Tripolar mitosis in human cells and embryos: occurrence, pathophysiology and medical implications

Chromosome remodeling and cytoplasmic distribution during embryonic development in fused pair embryos

Cell fusion is now widely employed as an in vitro model for inducing and investigating cell fate changes. In early embryo research, fusion of embryos is also a way to probe the mechanisms of mammalian oogenesis and preimplantation development. To establish a novel model for porcine early embryo studies and investigate its developmental mechanisms, pair of zona pellucida (ZP)-free oocytes were electro fused to produce the fused pair (FP) embryos, which were further in vitro cultured to the blastocyst stage. Firstly, developmental competence was assessed, revealing a cleavage rate of 92.27 ± 5.59 % and a blastocyst rate of 26.12 ± 6.61 %, which were similar to the parthenogenetic activation (PA) embryos (p > 0.05). Subsequently, nuclear and spindle staining was performed on FP embryos collected at 14-22 h, with 67.18 ± 3.18 % of the embryos spindle reorganization occurred and nuclei fusion, whereas a few displayed independent division of the two nuclei or tripolar spindle. Lastly, the distribution of lipid droplets (LDs) and mitochondria in FP embryos was assessed via fluorescent staining. Results showed that the even distribution of LDs from one oocyte was observed in each blastomere of 4-cell to blastocysts. A similar distribution pattern was observed for mitochondria, which was being observed at the 2-cell stage, a relatively earlier developmental stage than that of LDs. Results suggested that cytoplasm including mitochondria and LDs could redistribute once two oocytes fused into a single embryo. More studies are needed for the underlying mechanism and potential impact on the developmental ability of FP embryos.

Case Report: Androgenetic/biparental chimera with two biparental cell lines leading to placental mesenchymal dysplasia: a possible novel mechanism of formation

Placental mesenchymal dysplasia (PMD) is a rare placental pathology that may be associated with Beckwith-Wiedemann features in the fetus and may be due to the presence of an androgenetic cell line. Many of the reported PMD cases describe the presence of a biparental and an isodisomic androgenetic cell line. The proposed mechanism of formation is by fertilization of a haploid ovum by a haploid sperm and duplication of the male pronucleus. We present a case with evidence of the participation of three different haploid gametes, one ovum and two spermatozoa, which led to an androgenetic/biparental chimera (ABC) in which three fetal cell lines were detected: two biparental, genetically different, cell lines but with the same maternal contribution, and one heterodisomic androgenetic cell line. To our knowledge, this is the first described case of ABC with two different biparental cell lines. We propose a novel mechanism based on the heterogoneic division of the tripronucleated zygote to explain the formation of this rare ABC.

Cell cycle dysregulation in cancer

Cancer is a systemic manifestation of aberrant cell cycle activity and dysregulated cell growth. Genetic mutations can determine tumor onset by either augmenting cell division rates or restraining normal controls such as cell cycle arrest or apoptosis. As a result, tumor cells not only undergo uncontrolled cell division but also become compromised in their ability to exit the cell cycle accurately. Regulation of cell cycle progression is enabled by specific surveillance mechanisms known as cell cycle checkpoints, and aberrations in these signaling pathways often culminate in cancer. For instance, DNA damage checkpoints, which preclude the generation and augmentation of DNA damage in the G1, S, and G2 cell cycle phases, are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Notably, tumors have evolved to become dependent on checkpoints for their survival. For example, checkpoint pathways such as the DNA replication stress checkpoint and the mitotic checkpoint rarely undergo mutations and remain intact because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation leading to cell death. In this review, we initially focus on cell cycle control pathways and specific functions of checkpoint signaling involved in normal and cancer cells and then proceed to examine how cell cycle control and checkpoint mechanisms can provide new therapeutic windows that can be exploited for cancer therapy. SIGNIFICANCE STATEMENT: DNA damage checkpoints are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Conversely, DNA replication stress and mitotic checkpoints rarely undergo mutations because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation, leading to cancer cell death. This review focuses on the checkpoint signaling mechanisms involved in cancer cells and how an emerging understanding of these pathways can provide new therapeutic opportunities for cancer therapy.

Synaptic vesicle glycoprotein 2 enables viable aneuploidy following centrosome amplification

Amplified centrosome number causes genomic instability, most severely through division into more than two aneuploid daughter cells (multipolar mitosis). Several mechanisms that suppress multipolar division have been uncovered, yet mechanisms that favor viable multipolar division are poorly understood. To uncover factors that promote viability in cells with frequent centrosome amplification and multipolar division, we conducted an unbiased Drosophila genetic screen. In 642 mutagenized lines, we exploited the ability of intestinal papillar cells to form and function despite multipolar divisions. Our top hit is an unnamed gene, CG3168 . We name this gene synaptic vesicle glycoprotein 2 , reflecting homology to human Synaptic Vesicle Glycoprotein 2 (SV2) proteins. GFP-tagged SV2 localizes to the plasma membrane. In cells with amplified centrosomes, SV2 positions membrane-adjacent centrosomes, which prevents severe errors in chromosome alignment and segregation. Our results uncover membrane-based multipolar division regulation and reveal a novel vulnerability in cells with common cancer properties.

ConvNext Mitosis Identification-You Only Look Once (CNMI-YOLO): Domain Adaptive and Robust Mitosis Identification in Digital Pathology

In digital pathology, accurate mitosis detection in histopathological images is critical for cancer diagnosis and prognosis. However, this remains challenging due to the inherent variability in cell morphology and the domain shift problem. This study introduces ConvNext Mitosis Identification-You Only Look Once (CNMI-YOLO), a new 2-stage deep learning method that uses the YOLOv7 architecture for cell detection and the ConvNeXt architecture for cell classification. The goal is to improve the identification of mitosis in different types of cancers. We utilized the Mitosis Domain Generalization Challenge 2022 data set in the experiments to ensure the model's robustness and success across various scanners, species, and cancer types. The CNMI-YOLO model demonstrates superior performance in accurately detecting mitotic cells, significantly outperforming existing models in terms of precision, recall, and F1 score. The CNMI-YOLO model achieved an F1 score of 0.795 on the Mitosis Domain Generalization Challenge 2022 and demonstrated robust generalization with F1 scores of 0.783 and 0.759 on the external melanoma and sarcoma test sets, respectively. Additionally, the study included ablation studies to evaluate various object detection and classification models, such as Faster-RCNN and Swin Transformer. Furthermore, we assessed the model's robustness performance on unseen data, confirming its ability to generalize and its potential for real-world use in digital pathology, using soft tissue sarcoma and melanoma samples not included in the training data set.

Two types of cleavage, from zygote to three cells, result in different clinical outcomes and should be treated differently

Research Question

What is the utilization rate of embryos that exert inadequate zygote cleavage into three daughter cells?

Design

This study used a retrospective dataset from a single IVF Unit. A total of 3,060 embryos from 1,811 fresh IVF cycles were analyzed. The cleavage pattern, morphokinetics, and outcome were recorded. Only 2pn embryos, fertilized by ejaculated sperm, and cultured in a time-lapse system for at least 5 days were included. We generated three study groups according to the embryo's cleavage pattern: (I) Control, normal cleavage (n = 551); (II) fast cleavage, zygote to three cells within 5 h (n = 1,587); and (III) instant direct tripolar cleavage (IDC) from zygote to three cells (n = 922).

