Infertility patients with chromosome inversions are not susceptible to an inter-chromosomal effect

PURPOSE

The aim of this study was to evaluate the incidence of an inter-chromosomal effect (ICE) in blastocyst-stage embryos from carriers of balanced chromosome inversions.

METHODS

Infertility patients (n = 52) with balanced inversions (n = 66 cycles), and maternal age-matched controls that concurrently cycled (n = 66), consented to an IVF cycle with preimplantation genetic testing for aneuploidy (PGT-A). Blastocyst-stage embryos underwent trophectoderm biopsy for PGT-A with only euploid blastocysts transferred in a subsequent frozen embryo transfer. Subtypes of inversions were included in aggregate: paracentric/pericentric, polymorphic/non-polymorphic, male/female carriers, and varying inversion sizes.

RESULTS

The incidence of aneuploidy was not significantly higher for the inversion patients compared to the controls (inversion = 48.8% vs. control = 47.2% ns). Following euploid blastocyst transfer, there were excellent live birth outcomes.

CONCLUSIONS

Carriers of balanced chromosome inversions did not exhibit higher aneuploidy rates for chromosomes that were not involved in the inversion compared to maternal age-matched controls, signifying the absence of an inter-chromosomal effect for this data set. These results provide the largest investigation of blastocyst embryos regarding the debated existence of an ICE resulting from the presence of an inversion during meiosis. However, further studies are warranted to investigate an ICE among inversions subtypes that were outside the scope of this study.

Human and mouse embryonic development, metabolism and gene expression are altered by an ammonium gradient in vitro

Ammonium is generated in culture media by the spontaneous deamination of amino acids at 37 °C and through the metabolism of amino acids by human embryos. The appearance of ammonium is a time-dependent phenomenon and can compromise embryo physiology, development and viability. In this study, the effects of a gradient of ammonium on the development, metabolism and transcriptome of human and mouse embryos were investigated. Pronucleate oocytes were cultured in the presence of an ammonium gradient that mimicked the spontaneous deamination of Eagle's amino acids together with 1 mM glutamine. All embryos were cultured in sequential media G1/G2 at 5% O2, 6% CO2 and 89% N2. Human embryo metabolism was assessed through a non-invasive fluorometric analysis of pyruvate consumption. Transcriptome analysis was performed on the resultant blastocysts from both species using a microarray technology. Embryo development prior to compaction was negatively affected by the presence of low levels of ammonium in both species. Human embryo metabolism was significantly inhibited after just 24 and 48 h of culture. Transcriptome analysis of blastocysts from both species revealed significantly altered gene expression profiles, both decreased and increased. Functional annotation of the altered genes revealed the following over represented biological processes: metabolism, cell growth and/or maintenance, transcription, cell communication, transport, development and transcription regulation. These data emphasize the enhanced sensitivity of the cleavage-stage embryo to its environment and highlight the requirement to renew culture media at frequent intervals in order to alleviate the in vitro induced effects of ammonium build-up in the environment surrounding the embryo.

Embryos whose polar bodies contain isolated reciprocal chromosome aneuploidy are almost always euploid

STUDY QUESTION

When a chromosome aneuploidy is detected in the first polar body and a reciprocal loss or gain of the same chromosome is detected in the second polar body, is the resulting embryo usually aneuploid for that chromosome?

SUMMARY ANSWER

When reciprocal aneuploidy occurs in polar bodies, the resulting embryo is usually normal for that chromosome, indicating that premature separation of sister chromatids (PSSC)—not non-disjunction—likely occurred in meiosis I.

WHAT IS KNOWN ALREADY

Single-nucleotide polymorphism-based microarray analysis can be used to accurately determine the chromosomal status of polar bodies and embryos. Sometimes, the only abnormality found is a reciprocal gain or loss of one or two chromosomes in the two polar bodies. Prediction of the status of the resulting embryo in these cases is problematic.

STUDY DESIGN, SIZE, DURATION

Blinded microarray analysis of previously diagnosed aneuploid embryos that had reciprocal polar body aneuploidy.

MATERIALS, SETTING, METHODS

IVF cycles were performed between 2008 and 2011 in patients aged 40 ± 3 years (range 35–47 years) with an indication for polar body-based aneuploidy screening. Thirty-five aneuploid vitrified Day 3 embryos were warmed, cultured to Day 5 and biopsied for microarray analysis. Predictions were made for the ploidy status of the embryo if PSSC or non-disjunction had occurred. The signal intensity for the aneuploid chromosome in the first polar body was compared between those that resulted in euploid and aneuploid embryos.

