Time-lapse imaging of human embryos fertilized with testicular sperm reveals an impact on the first embryonic cell cycle.

Testicular sperm is increasingly used during in vitro fertilization treatment. Testicular sperm has the ability to fertilize the oocyte after intracytoplasmic sperm injection (ICSI), but they have not undergone maturation during epididymal transport. Testicular sperm differs from ejaculated sperm in terms of chromatin maturity, incidence of DNA damage, and RNA content. It is not fully understood what the biological impact is of using testicular sperm, on fertilization, preimplantation embryo development, and postimplantation development. Our goal was to investigate differences in human preimplantation embryo development after ICSI using testicular sperm (TESE-ICSI) and ejaculated sperm. We used time-lapse embryo culture to study these possible differences. Embryos (n = 639) originating from 208 couples undergoing TESE-ICSI treatment were studied and compared to embryos (n = 866) originating from 243 couples undergoing ICSI treatment with ejaculated sperm. Using statistical analysis with linear mixed models, we observed that pronuclei appeared 0.55 h earlier in TESE-ICSI embryos, after which the pronuclear stage lasted 0.55 h longer. Also, significantly more TESE-ICSI embryos showed direct unequal cleavage from the 1-cell stage to the 3-cell stage. TESE-ICSI embryos proceeded faster through the cleavage divisions to the 5- and the 6-cell stage, but this effect disappeared when we adjusted our model for maternal factors. In conclusion, sperm origin affects embryo development during the first embryonic cell cycle, but not developmental kinetics to the 8-cell stage. Our results provide insight into the biological differences between testicular and ejaculated sperm and their impact during human fertilization.

Effect of parental and ART treatment characteristics on perinatal outcomes.

STUDY QUESTION: Do parental characteristics and treatment with ART affect perinatal outcomes in singleton pregnancies? SUMMARY ANSWER: Both parental and ART treatment characteristics affect perinatal outcomes in singleton pregnancies. WHAT IS KNOWN ALREADY: Previous studies have shown that singleton pregnancies resulting from ART are at risk of preterm birth. ART children are lighter at birth after correction for duration of gestation and at increased risk of congenital abnormalities compared to naturally conceived children. This association is confounded by parental characteristics that are also known to affect perinatal outcomes. It is unclear to which extent parental and ART treatment characteristics independently affect perinatal outcomes. STUDY DESIGN, SIZE, DURATION: All IVF clinics in the Netherlands (n = 13) were requested to provide data on all ART treatment cycles (IVF, ICSI and frozen-thawed embryo transfers (FET)), performed between 1 January 2000, and 1 January 2011, which resulted in a pregnancy. Using probabilistic data-linkage, these data (n = 36 683) were linked to the Dutch Perinatal Registry (Perined), which includes all children born in the Netherlands in the same time period (n = 2 548 977). PARTICIPANTS/MATERIALS, SETTING, METHODS: Analyses were limited to singleton pregnancies that resulted from IVF, ICSI or FET cycles. Multivariable models for linear and logistic regression were fitted including parental characteristics as well as ART treatment characteristics. Analyses were performed separately for fresh cycles and for fresh and FET cycles combined. We assessed the impact on the following perinatal outcomes: birth weight, preterm birth below 37 or 32 weeks of gestation, congenital malformations and perinatal mortality. MAIN RESULTS AND THE ROLE OF CHANCE: The perinatal outcomes of 31 184 out of the 36 683 ART treatment cycles leading to a pregnancy were retrieved through linkage with the Perined (85% linkage). Of those, 23 671 concerned singleton pregnancies resulting from IVF, ICSI or FET. Birth weight was independently associated with both parental and ART treatment characteristics. Characteristics associated with lower birth weight included maternal hypertensive disease, non-Dutch maternal ethnicity, nulliparity, increasing duration of subfertility, hCG for luteal phase support (compared to progesterone), shorter embryo culture duration, increasing number of oocytes retrieved and fresh embryo transfer. The parental characteristic with the greatest effect size on birth weight was maternal diabetes (adjusted difference 283 g, 95% CI 228-338). FET was the ART treatment characteristic with the greatest effect size on birth weight (adjusted difference 100 g, 95% CI 84-117) compared to fresh embryo transfer. Preterm birth was more common among mothers of South-Asian ethnicity. Preterm birth was less common among multiparous women and women with 'male factor' as treatment indication (compared to 'tubal factor'). LIMITATIONS, REASONS FOR CAUTION: Due to the retrospective nature of our study, we cannot prove causality. Further limitations of our study were the inability to adjust for mothers giving birth more than once in our dataset, missing values for several variables and limited information on parental lifestyle and general health. WIDER IMPLICATIONS OF THE FINDINGS: Multiple parental and ART treatment characteristics affect perinatal outcomes, with birth weight being influenced by the widest range of factors. This highlights the importance of assessing both parental and ART treatment characteristics in studies that focus on the health of ART-offspring, with the purpose of modifying these factors where possible. Our results further support the hypothesis that the embryo is sensitive to its early environment. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by Foreest Medical School, Alkmaar, the Netherlands (grants: FIO 1307 and FIO 1505). B.W.M. reports grants from NHMRC and consultancy for ObsEva, Merck KGaA, iGenomics and Guerbet. F.B. reports research support grants from Merck Serono and personal fees from Merck Serono. A.C. reports travel support from Ferring BV. and Theramex BV. and personal fees from UpToDate (Hyperthecosis), all outside the remit of the current work. The remaining authors report no conflict of interests. TRIAL REGISTRATION NUMBER: N/A.

