A compact, high-throughput semi-automated embryo vitrification system based on hydrogel.

RESEARCH QUESTION: What is the efficiency and efficacy of the novel Biorocks semi-automated vitrification system, which is based on a hydrogel? DESIGN: This comparative experimental laboratory study used mouse model and human day 6 blastocysts. Mouse oocytes and embryos were quality assessed post-vitrification. RESULTS: The Biorocks system successfully automated the solution exchanges during the vitrification process, achieving a significantly improved throughput of up to 36 embryos/oocytes per hour. Using hydrogel for cryoprotective agent delivery, 12 vessels could be processed simultaneously, fitting comfortably within an assisted reproductive technology (ART) workstation. In tests involving the cryopreservation of oocytes and embryos, the system yielded outcomes equivalent to the manual Cryotop method. For example, the survival rate for mouse oocytes was 98% with the Biorocks vitrification system (n = 46) and 95% for the manual Cryotop method (n = 39), of which 46% and 41%, respectively, progressed to blastocysts on day 5 after IVF. CC-grade day 6 human blastocysts processed with the Biorocks system (n = 39) were associated with a 92% 2 h re-expansion rate, equivalent to the 90% with Cryotop (n = 30). The cooling/warming rates achieved by the Biorocks system were 31,900°C/minute and 24,700°C/minute, respectively. Oocyte quality was comparable or better post-vitrification for Biorocks than Cryotop. CONCLUSIONS: The Biorocks semi-automated vitrification system offers enhanced throughput without compromising the survival and developmental potential of oocytes and embryos. This innovative system may help to increase the efficiency and standardization of vitrification in ART clinics. Further investigations are needed to confirm its efficacy in a broader clinical context.

Embryological characteristics and clinical outcomes of oocytes with different degrees of abnormal zona pellucida during assisted reproductive treatment.

Abnormalities in the zona pellucida (ZP) adversely affect oocyte maturation, embryo development and pregnancy outcomes. However, the assessment of severity is challenging. To evaluate the effects of different degrees of ZP abnormalities on embryo development and clinical outcomes, in total, 590 retrieval cycles were scored and divided into four categories (control, mild, moderate and severe) based on three parameters: perivitelline space, percentage of immature oocytes and percentage of oocytes with abnormal morphology. As the severity of abnormal ZP increased, both the number of retrieved oocytes and mature oocytes decreased. The fertilization rate did not differ significantly among groups. The rates of embryo cleavage and day-3 high-quality embryos in the mild group and the moderate group did not vary significantly between the two groups but were significantly higher than those in the severe group. The blastulation rates of the abnormal ZP groups were similar; however, they were lower than those of the control group. Moreover, the cycle cancellation rate of the severe abnormal ZP group was as high as 66.20%, which was significantly higher than that of the other three groups. Although the rates of cumulative clinical pregnancy and live births were lower than those in the control group, they were comparable among the abnormal ZP groups. There were no differences in the neonatal outcomes of the different groups. Together, ZP abnormalities show various degrees of severity, and in all patients regardless of the degree of ZP abnormalities who achieve available embryos, there will be an opportunity to eventually give birth.

Decreased HAT1 expression in granulosa cells disturbs oocyte meiosis during mouse ovarian aging.

