The beneficial effects of reduced magnesium during the oocyte-to-embryo transition are conserved in mice, domestic cats and humans

FGF2, LIF, and IGF-1 supplementation improves mouse oocyte in vitro maturation via increased glucose metabolism†

Chemically defined oocyte maturation media supplemented with FGF2, LIF, and IGF-1 (FLI medium) enabled significantly improved oocyte quality in multiple farm animals, yet the molecular mechanisms behind such benefits were poorly defined. Here, we first demonstrated that FLI medium enhanced mouse oocyte quality assessed by blastocyst formation after in vitro fertilization and implantation and fetal development after embryo transfer. We then analyzed the glucose concentrations in the spent media; reactive oxygen species concentrations; mitochondrial membrane potential; spindle morphology in oocytes; and the abundance of transcripts of endothelial growth factor-like factors, cumulus expansion factors, and glucose metabolism-related genes in cumulus cells. We found that FLI medium enabled increased glucose metabolism through glycolysis, pentose phosphate pathway, and hexosamine biosynthetic pathway, as well as more active endothelial growth factor-like factor expressions in cumulus cells, resulting in improved cumulus cell expansion, decreased spindle abnormality, and overall improvement in oocyte quality. In addition, the activities of MAPK1/3, PI3K/AKT, JAK/STAT3, and mTOR signaling pathways in cumulus cells were assessed by the phosphorylation of MAPK1/3, AKT, STAT3, and mTOR downstream target RPS6KB1. We demonstrated that FLI medium promoted activations of all these signaling pathways at multiple different time points during in vitro maturation.

Control of mitochondrial integrity influences oocyte quality during reproductive aging

Reduced quality in oocytes from women of advanced maternal age (AMA) is associated with dysfunctional mitochondria. The objective of this study was to investigate the mechanisms controlling mitochondrial quality during maternal aging in mouse and human oocytes. We first evaluated the expression of proteins involved in the mitochondrial unfolded protein response (UPRmt) and mitophagy in in vivo matured metaphase II (MII) oocytes collected from young and aged mice. Expression of UPRmt proteins, HSPD1 and LONP1, and mitophagy proteins, total-PRKN and phosphorylated-PRKN, was significantly decreased in aged compared to young oocytes. Treatment of aged oocytes during in vitro maturation with the mitochondrially targeted antioxidant mitoquinone (MQ) specifically restored total-PRKN and phosphorylated-PRKN expression to levels seen in young oocytes. We next investigated whether maturing young oocytes under a high-oxygen environment would mimic the effects observed in oocytes from aged females. Phosphorylated-PRKN expression in oxidatively stressed young oocytes was reduced compared to that in oocytes matured under normal oxygen levels, and the mitochondrial DNA (mtDNA) copy number was increased. Treating oxidatively challenged young oocytes with MQ restored the phosphorylated-PRKN expression and mtDNA copy numbers. Treatment of oxidatively challenged oocytes with MQ also increased the co-localization of mitochondria and lysosomes, suggesting increased mitophagy. These data correlated with the developmental potential of the oocytes, as blastocyst development and hatching of oxidatively stressed oocytes were reduced, while treatment with MQ resulted in a significant increase in blastocyst development and hatching, and in the percentage of inner cell mass. Consistent with our results in mice, MII oocytes from women of AMA exhibited a significant decrease in phosphorylated-PKRN and total-PRKN compared to those of young women. Our findings suggest that the protein machinery to control the health of the mitochondria via UPRmt and mitophagy may be compromised in oocytes from aged females, which may result in inefficient clearance of dysfunctional mitochondria and reduced oocyte quality.

Estrogen signaling encourages blastocyst development and implantation potential

PURPOSE

Estrogen is well-known for preparing uterine receptivity. However, its roles in regulating embryo development and implantation are unclear. Our objective was to characterize estrogen receptor 1 (ESR1) in human and mouse embryos and determine the effect of estradiol (E2) supplementation on pre- and peri-implantation blastocyst development.

METHODS

Mouse embryos, 8-cell through hatched blastocyst stages, and human embryonic days 5-7 blastocysts were stained for ESR1 and imaged using confocal microscopy. We then treated 8-cell mouse embryos with 8 nM E2 during in vitro culture (IVC) and examined embryo morphokinetics, blastocyst development, and cell allocation into the inner cell mass (ICM) and trophectoderm (TE). Finally, we disrupted ESR1, using ICI 182,780, and evaluated peri-implantation development.

