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Horakova A, Konecna M, Anger M. Chromosome Division in Early Embryos-Is Everything under Control? And Is the Cell Size Important? Int J Mol Sci 2024; 25:2101. [PMID: 38396778 PMCID: PMC10889803 DOI: 10.3390/ijms25042101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 02/02/2024] [Accepted: 02/06/2024] [Indexed: 02/25/2024] Open
Abstract
Chromosome segregation in female germ cells and early embryonic blastomeres is known to be highly prone to errors. The resulting aneuploidy is therefore the most frequent cause of termination of early development and embryo loss in mammals. And in specific cases, when the aneuploidy is actually compatible with embryonic and fetal development, it leads to severe developmental disorders. The main surveillance mechanism, which is essential for the fidelity of chromosome segregation, is the Spindle Assembly Checkpoint (SAC). And although all eukaryotic cells carry genes required for SAC, it is not clear whether this pathway is active in all cell types, including blastomeres of early embryos. In this review, we will summarize and discuss the recent progress in our understanding of the mechanisms controlling chromosome segregation and how they might work in embryos and mammalian embryos in particular. Our conclusion from the current literature is that the early mammalian embryos show limited capabilities to react to chromosome segregation defects, which might, at least partially, explain the widespread problem of aneuploidy during the early development in mammals.
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Affiliation(s)
- Adela Horakova
- Department of Genetics and Reproductive Biotechnologies, Veterinary Research Institute, 621 00 Brno, Czech Republic
- Institute of Animal Physiology and Genetics, Czech Academy of Science, 277 21 Libechov, Czech Republic
- Faculty of Science, Masaryk University, 602 00 Brno, Czech Republic
| | - Marketa Konecna
- Department of Genetics and Reproductive Biotechnologies, Veterinary Research Institute, 621 00 Brno, Czech Republic
- Institute of Animal Physiology and Genetics, Czech Academy of Science, 277 21 Libechov, Czech Republic
- Faculty of Science, Masaryk University, 602 00 Brno, Czech Republic
| | - Martin Anger
- Department of Genetics and Reproductive Biotechnologies, Veterinary Research Institute, 621 00 Brno, Czech Republic
- Institute of Animal Physiology and Genetics, Czech Academy of Science, 277 21 Libechov, Czech Republic
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2
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Verdyck P, Altarescu G, Santos-Ribeiro S, Vrettou C, Koehler U, Griesinger G, Goossens V, Magli C, Albanese C, Parriego M, Coll L, Ron-El R, Sermon K, Traeger-Synodinos J. Aneuploidy in oocytes from women of advanced maternal age: analysis of the causal meiotic errors and impact on embryo development. Hum Reprod 2023; 38:2526-2535. [PMID: 37814912 DOI: 10.1093/humrep/dead201] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 09/06/2023] [Indexed: 10/11/2023] Open
Abstract
STUDY QUESTION In oocytes of advanced maternal age (AMA) women, what are the mechanisms leading to aneuploidy and what is the association of aneuploidy with embryo development? SUMMARY ANSWER Known chromosome segregation errors such as precocious separation of sister chromatids explained 90.4% of abnormal chromosome copy numbers in polar bodies (PBs), underlying impaired embryo development. WHAT IS KNOWN ALREADY Meiotic chromosomal aneuploidies in oocytes correlate with AMA (>35 years) and can affect over half of oocytes in this age group. This underlies the rationale for PB biopsy as a form of early preimplantation genetic testing for aneuploidy (PGT-A), as performed in the 'ESHRE STudy into the Evaluation of oocyte Euploidy by Microarray analysis' (ESTEEM) randomized controlled trial (RCT). So far, chromosome analysis of oocytes and PBs has shown that precocious separation of sister chromatids (PSSC), Meiosis II (MII) non-disjunction (ND), and reverse segregation (RS) are the main mechanisms leading to aneuploidy in oocytes. STUDY DESIGN, SIZE, DURATION Data were sourced from the ESTEEM study, a multicentre RCT from seven European centres to assess the clinical utility of PGT-A on PBs using array comparative genomic hybridization (aCGH) in patients of AMA (36-40 years). This