermy barrier is also compromised by loss of the chitin-binding protein CBD-1 or the GLD-1-regulated LDL receptor-like EGG-1, together with its homolog, EGG-2. Loss of CBD-1 or EGG-1/2 disrupts oocyte cortical distribution of CHS-1, as well as MBK-2 and EGG-3. In CBD-1 or EGG-1/2 deficiency, chitin is synthesized but the eggshell is fractured, suggesting aberrantly clustered CHS-1/MBK-2/EGG-3 may fail to support construction of a continuous eggshell. Together, our results show that eggshell chitin is required to prevent polyspermy in C. elegans, in addition to its previously reported requirement in polar body extrusion and polarization of the zygote.

Size of the perivitelline space and incidence of polyspermy in rabbit and hamster oocytes

Purpose

The size of the perivitelline space and the incidence of polyspermy were observed in ovulated and cultured oocytes from rabbits and hamsters with or without treatment by 4-methylumbelliferone (MU), an inhibitor of hyaluronic acid (HA) synthase, in order to examine the relationship between the incidence of polyspermy and the size of the perivitelline space. The amount of HA in the medium with MU-treated hamster oocytes was measured and compared with that in the medium with untreated oocytes.

Methods

The perivitelline space of oocytes with 1st polar bodies was measured by use of a micrometer under a microscope, and the incidence of polyspermy was observed in the oocytes after insemination. The amount of HA in the medium was examined using an enzyme-linked immunosorbent assay. The distribution of cortical granules was observed by staining with FITC-conjugated LCA.

Results

In both rabbit and hamster, the mean size of the perivitelline space was significantly smaller and the incidence of polyspermy was significantly higher in the cultured and MU-treated oocytes than in the ovulated and untreated oocytes. The mean amount of HA in the medium with MU-treated oocytes (8.96 pg) was significantly smaller than that in the medium with untreated oocytes (21.77 pg). The distribution of cortical granules did not differ among the ovulated, cultured, and MU-treated oocytes.

Conclusions

These findings suggest that the size of the perivitelline space is closely related to the incidence of polyspermy, and that the oocyte itself synthesizes and secretes the HA involved in the enlargement of the perivitelline space.