RESULTS

ESR1 exhibits nuclear localization in early blastocysts followed by aggregation, predominantly in the TE of hatching and hatched blastocysts, in human and mouse embryos. During IVC, most E2 was absorbed by the mineral oil, and no effect on embryo development was found. When IVC was performed without an oil overlay, embryos treated with E2 exhibited increased blastocyst development and ICM:TE ratio. Additionally, embryos treated with ICI 182,780 had significantly decreased trophoblast outgrowth during extended embryo culture.

CONCLUSION

Similar ESR1 localization in mouse and human blastocysts suggests a conserved role in blastocyst development. These mechanisms may be underappreciated due to the use of mineral oil during conventional IVC. This work provides important context for how estrogenic toxicants may impact reproductive health and offers an avenue to further optimize human-assisted reproductive technology (ART) to treat infertility.

Electrophysiology of Human Gametes: A Systematic Review

PURPOSE

Oocytes and spermatozoa are electrogenic cells with the ability to respond to electrical stimuli and modulate their electrical properties accordingly. Determination of the ionic events during the gamete maturation helps to design suitable culture media for gametes in assisted reproductive technology (ART). The present systematic review focuses on the electrophysiology of human gametes during different stages of maturation and also during fertilization.

MATERIALS AND METHODS

The reports published in the English language between January 2000 and July 2021 were extracted from various electronic scientific databases following the PRISMA checklist using specific MeSH keywords.

RESULTS

Subsequent to the screening process with defined inclusion and exclusion criteria, 60 articles have been included in this review. Among them, 11 articles were directly related to the electrophysiology of human oocytes and 49 physiology department to the electrophysiology of human spermatozoa.

CONCLUSIONS

Gametes generate electrical currents by ionic exchange, particularly Na+, K+, Cl-, H+, Zn2+, Cu2+, Se2+, Mg2+, HCO3-, and Ca2+ through specific ion channels in different stages of gamete maturation. The ionic concentrations, pH, and other physicochemical variables are modulated during the gametogenesis, maturation, activation, and the fertilization process following gamete function and metabolism. The electrical properties of human gametes change during different stages of maturation. Although it is demonstrated that the electrical properties are significant regulators of cell signaling and are fundamental to gamete maturation and fertilization, their exact roles in these processes are still poorly understood. Further research is required to unveil the intricate electrophysiological processes of human gamete maturation.

Deletion of TRPV3 and CaV3.2 T-type channels in mice undermines fertility and Ca2+ homeostasis in oocytes and eggs

Ca2+ influx during oocyte maturation and after sperm entry is necessary to fill the internal Ca2+ stores and for complete egg activation. We knocked out the transient receptor potential vanilloid member 3 (TRPV3) and the T-type channel, CaV3.2, to determine their necessity for maintaining these functions in mammalian oocytes/eggs. Double-knockout (dKO) females were subfertile, their oocytes and eggs showed reduced internal Ca2+ stores, and, following sperm entry or Plcz (also known as Plcz1) cRNA injection, fewer dKO eggs displayed Ca2+ responses compared to wild-type eggs, which were also of lower frequency. These parameters were rescued and/or enhanced by removing extracellular Mg2+, suggesting that the residual Ca2+ influx could be mediated by the TRPM7 channel, consistent with the termination of divalent-cation oscillations in dKO eggs by a TRPM7 inhibitor. In total, we demonstrated that TRPV3 and CaV3.2 mediate the complete filling of the Ca2+ stores in mouse oocytes and eggs. We also showed that they are required for initiating and maintaining regularly spaced-out oscillations, suggesting that Ca2+ influx through PM ion channels dictates the periodicity and persistence of Ca2+ oscillations during mammalian fertilization.

Fatty acids present in commercial albumin preparations differentially affect development of murine embryos before and during implantation

OBJECTIVE

To characterize fatty acid (FA) profile of commercially available albumin products and determine their effect on embryonic development.

DESIGN

Research study.

SETTING

Private research facility.

ANIMAL(S)

Outbred mice aged 4-8 weeks.

INTERVENTION(S)

Gas chromatography-mass spectrometry was used to quantify the FA content of 15 commercial albumins. Embryos were produced in media containing different albumin products, with or without carnitine or exogenous FA supplementation, to determine their effect on embryo development in vitro.

MAIN OUTCOME MEASURE(S)

Total micrograms of FA per milligram of albumin for the 15 albumin products, blastocyst development, cell number, allocation to the trophectoderm (TE) or inner cell mass (ICM), and evaluation of morphology during implantation.