Results

The rate of usable fast cleavage blastocysts was 108/1,587 (6.81%) and usable control blastocysts was 180/551 (32.67%). The time of PN fading and from fading to first cleavage differed significantly between the three groups. Although the pregnancy rate of control and fast cleavage blastocysts were comparable (40.35% and 42.55%, respectively), the amount of instant direct cleavage embryos that reached blastocyst stage was neglectable (only four embryos out of 922 analyzed IDC embryos) and unsuitable for statistical comparison of pregnancy rates.

Conclusion

Our results indicate the need to culture instant direct cleavage embryos for 5 days, up to the blastocyst stage, and avoid transfer of embryos that are fated to arrest even when their morphological grade on day 3 is acceptable, whereas fast cleavage embryos could be transferred on day 3 when there is no alternative.

Association of early cleavage, morula compaction and blastocysts ploidy of IVF embryos cultured in a time-lapse system and biopsied for genetic test for aneuploidy

IVF embryos have historically been evaluated by morphological characteristics. The time-lapse system (TLS) has become a promising tool, providing an uninterrupted evaluation of morphological and dynamic parameters of embryo development. Furthermore, TLS sheds light on unknown phenomena such as direct cleavage and incomplete morula compaction. We retrospectively analyzed the morphology (Gardner Score) and morphokinetics (KIDScore) of 835 blastocysts grown in a TLS incubator (Embryoscope+), which were biopsied for preimplantation genetic testing for aneuploidy (PGT-A). Only the embryos that reached the blastocyst stage were included in this study and time-lapse videos were retrospectively reanalysed. According to the pattern of initial cleavages and morula compaction, the embryos were classified as: normal (NC) or abnormal (AC) cleavage, and fully (FCM) or partially compacted (PCM) morulae. No difference was found in early cleavage types or morula compaction patterns between female age groups (< 38, 38-40 and > 40 yo). Most of NC embryos resulted in FCM (≅ 60%), while no embryos with AC resulted in FCM. Aneuploidy rate of AC-PCM group did not differ from that of NC-FCM group in women < 38 yo, but aneuploidy was significantly higher in AC-PCM compared to NC-FCM of women > 40 yo. However, the quality of embryos was lower in AC-PCM blastocysts in women of all age ranges. Morphological and morphokinetic scores declined with increasing age, in the NC-PCM and AC-PCM groups, compared to the NC-FCM. Similar aneuploidy rates among NC-FCM and AC-PCM groups support the hypothesis that PCM in anomalous-cleaved embryos can represent a potential correction mechanism, even though lower morphological/morphokinetic scores are seen on AC-PCM. Therefore, both morphological and morphokinetic assessment should consider these embryonic development phenomena.

Meiotic and mitotic aneuploidies drive arrest of in vitro fertilized human preimplantation embryos

BACKGROUND

The high incidence of aneuploidy in early human development, arising either from errors in meiosis or postzygotic mitosis, is the primary cause of pregnancy loss, miscarriage, and stillbirth following natural conception as well as in vitro fertilization (IVF). Preimplantation genetic testing for aneuploidy (PGT-A) has confirmed the prevalence of meiotic and mitotic aneuploidies among blastocyst-stage IVF embryos that are candidates for transfer. However, only about half of normally fertilized embryos develop to the blastocyst stage in vitro, while the others arrest at cleavage to late morula or early blastocyst stages.

METHODS

To achieve a more complete view of the impacts of aneuploidy, we applied low-coverage sequencing-based PGT-A to a large series (n = 909) of arrested embryos and trophectoderm biopsies. We then correlated observed aneuploidies with abnormalities of the first two cleavage divisions using time-lapse imaging (n = 843).

RESULTS

The combined incidence of meiotic and mitotic aneuploidies was strongly associated with blastocyst morphological grading, with the proportion ranging from 20 to 90% for the highest to lowest grades, respectively. In contrast, the incidence of aneuploidy among arrested embryos was exceptionally high (94%), dominated by mitotic aneuploidies affecting multiple chromosomes. In turn, these mitotic aneuploidies were strongly associated with abnormal cleavage divisions, such that 51% of abnormally dividing embryos possessed mitotic aneuploidies compared to only 23% of normally dividing embryos.

CONCLUSIONS

We conclude that the combination of meiotic and mitotic aneuploidies drives arrest of human embryos in vitro, as development increasingly relies on embryonic gene expression at the blastocyst stage.

Cell fragmentation in mouse preimplantation embryos induced by ectopic activation of the polar body extrusion pathway

Cell fragmentation is commonly observed in human preimplantation embryos and is associated with poor prognosis during assisted reproductive technology (ART) procedures. However, the mechanisms leading to cell fragmentation remain largely unknown. Here, light sheet microscopy imaging of mouse embryos reveals that inefficient chromosome separation due to spindle defects, caused by dysfunctional molecular motors Myo1c or dynein, leads to fragmentation during mitosis. Extended exposure of the cell cortex to chromosomes locally triggers actomyosin contractility and pinches off cell fragments. This process is reminiscent of meiosis, during which small GTPase-mediated signals from chromosomes coordinate polar body extrusion (PBE) by actomyosin contraction. By interfering with the signals driving PBE, we find that this meiotic signaling pathway remains active during cleavage stages and is both required and sufficient to trigger fragmentation. Together, we find that fragmentation happens in mitosis after ectopic activation of actomyosin contractility by signals emanating from DNA, similar to those observed during meiosis. Our study uncovers the mechanisms underlying fragmentation in preimplantation embryos and, more generally, offers insight into the regulation of mitosis during the maternal-zygotic transition.

Morphological and morphokinetic associations with aneuploidy: a systematic review and meta-analysis

BACKGROUND

A time lapse system (TLS) is utilized in some fertility clinics with the aim of predicting embryo viability and chance of live birth during IVF. It has been hypothesized that aneuploid embryos display altered morphokinetics as a consequence of their abnormal chromosome complement. Since aneuploidy is one of the fundamental reasons for IVF failure and miscarriage, attention has focused on utilizing morphokinetics to develop models to non-invasively risk stratify embryos for ploidy status. This could avoid or reduce the costs associated with pre-implantation genetic testing for aneuploidy (PGT-A). Furthermore, TLS have provided an understanding of the true prevalence of other dysmorphisms. Hypothetically, the incorporation of morphological features into a model could act synergistically, improving a model's discriminative ability to predict ploidy status.

OBJECTIVE AND RATIONALE

The aim of this systematic review and meta-analysis was to investigate associations between ploidy status and morphokinetic or morphological features commonly denoted on a TLS. This will determine the feasibility of a prediction model for euploidy and summarize the most useful prognostic markers to be included in model development.

SEARCH METHODS

Five separate searches were conducted in Medline, Embase, PubMed and Cinahl from inception to 1 July 2021. Search terms and word variants included, among others, PGT-A, ploidy, morphokinetics and time lapse, and the latter were successively substituted for the following morphological parameters: fragmentation, multinucleation, abnormal cleavage and contraction. Studies were limited to human studies.