included data on the chromosome complement in PB pairs (PGT-A group), and on embryo morphology in a subset of embryos, up to Day 6 post-insemination, from both the intervention (PB biopsy and PGT-A) and control groups. PARTICIPANTS/MATERIALS, SETTING, METHODS ESTEEM recruited 396 AMA patients: 205 in the intervention group and 191 in the control group. Complete genetic data from 693 PB pairs were analysed. Additionally, the morphology from 1034 embryos generated from fertilized oocytes (two pronuclei) in the PB biopsy group and 1082 in the control group were used for statistical analysis. MAIN RESULTS AND THE ROLE OF CHANCE Overall, 461/693 PB pairs showed abnormal segregation in 1162/10 810 chromosomes. The main observed abnormal segregations were compatible with PSSC in Meiosis I (MI) (n = 568/1162; 48.9%), ND of chromatids in MII or RS (n = 417/1162; 35.9%), and less frequently ND in MI (n = 65/1162; 5.6%). For 112 chromosomes (112/1162; 9.6%), we observed a chromosome copy number in the first PB (PB1) and second PB (PB2) that is not explained by any of the known mechanisms causing aneuploidy in oocytes. We observed that embryos in the PGT-A arm of the RCT did not have a significantly different morphology between 2 and 6 days post-insemination compared to the control group, indicating that PB biopsy did not affect embryo quality. Following age-adjusted multilevel mixed-effect ordinal logistic regression models performed for each embryo evaluation day, aneuploidy was associated with a decrease in embryo quality on Day 3 (adjusted odds ratio (aOR) 0.62, 95% CI 0.43-0.90), Day 4 (aOR 0.15, 95% CI 0.06-0.39), and Day 5 (aOR 0.28, 95% CI 0.14-0.58). LIMITATIONS, REASON FOR CAUTION RS cannot be distinguished from normal segregation or MII ND using aCGH. The observed segregations were based on the detected copy number of PB1 and PB2 only and were not confirmed by the analysis of embryos. The embryo morphology assessment was static and single observer. WIDER IMPLICATIONS OF THE FINDINGS Our finding of frequent unexplained chromosome copy numbers in PBs indicates that our knowledge of the mechanisms causing aneuploidy in oocytes is incomplete. It challenges the dogma that aneuploidy in oocytes is exclusively caused by mis-segregation of chromosomes during MI and MII. STUDY FUNDING/COMPETING INTEREST(S) Data were mined from a study funded by ESHRE. Illumina provided microarrays and other consumables necessary for aCGH testing of PBs. None of the authors have competing interests. TRIAL REGISTRATION NUMBER Data were mined from the ESTEEM study (ClinicalTrials.gov Identifier NCT01532284).
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Affiliation(s)
- P Verdyck
- Centre for Medical Genetics, Vrije Universiteit Brussel (VUB), Universitair Ziekenhuis Brussel (UZ Brussel), Brussels, Belgium
- Research Group Reproduction and Genetics, Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - G Altarescu
- Shaare-Zedek Medical Center, The Hebrew University School of Medicine, Jerusalem, Israël
| | - S Santos-Ribeiro
- IVI-RMA Lisboa, Lisbon, Portugal
- Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - C Vrettou
- Laboratory of Medical Genetics, National and Kapodistrian University of Athens, 'Aghia Sophia' Children's Hospital, Athens, Greece
| | - U Koehler
- MGZ-Medizinisch Genetisches Zentrum, Munich, Germany
| | - G Griesinger
- Department of Gynecological Endocrinology and Reproductive Medicine, University Hospital of Schleswig-Holstein, Campus Luebeck, Lübeck, Germany
| | - V Goossens
- The European Society of Human Reproduction and Embryology, Strombeek-Bever, Belgium
| | - C Magli
- SISMER, Reproductive Medicine Unit, Bologna, Italy
| | - C Albanese
- SISMER, Reproductive Medicine Unit, Bologna, Italy
| | - M Parriego
- Department of Obstetrics, Gynecology and Reproductive Medicine, Dexeus University Hospital, Barcelona, Spain
| | - L Coll
- Department of Obstetrics, Gynecology and Reproductive Medicine, Dexeus University Hospital, Barcelona, Spain
| | - R Ron-El
- Shaare-Zedek Medical Center, The Hebrew University School of Medicine, Jerusalem, Israël
| | - K Sermon
- Research Group Reproduction and Genetics, Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - J Traeger-Synodinos
- Laboratory of Medical Genetics, National and Kapodistrian University of Athens, 'Aghia Sophia' Children's Hospital, Athens, Greece