RESULT(S)

The albumin products contained 0.07-16.77 μg total FA/mg albumin. Compared to media with with >1.4 μg FA/mg albumin, media with <0.5 μg FA/mg albumin supported improved blastocyst development, and addition of carnitine mitigated this difference. Addition of palmitoleic acid or oleic acid individually did not improve blastocyst development and decreased ICM:TE ratio. However, in the presence of carnitine, there was improved blastocyst development and maintenance of the ICM:TE ratio. Embryos cultured in Vitrolife human serum albumin with supplementation of carnitine, palmitoleic acid, and oleic acid were more likely to develop cells positive for POU5F1 in an extended embryo culture than embryos cultured in Origio serum protein substitute.

CONCLUSION(S)

Commercial albumin products contain FAs, which vary in abundance. These FAs have different effects on embryo development and quality before and during the implantation stage. Several of these albumin preparations are routinely used for human-assisted reproductive technologies; therefore, serious consideration is warranted when selecting a product for clinical use.

A novel culture medium with reduced nutrient concentrations supports the development and viability of mouse embryos

Further refinement of culture media is needed to improve the quality of embryos generated in vitro. Previous results from our laboratory demonstrated that uptake of nutrients by the embryo is significantly less than what is supplied in traditional culture media. Our objective was to determine the impact of reduced nutrient concentrations in culture medium on mouse embryo development, metabolism, and quality as a possible platform for next generation medium formulation. Concentrations of carbohydrates, amino acids, and vitamins could be reduced by 50% with no detrimental effects, but blastocyst development was impaired at 25% of standard nutrient provision (reduced nutrient medium; RN). Addition of pyruvate and L-lactate (+PL) to RN at 50% of standard concentrations restored blastocyst development, hatching, and cell number. In addition, blastocysts produced in RN + PL contained more ICM cells and ATP than blastocysts cultured in our control (100% nutrient) medium; however, metabolic activity was altered. Similarly, embryos produced in the RN medium with elevated (50% control) concentrations of pyruvate and lactate in the first step medium and EAA and Glu in the second step medium were competent to implant and develop into fetuses at a similar rate as embryos produced in the control medium. This novel approach to culture medium formulation could help define the optimal nutrient requirements of embryos in culture and provide a means of shifting metabolic activity towards the utilization of specific metabolic pathways that may be beneficial for embryo viability.

Increasing associations between defects in phospholipase C zeta and conditions of male infertility: not just ICSI failure?

PURPOSE

Oocyte activation is a fundamental event at mammalian fertilization. In mammals, this process is initiated by a series of characteristic calcium (Ca²⁺) oscillations, induced by a sperm-specific phospholipase C (PLC) termed PLCzeta (PLCζ). Dysfunction/reduction/deletion of PLCζ is associated with forms of male infertility where the sperm is unable to initiate Ca²⁺ oscillations and oocyte activation, specifically in cases of fertilization failure. This review article aims to systematically summarize recent advancements and controversies in the field to update expanding clinical associations between PLCζ and various male factor conditions. This article also discusses how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic PLCζ approaches, aiming to direct future research efforts to utilize such knowledge clinically.

METHODS

An extensive literature search was performed using literature databases (PubMed/MEDLINE/Web of Knowledge) focusing on phospholipase C zeta (PLCzeta; PLCζ), oocyte activation, and calcium oscillations, as well as specific male factor conditions.

RESULTS AND DISCUSSION

Defective PLCζ or PLCζ-induced Ca²⁺ release can be linked to multiple forms of male infertility including abnormal sperm parameters and morphology, sperm DNA fragmentation and oxidation, and abnormal embryogenesis/pregnancies. Such sperm exhibit absent/reduced levels, and abnormal localization patterns of PLCζ within the sperm head.

CONCLUSIONS

Defective PLCζ and abnormal patterns of Ca²⁺ release are increasingly suspected a significant causative factor underlying abnormalities or insufficiencies in Ca²⁺ oscillation-driven early embryogenic events. Such cases could potentially strongly benefit from relevant therapeutic and diagnostic applications of PLCζ, or even alternative mechanisms, following further focused research efforts.

Egg cylinder development during in vitro extended embryo culture predicts the post transfer developmental potential of mouse blastocysts

PURPOSE

To establish parameters during mouse extended embryo culture that accurately predict fetal developmental potential of a blastocyst without performing embryo transfer.