Chromosome segregation regulation in human zygotes: altered mitotic histone phosphorylation dynamics underlying centromeric targeting of the chromosomal passenger complex.

STUDY QUESTION: Are the kinase feedback loops that regulate activation and centromeric targeting of the chromosomal passenger complex (CPC), functional during mitosis in human embryos? SUMMARY ANSWER: Investigation of the regulatory kinase pathways involved in centromeric CPC targeting revealed normal phosphorylation dynamics of histone H2A at T120 (H2ApT120) by Bub1 kinase and subsequent recruitment of Shugoshin, but phosphorylation of histone H3 at threonine 3 (H3pT3) by Haspin failed to show the expected centromeric enrichment on metaphase chromosomes in the zygote. WHAT IS KNOWN ALREADY: Human cleavage stage embryos show high levels of chromosomal instability. What causes this high error rate is unknown, as mechanisms used to ensure proper chromosome segregation in mammalian embryos are poorly described. STUDY DESIGN, SIZE, DURATION: In this study, we investigated the pathways regulating CPC targeting to the inner centromere in human embryos. We characterized the distribution of the CPC in relation to activity of its two main centromeric targeting pathways: the Bub1-H2ApT120-Sgo-CPC and Haspin-H3pT3-CPC pathways. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was conducted between May 2012 and March 2014 on human surplus embryos resulting from in vitro fertilization treatment and donated for research. In zygotes, nuclear envelope breakdown was monitored by time-lapse imaging to allow timed incubations with specific inhibitors to arrest at prometaphase and metaphase, and to interfere with Haspin and Aurora B/C kinase activity. Functionality of the targeting pathways was assessed through characterization of histone phosphorylation dynamics by immunofluorescent analysis, combined with gene expression by RT-qPCR and immunofluorescent localization of key pathway proteins. MAIN RESULTS AND THE ROLE OF CHANCE: Immunofluorescent analysis of the CPC subunit Inner Centromere Protein revealed the pool of stably bound CPC proteins was not strictly confined to the inner centromere of prometaphase chromosomes in human zygotes, as observed in later stages of preimplantation development and somatic cells. Investigation of the regulatory kinase pathways involved in centromeric CPC targeting revealed normal phosphorylation dynamics of histone H2A at T120 (H2ApT120) by Bub1 kinase and subsequent recruitment of Shugoshin. However, phosphorylation of histone H3 at threonine 3 (H3pT3) by Haspin kinase failed to show the expected centromeric enrichment on metaphase chromosomes in the zygote, but not at later stages. Inhibition of Haspin revealed this activity to be essential for proper mitotic checkpoint complex activation in human zygotes, thus demonstrating an active mitotic checkpoint under normal conditions. Abolishment of H3pT3 during zygotic prometaphase further shows that centromeric H2ApT120 alone is not sufficient for proper shugoshin and CPC localization. As the removal of H3pT3 from the chromosome arms during prometaphase normally contributes to further centromeric enrichment of the CPC in somatic cells, CPC targeting may be less accurate in human zygotes. LIMITATIONS, REASONS FOR CAUTION: Owing to ethical limitations, tripronuclear zygotes were used in functional experiments. Although these represent the best available models, it is unknown if they are completely representative for dipronuclear zygotes. In addition, further research is needed to determine to what extent the differences we observed in H3T3 phosphorylation dynamics and CPC localization affect chromosome attachment. WIDER IMPLICATIONS OF THE FINDINGS: In the zygote, paternal and maternal chromosomes coming from two separate pronuclei, and with contrasting epigenetic signatures, need to be aligned on a single metaphase plate. Our results suggest that adaptations in mechanisms regulating CPC targeting exist in the human zygote, to ensure symmetric recruitment despite the epigenetic asymmetry between maternal and paternal chromosomes. This adaptation may come at a price regarding chromosome segregation fidelity. STUDY FUNDING/COMPETING INTERESTS: This study was funded by the Portuguese Fundação para a Ciência e Tecnologia and the Netherlands Organization for Scientific Research. The authors have no conflicts of interest to declare.