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3
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Dong J, Jin L, Bao S, Chen B, Zeng Y, Luo Y, Du X, Sang Q, Wu T, Wang L. Ectopic expression of human TUBB8 leads to increased aneuploidy in mouse oocytes. Cell Discov 2023; 9:105. [PMID: 37875488 PMCID: PMC10598138 DOI: 10.1038/s41421-023-00599-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 08/26/2023] [Indexed: 10/26/2023] Open
Abstract
Aneuploidy seriously compromises female fertility and increases incidence of birth defects. Rates of aneuploidy in human eggs from even young women are significantly higher than those in other mammals. However, intrinsic genetic factors underlying this high incidence of aneuploidy in human eggs remain largely unknown. Here, we found that ectopic expression of human TUBB8 in mouse oocytes increases rates of aneuploidy by causing kinetochore-microtubule (K-MT) attachment defects. Stretched bivalents in mouse oocytes expressing TUBB8 are under less tension, resulting in continuous phosphorylation status of HEC1 by AURKB/C at late metaphase I that impairs the established correct K-MT attachments. This reduced tension in stretched bivalents likely correlates with decreased recruitment of KIF11 on meiotic spindles. We also found that ectopic expression of TUBB8 without its C-terminal tail decreases aneuploidy rates by reducing erroneous K-MT attachments. Importantly, variants in the C-terminal tail of TUBB8 were identified in patients with recurrent miscarriages. Ectopic expression of an identified TUBB8 variant in mouse oocytes also compromises K-MT attachments and increases aneuploidy rates. In conclusion, our study provides novel understanding for physiological mechanisms of aneuploidy in human eggs as well as for pathophysiological mechanisms involved in recurrent miscarriages.
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Affiliation(s)
- Jie Dong
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Liping Jin
- Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Shihua Bao
- Department of Reproductive Immunology, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Biaobang Chen
- NHC Key Lab of Reproduction Regulation, Shanghai Institute for Biomedical and Pharmaceutical Technologies, Fudan University, Shanghai, China
| | - Yang Zeng
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Yuxi Luo
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Xingzhu Du
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Qing Sang
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.
| | - Tianyu Wu
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.
| | - Lei Wang
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, The State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China.
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4
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Charalambous C, Webster A, Schuh M. Aneuploidy in mammalian oocytes and the impact of maternal ageing. Nat Rev Mol Cell Biol 2023; 24:27-44. [PMID: 36068367 DOI: 10.1038/s41580-022-00517-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 48.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/05/2022] [Indexed: 11/09/2022]
Abstract
During fertilization, the egg and the sperm are supposed to contribute precisely one copy of each chromosome to the embryo. However, human eggs frequently contain an incorrect number of chromosomes - a condition termed aneuploidy, which is much more prevalent in eggs than in either sperm or in most somatic cells. In turn, aneuploidy in eggs is a leading cause of infertility, miscarriage and congenital syndromes. Aneuploidy arises as a consequence of aberrant meiosis during egg development from its progenitor cell, the oocyte. In human oocytes, chromosomes often segregate incorrectly. Chromosome segregation errors increase in women from their mid-thirties, leading to even higher levels of aneuploidy in eggs from women of advanced maternal age, ultimately causing age-related infertility. Here, we cover the two main areas that contribute to aneuploidy: (1) factors that influence the fidelity of chromosome segregation in eggs of women from all ages and (2) factors that change in response to reproductive ageing. Recent discoveries reveal new error-causing pathways and present a framework for therapeutic strategies to extend the span of female fertility.