BACKGROUND: With advanced maternal age, abnormalities during oocyte meiosis increase significantly. Aneuploidy is an important reason for the reduction in the quality of aged oocytes. However, the molecular mechanism of aneuploidy in aged oocytes is far from understood. Histone acetyltransferase 1 (HAT1) has been reported to be essential for mammalian development and genome stability, and involved in multiple organ aging. Whether HAT1 is involved in ovarian aging and the detailed mechanisms remain to be elucidated. METHODS: The level of HAT1 in aged mice ovaries was detected by immunohistochemical and immunoblotting. To explore the function of HAT1 in the process of mouse oocyte maturation, we used Anacardic Acid (AA) and small interfering RNAs (siRNA) to culture cumulus-oocyte complexes (COCs) from ICR female mice in vitro and gathered statistics of germinal vesicle breakdown (GVBD), the first polar body extrusion (PBE), meiotic defects, aneuploidy, 2-cell embryos formation, and blastocyst formation rate. Moreover, the human granulosa cell (GC)-like line KGN cells were used to investigate the mechanisms of HAT1 in this progress. RESULTS: HAT1 was highly expressed in ovarian granulosa cells (GCs) from young mice and the expression of HAT1 was significantly decreased in aged GCs. AA and siRNAs mediated inhibition of HAT1 in GCs decreased the PBE rate, and increased meiotic defects and aneuploidy in oocytes. Further studies showed that HAT1 could acetylate Forkhead box transcription factor O1 (FoxO1), leading to the translocation of FoxO1 into the nucleus. Resultantly, the translocation of acetylated FoxO1 increased the expression of amphiregulin (AREG) in GCs, which plays a significant role in oocyte meiosis. CONCLUSION: The present study suggests that decreased expression of HAT1 in GCs is a potential reason corresponding to oocyte age-related meiotic defects and provides a potential therapeutic target for clinical intervention to reduce aneuploid oocytes.

Blastocyst development rate influences singleton gestational age of similarly graded blastocysts after vitrified-warmed single embryo transfer cycles.

RESEARCH QUESTION: Does the development rate of blastocysts influence neonatal outcomes after blastocyst transfer cycles when the morphological score of the transferred blastocysts is similar? DESIGN: A retrospective study involving singleton live births born to 1280 women undergoing single frozen blastocyst transfers (FBTs) between January 2016 and December 2018 at a tertiary care centre. Patients were grouped into day-5 or day-6 groups depending on the development rate of blastocysts. These were further grouped into four groups based on the blastocyst inner cell mass and trophectoderm scoring: excellent (AA); good (AB or BA); average (AC, CA or BB); and poor (BC or CB). The primary outcomes were gestational age and singleton birth weight. RESULTS: Singletons resulting from day-5 single FBT were at a lower risk of preterm birth than those resulting from day-6 single FBT (adjusted OR 0.63, 95% CI 0.41 to 0.97, P = 0.035). In the day-5 good-quality blastocyst group and day-5 average-quality blastocyst group, singletons were at a lower risk of preterm birth than those resulting from day-6 groups, respectively (adjusted OR 0.22, 95% CI 0.08 to 0.63, P = 0.005 and adjusted OR 0.52, 95% CI 0.29 to 0.94, P = 0.03). CONCLUSIONS: Day-6 single FBT was associated with a higher risk of preterm birth compared with day-5 single FBT in good and average morphological scoring blastocysts. Our analysis was restricted to women with singleton births from single FBTs. Future prospective studies are required to confirm the findings.

The influence of day 3 embryo cell number on the clinical pregnancy and live birth rates of day 5 single blastocyst transfer from frozen embryo transfer cycles.

BACKGROUND: To evaluate the influence of day 3 embryo cell number on the clinical pregnancy and live birth rates of day 5 single blastocyst transfer in frozen embryo transfer (FET) cycles. METHODS: Our retrospective study included 3761 day 5 single blastocyst FET cycles between January 2015 and December 2019. These FET cycles were divided into three groups according to the day 3 embryo cell number: 939 cycles in the < 8-cell group, 1224 cycles in the 8-cell group and 1598 cycles in the > 8-cell group. The clinical pregnancy and live birth rates were compared among the three groups. RESULTS: The clinical pregnancy rate of day 5 single blastocyst transfer in FET cycles increased significantly as the day 3 embryo cell number increased (52.2%, 61.4% and 66.8%, P < 0.001). Similarly, the live birth rate increased significantly as the day 3 embryo cell number increased (42.7%, 49.8% and 54.9%, P < 0.001). The results of the subgroup analysis showed that the clinical pregnancy and live birth rates were not significantly different among the three groups when good-quality blastocysts were transferred. The clinical pregnancy and live birth rates increased significantly as the day 3 embryo cell number increased when fair- and poor-quality blastocysts were transferred. CONCLUSION: The day 3 embryo cell number needs to be considered when day 5 single blastocyst transfer is performed in FET cycles, especially when fair- and poor-quality blastocysts are used for transfer. The transfer of a day 5 single blastocyst derived from an embryo with faster development on day 3 may shorten the time to achieving a live birth.