OUTCOMES

Overall, 58 studies were included incorporating over 40 000 embryos. All except one study had a moderate risk of bias in at least one domain when assessed by the quality in prognostic studies tool. Ten morphokinetic variables were significantly delayed in aneuploid embryos. When excluding studies using less reliable genetic technologies, the most notable variables were: time to eight cells (t8, 1.13 h, 95% CI: 0.21-2.05; three studies; n = 742; I2 = 0%), t9 (2.27 h, 95% CI: 0.5-4.03; two studies; n = 671; I2 = 33%), time to formation of a full blastocyst (tB, 1.99 h, 95% CI 0.15-3.81; four studies; n = 1640; I2 = 76%) and time to expanded blastocyst (tEB, 2.35 h, 95% CI: 0.06-4.63; four studies; n = 1640; I2 = 83%). There is potentially some prognostic potential in the degree of fragmentation, multinucleation persisting to the four-cell stage and frequency of embryo contractions. Reverse cleavage was associated with euploidy in this meta-analysis; however, this article argues that these are likely spurious results requiring further investigation. There was no association with direct unequal cleavage in an embryo that progressed to a blastocyst, or with multinucleation assessed on Day 2 or at the two-cell stage. However, owing to heterogeneous results and poor-quality evidence, associations between these morphological components needs to be investigated further before conclusions can be reliably drawn.

WIDER IMPLICATIONS

This first systematic review and meta-analysis of morphological and morphokinetic associations with ploidy status demonstrates the most useful morphokinetic variables, namely t8, t9 and tEB to be included in future model development. There is considerable variability within aneuploid and euploid embryos making definitively classifying them impossible; however, it is feasible that embryos could be prioritized for biopsy. Furthermore, these results support the mechanism by which algorithms for live birth may have predictive ability, suggesting aneuploidy causes delayed cytokinesis. We highlight significant heterogeneity in our results secondary to local conditions and diverse patient populations, therefore calling for future models to be robustly developed and tested in-house. If successful, such a model would constitute a meaningful breakthrough when accessing PGT-A is unsuitable for couples.

Transmission ratio distortion of mutations in the master regulator of centriole biogenesis PLK4

The evolutionary conserved Polo-like kinase 4 (PLK4) is essential for centriole duplication, spindle assembly, and de novo centriole formation. In man, homozygous mutations in PLK4 lead to primary microcephaly, altered PLK4 expression is associated with aneuploidy in human embryos. Here, we report on a consanguineous four-generation family with 8 affected individuals compound heterozygous for a novel missense variant, c.881 T > G, and a deletion of the PLK4 gene. The clinical phenotype of the adult patients is mild compared to individuals with previously described PLK4 mutations. One individual was homozygous for the variant c.881G and phenotypically unaffected. The deletion was inherited by 14 of 16 offspring and thus exhibits transmission ratio distortion (TRD). Moreover, based on the already published families with PLK4 mutations, it could be shown that due to the preferential transmission of the mutant alleles, the number of affected offspring is significantly increased. It is assumed that reduced expression of PLK4 decreases the intrinsically high error rate of the first cell divisions after fertilization, increases the number of viable embryos and thus leads to preferential transmission of the deleted/mutated alleles.

Assessment of mitotic activity in breast cancer: revisited in the digital pathology era

The assessment of cell proliferation is a key morphological feature for diagnosing various pathological lesions and predicting their clinical behaviour. Visual assessment of mitotic figures in routine histological sections remains the gold-standard method to evaluate the proliferative activity and grading of cancer. Despite the apparent simplicity of such a well-established method, visual assessment of mitotic figures in breast cancer (BC) remains a challenging task with low concordance among pathologists which can lead to under or overestimation of tumour grade and hence affects management. Guideline recommendations for counting mitoses in BC have been published to standardise methodology and improve concordance; however, the results remain less satisfactory. Alternative approaches such as the use of the proliferation marker Ki67 have been recommended but these did not show better performance in terms of concordance or prognostic stratification. The advent of whole slide image technology has brought the issue of mitotic counting in BC into the light again with more challenges to develop objective criteria for identifying and scoring mitotic figures in digitalised images. Using reliable and reproducible morphological criteria can provide the highest degree of concordance among pathologists and could even benefit the further application of artificial intelligence (AI) in breast pathology, and this relies mainly on the explicit description of these figures. In this review, we highlight the morphology of mitotic figures and their mimickers, address the current caveats in counting mitoses in breast pathology and describe how to strictly apply the morphological criteria for accurate and reliable histological grade and AI models.

Sperm DNA fragmentation measured by sperm chromatin dispersion impacts morphokinetic parameters, fertilization rate and blastocyst quality in ICSI treatments

To determine the effects of sperm DNA fragmentation (SDF) on embryo morphokinetic parameters, cleavage patterns and embryo quality, this retrospective study analyzed 151 intracytoplasmic sperm injection (ICSI) cycles (1152 embryos collected) between November 2016 and June 2019. SDF was assessed using sperm chromatin dispersion. The cycles were divided into two groups based on the SDF rate: SDF < 15% (n = 114) and SDF ≥ 15% (n = 37). The embryo morphokinetic parameters, cleavage patterns, and embryo quality were compared between the two groups. The morphokinetic parameters tPNf, t2, t3, t4, t5, t6, and t8 were achieved significantly earlier in the SDF < 15% group compared with in the SDF ≥ 15% group. The fertilization and 2PN rates seemed to be significantly higher in the SDF < 15% group compared with in the SDF ≥ 15% group, while the abnormal cleavage rates were similar. However, a significantly higher rate of chaotic cleavage (CC) was observed in the SDF ≥ 15% group. The D3 high-quality embryo and available embryo rates were similar between the two groups. The blastocyst formation, high-quality blastocyst, and available blastocyst rates in the SDF < 15% group were significantly higher than those in the SDF ≥ 15% group. With an increase in SDF level, the chemical pregnancy, clinical pregnancy and implantation rates tended to decrease, while the miscarriage rate increased. This study demonstrated that SDF ≥ 15% reduces the fertilization rate of ICSI cycles and affects certain morphokinetic parameters. A higher SDF level can also induce a higher rate of CC, with subsequent decreases in the blastocyst formation rate and blastocyst quality.

Rescuing monopronucleated-derived human blastocysts: a model to study chromosomal topography and fingerprinting

OBJECTIVE

To quantify the percentage of monopronuclear-derived blastocysts (MNBs) that are potentially useful for reproductive purposes using classic and state-of-the-art chromosome analysis approaches, and to study chromosomal distribution in the inner cell mass (ICM) and trophectoderm (TE) for intertissue/intratissue concordance comparison.

DESIGN

Prospective experimental study.

SETTING

Single-center in vitro fertilization clinic and reproductive genetics laboratory.

PATIENT(S)

A total of 1,128 monopronuclear zygotes were obtained between June 2016 and December 2018.

INTERVENTION(S)

MNBs were whole-fixed or biopsied to obtain a portion of ICM and 2 TE portions (TE1 and TE2) and were subsequently analyzed by fluorescence in situ hybridization, new whole-genome sequencing, and fingerprinting by single-nucleotide polymorphism array-based techniques (a-SNP).

MAIN OUTCOME MEASURE(S)

We assessed MNB rate, ploidy rate, and chromosomal constitution by new whole-genome sequencing, and parental composition by comparative a-SNP, performed in a "trio"-format (embryo/parents). The 24-chromosome distribution was compared between the TE and the ICM and within the TE.