METHODS

Embryos of three varying qualities were produced: poor quality embryos produced from in vitro matured oocytes (IVM), intermediate quality embryos produced from in vivo matured oocytes followed by in vitro fertilization and embryo culture (IVF); high quality embryos developed in vivo (VIVO). Embryonic day (E) 3.5 embryos from each group with similar morphologies were used for surgical embryo transfer to assess implantation and fetal developmental potential, in addition to placing these embryos into extended culture until E 8.5 to examine outgrowth area, egg cylinder volume, epiblast cell number, and outgrowth morphologies by immunofluorescence and 3D confocal microscopy.

RESULTS

The proportional differences in epiblast cell number are strikingly similar to fetal development following embryo transfer, suggesting that this parameter may be indicative of the potential of an embryo to successfully develop into a fetus.

CONCLUSION

Extended embryo culture provides more accurate information regarding developmental potential than blastocyst morphological assessment. Specifically, epiblast cell number is an accurate and valuable predictor of fetal developmental potential. This work sets the stage for routine evaluation of embryo quality past the time embryos would normally be transferred. The ability to determine post implantation potential without embryo transfer may greatly improve efforts to culture higher quality embryos in vitro for human IVF, as well as reducing animal use and eliminating confounding maternal factors associated with embryo transfer experiments in research.

Ca2+ Signaling and Homeostasis in Mammalian Oocytes and Eggs

Changes in the intracellular concentration of calcium ([Ca2+]i) represent a vital signaling mechanism enabling communication between and among cells as well as with the environment. Cells have developed a sophisticated set of molecules, "the Ca2+ toolkit," to adapt [Ca2+]i changes to specific cellular functions. Mammalian oocytes and eggs, the subject of this review, are not an exception, and in fact the initiation of embryo devolvement in all species is entirely dependent on distinct [Ca2+]i responses. Here, we review the components of the Ca2+ toolkit present in mammalian oocytes and eggs, the regulatory mechanisms that allow these cells to accumulate Ca2+ in the endoplasmic reticulum, release it, and maintain basal and stable cytoplasmic concentrations. We also discuss electrophysiological and genetic studies that have uncovered Ca2+ influx channels in oocytes and eggs, and we analyze evidence supporting the role of a sperm-specific phospholipase C isoform as the trigger of Ca2+ oscillations during mammalian fertilization including its implication in fertility.

Magnesium is a critical element for competent development of bovine embryos

The study was designed to determine the impact of magnesium (Mg²⁺) on bovine embryo development. We found that two commercially available sources of bovine serum albumin (BSA) and fetal bovine serum (FBS) contained different amounts of Mg²⁺ residue: 4 ppm in ICPbio BSA, 114 ppm in Sigma BSA, and 44 ppm in FBS. When CR1 was used as basal medium, PVA and ICPbio BSA produced the lowest blastocyst yield (2.2-2.3%), whereas Sigma BSA increased blastocyst yield to 18.9% (P < 0.05). Supplementation of 1.4 mM MgCl₂ into the medium increased the blastocyst rate in the ICPbio BSA group (29.4%) but not in the PVA group (5.4%; P < 0.05) to a level comparable to that of the FBS group (33.7%; P > 0.05). We next found that increasing concentrations of MgCl₂ in the culture medium (ICPbio BSA) elevated blastocyst rate from 2.6% (0 mM), 38.4% (0.35 mM) to 50.2% (1.4 mM; P < 0.05), further maintained at 44.9% (2.1 mM) and 43.4% (2.8 mM) (P > 0.05). However, blastocyst rate was reduced to 31.4% (4.2 mM) and 29.4% (5.6 mM) when MgCl₂ supplement was increased (P < 0.05). Comparable blastocyst development was achieved in both ICPbio BSA (30.0-33.1%) and Sigma BSA (37.4-38.7%) groups when 1.4 mM Mg²⁺ was supplemented regardless of its source (MgCl₂ vs. MgSO₄; P > 0.05). In embryo transfer experiments, higher rates of pregnancy (54.3 vs. 41.5%) and calving (44.3 vs. 32.5%) were achieved in the CR1-Mg²⁺-supplemented BSA group compared with the FBS group with co-culture, respectively (P < 0.05). These results demonstrate that Mg²⁺ is a key ion that promotes competent blastocyst and term development. Therefore, a simple and efficient defined medium (CR1-Mg²⁺-BSA) can successfully replace complex serum and somatic cell co-culture.