The effects of the day of trophectoderm biopsy and blastocyst grade on the clinical and neonatal outcomes of preimplantation genetic testing-frozen embryo transfer cycles.

This study analyzed the effects of the day of trophectoderm (TE) biopsy and blastocyst grade on clinical and neonatal outcomes. The results showed that the implantation and live birth rates of day 5 (D5) TE biopsy were significantly higher compared with those of D6 TE biopsy. The miscarriage rate of the former was lower than that of the latter, but there was no statistically significant difference. Higher quality blastocysts can achieve better implantation and live birth rates. Among good quality blastocysts, the implantation and live birth rates of D5 and D6 TE biopsy were not significantly different. Among fair quality and poor quality blastocysts, the implantation and live birth rates of D5 TE biopsy were significantly higher compared with those of D6 TE biopsy. Neither blastocyst grade nor the day of TE biopsy significantly affected the miscarriage rate. Neonatal outcomes, including newborn sex, gestational age, preterm birth, birth weight and low birth weight in the D5 and D6 TE biopsies were not significantly different. Both blastocyst grade and the day of TE biopsy must be considered at the same time when performing preimplantation genetic testing-frozen embryo transfer.

Translation repression by maternal RNA binding protein Zar1 is essential for early oogenesis in zebrafish.

A large amount of maternal RNA is deposited in oocytes and is reserved for later development. Control of maternal RNA translation during oocyte maturation has been extensively investigated and its regulatory mechanisms are well documented. However, translational regulation of maternal RNA in early oogenesis is largely unexplored. In this study, we generated zebrafish zar1 mutants that result in early oocyte apoptosis and fully penetrant male development. Loss of p53 suppresses the apoptosis in zar1 mutants and restores oocyte development. zar1 immature ovaries show upregulation of proteins implicated in endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). More importantly, loss of Zar1 causes marked upregulation of zona pellucida (ZP) family proteins, while overexpression of ZP proteins in oocytes causes upregulation of stress-related activating transcription factor 3 (atf3), arguing that tightly controlled translation of ZP proteins is essential for ER homeostasis during early oogenesis. Furthermore, Zar1 binds to ZP gene mRNAs and represses their translation. Together, our results indicate that regulation of translational repression and de-repression are essential for precisely controlling protein expression during early oogenesis.

Effects of the normal sperm morphology rate on the clinical and neonatal outcomes of conventional IVF cycles.

The present study assessed the influences of the normal sperm morphology rate on the clinical and neonatal outcomes of conventional in vitro fertilisation cycles. This retrospective study analysed 427 and 2,728 cycles from the normal sperm morphology rate <4% and ≥4% group respectively. The clinical (total fertilisation failure, clinical pregnancy, implantation and abortion) and neonatal (sex, gestational age, preterm birth, birthweight, low birth weight, live births and birth defects of newborns) outcomes were compared. The rate of total fertilisation failure in the normal sperm morphology rate <4% group was significantly higher compared with that in the normal sperm morphology rate ≥4% group (2.8% versus 1.2%, p = .012). Total fertilisation failure was completely resolved by early rescue intracytoplasmic sperm injection. The clinical pregnancy, implantation and abortion rates were not significantly different between the two groups. Additionally, the sex, preterm birth, low birth weight, live births and birth defect rates, gestational age and birthweight of newborns were not significantly different between the two groups. Thus, normal sperm morphology rate <4% significantly increased the total fertilisation failure rate but did not affect the clinical or neonatal outcomes.

The impact of follicle-flushing during oocyte collection on embryo development of in-vitro fertilization.