MAIN RESULTS AND THE ROLE OF CHANCE

Among 34 embryos with evaluable results, 31 were euploid on re-analysis. Of 43 chromosomes that had reciprocal aneuploidy in the polar bodies, 41 were disomic in the embryo, indicating that PSSC was likely to have occurred 95% (95% confidence interval 85–99%) of the time. The log 2 ratio signal intensity from the chromosomes that underwent non-disjunction, resulting in unbalanced embryos, were outliers when compared with those that underwent PSSC.

LIMITATIONS, REASONS FOR CAUTION

Although most embryos with reciprocal aneuploid polar bodies were euploid, it is unknown whether they maintain equivalent reproductive potential when transferred. Further study is needed to determine whether these embryos should be re-biopsied and considered for transfer.

WIDER IMPLICATIONS OF THE FINDINGS

This study is consistent with increasing evidence that PSSC is the primary cause of meiosis I errors in embryos from women of advanced reproductive age. Clinicians should be cautious in interpreting results from polar body aneuploidy screening, especially when only the first polar body is tested.

STUDY FUNDING/COMPETING INTEREST(S)

None.

The role of proteomics in defining the human embryonic secretome

Non-invasive gamete and embryo assessment is considered an important focus in assisted reproductive technologies (ART). Currently, the selection of embryos for transfer is based on morphological indices. Though successful, the field of ART would benefit from a non-invasive quantitative method of viability determination. Omics technologies, including transcriptomics, proteomics and metabolomics, have already begun providing evidence that viable gametes and embryos possess unique molecular profiles with potential biomarkers that can be utilized for developmental and/or viability selection. Unlike the human genome that is relatively fixed and steady throughout the human body, the human proteome, estimated at over a million proteins, is more complex, diverse and dynamic. It is the proteins themselves that contribute to the physiological homeostasis in any cell or tissue. Of particular interest in ART is the secretome, those proteins that are produced within the embryo and secreted into the surrounding environment. Defining the human embryonic secretome has the potential to expand our knowledge of embryonic cellular processes, including the complex dialogue between the developing embryo and its maternal environment, and may also assist in identifying those embryos with the highest implantation potential. Advances in proteomic technologies have allowed the non-invasive profiling of the human embryonic secretome with ongoing research focused on correlation with outcome. From a clinical perspective, embryo selection based on morphological assessment and non-invasive analysis of the human embryonic secretome may improve IVF success and lead to routine single embryo transfers.

Transcriptome analysis of in vivo and in vitro matured bovine MII oocytes

In vitro maturation (IVM) of mammalian oocytes does not support the same rates of embryo development or pregnancy when compared to oocytes that have matured in vivo. Therefore, environment has a significant influence on the oocyte's ability to complete maturation and acquire the mRNA and proteins required for successful fertilization and normal embryonic development. The aim of this study was to analyze the MII oocyte transcriptome between in vivo and in vitro conditions. Total RNA was extracted, processed and hybridized to the Affymetrix GeneChip Bovine Genome Array. Following normalization of the microarray data, analysis revealed 10 differentially expressed genes after IVM compared to in vivo matured controls, including Aqp3, Sept7, Abhd4 and Siah2 (P<0.05). K-means cluster analysis coupled with associated gene ontology, identified several biological processes affected by IVM, including metabolism, energy pathways, cell organization and biogenesis, and cell growth and maintenance. Quantitative real-time PCR validated the microarray data and also revealed altered expression levels after IVM of specific putatively imprinted genes, Igf2r, Peg3 and Snrpn (P<0.05). Distinct IVM transcription patterns reflected the oocyte's response to its surrounding environment. Monitoring transcription levels of key oocyte maturation genes may subsequently assist in improving IVM success.

Symposium: innovative techniques in human embryo viability assessment. Can proteomics help to shape the future of human assisted conception?

Proteomics describes the changes in all proteins expressed and translated from a single genome. At present little is known regarding either the genome or proteome of human gametes or the preimplantation embryo. The unravelling of this information is fundamental to understanding the complexity of reproductive physiology, including the dialogue between the developing embryo and its maternal environment. To date, a lack of sensitivity has been the main reason behind the inability to introduce proteomics technology into assisted reproduction techniques. Proteomics alone involves several sophisticated techniques including imaging, mass spectrometry and bioinformatics to identify, quantify and characterize a proteome. The recent increased sensitivity of these techniques has allowed for the development of new protocols that are capable of not only profiling the proteome of individual human oocytes and embryos, but also the proteins produced by the embryo into the surrounding medium (the secretome). Hence, the identification of proteins that are involved in oocyte maturation, embryo development and implantation could lead to further improvements in assisted reproduction techniques as well as the development of new diagnostic tests. Furthermore, proteomics may contribute in the design of a non-invasive viability assay to assist in the selection of embryos for transfer in human assisted reproduction.