In Vitro Culture of Embryos from Domestic Cats

A variety of protocols are available for the production of feline blastocysts from oocytes that are matured and fertilized in vitro. However, most of these protocols utilize media that were developed for other cell types or the embryos of other species. The protocol outlined in this chapter is based on a series of studies that led to the development of feline optimized culture medium (FOCM), a feline-specific, sequential medium system. The initial embryo culture medium was subsequently modified for both IVM and IVF. Using a small number of stock solutions, a series of media can be easily prepared that allows for immature cat oocytes to be matured and fertilized in vitro, with the resulting embryos developing to the blastocyst stage without the use of serum.

TRPM7 and CaV3.2 channels mediate Ca2+ influx required for egg activation at fertilization

The success of mammalian development following fertilization depends on a series of transient increases in egg cytoplasmic Ca²⁺, referred to as Ca²⁺ oscillations. Maintenance of these oscillations requires Ca²⁺ influx across the plasma membrane, which is mediated in part by T-type, Ca_V3.2 channels. Here we show using genetic mouse models that TRPM7 channels are required to support this Ca²⁺ influx. Eggs lacking both TRPM7 and Ca_V3.2 stop oscillating prematurely, indicating that together they are responsible for the majority of Ca²⁺ influx immediately following fertilization. Fertilized eggs lacking both channels also frequently display delayed resumption of Ca²⁺ oscillations, which appears to require sperm-egg fusion. TRPM7 and Ca_V3.2 channels almost completely account for Ca²⁺ influx observed following store depletion, a process previously attributed to canonical store-operated Ca²⁺ entry mediated by STIM/ORAI interactions. TRPM7 serves as a membrane sensor of extracellular Mg²⁺ and Ca²⁺ concentrations and mediates the effects of these ions on Ca²⁺ oscillation frequency. When bred to wild-type males, female mice carrying eggs lacking TRPM7 and Ca_V3.2 are subfertile, and their offspring have increased variance in postnatal weight. These in vivo findings confirm previous observations linking in vitro experimental alterations in Ca²⁺ oscillatory patterns with developmental potential and offspring growth. The identification of TRPM7 and Ca_V3.2 as key mediators of Ca²⁺ influx following fertilization provides a mechanistic basis for the rational design of culture media that optimize developmental potential in research animals, domestic animals, and humans.

A pre-in vitro maturation medium containing cumulus oocyte complex ligand-receptor signaling molecules maintains meiotic arrest, supports the cumulus oocyte complex and improves oocyte developmental competence

STUDY QUESTION

Can a pre-in vitro maturation (pre-IVM) medium containing signaling molecules rather than chemical/pharmaceutical agents, sustain meiotic arrest and improve developmental competence of in vitro matured oocytes in CF1 outbred mice?

SUMMARY ANSWER

A short 2 h period of pre-IVM prevents spontaneous meiotic resumption, improves mitochondria activity in subsequently matured oocytes, and increases developmental competence, pregnancy rate and implantation of resulting embryos.

WHAT IS KNOWN ALREADY

Spontaneous resumption of meiosis in vitro is detrimental for oocyte developmental competence. Pre-IVM systems that prevent spontaneous meiotic resumption with chemical/pharmaceutical agents are a promising approach to improving IVM oocyte competence; however, the success of these methods has proven to be inconsistent.

STUDY DESIGN, SIZE, DURATION

This study consisted of a series of experiments using cumulus oocyte complexes (COC) derived from outbred mice following ovarian stimulation. The study was designed to examine if a novel, ligand/receptor-based pre-IVM treatment could sustain meiotic arrest in vitro and improve oocyte developmental competence, compared to control IVM. Two pre-IVM durations (2 h and 24 h) were evaluated, and the effect of the mitochondrial stimulator PQQ during 24 h pre-IVM was studied.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Murine (outbred CF1) immature COC were cultured in vitro in the presence of C-type natriuretic peptide (CNP) (30 nM), estradiol (100 nM), FSH (1 × 10-4 IU/ml) and bone morphogenic protein 15 (BMP15) (100 ng/ml) for 2 h or 24 h prior to IVM. Meiotic status during pre-IVM and IVM was analyzed using orcein staining, and functionality of gap junction communication was confirmed using the functional gap junction inhibitor carbenoxolone (CBX). Oocytes exposed to pre-IVM treatment were compared to control oocytes collected on the same day from the same females and undergoing standard IVM. Developmental competence and embryo viability was assessed by oocyte mitochondrial activity and ATP concentration, in vitro embryo development following IVF and in vitro culture, blastocyst cell number and allocation, embryo morphokinetics, and embryo transfer. Differences were determined to be significant when P < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Both a short (2 h) and long (24 h) pre-IVM period successfully prevented spontaneous resumption of meiosis. Moreover, gap junctions remained open during the pre-IVM period, as shown by the resumption of meiosis (95.9 ± 2.1%) in the presence of CBX during pre-IVM. A 2 h pre-IVM treatment improved blastocyst development after 96 h of culture per cleaved embryo compared to control (71.9 ± 7.4% versus 53.3 ± 6.2%, respectively), whereas a longer 24 h pre-IVM had no effect on development. A short 2 h period of pre-IVM increased mitochondrial activity in mature oocytes. On the contrary, mitochondrial activity was reduced in mature oocytes following 24 h of arrest and IVM. Treatment of arrested COC with pyrroloquinoline quinone (PQQ) during the 24 h pre-IVM period successfully maintained mitochondrial activity equal to control. However, PQQ was not able to improve blastocyst development compared to pre-IVM 24 h without PQQ. Moreover, ATP concentration in mature oocytes following pre-IVM and/or IVM, did not differ between treatments. A 2 h pre-IVM period prior to IVM improved pregnancy rate following transfer to recipient females. Implantation was also improved after transfer of embryos derived from oocytes arrested for either 2 h or 24 h prior to IVM, compared to control IVM derived embryos (41.9 ± 9%, 37.2 ± 9.5% and 17.2 ± 8.3%, respectively), although fetal development did not differ.