BACKGROUND: To evaluate the impact of follicle-flushing during oocyte collection on embryo development potential retrospectively. METHODS: A total of 1714 cases, including 133 who experienced retrieval difficulty (repeated follicle-flushing) on the day of oocyte retrieval (difficulty group) and the control 1581 cases (control group), were assessed in this retrospective study. The number of oocytes recovered, two pro-nuclei fertilization (2PN-fertilization), day 3 good-quality embryo and day 5/6 blastocyst utilization rates were compared between the difficulty group and control group correspondingly. Embryo implantation, clinical pregnancy and neonatal outcomes were further analyzed between the two groups in the fresh day- 3 embryo transfer cycles. RESULTS: The number of oocytes recovered in the difficulty group (9.08 ± 4.65) were significantly reduced compared with the control group (12.13 ± 5.27),P < 0.001; The 2PN-fertilization, day 3 good-quality embryo and blastocyst utilization rates were significantly lower in the difficulty group compared with controls (71.7% vs. 75.7%; 52.7% vs. 56.5%; 31.9% vs. 37.0%, all P < 0.05). Embryo implantation in the difficulty group was 53.2%, which was lower than the control value of 58.7%, although not reaching statistical significance. The rate of fresh embryo transfer cycles in the difficulty group was lower than normal ones (51.88% vs. 61.99%, P = 0.026). The pregnancy and live birth rates were similar between the two groups. But the rate of spontaneous miscarriages of the difficulty group was higher than the control group, although not reaching statistical significance. The neonatal outcomes had no statistical difference between the two groups. CONCLUSIONS: Oocyte retrieval difficulty, which include repeated flushing and the corresponded extending time required for oocyte recovery, significantly reduced day 3 good-quality embryo and blastocyst utilization rates of these patients. But the live birth rate had no difference between the difficulty group and the normal ones.

Comparison of the pregnancy and obstetric outcomes between single cleavage-stage embryo transfer and single blastocyst transfer by time-lapse selection of embryos.

To compare the pregnancy and obstetric outcomes following single cleavage-stage embryo transfer (SCT) and single blastocyst transfer (SBT) using time-lapse imaging (TLI), a total of 2066 normally fertilized and cleaved embryos from 233 patients were divided into Day 3 SCT group (n = 171) and Day 5 SBT group (n = 62) according to patient's willingness. Embryo selection criteria were based on embryo cleavage patterns, timing parameters, and blastocyst quality. The pregnancy and obstetric outcomes of each group were evaluated. There were no statistically significant differences with regard to pregnancy outcomes including the implantation rate, early abortion rate, ongoing pregnancy rate and live birth rate, and obstetric outcomes including preterm birth rate, gestational week, birth height, birth weight and fetal malformation rate between SCT group and SBT group. SBT group had significantly higher monozygotic twinning (MZT) rates than SCT group (6.98% vs. 0, p < .05). Although not statistically significant, there was a trend of higher proportion of male-to-female sex ratio at birth in SBT group than SCT group (1.38 vs. 1.05). Based on the combination of cleavage patterns and timing parameters, SCT may be an alternative to SBT because it can provide similar pregnancy and obstetric outcomes and meanwhile lower monozygotic twinning rates.

Effect of embryo and blastocyst transfer on the birthweight of live-born singletons from FET cycles.

PURPOSE: To evaluate the effect of culture duration (embryo (day 3) transfer vs. blastocyst (day 5-6) transfer) on the birthweight of singletons from frozen embryo transfer (FET) cycles. METHODS: A total of 1092 singletons were analyzed in this retrospective study. The distribution of large for gestational age (LGA) infants, the mean birthweight, and z scores of singletons were compared between the day 3 and day 5-6 transfer groups. Multiple linear regression analysis was performed to evaluate the relationships between confounding factors and singleton birthweight. RESULTS: The proportion of LGA infants significantly increased with BMI (BMI < 20, 12.8%; 20 ≤ BMI ≤ 25, 23.2%; BMI > 25, 32.3%; P < 0.0001). However, the proportions of small for gestational age (SGA) and LGA infants were not significantly different between day 3 and day 5-6 transfers. The absolute mean birthweight of singletons was not significantly different between day 3 transfer (3422 ± 547 g) and day 5-6 transfer (3433 ± 559 g; P = 0.732). The z scores (calculated from a reference population) of singletons were also not significantly different between the two groups (0.499 vs. 0.533, P = 0.625). Multiple linear regression analysis showed that maternal BMI, gestational age, and infant gender had significant effects on singleton birthweight, while culture duration (P = 0.731) did not significantly affect singleton birthweight. CONCLUSIONS: In vitro culture duration did not affect the birthweight of newborns resulting from day 3 to day 5-6 transfers in FET cycles.