Parental origin of chromatin in human monopronuclear zygotes revealed by asymmetric histone methylation patterns, differs between IVF and ICSI.

In mouse zygotes, many post-translational histone modifications are asymmetrically present in male and female pronuclei. We investigated whether this principle could be used to determine the genetic composition of monopronuclear human zygotes in conventional IVF and ICSI. First we determined whether male female asymmetry is conserved from mouse to human by staining polypronuclear zygotes with antibodies against a subset of histone N-tail post-translational modifications. To analyze human monopronuclear zygotes, a modification, H3K9me3, was selected that is present in the maternal chromatin. After IVF a total of 45 monopronuclear zygotes were obtained. In 39 (87%) of zygotes a nonuniform staining pattern was observed, proof of a bi-parental origin and assumed to result into a diploid conception. Two zygotes showed no staining for the modification, indicating that the single pronucleus was of paternal origin. Four zygotes contained only maternally derived chromatin. ICSI-derived monopronuclear zygotes (n = 33) could also be divided into three groups based on the staining pattern of their chromatin: (1) of maternal origin (n = 15), (2) of paternal origin (n = 8) or (3) consisting of two chromatin domains as dominating in IVF (n = 10). Our data show that monopronuclear zygotes originating from IVF generally arise through fusion of parental chromatin after sperm penetration. Monopronuclear zygotes derived from ICSI in most cases contain uni-parental chromatin. The fact that chromatin was of paternal origin in 24% of ICSI and in 4% of the IVF zygotes confirms earlier results obtained by FISH on cleavage stages. Our findings are of clinical importance in IVF and ICSI practice.

Anti-Müllerian hormone: a marker for oocyte quantity, oocyte quality and embryo quality?

Serum anti-Müllerian hormone (AMH) concentrations decline with increasing age and constitute a sensitive marker for ovarian ageing. In addition, basal serum AMH concentrations predict ovarian response during IVF cycles. Concomitantly, oocyte quantity and embryo quality decrease with advancing age. Hence, it was postulated that AMH in serum constitutes a marker for embryo quality. Women aged 37 years and younger with regular menstrual cycles, normal body mass index and partners with normal semen parameters were randomly assigned to either a standard or mild stimulation protocol for IVF treatment. Blood samples were drawn at cycle day 3 and at the day of human chorionic gonadotrophin administration. Embryo quality was assessed using embryo morphology score and preimplantation genetic screening. Serum AMH concentrations on cycle day 3 were correlated with the number of oocytes retrieved in both groups. AMH and embryo morphology were correlated after mild stimulation, but not after conventional ovarian stimulation. AMH and the chromosomal competence of embryos were not correlated. Serum AMH is predictive for ovarian response to stimulation. However, the lack of a consistent correlation with embryo morphology and embryo aneuploidy rate is not in favour of a direct relationship between oocyte quantity and embryo quality.