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Affiliation(s)
- Chloe Charalambous
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Alexandre Webster
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Melina Schuh
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
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5
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Wu T, Gu H, Luo Y, Wang L, Sang Q. Meiotic defects in human oocytes: Potential causes and clinical implications. Bioessays 2022; 44:e2200135. [PMID: 36207289 DOI: 10.1002/bies.202200135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 09/14/2022] [Accepted: 09/16/2022] [Indexed: 11/09/2022]
Abstract
Meiotic defects cause abnormal chromosome segregation leading to aneuploidy in mammalian oocytes. Chromosome segregation is particularly error-prone in human oocytes, but the mechanisms behind such errors remain unclear. To explain the frequent chromosome segregation errors, recent investigations have identified multiple meiotic defects and explained how these defects occur in female meiosis. In particular, we review the causes of cohesin exhaustion, leaky spindle assembly checkpoint (SAC), inherently unstable meiotic spindle, fragmented kinetochores or centromeres, abnormal aurora kinases (AURK), and clinical genetic variants in human oocytes. We mainly focus on meiotic defects in human oocytes, but also refer to the potential defects of female meiosis in mouse models.
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Affiliation(s)
- Tianyu Wu
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, the State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Hao Gu
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, the State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Yuxi Luo
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, the State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Lei Wang
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, the State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
| | - Qing Sang
- Institute of Pediatrics, Children's Hospital of Fudan University and Institutes of Biomedical Sciences, the State Key Laboratory of Genetic Engineering, Fudan University, Shanghai, China
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6
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So C, Menelaou K, Uraji J, Harasimov K, Steyer AM, Seres KB, Bucevičius J, Lukinavičius G, Möbius W, Sibold C, Tandler-Schneider A, Eckel H, Moltrecht R, Blayney M, Elder K, Schuh M. Mechanism of spindle pole organization and instability in human oocytes. Science 2022; 375:eabj3944. [PMID: 35143306 DOI: 10.1126/science.abj3944] [Citation(s) in RCA: 50] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Human oocytes are prone to assembling meiotic spindles with unstable poles, which can favor aneuploidy in human eggs. The underlying causes of spindle instability are unknown. We found that NUMA (nuclear mitotic apparatus protein)-mediated clustering of microtubule minus ends focused the spindle poles in human, bovine, and porcine oocytes and in mouse oocytes depleted of acentriolar microtubule-organizing centers (aMTOCs). However, unlike human oocytes, bovine, porcine, and aMTOC-free mouse oocytes have stable spindles. We identified the molecular motor KIFC1 (kinesin superfamily protein C1) as a spindle-stabilizing protein that is deficient in human oocytes. Depletion of KIFC1 recapitulated spindle instability in bovine and aMTOC-free mouse oocytes, and the introduction of exogenous KIFC1 rescued spindle instability in human oocytes. Thus, the deficiency of KIFC1 contributes to spindle instability in human oocytes.
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Affiliation(s)
- Chun So
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Katerina Menelaou
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Bourn Hall Clinic, Cambridge, UK
| | - Julia Uraji
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Bourn Hall Clinic, Cambridge, UK
| | - Katarina Harasimov
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Anna M Steyer
- Electron Microscopy Core Unit, Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - K Bianka Seres
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Bourn Hall Clinic, Cambridge, UK
| | - Jonas Bucevičius
- Chromatin Labeling and Imaging Group, Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Gražvydas Lukinavičius
- Chromatin Labeling and Imaging Group, Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Wiebke Möbius
- Electron Microscopy Core Unit, Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | | | | | - Heike Eckel
- Kinderwunschzentrum Göttingen, Göttingen, Germany
| | | | | | | | - Melina Schuh
- Department of Meiosis, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
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7
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Distinct classes of lagging chromosome underpin age-related oocyte aneuploidy in mouse. Dev Cell 2021; 56:2273-2283.e3. [PMID: 34428397 DOI: 10.1016/j.devcel.2021.07.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 06/07/2021] [Accepted: 07/29/2021] [Indexed: 12/18/2022]
Abstract
Chromosome segregation errors that cause oocyte aneuploidy increase in frequency with maternal age and are considered a major contributing factor of age-related fertility decline in females. Lagging anaphase chromosomes are a common age-associated phenomenon in oocytes, but whether anaphase laggards actually missegregate and cause aneuploidy is unclear. Here, we show that lagging chromosomes in mouse oocytes comprise two mechanistically distinct classes of chromosome motion that we refer to as "class-I" and "class-II" laggards. We use imaging approaches and mechanistic interventions to dissociate the two classes and find that whereas class-II laggards are largely benign, class-I laggards frequently directly lead to aneuploidy. Most notably, a controlled prolongation of meiosis I specifically lessens class-I lagging to prevent aneuploidy. Our data thus reveal lagging chromosomes to be a cause of age-related aneuploidy in mouse oocytes and suggest that manipulating the cell cycle could increase the yield of useful oocytes in some contexts.