Embryology in the era of proteomics

Currently, relatively little is known regarding the protein production of mammalian embryos. Unlike the genome, the proteome itself is dynamic reflecting both internal and external environmental stimuli. Until now the lack of sensitivity has remained a stumbling block for the global introduction of proteomics into the field of mammalian embryology. However, new developments in mass spectrometry have been revolutionary, utilizing protein profiling and peptide sequencing to elucidate underlying biological processes. The sensitivity of these platforms have allowed for the development of new protocols that are capable of profiling the proteome of individual mammalian oocytes and embryos. This information is fundamental to unravelling the complexity of embryo physiology including the dialogue between the developing embryo and its maternal environment. Such proteomic approaches are also assisting in the optimization of ART techniques, including oocyte cryopreservation and in vitro maturation. Embryo selection for transfer is another area of ART that should benefit in this era of proteomics. Currently, mammalian embryos are selected for transfer based on morphological grading systems. Although of great value, analysis of morphology alone cannot determine the embryo's physiological state or chromosomal complement. Subsequently, there is a need to identify in culture those embryos with the highest implantation potential. Proteomic analysis of the embryonic secretome (proteins produced by the embryo and secreted into the surrounding medium) followed by the identification of specific proteins critical for implantation, may lead to the development of a non-invasive viability assay to assist in the selection of embryos for transfer.

270 IN VITRO MATURATION ALTERS THE EXPRESSION OF SPECIFIC PUTATIVELY IMPRINTED GENES IN BOVINE MII OOCYTES

Genomic imprinting is an epigenetic form of gene regulation resulting in only one parental allele being expressed. Imprinted genes have diverse functions including the regulation of growth and development in mammals. Errors in genomic imprinting have been associated with human disease (e.g. Beckwith-Wiedemann Syndrome) and large offspring syndrome of in vitro-produced ruminant fetuses. The aim of this study was to investigate the effect of in vitro maturation (IVM) on the expression of specific putatively imprinted genes in the bovine oocyte. Cumulus-enclosed immature oocytes were collected from cattle after 6 injections of 50 mg FSH with transvaginal aspiration (TVA) performed 48 h post-final FSH injection. The oocytes were cultured in groups of 10 for 23 h in a defined maturation medium (G-Mat) with 5 mg of HSA and 100 ng mL-1 of epidermal growth factor (EGF; group A) or with 20% serum and 100 ng mL-1 of EGF (group B) at 38.5�C in 6% CO2 in air. In vivo-matured oocytes (group C) were also collected via TVA after the administration of 6 FSH injections (50 mg), prostaglandin (PG) with last FSH injection, and GnRH 37 h post-PG. Total RNA was extracted from individual MII oocytes in all 3 groups, and expression profiles of putatively imprinted genes (Igf2r, Peg3, and Snrpn) were assayed by real-time PCR (Roche Applied Biosciences, Indianapolis, IN, USA), relative to the housekeeping gene GAPDH. Statistical analysis of expression profiles was performed using REST software. Expression of the Igf2r and Peg3 putatively imprinted genes was significantly up-regulated in individual in vitro-matured MII oocytes (groups A and B, n = 5 replicates per group) when compared with control, individual in vivo-matured MII oocytes (group C, n = 5 replicates; P &lt; 0.05). Gene expression did not differ between in vitro- and in vivo-matured MII oocytes for the putatively imprinted gene, Snrpn. In conclusion, following in vitro maturation of bovine oocytes, the putatively imprinted genes Igf2r and Peg3 were aberrantly expressed in individual oocytes relative to in vivo controls. Both of these putatively imprinted genes have been implicated in the regulation of growth and apoptotic pathways during mammalian development. Analysis of such putatively imprinted genes will facilitate the development of more suitable oocyte maturation conditions. This research was supported by the Serono Research Institute.

1,2-propanediol and the type of cryopreservation procedure adversely affect mouse oocyte physiology

BACKGROUND

The aim of this work was to examine the effect of 1,2-propanediol (PrOH) and type of cryopreservation procedure (slow freezing and vitrification) on oocyte physiology.

METHODS

Intracellular calcium of mouse metaphase II (MII) oocytes was quantified by fluorescence microscopy. The effect of PrOH on cell physiology was further assessed through analysis of zona pellucida hardening and cellular integrity. Protein profiles of cryopreserved oocytes were generated by time-of-flight mass spectrometry (TOF-MS).

RESULTS

PrOH caused a protracted increase in calcium, which was sufficient to induce zona pellucida hardening and cellular degeneration. Using 'nominally calcium free' media during PrOH exposure significantly reduced the detrimental effects. Proteomic analysis identified numerous up- and down-regulated proteins after slow freezing when compared with control and vitrified oocytes.

