The severity of meiotic aneuploidy is associated with altered morphokinetic variables of mouse oocyte maturation.

STUDY QUESTION: Is there an association between morphokinetic variables of meiotic maturation and the severity of aneuploidy following in vitro maturation (IVM) in the mouse? SUMMARY ANSWER: The severity of meiotic aneuploidy correlates with an extended time to first polar body extrusion (tPB1) and duration of meiosis I (dMI). WHAT IS KNOWN ALREADY: Morphokinetic variables measured using time-lapse technology allow for the non-invasive evaluation of preimplantation embryo development within clinical assisted reproductive technology (ART). We recently applied this technology to monitor meiotic progression during IVM of mouse gametes. Whether there is a relationship between morphokinetic variables of meiotic progression and aneuploidy in the resulting egg has not been systematically examined at the resolution of specific chromosomes. Next-generation sequencing (NGS) is a robust clinical tool for determining aneuploidy status and has been reverse-translated in mouse blastocysts and oocytes. Therefore, we harnessed the technologies of time-lapse imaging and NGS to determine the relationship between the morphokinetics of meiotic progression and egg aneuploidy. STUDY DESIGN SIZE DURATION: Cumulus-oocyte complexes were collected from large antral follicles from hyperstimulated CD-1 mice. Cumulus cells were removed, and spontaneous IVM was performed in the absence or presence of two doses of Nocodazole (25 or 50 nM) to induce a spectrum of spindle abnormalities and chromosome segregation errors during oocyte meiosis. Comprehensive chromosome screening was then performed in the resulting eggs, and morphokinetic variables and ploidy status were compared across experimental groups (control, n = 11; 25 nM Nocodazole, n = 13; 50 nM Nocodazole, n = 23). PARTICIPANTS/MATERIALS SETTING METHODS: We monitored IVM in mouse oocytes using time-lapse microscopy for 16 h, and time to germinal vesicle breakdown (tGVBD), tPB1, and dMI were analyzed. Following IVM, comprehensive chromosome screening was performed on the eggs and their matched first polar bodies via adaptation of an NGS-based preimplantation genetic testing for aneuploidy (PGT-A) assay. Bioinformatics analysis was performed to align reads to the mouse genome and determine copy number-based predictions of aneuploidy. The concordance of each polar body-egg pair (reciprocal errors) was used to validate the results. Ploidy status was categorized as euploid, 1-3 chromosomal segregation errors, or ≥4 chromosomal segregation errors. Additionally, aneuploidy due to premature separation of sister chromatids (PSSC) versus non-disjunction (NDJ) was distinguished. MAIN RESULTS AND THE ROLE OF CHANCE: We applied and validated state-of-the-art NGS technology to screen aneuploidy in individual mouse eggs and matched polar bodies at the chromosome-specific level. By performing IVM in the presence of different doses of Nocodazole, we induced a range of aneuploidy. No aneuploidy was observed in the absence of Nocodazole (0/11), whereas IVM in the presence of 25 and 50 nM Nocodazole resulted in an aneuploidy incidence of 7.69% (1/13) and 82.61% (19/23), respectively. Of the aneuploid eggs, 5% (1/20) was due to PSSC, 65% (13/20) to NDJ, and the remainder to a combination of both. There was no relationship between ploidy status and tGVBD, but tPB1 and the dMI were both significantly prolonged in eggs with reciprocal aneuploidy events compared to the euploid eggs, and this scaled with the severity of aneuploidy. Eggs with ≥4 aneuploid chromosomes had the longest tPB1 and dMI (P < 0.0001), whereas eggs with one to three aneuploid chromosomes exhibited intermediate lengths of time (P < 0.0001). LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: We used Nocodazole in this study to disrupt the meiotic spindle and induce aneuploidy in mouse oocytes. Whether the association between morphokinetic variables of meiotic progression and the severity of aneuploidy occurs with other compounds that induce chromosome segregation errors remain to be investigated. In addition, unlike mouse oocytes, human IVM requires the presence of cumulus cells, which precludes visualization of morphokinetic variables of meiotic progression. Thus, our study may have limited direct clinical translatability. WIDER IMPLICATIONS OF THE FINDINGS: We validated NGS in mouse eggs to detect aneuploidy at a chromosome-specific resolution which greatly improves the utility of the mouse model. With a tractable and validated model system for characterizing meiotic aneuploidy, investigations into the molecular mechanisms and factors which may influence aneuploidy can be further elaborated. Time-lapse analyses of morphokinetic variables of meiotic progression may be a useful non-invasive predictor of aneuploidy severity. STUDY FUNDING/COMPETING INTERESTS: This work was supported by the Bill & Melinda Gates Foundation (INV-003385). Under the grant conditions of the Foundation, a Creative Commons Attribution 4.0 Generic License has already been assigned to the Author Accepted Manuscript version that might arise from this submission. The authors have no conflict of interest to disclose.