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8
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Courtois A, Yoshida S, Takenouchi O, Asai K, Kitajima TS. Stable kinetochore-microtubule attachments restrict MTOC position and spindle elongation in oocytes. EMBO Rep 2021; 22:e51400. [PMID: 33655692 PMCID: PMC8024892 DOI: 10.15252/embr.202051400] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 01/14/2021] [Accepted: 01/28/2021] [Indexed: 01/13/2023] Open
Abstract
In mouse oocytes, acentriolar MTOCs functionally replace centrosomes and act as microtubule nucleation sites. Microtubules nucleated from MTOCs initially assemble into an unorganized ball‐like structure, which then transforms into a bipolar spindle carrying MTOCs at its poles, a process called spindle bipolarization. In mouse oocytes, spindle bipolarization is promoted by kinetochores but the mechanism by which kinetochore–microtubule attachments contribute to spindle bipolarity remains unclear. This study demonstrates that the stability of kinetochore–microtubule attachment is essential for confining MTOC positions at the spindle poles and for limiting spindle elongation. MTOC sorting is gradual and continues even in the metaphase spindle. When stable kinetochore–microtubule attachments are disrupted, the spindle is unable to restrict MTOCs at its poles and fails to terminate its elongation. Stable kinetochore fibers are directly connected to MTOCs and to the spindle poles. These findings suggest a role for stable kinetochore–microtubule attachments in fine‐tuning acentrosomal spindle bipolarity.
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Affiliation(s)
- Aurélien Courtois
- Laboratory for Chromosome Segregation, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Shuhei Yoshida
- Laboratory for Chromosome Segregation, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Osamu Takenouchi
- Laboratory for Chromosome Segregation, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Kohei Asai
- Laboratory for Chromosome Segregation, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan.,Graduate School of Biostudies, Kyoto University, Kyoto, Japan
| | - Tomoya S Kitajima
- Laboratory for Chromosome Segregation, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan.,Graduate School of Biostudies, Kyoto University, Kyoto, Japan
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9
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Aneuploidy in human eggs: contributions of the meiotic spindle. Biochem Soc Trans 2021; 49:107-118. [PMID: 33449109 PMCID: PMC7925012 DOI: 10.1042/bst20200043] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 12/03/2020] [Accepted: 12/11/2020] [Indexed: 12/12/2022]
Abstract
Human eggs frequently contain an incorrect number of chromosomes, a condition termed aneuploidy. Aneuploidy affects ∼10-25% of eggs in women in their early 30s, and more than 50% of eggs from women over 40. Most aneuploid eggs cannot develop to term upon fertilization, making aneuploidy in eggs a leading cause of miscarriages and infertility. The cellular origins of aneuploidy in human eggs are incompletely understood. Aneuploidy arises from chromosome segregation errors during the two meiotic divisions of the oocyte, the progenitor cell of the egg. Chromosome segregation is driven by a microtubule spindle, which captures and separates the paired chromosomes during meiosis I, and sister chromatids during meiosis II. Recent studies reveal that defects in the organization of the acentrosomal meiotic spindle contribute to human egg aneuploidy. The microtubules of the human oocyte spindle are very frequently incorrectly attached to meiotic kinetochores, the multi-protein complexes on chromosomes to which microtubules bind. Multiple features of human oocyte spindles favour incorrect attachments. These include spindle instability and many age-related changes in chromosome and kinetochore architecture. Here, we review how the unusual spindle assembly mechanism in human oocytes contributes to the remarkably high levels of aneuploidy in young human eggs, and how age-related changes in chromosome and kinetochore architecture cause aneuploidy levels to rise even higher as women approach their forties.