RESULT(S)

A total of 18.4% of monopronuclear zygotes progressed to blastocysts; 77.6% of MNBs were diploid; 20% of MNBs were male and euploid, which might be reproductively useful. Seventy-five percent of MNBs were biparental and half of them were euploid, indicating that 40% might be reproductively useful. Intratissue concordance (TE1/TE2) was established for 93.3% and 73.3% for chromosome matching. Intertissue concordance (TE/ICM) was established for 78.8%, but 57.6% for chromosome matching. When segmental aneuploidy was not considered, intratissue concordance and chromosome matching increased to 100% and 80%, respectively, and intertissue concordance and chromosome matching increased to 84.8% and 75.8%, respectively.

CONCLUSION(S)

The a-SNP-trio strategy provides information about ploidy, euploidy, and parental origin in a single biopsy. This approach enabled us to identify 40% of MNBs with reproductive potential, which can have a significant effect in the clinical setting. Additionally, segmental aneuploidy is relevant for mismatched preimplantation genetic testing of aneuploidies, both within and between MNB tissues. Repeat biopsy might clarify whether segmental aneuploidy is a prone genetic character.

A Cascade of 2.5D CNN and Bidirectional CLSTM Network for Mitotic Cell Detection in 4D Microscopy Image

Mitosis detection is one of the challenging steps in biomedical imaging research, which can be used to observe the cell behavior. Most of the already existing methods that are applied in detecting mitosis usually contain many nonmitotic events (normal cell and background) in the result (false positives, FPs). In order to address such a problem, in this study, we propose to apply 2.5-dimensional (2.5D) networks called CasDetNet_CLSTM, which can accurately detect mitotic events in 4D microscopic images. This CasDetNet_CLSTM involves a 2.5D faster region-based convolutional neural network (Faster R-CNN) as the first network, and a convolutional long short-term memory (CLSTM) network as the second network. The first network is used to select candidate cells using the information from nearby slices, whereas the second network uses temporal information to eliminate FPs and refine the result of the first network. Our experiment shows that the precision and recall of our networks yield better results than those of other state-of-the-art methods.

Accurate and fast mitotic detection using an anchor-free method based on full-scale connection with recurrent deep layer aggregation in 4D microscopy images

BACKGROUND

To effectively detect and investigate various cell-related diseases, it is essential to understand cell behaviour. The ability to detection mitotic cells is a fundamental step in diagnosing cell-related diseases. Convolutional neural networks (CNNs) have been successfully applied to object detection tasks, however, when applied to mitotic cell detection, most existing methods generate high false-positive rates due to the complex characteristics that differentiate normal cells from mitotic cells. Cell size and orientation variations in each stage make detecting mitotic cells difficult in 2D approaches. Therefore, effective extraction of the spatial and temporal features from mitotic data is an important and challenging task. The computational time required for detection is another major concern for mitotic detection in 4D microscopic images.

RESULTS

In this paper, we propose a backbone feature extraction network named full scale connected recurrent deep layer aggregation (RDLA++) for anchor-free mitotic detection. We utilize a 2.5D method that includes 3D spatial information extracted from several 2D images from neighbouring slices that form a multi-stream input.

CONCLUSIONS

Our proposed technique addresses the scale variation problem and can efficiently extract spatial and temporal features from 4D microscopic images, resulting in improved detection accuracy and reduced computation time compared with those of other state-of-the-art methods.

Mitotic Figures-Normal, Atypical, and Imposters: A Guide to Identification

Counting mitotic figures (MF) in hematoxylin and eosin-stained histologic sections is an integral part of the diagnostic pathologist's tumor evaluation. The mitotic count (MC) is used alone or as part of a grading scheme for assessment of prognosis and clinical decisions. Determining MCs is subjective, somewhat laborious, and has interobserver variation. Proposals for standardizing this parameter in the veterinary field are limited to terminology (use of the term MC) and area (MC is counted in an area measuring 2.37 mm²). Digital imaging techniques are now commonplace and widely used among veterinary pathologists, and field of view area can be easily calculated with digital imaging software. In addition to standardizing the methods of counting MF, the morphologic characteristics of MF and distinguishing atypical mitotic figures (AMF) versus mitotic-like figures (MLF) need to be defined. This article provides morphologic criteria for MF identification and for distinguishing normal phases of MF from AMF and MLF. Pertinent features of digital microscopy and application of computational pathology (CPATH) methods are discussed. Correct identification of MF will improve MC consistency, reproducibility, and accuracy obtained from manual (glass slide or whole-slide imaging) and CPATH approaches.

Assessing equine embryo developmental competency by time-lapse image analysis

The timing of early mitotic events during preimplantation embryo development is important for subsequent embryogenesis in many mammalian species, including mouse and human, but, to date, no study has closely examined mitotic timing in equine embryos from oocytes obtained by ovum pick-up. Here, cumulus-oocyte complexes were collected by transvaginal follicular aspiration, matured invitro and fertilised via intracytoplasmic sperm injection. Each fertilised oocyte was cultured up to the blastocyst stage and monitored by time-lapse imaging for the measurement of cell cycle intervals and identification of morphological criteria indicative of developmental potential. Of the 56 fertilised oocytes, 35 initiated mitosis and 11 progressed to the blastocyst stage. Analysis of the first three mitotic divisions in embryos that formed blastocysts determined that typical blastocyst timing (median±IQR) is 30.0±17.5min, 8.8±1.7h and 0.6±1.4h respectively. Frequent cellular fragmentation, multipolar divisions and blastomere exclusion suggested that equine embryos likely contend with a high incidence of chromosomal missegregation. Indeed, chromosome-containing micronuclei and multinuclei with extensive DNA damage were observed throughout preimplantation embryogenesis. This indicates that time-lapse image analysis may be used as a non-invasive method to assess equine embryo quality in future studies.

Mitosis detection in breast cancer histopathology images using hybrid feature space

Breast Cancer grading is a challenging task as regards image analysis, which is normally based on mitosis count rate. The mitotic count provides an estimate of aggressiveness of the tumor. The detection of mitosis is a challenging task because in a frame of slides at X40 magnification, there are hundreds of nuclei containing few mitotic nuclei. However, manual counting of mitosis by pathologists is a difficult and time intensive job, moreover conventional method rely mainly on the shape, color, and/or texture features as well as pathologist experience. The objective of this study is to accept the atypaia-2014 mitosis detection challenge, automate the process of mitosis detection and a proposal of a hybrid feature space that provides better discrimination of mitotic and non-mitotic nuclei by combining color features with morphological and texture features. To exploit color channels, they were first selected, and then normalized and cumulative histograms were computed in wavelet domain. A detailed analysis presented on these features in different color channels of respective color spaces using Random Forest (RF) and Support Vector Machine (SVM) classifiers. The proposed hybrid feature space when used with SVM classifier achieved a detection rate of 78.88% and F-measure of 72.07%. Our results, especially high detection rate, indicate that proposed hybrid feature space model contains discriminant information for mitotic nuclei, being therefore a very capable are for exploration to improve the quality of the diagnostic assistance in histopathology.