LIMITATIONS, REASONS FOR CAUTION

Slower meiotic resumption and enhanced mitochondrial activity likely contribute to improved developmental competence of oocytes exposed to pre-IVM for 2 h, but further experiments are required to identify specific mechanisms. Maintaining oocytes in meiotic arrest for 24 h with this approach could be a potential window to improve oocyte quality. However, an initial attempt to utilize this period of arrest to manipulate quality with PQQ, a mitochondrial stimulator, did not improve oocyte competence.

WIDER IMPLICATIONS OF THE FINDINGS

IVM could be an attractive clinical alternative to conventional IVF, with reduced time, cost and reliance on high doses of exogenous hormones to stimulate follicle growth, thus eliminating ovarian hyperstimulation syndrome (OHSS). Currently IVM is not widely used as it results in reduced embryo development and lower pregnancy outcomes compared to embryos produced from in vivo matured oocytes. Our approach to IVM, incorporating a ligand/receptor pre-IVM period, could improve human oocyte quality following IVM leading to routine adoption of this patient friendly technology. In addition, our methodology of pre-IVM containing signaling molecules rather than chemical/pharmaceutical agents may prove to be more consistent at improving oocyte quality than those focusing only on cAMP modulation with pharmacological agents. Finally, a reliable method of maintaining oocytes in meiotic arrest in vitro provides a novel window of opportunity in which the oocyte may be manipulated to address specific physiological deficiencies prior to meiotic resumption.

LARGE SCALE DATA

N/A.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Colorado Center for Reproductive Medicine (CCRM, Lone Tree, Colorado USA). We declare no conflict of interest.

Culture conditions affect Ca2+ release in artificially activated mouse and human oocytes

Inconsistent fertilisation and pregnancy rates have been reported by different laboratories after application of ionomycin as a clinical method of assisted oocyte activation (AOA) to overcome fertilisation failure. Using both mouse and human oocytes, in the present study we investigated the effects of ionomycin and Ca2+ concentrations on the pattern of Ca2+ release and embryonic developmental potential. In the mouse, application of 5 μM ionomycin in potassium simplex optimisation medium (KSOM) or 10 µM ionomycin in Ca2+-free KSOM significantly reduced the Ca2+ flux and resulted in failure of blastocyst formation compared with 10 μM ionomycin in KSOM. Increasing the Ca2+ concentration up to three- or sixfold did not benefit mouse embryonic developmental potential. Similarly, 10 μM ionomycin-induced rise in Ca2+ in human oocytes increased with increasing total calcium concentrations in the commercial medium. Remarkably, we observed significantly reduced mouse embryo development when performing AOA over a period of 10 min in Quinn’s AdvantageTM Fertilisation medium (Cooper Surgical) and IVFTM medium (Vitrolife) compared with Sydney IVF COOK cleavage medium (Cook Ireland), using the same sequential culture system from the post-activation stage to blastocyst formation stage in different AOA groups. In conclusion, concentrations of both ionomycin and Ca2+ in culture media used during AOA can have significant effects on Ca2+ release and further embryonic developmental potential.

Exogenous growth factors do not affect the development of individually cultured murine embryos

PURPOSE

The objective of this study was to evaluate the effects of multiple growth factors on the development of individually cultured murine embryos.