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10
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Mogessie B. Advances and surprises in a decade of oocyte meiosis research. Essays Biochem 2020; 64:263-275. [PMID: 32538429 DOI: 10.1042/ebc20190068] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 05/22/2020] [Accepted: 05/26/2020] [Indexed: 12/30/2022]
Abstract
Eggs are produced from progenitor oocytes through meiotic cell division. Fidelity of meiosis is critical for healthy embryogenesis - fertilisation of aneuploid eggs that contain the wrong number of chromosomes is a leading cause of genetic disorders including Down's syndrome, human embryo deaths and infertility. Incidence of meiosis-related oocyte and egg aneuploidies increases dramatically with advancing maternal age, which further complicates the 'meiosis problem'. We have just emerged from a decade of meiosis research that was packed with exciting and transformative research. This minireview will focus primarily on studies of mechanisms that directly influence chromosome segregation.
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Affiliation(s)
- Binyam Mogessie
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K
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11
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Prc1-rich kinetochores are required for error-free acentrosomal spindle bipolarization during meiosis I in mouse oocytes. Nat Commun 2020; 11:2652. [PMID: 32461611 PMCID: PMC7253481 DOI: 10.1038/s41467-020-16488-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 05/01/2020] [Indexed: 12/18/2022] Open
Abstract
Acentrosomal meiosis in oocytes represents a gametogenic challenge, requiring spindle bipolarization without predefined bipolar cues. While much is known about the structures that promote acentrosomal microtubule nucleation, less is known about the structures that mediate spindle bipolarization in mammalian oocytes. Here, we show that in mouse oocytes, kinetochores are required for spindle bipolarization in meiosis I. This process is promoted by oocyte-specific, microtubule-independent enrichment of the antiparallel microtubule crosslinker Prc1 at kinetochores via the Ndc80 complex. In contrast, in meiosis II, cytoplasm that contains upregulated factors including Prc1 supports kinetochore-independent pathways for spindle bipolarization. The kinetochore-dependent mode of spindle bipolarization is required for meiosis I to prevent chromosome segregation errors. Human oocytes, where spindle bipolarization is reportedly error prone, exhibit no detectable kinetochore enrichment of Prc1. This study reveals an oocyte-specific function of kinetochores in acentrosomal spindle bipolarization in mice, and provides insights into the error-prone nature of human oocytes. Oocyte meiosis must achieve spindle bipolarization without predefined spatial cues. Yoshida et al. demonstrate that spindle bipolarization during meiosis I in mouse oocytes requires kinetochores to prevent chromosome segregation errors, a phenomenon that does not occur in error-prone human oocytes.
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12
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Rémillard-Labrosse G, Dean NL, Allais A, Mihajlović AI, Jin SG, Son WY, Chung JT, Pansera M, Henderson S, Mahfoudh A, Steiner N, Agapitou K, Marangos P, Buckett W, Ligeti-Ruiter J, FitzHarris G. Human oocytes harboring damaged DNA can complete meiosis I. Fertil Steril 2020; 113:1080-1089.e2. [PMID: 32276763 DOI: 10.1016/j.fertnstert.2019.12.029] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 12/19/2019] [Accepted: 12/20/2019] [Indexed: 10/24/2022]
Abstract
OBJECTIVE To determine whether human oocytes possess a checkpoint to prevent completion of meiosis I when DNA is damaged. DESIGN DNA damage is considered a major threat to the establishment of healthy eggs and embryos. Recent studies found that mouse oocytes with damaged DNA can resume meiosis and undergo germinal vesicle breakdown (GVBD), but then arrest in metaphase of meiosis I in a process involving spindle assembly checkpoint (SAC) signaling. Such a mechanism could help prevent the generation of metaphase II (MII) eggs with damaged DNA. Here, we compared the impact of DNA-damaging agents with nondamaged control samples in mouse and human oocytes. SETTING University-affiliated clinic and research center. PATIENT(S) Patients undergoing ICSI cycles donated GV-stage oocytes after informed consent; 149 human oocytes were collected over 2 years (from 50 patients aged 27-44 years). INTERVENTIONS(S) Mice and human oocytes were treated with DNA-damaging drugs. MAIN OUTCOME MEASURE(S) Oocytes were monitored to evaluate GVBD and polar body extrusion (PBE), in addition to DNA damage assessment with the use of γH2AX antibodies and confocal microscopy. RESULT(S) Whereas DNA damage in mouse oocytes delays or prevents oocyte maturation, most human oocytes harboring experimentally induced DNA damage progress through meiosis I and subsequently form an MII egg, revealing the absence of a DNA damage-induced SAC response. Analysis of the resulting MII eggs revealed damaged DNA and chaotic spindle apparatus, despite the oocyte appearing morphologically normal. CONCLUSION(S) Our data indicate that experimentally induced DNA damage does not prevent PBE in human oocytes and can persist in morphologically normal looking MII eggs.