Gas Phase Experimental and Computational Studies of AlkB Substrates: Intrinsic Properties and Biological Implications.

The gas phase acidity and proton affinity of nucleobases that are substrates for the DNA repair enzyme AlkB have been examined using both computational and experimental methods. These thermochemical values have not heretofore been measured and provide experimental data that help benchmark the theoretical results. We also use our gas phase results to lend insight into the AlkB mechanism, particularly in terms of the role AlkB plays in DNA repair, versus its complementary enzyme AlkA.

Accurate detection and frequency of abnormal ploidy in the human blastocyst.

OBJECTIVE: To validate the detection of abnormal ploidy in preimplantation embryos and evaluate its frequency in transferrable blastocysts. DESIGN: A high-throughput genome-wide single nucleotide polymorphism microarray-based preimplantation genetic testing (PGT) platform was validated using multiple positive controls, including cell lines of known haploid and triploid karyotypes and rebiopsies of embryos with initial abnormal ploidy results. This platform was then tested on all trophectoderm biopsies in a single PGT laboratory to calculate the frequency of abnormal ploidy and the parental and cell division origins of error. SETTING: Preimplantation genetic testing laboratory. PATIENT(S): The embryos from in vitro fertilization patients who elected for PGT were evaluated. Any patients who provided saliva samples were further analyzed for the parental and cell division origins of abnormal ploidy. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Evaluable positive controls showed 100% concordance with original karyotypes. The overall frequency of abnormal ploidy within a single PGT laboratory cohort was 1.43%. RESULT(S): All cell lines showed 100% concordance with the expected karyotype. Additionally, all evaluable rebiopsies showed 100% concordance with the original abnormal ploidy karyotype. The frequency of abnormal ploidy was 1.43%, with 29% of those being haploid or uniparental isodiploid, 2.5% uniparental heterodiploid, 68% triploid, and 0.4% tetraploid. Twelve haploid embryos contained maternal deoxyribonucleic acid, and 3 contained paternal deoxyribonucleic acid. Thirty-four triploid embryos were of maternal origin, and 2 were of paternal origin. Thirty-five triploid embryos had a meiotic origin of error, and 1 was of mitotic error. Of those 35 embryos, 5 originated from meiosis I, 22 originated from meiosis II, and 8 were deemed inconclusive. On the basis of specific abnormal ploidy karyotypes, 41.2% of embryos would be falsely classified as euploid, and 22.7% would be false-positive mosaics with the use of the conventional next-generation sequencing-based PGT methods. CONCLUSION(S): This study demonstrates the validity of a high-throughput genome-wide single nucleotide polymorphism microarray-based PGT platform to accurately detect abnormal ploidy karyotypes and predict the parental and cell division origins of error of evaluable embryos. This unique method improves the sensitivity of detection for abnormal karyotypes, which can reduce the chances of adverse pregnancy outcomes.