Morphologic Forms and Classification of Dermal Mitotic Figure Density in Primary Cutaneous Melanoma: A Retrospective Study

New American Joint Committee on Cancer eighth edition staging parameters have removed mitotic rate as a stage T1 category criterion, but it remains embedded in the synopsis of primary cutaneous melanoma (CM). A paucity of data is available, characterizing atypical mitotic forms in CM. In this study, we classify the various morphologic forms of atypical mitoses, characterize mitotic figure density, and examine the correlation between atypical mitotic figures and Breslow depth. We performed a retrospective study of 185 thick (>0.8 mm) and thin (<0.8 mm) CM specimens. Metaphase mitotic figures represented the highest percentage of total mitotic figures in cases of thick melanoma (40%) and were the second most common in thin melanoma (18%). The average Breslow depth for melanoma harboring starburst mitoses was 2.85 mm, compared with the average Breslow depth of all thick melanoma cases, 1.88 mm. The average thickness of melanoma cases containing tripolar mitoses was 2.28 mm. Breslow depth correlated with the number of atypical mitotic figures in both thick and thin melanomas (the Pearson correlation test, r = +0.18, P < 0.01). Metaphase and prophase mitoses are a common finding in both thick and thin melanomas. Although atypical mitoses were indiscriminate, starburst and tripolar (ie, multipolar) mitoses were only inherent to cases of thick melanoma (stage T3). In sum, our study reveals a parallel relationship between the density of atypical mitotic figures and Breslow depth.

In Vivo Lineage Tracing of Polyploid Hepatocytes Reveals Extensive Proliferation during Liver Regeneration

The identity of cellular populations that drive liver regeneration after injury is the subject of intense study, and the contributions of polyploid hepatocytes to organ regeneration and homeostasis have not been systematically assessed. Here, we developed a multicolor reporter allele system to genetically label and trace polyploid cells in situ. Multicolored polyploid hepatocytes undergo ploidy reduction and subsequent re-polyploidization after transplantation, providing direct evidence of the hepatocyte ploidy conveyor model. Marker segregation revealed that ploidy reduction rarely involves chromosome missegregation in vivo. We also traced polyploid hepatocytes in several different liver injury models and found robust proliferation in all settings. Importantly, ploidy reduction was seen in all injury models studied. We therefore conclude that polyploid hepatocytes have extensive regenerative capacity in situ and routinely undergo reductive mitoses during regenerative responses.

Toxoplasma gondii-induced host cellular cell cycle dysregulation is linked to chromosome missegregation and cytokinesis failure in primary endothelial host cells

Toxoplasma gondii is a zoonotic and intracellular parasite with fast proliferating properties leading to rapid host cell lysis. T. gondii modulates its host cell on numerous functional levels. T. gondii was previously reported to influence host cellular cell cycle and to dampen host cell division. By using primary endothelial host cells, we show for the first time that T. gondii tachyzoite infections led to increased host cell proliferation and to an enhanced number of multi-nucleated host cells. As detected on DNA content level, parasite infections induced a G2/M cell cycle arrest without affecting expression of G2-specific cyclin B1. In line, parasite-driven impairment mainly concerned mitotic phase of host cells by propagating several functional alterations, such as chromosome segregation errors, mitotic spindle alteration and blockage of cytokinesis progression, with the latter most likely being mediated by the downregulation of the Aurora B kinase expression.

When Three Isn't a Crowd: A Digyny Concept for Treatment-Resistant, Near-Triploid Human Cancers

Near-triploid human tumors are frequently resistant to radio/chemotherapy through mechanisms that are unclear. We recently reported a tight association of male tumor triploidy with XXY karyotypes based on a meta-analysis of 15 tumor cohorts extracted from the Mitelman database. Here we provide a conceptual framework of the digyny-like origin of this karyotype based on the germline features of malignant tumors and adaptive capacity of digyny, which supports survival in adverse conditions. Studying how the recombinatorial reproduction via diploidy can be executed in primary cancer samples and HeLa cells after DNA damage, we report the first evidence that diploid and triploid cell sub-populations constitutively coexist and inter-change genomes via endoreduplicated polyploid cells generated through genotoxic challenge. We show that irradiated triploid HeLa cells can enter tripolar mitosis producing three diploid sub-subnuclei by segregation and pairwise fusions of whole genomes. Considering the upregulation of meiotic genes in tumors, we propose that the reconstructed diploid sub-cells can initiate pseudo-meiosis producing two "gametes" (diploid "maternal" and haploid "paternal") followed by digynic-like reconstitution of a triploid stemline that returns to mitotic cycling. This process ensures tumor survival and growth by (1) DNA repair and genetic variation, (2) protection against recessive lethal mutations using the third genome.

Abnormal cleavage and developmental arrest of human preimplantation embryos in vitro

Despite improvements in culture conditions and laboratory techniques still only about 50% of human embryos reach the blastocyst stage of development in vitro. While many factors influence embryo development, aberrant cleavage divisions have only recently been shown to directly affect the genome in individual cells of human embryos resulting in chromosome loss, mosaicism and cell arrest. In this article we review the current literature in the area of aberrant cleavage in human embryos and its effect on blastocyst development. Further to this, we propose a series of common abnormal cleavage events, with particular attention to timing and frequency, and illustrate how these might influence a number of different embryo fates.

Tripolar chromosome segregation drives the association between maternal genotype at variants spanning PLK4 and aneuploidy in human preimplantation embryos

Aneuploidy is prevalent in human embryos and is the leading cause of pregnancy loss. Many aneuploidies arise during oogenesis, increasing with maternal age. Superimposed on these meiotic aneuploidies are frequent errors occurring during early mitotic divisions, contributing to widespread chromosomal mosaicism. Here we reanalyzed a published dataset comprising preimplantation genetic testing for aneuploidy in 24 653 blastomere biopsies from day-3 cleavage-stage embryos, as well as 17 051 trophectoderm biopsies from day-5 blastocysts. We focused on complex abnormalities that affected multiple chromosomes simultaneously, seeking insights into their formation. In addition to well-described patterns such as triploidy and haploidy, we identified 4.7% of blastomeres possessing characteristic hypodiploid karyotypes. We inferred this signature to have arisen from tripolar chromosome segregation in normally fertilized diploid zygotes or their descendant diploid cells. This could occur via segregation on a tripolar mitotic spindle or by rapid sequential bipolar mitoses without an intervening S-phase. Both models are consistent with time-lapse data from an intersecting set of 77 cleavage-stage embryos, which were enriched for the tripolar signature among embryos exhibiting abnormal cleavage. The tripolar signature was strongly associated with common maternal genetic variants spanning the centrosomal regulator PLK4, driving the association we previously reported with overall mitotic errors. Our findings are consistent with the known capacity of PLK4 to induce tripolar mitosis or precocious M-phase upon dysregulation. Together, our data support tripolar chromosome segregation as a key mechanism generating complex aneuploidy in cleavage-stage embryos and implicate maternal genotype at a quantitative trait locus spanning PLK4 as a factor influencing its occurrence.

Comparing the effects of vitamin E tocotrienol-rich fraction supplementation and α-tocopherol supplementation on gene expression in healthy older adults

OBJECTIVES

This study aims to compare the differential gene expression resulting from tocotrienol-rich fraction and α-tocopherol supplementation in healthy older adults.

METHODS

A total of 71 eligible subjects aged 50 to 55 years from Gombak and Kuala Lumpur, Malaysia, were divided into three groups and supplemented with placebo (n=23), α-tocopherol (n=24) or tocotrienol-rich fraction (n=24). Blood samples were collected at baseline and at 3 and 6 months of supplementation for microarray analysis.