Involvement of Protein Acyltransferase ZDHHC3 in Maintaining Oocyte Meiotic Arrest in Xenopus laevis.

Fully grown oocytes of most vertebrates are arrested at prophase I of meiosis (G2 arrest). Upon exposure to steroid hormones, oocytes resume meiotic process, also called G2/M transition. The G protein-signaling pathway has been shown to play essential roles in the meiotic arrest at G2 phase. Previously, we showed that long chain fatty acyl-coenzyme A synthetase acsl1b was required for maintaining the meiotic arrest in Xenopus Acsl1b presumably synthesizes palmitoyl-coenzyme A that can be utilized by acyltransferases to modify proteins essential for the G2 arrest. In the present study, we report that protein acyltransferase ZDHHC3 functions downstream of acsl1b to maintain oocyte meiotic arrest. Depletion of maternal ZDHHC3 RNA in oocytes reduces the progesterone threshold to promote G2/M transition from 2 to 0.01 µM. As expected, Gs alpha palmitoylation level is greatly decreased in ZDHHC3-depleted oocytes. Furthermore, we mapped ZDHHC3 palmitoylation sites in Gs alpha and showed that palmitoylation-deficient Gs alpha failed to arrest oocytes at G2. We also identified a critical residue in ZDHHC3 critically required for its palmitoylation activity toward Gs alpha. Taken together, ZDHHC3 is a key acyltransferase to palmitoylate proteins in order to maintain G2 arrest in Xenopus oocytes.

RNF2/Ring1b negatively regulates p53 expression in selective cancer cell types to promote tumor development.

Large numbers of studies have focused on the posttranslational regulation of p53 activity. One of the best-known negative regulators for p53 is MDM2, an E3 ubiquitin ligase that promotes p53 degradation through proteasome degradation pathways. Additional E3 ligases have also been reported to negatively regulate p53. However, whether these E3 ligases have distinct/overlapping roles in the regulation of p53 is largely unknown. In this study, we identify RNF2 (ring finger protein 2) as an E3 ligase that targets p53 for degradation. The E3 ligase activity of RNF2 requires Bmi1 protein, a component of the polycomb group (PcG) complex. The up-regulation of p53 does not affect RNF2 expression. Unlike Mdm2, RNF2 only degrades p53 in selective cell lines, such as those from germ-cell tumors. The knockdown of RNF2 induces apoptosis, which can be rescued through the reduction of p53 expression. Moreover, the down-regulation of RNF2 expression in germ-cell tumors significantly reduces tumor cell growth, while the simultaneous down-regulation of both genes restores tumor cell growth in vitro and in tumor xenograft models. Furthermore, a reverse correlation between RNF2 and p53 expression was detected in human ovarian cancer tissues. Together, these results indicate that RNF2 is an E3 ligase for p53 degradation in selective cells, implicating RNF2 as a therapeutic target to restore tumor suppression through p53 in certain tumor cells.

What sperm parameters effect blastocyst formation and quality during ICSI with severe male infertility.

Sperm-derived genetic material contributes half of the genome to the embryo, hence it's crucial to investigate which sperm parameter influences blastocyst formation in the intracytoplasmic sperm injection (ICSI) cycles with severe male infertility. The retrospective study analyzed 296 ICSI cycles with severe oligoasthenoteratozoospermia (OAT) and 99 ICSI cycles with preimplantation genetic testing for aneuploidy (PGT-A). Following the correlation analysis, data stratifications were performed in the OAT ICSI subgroup. The results showed that the matching blastocyst in the OAT ICSI cycles had inferior sperm parameters. DFI and sperm morphology had an influence on the blastocyst formation rate and the high-quality blastocysts formation rate on Day6, but no significant effect on the blastocyst development on Day 5. The high-quality blastocysts formation rate and ratio of high-quality blastocyst on Day 6 were demonstrably better in the subgroup of the teratozoospermic morphology when DFI was within the normal range. In the case of the normal sperm morphology, no statistically significant difference was found in blastocyst development, although there were numerical differences within different DFI subgroups. It was concluded that the blastocyst quality and development declined with the decreased sperm qualities.