METHODS

Embryos produced by in vitro fertilization using in vitro (IVM) or in vivo (IVO) matured oocytes from three strains of mice (CF1, Swiss Webster, B6D2F1) were cultured individually (10 μl) in the absence (control) or presence of growth factors (paf, epidermal growth factor [EGF], insulin-like growth factor 1 [IGF-1], and granulocyte-macrophage colony-stimulating factor [GM-CSF]). Blastocyst formation, hatching, and blastocyst cell numbers (trophectoderm, inner cell mass, and total) were evaluated on days 4 and 5 of culture. Post-hatching development of CF1 IVO embryos was also evaluated in vitro and in vivo.

RESULTS

The presence of growth factors did not improve the proportion of embryos forming blastocysts or initiating hatching for any of the types of embryos tested. The only significant (P < 0.05) effect of growth factors was a decrease in the proportion of embryos that formed blastocysts by day 5 in CF1 IVM embryos. The presence of growth factors also did not affect blastocyst cell numbers. For CF1 IVO embryos, the presence of growth factors during culture did not affect the proportion of embryos that attached to fibronectin-coated dishes, the size of the resulting outgrowths, or in vivo development following transfer.

CONCLUSION

Combinations of paf, EGF, GM-CSF, and IGF-1 did not improve development of murine embryos cultured individually in a sequential medium containing a defined protein source.

Applying metabolomic analyses to the practice of embryology: physiology, development and assisted reproductive technology

The advent of metabolomics technology and its application to small samples has allowed us to non-invasively monitor the metabolic activity of embryos in a complex culture environment. The aim of this study was to apply metabolomics technology to the analysis of individual embryos from several species during in vitro development to gain an insight into the metabolomics pathways used by embryos and their relationship with embryo quality. Alanine is produced by both in vivo- and in vitro-derived human, murine, bovine and porcine embryos. Glutamine is also produced by the embryos of these four species, but only those produced in vitro. Across species, blastocysts significantly consumed amino acids from the culture medium, whereas glucose was not significantly taken up. There are significant differences in the metabolic profile of in vivo- compared with in vitro-produced embryos at the blastocyst stage. For example, in vitro-produced murine embryos consume arginine, asparagine, glutamate and proline, whereas in vivo-produced embryos do not. Human embryos produce more alanine, glutamate and glutamine, and consume less pyruvate, at the blastocyst compared with cleavage stages. Glucose was consumed by human blastocysts, but not at a high enough level to reach significance. Consumption of tyrosine by cleavage stage human embryos is indicative of blastocyst development, although tyrosine consumption is not predictive of blastocyst quality. Similarly, although in vivo-produced murine blastocysts consumed less aspartate, lactate, taurine and tyrosine than those produced in vitro, consumption of these four amino acids by in vitro-derived embryos with high octamer-binding transcription factor 4 (Oct4) expression, indicative of high quality, did not differ from those with low Oct4 expression. Further application of metabolomic technologies to studies of the consumption and/or production of metabolites from individual embryos in a complete culture medium could transform our understanding of embryo physiology and improve our ability to produce developmentally competent embryos in vitro.

Composition of single-step media used for human embryo culture

OBJECTIVE

To determine compositions of commercial single-step culture media and test with a murine model whether differences in composition are biologically relevant.

DESIGN

Experimental laboratory study.

SETTING

University-based laboratory.

ANIMAL(S)

Inbred female mice were superovulated and mated with outbred male mice.

INTERVENTION(S)

Amino acid, organic acid, and ions content were determined for single-step culture media: CSC, Global, G-TL, and 1-Step. To determine whether differences in composition of these media are biologically relevant, mouse one-cell embryos were cultured for 96 hours in each culture media at 5% and 20% oxygen in a time-lapse incubator.

MAIN OUTCOME MEASURE(S)

Compositions of four culture media were analyzed for concentrations of 30 amino acids, organic acids, and ions. Blastocysts at 96 hours of culture and cell cycle timings were calculated, and experiments were repeated in triplicate.

RESULT(S)

Of the more than 30 analytes, concentrations of glucose, lactate, pyruvate, amino acids, phosphate, calcium, and magnesium varied in concentrations. Mouse embryos were differentially affected by oxygen in G-TL and 1-Step.

CONCLUSION(S)

Four single-step culture media have compositions that vary notably in pyruvate, lactate, and amino acids. Blastocyst development was affected by culture media and its interaction with oxygen concentration.