RESULTS

The number of genes altered by α-tocopherol was higher after 6 months (1,410) than after 3 months (273) of supplementation. α-Tocopherol altered the expression of more genes in males (952) than in females (731). Similarly, tocotrienol-rich fraction modulated the expression of more genes after 6 months (1,084) than after 3 months (596) and affected more genes in males (899) than in females (781). α-Tocopherol supplementation modulated pathways involving the response to stress and stimuli, the immune response, the response to hypoxia and bacteria, the metabolism of toxins and xenobiotics, mitosis, and synaptic transmission as well as activated the mitogen-activated protein kinase and complement pathways after 6 months. However, tocotrienol-rich fraction supplementation affected pathways such as the signal transduction, apoptosis, nuclear factor kappa B kinase, cascade extracellular signal-regulated kinase-1 and extracellular signal-regulated kinase-2, immune response, response to drug, cell adhesion, multicellular organismal development and G protein signaling pathways.

CONCLUSION

Supplementation with either α-tocopherol or tocotrienol-rich fraction affected the immune and drug response and the cell adhesion and signal transduction pathways but modulated other pathways differently after 6 months of supplementation, with sex-specific responses.

Chromosome constitution of equal-sized three-cell embryos using next-generation sequencing technology

PURPOSE

To study the chromosome constitution of equal-sized three-cell embryo.

METHODS

We determined the chromosome constitution of 105 blastomeres from 35 embryos using multiple annealing and looping-based amplification cycles (MALBAC) together with NGS sequencing technology. Chromosomal copy number variation (CNV) analysis was successfully performed in 27 embryos. We also analyzed radius, perimeter, area, and volume of each blastomere to explore the possibility of selecting the normal embryos.

RESULTS

Majority of the embryos (77.8%, 21/27) studied were mosaic or aneuploid, and only 22.2% (6/27) had normal chromosome numbers. The aneuploid chromosomes spread across all chromosomes and the most frequent aneuploidies were for chromosomes 1, 16, and 18 followed by 13, 19, and 21. Statistical analyses showed no significant difference between euploid and aneuploid embryos regarding radius, perimeter, area, and volume of their blastomeres.

CONCLUSIONS

Our results showed that majority of the equal-sized three-cell embryos were chromosomally abnormal and could not be distinguished by morphology observation, so they should be given lower priority at selection for transfer.

Dual-spindle formation in zygotes keeps parental genomes apart in early mammalian embryos

At the beginning of mammalian life, the genetic material from each parent meets when the fertilized egg divides. It was previously thought that a single microtubule spindle is responsible for spatially combining the two genomes and then segregating them to create the two-cell embryo. We used light-sheet microscopy to show that two bipolar spindles form in the zygote and then independently congress the maternal and paternal genomes. These two spindles aligned their poles before anaphase but kept the parental genomes apart during the first cleavage. This spindle assembly mechanism provides a potential rationale for erroneous divisions into more than two blastomeric nuclei observed in mammalian zygotes and reveals the mechanism behind the observation that parental genomes occupy separate nuclear compartments in the two-cell embryo.

Time-Lapse Imaging for the Detection of Chromosomal Abnormalities in Primate Preimplantation Embryos

The use of time-lapse microscopic imaging has proven to be a powerful tool for the study of mitotic divisions and other cellular processes across diverse species and cell types. Although time-lapse monitoring (TLM) of human preimplantation development was first introduced to the in vitro fertilization (IVF) community several decades ago, it was not until relatively recently that TLM systems were commercialized for clinical embryology purposes. Traditionally, human IVF embryos are assessed by successful progression and morphology under a stereomicroscope at distinct time points prior to selection for transfer. Due to the high frequency of aneuploidy, embryos may also be biopsied at the cleavage or blastocyst stage for preimplantation genetic screening (PGS) of whole and/or partial chromosomal abnormalities. However, embryo biopsy is invasive and can hinder subsequent development, and there are additional concerns over chromosomal mosaicism and resolution with PGS. Moreover, embryos are typically outside of the incubator in suboptimal culture conditions for extended periods of time during these procedures. With TLM systems, embryos remain in the stable microenvironment of an incubator and are simultaneously imaged for noninvasive embryo evaluation using a fraction of the light exposure as compared to a stereomicroscope. Each image is then compiled into a time-lapse movie, the information from which can be extrapolated to correlate morphological, spatial, and temporal parameters with embryo quality and copy number status. Here, we describe the various TLM systems available for clinical and/or research use in detail and provide step-by-step instructions on how the measurement of specific timing intervals and certain morphological criteria can be implemented into IVF protocols to enhance embryo assessment and avoid the selection of aneuploid embryos. We also discuss the biological significance of processes unique to mitotically dividing embryos and the likelihood that complex chromosomal events such as chromothripsis occur during preimplantation development in humans and other mammals, particularly nonhuman primates.

Causes and consequences of chromosome segregation error in preimplantation embryos

Errors in chromosome segregation are common during the mitotic divisions of preimplantation development in mammalian embryos, giving rise to so-called ‘mosaic’ embryos possessing a mixture of euploid and aneuploid cells. Mosaicism is widely considered to be detrimental to embryo quality and is frequently used as criteria to select embryos for transfer in human fertility clinics. However, despite the clear clinical importance, the underlying defects in cell division that result in mosaic aneuploidy remain elusive. In this review, we summarise recent findings from clinical and animal model studies that provide new insights into the fundamental mechanisms of chromosome segregation in the highly unusual cellular environment of early preimplantation development and consider recent clues as to why errors should commonly occur in this setting. We furthermore discuss recent evidence suggesting that mosaicism is not an irrevocable barrier to a healthy pregnancy. Understanding the causes and biological impacts of mosaic aneuploidy will be pivotal in the development and fine-tuning of clinical embryo selection methods.

CIN and Aneuploidy: Different Concepts, Different Consequences

Chromosomal instability (CIN) and aneuploidy are similar concepts but not synonymous. CIN is the process that leads to chromosome copy number alterations, and aneuploidy is the result. While CIN and resulting aneuploidy often cause growth defects, they are also selected for in cancer cells. Although such contradicting fates may seem paradoxical at first, they can be better understood when CIN and aneuploidy are assessed separately, taking into account the in vitro or in vivo context, the rate of CIN, and severity of the aneuploid karyotype. As CIN can only be measured in living cells, which proves to be technically challenging in vivo, aneuploidy is more frequently quantified. However, CIN rates might be more predictive for tumor outcome than assessing aneuploidy rates alone. In reviewing the literature, we therefore conclude that there is an urgent need for new models in which we can monitor chromosome mis-segregation and its consequences in vivo. Also see the video abstract here: https://youtu.be/fL3LxZduchg.

Tripolar mitosis and partitioning of the genome arrests human preimplantation development in vitro

Following in vitro fertilisation (IVF), only about half of normally fertilised human embryos develop beyond cleavage and morula stages to form a blastocyst in vitro. Although many human embryos are aneuploid and genomically imbalanced, often as a result of meiotic errors inherited in the oocyte, these aneuploidies persist at the blastocyst stage and the reasons for the high incidence of developmental arrest remain unknown. Here we use genome-wide SNP genotyping and meiomapping of both polar bodies to identify maternal meiotic errors and karyomapping to fingerprint the parental chromosomes in single cells from disaggregated arrested embryos and excluded cells from blastocysts. Combined with time lapse imaging of development in culture, we demonstrate that tripolar mitoses in early cleavage cause chromosome dispersal to clones of cells with identical or closely related sub-diploid chromosome profiles resulting in intercellular partitioning of the genome. We hypothesise that following zygotic genome activation (ZGA), the combination of genomic imbalance and partial genome loss disrupts the normal pattern of embryonic gene expression blocking development at the morula-blastocyst transition. Failure to coordinate the cell cycle in early cleavage and regulate centrosome duplication is therefore a major cause of human preimplantation developmental arrest in vitro.