The clinical significance of the retrieval of a low number of oocytes following mild ovarian stimulation for IVF: a meta-analysis.

BACKGROUND: Milder ovarian stimulation protocols for in vitro fertilization (IVF) are being developed to minimize adverse effects. Mild stimulation regimens result in a decreased number of oocytes at retrieval. After conventional ovarian stimulation for IVF, a low number of oocytes are believed to represent poor ovarian reserve resulting in reduced success rates. Recent studies suggest that a similar response following mild stimulation is associated with better outcomes. METHODS: This review investigates whether the retrieval of a low number of oocytes following mild ovarian stimulation is associated with impaired implantation rates. Three randomized controlled trials comparing the efficacy of the mild ovarian stimulation regimen (involving midfollicular phase initiation of FSH and GnRH co-treatment) for IVF with a conventional long GnRH agonist co-treatment stimulation protocol could be identified by means of a systematic literature search. RESULTS: These studies comprised a total of 592 first treatment cycles. Individual patient data analysis showed that the mild stimulation protocol results in a significant reduction of retrieved oocytes compared with conventional ovarian stimulation (median 6 versus 9, respectively, P < 0.001). Optimal embryo implantation rates were observed with 5 oocytes retrieved following mild stimulation (31%) versus 10 oocytes following conventional stimulation (29%) (P = 0.045). CONCLUSIONS: The optimal number of retrieved oocytes depends on the ovarian stimulation regimen. After mild ovarian stimulation, a modest number of oocytes is associated with optimal implantation rates and does not reflect a poor ovarian response. Therefore, the fear of reducing the number of oocytes retrieved following mild ovarian stimulation appears to be unjustified.

FISH analysis of 15 chromosomes in human day 4 and 5 preimplantation embryos: the added value of extended aneuploidy detection.

OBJECTIVE: Screening for an increased number of chromosomes may improve the detection of abnormal embryos and thus contribute to the capability of preimplantation genetic screening (PGS) to detect the embryo(s) for transfer in IVF with the best chance for a healthy child. Good-quality day 4 and 5 embryos were analyzed after cryopreservation for the nine chromosomes mostly recommended for screening (13, 14, 15, 16, 18, 21, 22, X and Y), next to six additional chromosomes which are less well studied in this context (1, 2, 7, 6, 10 and 17). METHOD: The copy numbers of 15 chromosomes were investigated by fluorescence in situ hybridization (FISH) in three consecutive rounds. The proportion of aneuploid and mosaic embryos was determined and compared in retrospect to results in case only the recommended probe set had been analyzed. RESULTS: A total of 52 embryos from 29 infertile women were analyzed. Screening the embryos for six additional chromosomes increased the proportion of abnormal embryos from 67 to 81% (P = 0.03), owing to an increase in mosaic embryos. CONCLUSION: All but one of the meiotic aneuploidies found in this study would have been detected by the probe set most frequently used in PGS clinics. However, aneuploid cell lines originating from mitotic errors could be detected for almost all chromosomes, so screening of six additional chromosomes mainly increased the proportion of mosaic embryos. The added value of screening for six additional chromosomes in PGS for clinical practice will remain undetermined as long as the fate of mosaic embryos after transfer is unclear.

Preimplantation genetic screening reveals a high incidence of aneuploidy and mosaicism in embryos from young women undergoing IVF.