CONCLUSIONS

Using such approaches to assess effects on cellular physiology is fundamental to improving assisted reproduction techniques (ART). This study demonstrates that PrOH causes a significant rise in intracellular calcium. Using calcium-free media significantly reduced the increase in calcium and the associated detrimental physiological effects, suggesting that calcium-free media should be used with PrOH. In addition, analysis of the oocyte proteome following cryopreservation revealed that slow freezing has a significant effect on protein expression. In contrast, vitrification had a minimal impact, indicating that it has a fundamental advantage for the cryopreservation of oocytes.

330 THE PROTEIN EXPRESSION PROFILE (SECRETOME) OF INDIVIDUAL CUMULUS - OOCYTE COMPLEXES DURING IVM IN THE MOUSE IS AFFECTED BY FSH

Studies of the protein expression profile into the surrounding medium (secretome) of in vitro-matured cumulus-oocyte complexes (COCs) have the potential to elucidate biochemical pathways involved in oogenesis, including the complex dialogue between the oocyte and its supporting cells. The understanding of these processes should assist in improving IVM success and fertility outcome, as early embryo development reflects the quality of the oocyte and its cumulus cells. Through the analysis of the individual COC secretome, we have investigated the effects of adding follicle stimulating hormone (FSH) to a defined maturation medium during IVM. COCs were collected from 3-week-old female mice (C57BL/6 � CBA) 48 h post-pregnant mare serum gonadotropin (PMSG) (5/iu) injection. Individual COCs were cultured in 5-�L drops of a defined maturation medium (0.25 mg/mL recombinant albumin) with the addition of 0, 2, 20, or 200 ng/mL FSH, under oil for 17 h. Oocytes were denuded and maturity recorded. Each microdrop of media (n = 8 oocytes per group) was collected, processed through an optimized series of buffers and washes prior to analysis by time-of-flight mass spectrometry (TOF-MS). Differential protein expression profiles were obtained from the secretome of individual COCs producing MII oocytes after maturation in differing doses of FSH. Statistical analysis revealed significant differences observed across 10 proteins/biomarkers with mass-to-charge (m/z) ratios ranging from 2.7 to 6 kDa (Mann-Whitney non-parametric test; P < 0.05). In addition, hierarchical and horizontal clustering analysis identified unique clusters of both up-regulated and down-regulated proteins/biomarkers within the m/z range of 2 to 18 kDa in the 2 ng/mL FSH group. Several of the individual COCs from the 20 ng/mL FSH group were also clustered alongside the 2 ng/mL group with similar protein expression profiles. In contrast, COCs cultured in the presence of 0 ng/mL and 200 ng/mL FSH were observed to cluster as a separate branch with distinctly different protein expression profiles. This study has determined for the first time the secretome profiles of individual COCs after IVM. These data have shown that the FSH dose in a defined maturation medium affects the secretome of an individual COC. Further investigation is currently underway to characterize these protein differences. The development of this proteomics approach will assist in revealing the intricate cellular function of an individual COC and elucidate critical pathways involved in mammalian oocyte maturation.

Mitotic errors in chromosome 21 of human preimplantation embryos are associated with non-viability

Fluorescent in situ hybridization (FISH) studies of human preimplantation embryos have demonstrated a high proportion of chromosomal mosaicism. To investigate the different timings and nature of chromosomal mosaicism, we developed single cell multiplex fluorescent (FL)-PCR to distinguish meiotic and mitotic cell division errors. Chromosome 21 was investigated as the model chromosome as trisomy 21 (Down's syndrome) represents the most common chromosomal aneuploidy that reaches live birth. Sister blastomeres from a total of 25 chromosome 21 aneuploid embryos were analysed. Of these, 13 (52%) comprised cells with concordant DNA fingerprints indicative of meiotic non-disjunction errors. The remaining 12 (48%) aneuploid embryos comprised discordant sister blastomere allelic profiles and thus were mosaic. Errors at all stages including metaphase (MI) (12%) and first (38%), second (31%) and third (19%) mitotic cleavage divisions were identified from the types and proportion of different allelic profiles. In addition, three embryos showed combined meiotic and mitotic cell division errors including non-disjunction and anaphase lag, suggesting that diploid cells had resulted from an aneuploid zygote. However, the majority of the mosaic aneuploid embryos showed mitotic gains and losses from a diploid zygote occurring prior to the activation of the embryonic genome. Allelic profiling of amniocytes from 15 prenatal diagnosis samples displayed only meiotic errors. There appears to be a large difference between the proportion of mosaic mitotic-derived trisomy 21 embryos and fetuses. These findings indicate that mosaic mitotic error of chromosome 21 is associated with non-viability.