Mosaicism in Preimplantation Human Embryos: When Chromosomal Abnormalities Are the Norm

Along with errors in meiosis, mitotic errors during post-zygotic cell division contribute to pervasive aneuploidy in human embryos. Relatively little is known, however, about the genesis of these errors or their fitness consequences. Rapid technological advances are helping to close this gap, revealing diverse molecular mechanisms contributing to mitotic error. These include altered cell cycle checkpoints, aberrations of the centrosome, and failed chromatid cohesion, mirroring findings from cancer biology. Recent studies are challenging the idea that mitotic error is abnormal, emphasizing that the fitness impacts of mosaicism depend on its scope and severity. In light of these findings, technical and philosophical limitations of various screening approaches are discussed, along with avenues for future research.

Direct Unequal Cleavages: Embryo Developmental Competence, Genetic Constitution and Clinical Outcome

Objective

To investigate the prevalence, developmental potential, chromosomal constitution and clinical outcome of embryos with direct unequal cleavages (DUC).

Design

A retrospective observational study.

Setting

Academic Institution.

Participant

21,261 embryos from 3,155 cycles cultured in EmbryoScope^®.

Results

The total incidence of DUCs per embryo occupying the first three cleavages were 26.1%. Depending of the cell stage, DUC rate was 9.8% at first cleavage (DUC-1), 9.1% at second cleavage (DUC-2), and 3.7% at third cleavage (DUC-3) with 3.6% of embryos exhibiting multiple DUCs (DUC-Plus). The occurrence of DUCs was not correlated with female gamete age or source. The incidence of DUC-1 was significantly higher in embryos fertilized by epididymal and testicular sperm (13.6% and 11.4%, respectively) compared to ejaculated sperm (9.1%, all p<0.05). The total incidences of DUCs were strongly correlated with the onset of blastomere multinucleation (MNB) during the first three divisions. In MNB embryos, DUCs incidence are two to three times more likely to develop when compared to non-MNB embryos (OR = 3.11, 95% CI [2.64, 3.67] at 1-cell stage, OR = 2.64, 95% CI [2.39, 2.91] at 2-cell stage and OR = 2.51, 95% CI [1.84, 3.43] at 4-cell stage). The blastocyst formation rates gradually decreased from 61.0% in non-DUC to 40.2% in DUC-3, 18.8% in DUC-2, 8.2% in DUC-1 and 5.6% in multiple DUC embryos (DUC-Plus). The known implantation rates (FH) for day 3 (D3) transfers were 12.42% (n = 3172) in Non-DUC embryos, 6.3% (n = 127) in DUC-3, and 2.7% (n = 260) in DUC-2 embryos. No live births resulted from either DUC-1 (n = 225) or DUC-Plus (n = 100) embryo transfers. For blastocyst transfers, lower implantation rates (33.3%) but similar live birth (LB) rates (40%) were observed if DUC blastocysts were transferred. Comparatively rates in Non-DUC blastocyst were 45.2% and 34.8%, respectively. The euploid rate gradually increased from DUC-1, -2, -3 to Non-DUC (13.3%, 19.5%, 33.3%, 45.6%, p<0.001) for D3 biopsied embryos. Interestingly, the trend of decreased euploidy disappeared in DUC D5/6 biopsied embryos and similar rates were exemplified in DUC (D5 56.3%, D6 35.6%) vs. non-DUC (D5 51.4%, D6 33.8%) embryos.

Conclusion

Blastocyst formation, implantation potential and euploid rate were significantly reduced in DUC embryos. DUC embryos should be deselected for D3 transfers, but should be culture to blastocyst stage for possible ET.

Basic Molecular Pathology and Cytogenetics for Practicing Pathologists: Correlation With Morphology and With a Focus on Aspects of Diagnostic or Therapeutic Utility

Morphology, as confronted in the everyday practice, often correlates with specific molecular features, which have important implications not only in pathogenesis and in diagnosis but also in prognosis and therapy. Thus, it is important that the classical pathology includes a sound knowledge of molecular aspects of disease. These molecular concepts are complex and not easily understood by all engaged in the routine practice of histopathology. Thus, the aim of this review is to present a summary of most of the necessary concepts for pathologists involving molecular pathology and genetics, beginning from basic definitions and mechanisms to major abnormalities and the methodology to detect them, correlating at the same time, the specific morphologic features associated with every abnormality.

Amino Acid Metabolism in Human Embryos

The aim of this study was to find some relationship between amino acid metabolism and the embryo morphokinetic parameters studied via time-lapse analysis. Study included 48 human embryo samples and their culture media. Two groups of embryos were identified: embryos reached the 8-cell stage on day 3 (n=34) and embryos failed to develop at any point during the incubation (n=14). Amino acids levels were measured on day 3 of embryo development; using time-lapse analysis, the precise timing of embryo cleavage, synchrony of division, grade of fragmentation etc. were established. No statistically significant differences between dividing and arresting embryos were observed in terms of amino acids production/consumption and turnover. Amino acids which were part of the culture medium did not exhibit any statistically significant correlation with kinetic parameters with the exception of the grade of fragmentation on day 3; there were negative correlation with glutamate, and positive with glutamine, glycine and taurine. In some dividing and in some arresting embryos appeared new amino acids which strongly correlated with each other, with methionine, but not with any other amino acid that is a regular part of the culture medium.

1,2:3,4-Diepoxybutane Induces Multipolar Mitosis in Cultured Human Lymphocytes

1,3-Butadiene, a colorless gas regularly used in the production of plastics, thermoplastic resins, and styrene-butadiene rubber, poses an increased leukemia mortality risk to workers in this field. 1,3-Butadiene is also produced by incomplete combustion of motor fuels or by tobacco smoking. It is absorbed principally through the respiratory system and metabolized by several enzymes rendering 1,2:3,4-diepoxybutane (DEB), which has the highest genotoxic potency of all metabolites of 1,3-butadiene. DEB is considered a carcinogen mainly due to its high potential as clastogen, which induces structural chromosome aberrations such as sister chromatid exchanges, chromosomal breaks, and micronuclei. Due to its clastogenic effect, DEB is one of the most used agents for diagnostic studies of Fanconi anemia, a recessively inherited disease related to mutations affecting several genes involved in a common DNA repair pathway. When performing Fanconi anemia diagnostic tests in our laboratory, we have observed occasional multipolar mitosis (MM) in lymphocyte cultures exposed to 0.1 μg/ml of DEB and harvested in the absence of any mitotic spindle inhibitor. Although previous studies reported an aneugenic effect (i.e. it induces aneuploidy) of DEB, no mechanism was suggested to explain such observations. Therefore, the aim of this study was to investigate whether exposure to 0.1 μg/ml of DEB is significantly associated with the occurrence of MM. We blindly assessed the frequency of MM in lymphocyte cultures from 10 nonsmoking healthy individuals. Two series of 3 cultures were performed from each sample under different conditions: A, without DEB; B, with 0.1 μg/ml of DEB, and C, with 25 μM of mitomycin C as positive control. Cultures exposed to DEB showed higher frequencies of MM (23 of 2,000 cells) than did the unexposed ones (3 of 2,000 cells).