BACKGROUND: In order to assess the frequency of aneuploidy and mosaicism in embryos obtained from IVF patients aged <38 years, preimplantation genetic screening (PGS) was performed after biopsy of two blastomeres. Furthermore, the reliability of this diagnosis was assessed by performing reanalysis of the embryo on day 5. METHOD: The copy numbers of 10 chromosomes (1, 7, 13, 15, 16, 18, 21, 22, X and Y) were investigated by fluorescence in situ hybridization (FISH) analysis. Embryos that were found to be abnormal or of insufficient morphological quality were cultured until day 5 and reanalysed. Results obtained were compared to the day 3 blastomere analysis. RESULTS: After analysis of 196 embryos (one cell in 38% and two cells in 62%), only 36% of the embryos were found to be normal on day 3. After analysis of two blastomeres, 50% showed chromosomal mosaicism. Comparison of the FISH results from day 3 blastomeres and day 5 embryos yielded an overall cytogenetic confirmation rate of 54%. CONCLUSIONS: The rates of mosaicism and aneuploidy in these embryos from young IVF patients are similar to those published for older women. We found the best confirmation rate after a diagnosis based on two cells, where both blastomeres showed the same chromosomal abnormality. In contrast, after a mosaic diagnosis the confirmation rate was low. The present study provides the first detailed reanalysis data of embryos analysed by PGS and clearly demonstrates the impact of mosaicism on the reliability of the PGS diagnosis.

Screening for aneuploidies of ten different chromosomes in two rounds of FISH: a short and reliable protocol.

OBJECTIVE: To develop a DNA labelling protocol for the simultaneous detection of five different fluorescent chromosomal DNA probes within one round of hybridisation. In combination with a commercial five-colour probemix for the second round of hybridisation, this results in a fast and reliable Fluorescence in situ Hybridization (FISH) protocol, enabling the detection of 10 chromosomes within a working day. This is especially of use for Preimplantation Genetic Screening (PGS), when only single interphase nuclei are available for analysis and when time is restricted. METHOD: DNA probes were labelled with four different fluorochromes (Pacific Blue, Alexa Fluor 350, Alexa Fluor 594 and Alexa Fluor 488) using an ARES labelling kit, based on a two-step method. Aminoallyl-dUTPs were incorporated by nick translation, followed by chemical linking of the amino-modified fluorescent dye. The fifth colour was achieved by using two fluorescent dyes in the chemical reaction, resulting in dual labelling of the DNA probe and a fluorescence detectable with a specific filter set. These five probes were simultaneously hybridised in a first FISH round, followed by a second hybridisation with a commercial five-colour probemix, thus allowing the detection of chromosomes 1, 7, 13, 15, 16, 18, 21, 22, X and Y. The fixation and pre-treatment procedures of the blastomere nuclei were further optimised. RESULTS: Using this labelling and FISH protocol, probe hybridisation efficiency, when tested on lymphocyte nuclei, is 95 to 99%. With the fixation protocol, blastomere nuclei maintain good morphology and show condensed and clear signals even after the second round of hybridisation. CONCLUSION: This labelling method in combination with specific epifluorescence filters, enables an independent detection of five different chromosomes in one round of FISH. The whole process of biopsy, fixation and two rounds of hybridisation with the analysis of ten chromosomes can be completed within a day.

Distribution of Atr protein in primary spermatocytes of a mouse chromosomal mutant: a comparison of preparation techniques.

In this study, we examined the suitability of a three dimensional preparation technique for studying chromosome behaviour in the first meiotic prophase in the mouse chromosomal mutant T(1;13)H/T(1;13)Wa. To preserve cellular shape, primary spermatocytes were encapsulated in a fibrin clot. Conventionally sedimented prophase nuclei served as controls. Axial elements and lateral synaptonemal complex components were subsequently stained by immunofluorescence and the presence of axial elements at the pachytene stage was highlighted with indirect immunofluorescence against the Atr protein. We compared the distribution of Atr signal in the fibrin-embedded spermatocytes with surface-spread preparations and immunohistochemically stained histological sections of seminiferous tubules. Furthermore, fluorescence in situ hybridisation of the mouse minor satellite DNA was done on fibrin-embedded spermatocytes. The Atr signal is most conspicuous in fibrin-embedded nuclei on unpaired axial elements during pachytene, both for sex chromosomal and for autosomal segments, and expanding from these elements into the surrounding chromatin. Both spread and encapsulated zygotene nuclei with extended axial element formation proved to be positive for Atr. Mid- to late zygotene nuclei were devoid of 3,3'-diaminodibenzene deposition in the histological sections. Highlighting the unpaired axial elements in the small heteromorphic 1(13)H;1(13)Wa bivalent with an Atr signal enabled meiotic analysis of this bivalent to be carried out in a three-dimensional context. Thus, proximity of this bivalent with the sex chromosomes is found more often in three-dimensional preparations than in spread preparations. Furthermore, the development of the Atr signal over the sex chromosomes as pachytene proceeds helps in substaging of this long and heterogeneous meiotic phase, in sedimented but especially in fibrin-encapsulated nuclei.