ZP1-Y262C mutation causes abnormal zona pellucida formation and female infertility in humans.

Defective oocyte maturation is a common cause of female infertility. The loss of the zona pellucida (ZP) represents a specific condition of impaired oocyte maturation. The extracellular matrix known as the ZP envelops mammalian oocytes and preimplantation embryos, exerting significant influence on oogenesis, fertilization, and embryo implantation. However, the genetic factors leading to the loss of the ZP in oocytes are not well understood. This study focused on patients who underwent oocyte retrieval surgery after ovarian stimulation and were found to have abnormal oocyte maturation without the presence of the ZP. Ultrasonography was performed during the surgical procedure to evaluate follicle development. Peripheral blood samples from the patient were subjected to exome sequencing. Here, a novel, previously unreported heterozygous mutation in the ZP1 gene was identified. Within the ZP1 gene, we discovered a novel heterozygous mutation (ZP1 NM_207341.4:c.785A>G (p.Y262C)), specifically located in the trefoil domain. Bioinformatics comparisons further revealed conservation of the ZP1-Y262C mutation across different species. Model predictions of amino acid mutations on protein structure and cell immunofluorescence/western blot experiments collectively confirmed the detrimental effects of the ZP1-Y262C mutation on the function and expression of the ZP1 protein. The ZP1-Y262C mutation represents the novel mutation in the trefoil domain of the ZP1 protein, which is associated with defective oocyte maturation in humans. Our report enhances comprehension regarding the involvement of ZP-associated genes in female infertility and offers enriched understanding for the genetic diagnosis of this condition.

The effect of the day 3 embryo cell number on the neonatal outcomes of day 5 single blastocyst transfer in frozen embryo transfer cycles.

OBJECTIVE: To evaluate the influence of the day 3 embryo cell number on the neonatal outcomes of day 5 single blastocyst transfer in frozen embryo transfer (FET) cycles. METHODS: This retrospective study analysed a total of 2315 delivery cycles of day 5 single blastocyst transfer in FET cycles, including 489, 761 and 1103 live-born infants segregated according to a day 3 embryo cell number of <8, 8 and >8 cells, respectively. The neonatal outcomes of the three groups were compared. RESULTS: The day 3 embryo cell number did not significantly affect the incidence of monozygotic twins. The sex ratio increased as the day 3 embryo cell number increased, but the difference was not statistically significant. There were no significant differences in the rates of preterm birth or low birth weight among the three groups. The rates of stillbirths and neonatal deaths were also not significantly different among the three groups. Moreover, the day 3 embryo cell number did not increase the risk of birth defects in newborns. CONCLUSIONS: The day 3 embryo cell number did not significantly affect neonatal outcomes.

A novel homozygous variant in PADI6 is associate with human cleavage-stage embryonic arrest.

Repeated absence of useable embryos is a difficult problem for infertility patients. Among them, embryonic developmental arrest is more common, but the genetic cause is not known. The embryos of a patient who came to our hospital three times could not develop beyond the four-cell stage. In addition to recording the developmental details of the embryos by daily photo-taking, the PADI6 R132C homozygous variants was further confirmed by whole-exome sequencing. Subsequently, PADI6 R132C was analyzed by bioinformatics methods for conservativeness across species. In addition, the possible impact of the pathogenic mutation on the structure of the protein PADI6 were also assessed. Generally, we identified a homozygous variants [NM_207421.4, c.394C>T(p.R132C] in the middle protein-arginine deiminase domain in PADI6 gene. The homozygous variant is highly conserved across species. Homozygous variant in PADI6 R132C could cause a human cleavage-stage embryonic arrest in female patients. These findings provide further evidence for the important roles of the homozygous PADI6R132C variant in embryonic development. Our findings contribute to a deeper understanding of the molecular genetic basis of female infertility.