Abnormally cleaving embryos are able to produce live births: a time-lapse study

PURPOSE

This study investigated the prevalence of abnormally cleaved embryos and determined which types of abnormally cleaved embryos (1-3c, 2-4c, 3-5c, 4-6c), might be suitable for transfer based on live birth data.

METHODS

One hundred seventy-one women (whose transferred embryos were confirmed to be either fully implanted or fully unimplanted) provided 1256 embryos, which were analyzed.

RESULTS

Of these embryos, 320 embryos were transferred, of these transferred embryos, 291 embryos were normal and 29 embryos were abnormal, which five embryos were not analyzed because each one was presented one abnormal cleavage type. These 24 embryos were divided into four groups. Inclusion criteria were as follows: women under 37 years of age undergoing first fresh in vitro fertilization (IVF) treatment with a basal antral follicle count of 5-15, body mass index (BMI) of 18-25 kg/m(2), number of retrieved oocytes between 5 and 20, and tubal factors as the cause of infertility. Time-lapse imaging analysis software was used to compare temporal parameters of normal cleavage and abnormal cleavage groups (there were four abnormal groups, based on the prevalence of abnormal cleavage embryos). Cleavage times were analyzed before the abnormal cleavage occurred, and time intervals were analyzed after the abnormal cleavage based upon the types of abnormal cleavage. In addition, the time intervals of t4-t3 and t8-t5 were also analyzed; corresponding time parameters were measured in the normal group as well. Implantation rate, clinical pregnancy rate, ongoing pregnancy rate, and live birth rate were also measured in the normally cleaved and abnormally cleaved embryos. The prevalence of abnormal cleavage was 15.92% (200/1256). T8-t5 was the most important parameter in the prediction of potential development (production of a live-born baby) of abnormally cleaving embryos.

CONCLUSIONS

Abnormally cleaving embryos were able to produced live births with T8-t5 the best parameter to predict the developmental potential of abnormally cleaving embryos.

Chromosomal instability in mammalian pre-implantation embryos: potential causes, detection methods, and clinical consequences

Formation of a totipotent blastocyst capable of implantation is one of the first major milestones in early mammalian embryogenesis, but less than half of in vitro fertilized embryos from most mammals will progress to this stage of development. Whole chromosomal abnormalities, or aneuploidy, are key determinants of whether human embryos will arrest or reach the blastocyst stage. Depending on the type of chromosomal abnormality, however, certain embryos still form blastocysts and may be morphologically indistinguishable from chromosomally normal embryos. Despite the implementation of pre-implantation genetic screening and other advanced in vitro fertilization (IVF) techniques, the identification of aneuploid embryos remains complicated by high rates of mosaicism, atypical cell division, cellular fragmentation, sub-chromosomal instability, and micro-/multi-nucleation. Moreover, several of these processes occur in vivo following natural human conception, suggesting that they are not simply a consequence of culture conditions. Recent technological achievements in genetic, epigenetic, chromosomal, and non-invasive imaging have provided additional embryo assessment approaches, particularly at the single-cell level, and clinical trials investigating their efficacy are continuing to emerge. In this review, we summarize the potential mechanisms by which aneuploidy may arise, the various detection methods, and the technical advances (such as time-lapse imaging, "-omic" profiling, and next-generation sequencing) that have assisted in obtaining this data. We also discuss the possibility of aneuploidy resolution in embryos via various corrective mechanisms, including multi-polar divisions, fragment resorption, endoreduplication, and blastomere exclusion, and conclude by examining the potential implications of these findings for IVF success and human fecundity.

Mitotic index and multipolar mitosis in routine histologic sections as prognostic markers of pancreatic cancers: A clinicopathological study

OBJECTIVES

Pancreatic cancer is characterized by genomic complexity and chromosomal instability, and atypical mitotic figures are morphological features of this phenotype. In the present study, we determined the frequency and the clinicopathological and prognostic significance of mitotic figures in pancreatic cancers.

METHODS

We surveyed the mitotic figures of the normal ductal epithelium, acinar cells, pancreatic intraepithelial neoplasias, and pancreatic cancers on hematoxylin-and-eosin-stained tissue specimens (n = 121).

RESULTS

Pancreatic cancer cells showed significantly higher mitotic indices as compared with the ductal cells, acinar cells, and pancreatic intraepithelial neoplasias. Both normal and atypical mitosis were significantly elevated only in pancreatic cancers. In pancreatic cancers, approximately 30% of total mitosis was atypical including multipolar, lag-type, ring and asymmetrical mitosis, and anaphase bridges. The Kaplan-Meier curves in pancreatic cancers showed significant correlations between total mitosis and disease free survival. Furthermore, the cases with multipolar mitosis showed poorer prognosis than those without. Lymph node metastasis and multipolar mitosis were independent prognostic factors for overall survival of patients with pancreatic cancer. In addition, lymph node metastasis and total mitosis were independent factors for disease free survival.

CONCLUSION

These findings suggest that routinely obtained pathological specimens, even small biopsy or cytological specimens, can provide valuable information concerning the prognosis of pancreatic cancers.

Evidence of Selection against Complex Mitotic-Origin Aneuploidy during Preimplantation Development

Whole-chromosome imbalances affect over half of early human embryos and are the leading cause of pregnancy loss. While these errors frequently arise in oocyte meiosis, many such whole-chromosome abnormalities affecting cleavage-stage embryos are the result of chromosome missegregation occurring during the initial mitotic cell divisions. The first wave of zygotic genome activation at the 4-8 cell stage results in the arrest of a large proportion of embryos, the vast majority of which contain whole-chromosome abnormalities. Thus, the full spectrum of meiotic and mitotic errors can only be detected by sampling after the initial cell divisions, but prior to this selective filter. Here, we apply 24-chromosome preimplantation genetic screening (PGS) to 28,052 single-cell day-3 blastomere biopsies and 18,387 multi-cell day-5 trophectoderm biopsies from 6,366 in vitro fertilization (IVF) cycles. We precisely characterize the rates and patterns of whole-chromosome abnormalities at each developmental stage and distinguish errors of meiotic and mitotic origin without embryo disaggregation, based on informative chromosomal signatures. We show that mitotic errors frequently involve multiple chromosome losses that are not biased toward maternal or paternal homologs. This outcome is characteristic of spindle abnormalities and chaotic cell division detected in previous studies. In contrast to meiotic errors, our data also show that mitotic errors are not significantly associated with maternal age. PGS patients referred due to previous IVF failure had elevated rates of mitotic error, while patients referred due to recurrent pregnancy loss had elevated rates of meiotic error, controlling for maternal age. These results support the conclusion that mitotic error is the predominant mechanism contributing to pregnancy losses occurring prior to blastocyst formation. This high-resolution view of the full spectrum of whole-chromosome abnormalities affecting early embryos provides insight into the cytogenetic mechanisms underlying their formation and the consequences for human fertility.