Fluorescence in situ hybridization analysis of two blastomeres from day 3 frozen-thawed embryos followed by analysis of the remaining embryo on day 5.

BACKGROUND: Chromosomal mosaicism in human embryos may give rise to false positive or false negative results in preimplantation genetic diagnosis for aneuploidy screening (PGD-AS). Therefore, we have investigated whether the results obtained from a 2-cell biopsy of frozen-thawed embryos and fluorescence in situ hybridization (FISH) analysis are representative for the chromosome constitution of the remaining embryo on day 5. METHODS: Cryopreserved day 3 embryos were thawed and from surviving embryos two blastomeres were biopsied. FISH analysis was performed for chromosomes 1, 7, 13, 15, 16, 18, 21, 22, X and Y. After biopsy, the embryos were cultured until day 5 and further analysed using the same probe panels. RESULTS: In all, 17 embryos were available with a diagnosis based on two blastomeres on day 3 and confirmatory studies on day 5. In 10 of these 17 cases the initial diagnosis could be confirmed. However, in only six cases cytogenetic results were concordant. Besides the 10 cases with a 'correct' diagnosis, there were six false positive results and one false negative, all involving mosaicism. CONCLUSIONS: Investigating the chromosomal constitution of two blastomere nuclei offers a good opportunity to study the incidence of chromosomal mosaicism in early embryo development. The confirmation rate of the results obtained on day 3 depends on the interpretation and is higher when considered from a clinical than from a cytogenetic point of view.

Reduced oocyte activation and first cleavage rate after ICSI with spermatozoa from a sterile mouse chromosome mutant.

BACKGROUND: Male mice, heterozygous for two semi-identical reciprocal translocations T(1;13)70H and T(1;13)1Wa are usually sterile. We have investigated this oligoasthenoteratozoospermic mouse model using ICSI. METHODS: B6D2F1 oocytes were injected with epididymal or testicular sperm from fertile or sterile translocation carriers and from chromosomally normal fertile controls. ICSI efficiency was determined by pronucleus formation and first cleavage rates. For arrested zygotes, cell cycle progression was evaluated by BrdU incorporation and incubation with okadaic acid. RESULTS: Epididymal sperm from infertile translocation carriers showed a slightly lower fertilization rate (70% vs. 92%, 95% and 95% for fertile translocation carriers and two groups of normal fertile control males, respectively) and a severely reduced cleavage rate (33% vs. 87%, 96% and 89% for the same control groups). However, the use of testicular sperm significantly improved the cleavage rate (62% vs. 83% for normal fertile controls). Development of arrested zygotes was delayed or blocked during S- and G2-phase. CONCLUSIONS: Whereas control testicular and epididymal sperm performed equally well, the use of testicular sperm from oligospermic T/T' males significantly increased first cleavage rates when compared to the low rates with epididymal sperm. Epididymal storage in oligospermics may negatively influence zygote division.

Mouse MutS-like protein Msh5 is required for proper chromosome synapsis in male and female meiosis.

Members of the mammalian mismatch repair protein family of MutS and MutL homologs have been implicated in postreplicative mismatch correction and chromosome interactions during meiotic recombination. Here we demonstrate that mice carrying a disruption in MutS homolog Msh5 show a meiotic defect, leading to male and female sterility. Histological and cytological examination of prophase I stages in both sexes revealed an extended zygotene stage, characterized by impaired and aberrant chromosome synapsis, that was followed by apoptotic cell death. Thus, murine Msh5 promotes synapsis of homologous chromosomes in meiotic prophase I.