Maternal circadian disruption before pregnancy impairs the ovarian function of female offspring in mice.

Circadian disturbance brought on by shift employment, nighttime light pollution, and other factors is quite prevalent in contemporary culture. However, the effect of maternal circadian disruption before pregnancy on the reproduction of offspring in mice requires further research. Herein, we exposed female ICR mice to constant light to establish a model of preconceptional circadian disruption and then checked the ovarian function of female offspring (named the CLE group below). Our results revealed obesity, abnormal lipid metabolism and earlier puberty onset in the CLE group. Additionally, impaired ovarian follicle development, oocyte quality and preimplantation embryo development were shown in the CLE group. Moreover, the expression levels of Gnrh1 in the hypothalamus and Cyp17a1, Bmper, Bdnf and Lyve1 in ovaries, as well as circadian clock genes, including Clock, Cry1, Nr1d2 and Per2, were significantly downregulated in the CLE group. Mechanistically, immune responses, including the interleukin-17 (IL-17) signalling pathway, cytokine-cytokine receptor interaction and the chemokine signalling pathway, were altered in the CLE group, which may be responsible for the damaged ovarian function.

Granulosa cell mevalonate pathway abnormalities contribute to oocyte meiotic defects and aneuploidy.

With aging, abnormalities during oocyte meiosis become more prevalent. However, the mechanisms of aging-related oocyte aneuploidy are not fully understood. Here we performed Hi-C and SMART-seq of oocytes from young and old mice and reveal decreases in chromosome condensation and disrupted meiosis-associated gene expression in metaphase I oocytes from aged mice. Further transcriptomic analysis showed that meiotic maturation in young oocytes was correlated with robust increases in mevalonate (MVA) pathway gene expression in oocyte-surrounding granulosa cells (GCs), which was largely downregulated in aged GCs. Inhibition of MVA metabolism in GCs by statins resulted in marked meiotic defects and aneuploidy in young cumulus-oocyte complexes. Correspondingly, supplementation with the MVA isoprenoid geranylgeraniol ameliorated oocyte meiotic defects and aneuploidy in aged mice. Mechanically, we showed that geranylgeraniol activated LHR/EGF signaling in aged GCs and enhanced the meiosis-associated gene expression in oocytes. Collectively, we demonstrate that the MVA pathway in GCs is a critical regulator of meiotic maturation and euploidy in oocytes, and age-associated MVA pathway abnormalities contribute to oocyte meiotic defects and aneuploidy.

Activity of long-chain acyl-CoA synthetase is required for maintaining meiotic arrest in Xenopus laevis.

In most vertebrates, fully grown oocytes are arrested in meiotic prophase I and only resume the cell cycle upon external stimuli, such as hormones. The proper arrest and resumption of the meiotic cycle is critical for reproduction. A Galpha(S) signaling pathway essential for the arrest is conserved in organisms from Xenopus to mouse and human. A previous gene association study implicated that mutations of human ACSL6 may be related to premature ovarian failure. However, functional roles of ACSL6 in human infertility have yet to be reported. In the present study, we found that triacsin C, a potent and specific inhibitor for ACSL, triggers maturation in Xenopus and mouse oocytes in the absence of hormone, suggesting ACSL activity is required for the oocyte arrest. In Xenopus, acsl1b may fulfill a major role in the process, because inhibition of acsl1b by knocking down its RNA results in abnormal acceleration of oocyte maturation. Such abnormally matured eggs cannot support early embryonic development. Moreover, direct inhibition of protein palmitoylation, which lies downstream of ACSLs, also causes oocyte maturation. Furthermore, palmitoylation of Galpha(s), which is essential for its function, is inhibited when the ACSL activity is blocked by triacsin C in Xenopus. Thus, disruption of ACSL activity causes inhibition of the Galpha(s) signaling pathway in the oocytes, which may result in premature ovarian failure in human.