TRPM7-like channels are functionally expressed in oocytes and modulate post-fertilization embryo development in mouse

The Transient Receptor Potential (TRP) channels are a family of cationic ion channels widely distributed in mammalian tissues. In general, the global genetic disruption of individual TRP channels result in phenotypes associated with impairment of a particular tissue and/or organ function. An exception is the genetic ablation of the TRP channel TRPM7, which results in early embryonic lethality. Nevertheless, the function of TRPM7 in oocytes, eggs and pre-implantation embryos remains unknown. Here, we described an outward rectifying non-selective current mediated by a TRP ion channel in immature oocytes (germinal vesicle stage), matured oocytes (metaphase II eggs) and 2-cell stage embryos. The current is activated by specific agonists and inhibited by distinct blockers consistent with the functional expression of TRPM7 channels. We demonstrated that the TRPM7-like channels are homo-tetramers and their activation mediates calcium influx in oocytes and eggs, which is fundamental to support fertilization and egg activation. Lastly, we showed that pharmacological inhibition of the channel function delays pre-implantation embryo development and reduces progression to the blastocyst stage. Our data demonstrate functional expression of TRPM7-like channels in mouse oocytes, eggs and embryos that may play an essential role in the initiation of embryo development.

Next Generation Sequencing-Based Comprehensive Chromosome Screening in Mouse Polar Bodies, Oocytes, and Embryos

Advanced reproductive age is unequivocally associated with increased aneuploidy in human oocytes, which contributes to infertility, miscarriages, and birth defects. The frequency of meiotic chromosome segregation errors in oocytes derived from reproductively aged mice appears to be similar to that observed in humans, but a limitation of this important model system is our inability to accurately identify chromosome-specific aneuploidy. Here we report the validation and application of a new low-pass whole-genome sequencing approach to comprehensively screen chromosome aneuploidy in individual mouse oocytes and blastocysts. First, we validated this approach by using single mouse embryonic fibroblasts engineered to have stable trisomy 16. We further validated this method by identifying reciprocal chromosome segregation errors in the products of meiosis I (gamete and polar body) in oocytes from reproductively aged mice. Finally, we applied this technology to investigate the incidence of aneuploidy in blastocysts derived from in vitro- and in vivo-matured oocytes in both young and reproductively aged mice. Using this next generation sequencing approach, we quantitatively assessed meiotic and mitotic segregation errors at the single chromosome level, distinguished between errors due to premature separation of sister chromatids and classical nondisjunction of homologous chromosomes, and quantified mitochondrial DNA (mtDNA) segregation in individual cells. This whole-genome sequencing technique, therefore, greatly improves the utility of the mouse model system for the study of aneuploidy and is a powerful quantitative tool with which to examine the molecular underpinnings of mammalian gamete and early embryo chromosome segregation in the context of reproductive aging and beyond.

Building a better mouse embryo assay: effects of mouse strain and in vitro maturation on sensitivity to contaminants of the culture environment

PURPOSE

The aim of this study is to compare the sensitivity of the standard one-cell mouse embryo assay (MEA) to that using in vitro-matured oocytes from hybrid and outbred mice.

METHODS

The study was done by culturing embryos in the presence or absence of two concentrations (0.0005 or 0.001 % v/v) of Triton X-100 (TX100). Embryonic development, blastocyst cell numbers (total and allocation to the trophectoderm [TE] and inner cell mass [ICM]), and blastocyst gene expression were evaluated.

RESULTS

Neither concentration of TX100 affected (P > 0.05) cleavage, blastocyst development, or hatching in one-cell embryos from BDF1 mice. However, all cell number endpoints were reduced (P < 0.05) by the high concentration of TX100 and the number of ICM cells was reduced (P < 0.05) by the low concentration of TX100. Inhibitory (P < 0.05) effects of the high concentration of TX100 were observed in in vitro maturation (IVM) embryos from BDF1, CF1, and SW, but not ICR, mice. Cell number and allocation were negatively affected by the high concentration of TX100 in CF1 and SW embryos, but not in BDF1 or ICR embryos. The only developmental endpoints affected by the low concentration of TX100 were cleavage of BDF1 oocytes, blastocyst development of SW embryos, and cell numbers (total and inner cell mass (ICM)) of SW blastocysts.

CONCLUSIONS

The sensitivity of the MEA to TX100 is improved by using embryos from in vitro-matured oocytes, using oocytes from some outbred (SW or CF1, not ICR) strains of mice, and evaluating blastocyst cell number and allocation.