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Affiliation(s)
| | - Nicola L Dean
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Adélaïde Allais
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec, Canada
| | - Aleksandar I Mihajlović
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec, Canada; Département d'Obstétrique-Gynécologie, Université de Montréal, Montreal, Quebec, Canada
| | - Shao Guang Jin
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Weon-Young Son
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Jin-Tae Chung
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Melissa Pansera
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Sara Henderson
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Alina Mahfoudh
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Naama Steiner
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Kristy Agapitou
- Department of Applications and Technology, University of Ioannina, Ioannina, Greece; Institute of Life Fertility Unit, IASO Maternity Hospital, Athens, Greece
| | - Petros Marangos
- Department of Applications and Technology, University of Ioannina, Ioannina, Greece; Department of Biomedical Research, Institute of Molecular Biology and Biotechnology-Foundation for Research and Technology, Ioannina, Greece
| | - William Buckett
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Jacob Ligeti-Ruiter
- Reproductive Centre, McGill University Health Centre, Montreal, Quebec, Canada
| | - Greg FitzHarris
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montreal, Quebec, Canada; Département d'Obstétrique-Gynécologie, Université de Montréal, Montreal, Quebec, Canada.
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13
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Zielinska AP, Bellou E, Sharma N, Frombach AS, Seres KB, Gruhn JR, Blayney M, Eckel H, Moltrecht R, Elder K, Hoffmann ER, Schuh M. Meiotic Kinetochores Fragment into Multiple Lobes upon Cohesin Loss in Aging Eggs. Curr Biol 2019; 29:3749-3765.e7. [PMID: 31679939 PMCID: PMC6868511 DOI: 10.1016/j.cub.2019.09.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 07/23/2019] [Accepted: 09/04/2019] [Indexed: 01/02/2023]
Abstract
Chromosome segregation errors during female meiosis are a leading cause of pregnancy loss and human infertility. The segregation of chromosomes is driven by interactions between spindle microtubules and kinetochores. Kinetochores in mammalian oocytes are subjected to special challenges: they need to withstand microtubule pulling forces over multiple hours and are built on centromeric chromatin that in humans is decades old. In meiosis I, sister kinetochores are paired and oriented toward the same spindle pole. It is well established that they progressively separate from each other with advancing female age. However, whether aging also affects the internal architecture of centromeres and kinetochores is currently unclear. Here, we used super-resolution microscopy to study meiotic centromere and kinetochore organization in metaphase-II-arrested eggs from three mammalian species, including humans. We found that centromeric chromatin decompacts with advancing maternal age. Kinetochores built on decompacted centromeres frequently lost their integrity and fragmented into multiple lobes. Fragmentation extended across inner and outer kinetochore regions and affected over 30% of metaphase-II-arrested (MII) kinetochores in aged women and mice, making the lobular architecture a prominent feature of the female meiotic kinetochore. We demonstrate that a partial cohesin loss, as is known to occur in oocytes with advancing maternal age, is sufficient to trigger centromere decompaction and kinetochore fragmentation. Microtubule pulling forces further enhanced the fragmentation and shaped the arrangement of kinetochore lobes. Fragmented kinetochores were frequently abnormally attached to spindle microtubules, suggesting that kinetochore fragmentation could contribute to the maternal age effect in mammalian eggs.
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Affiliation(s)
- Agata P Zielinska
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Eirini Bellou
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Ninadini Sharma
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Ann-Sophie Frombach
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - K Bianka Seres
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany; Bourn Hall Clinic, High Street, Cambridge CB23 2TN, UK
| | - Jennifer R Gruhn
- DNRF Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3, Copenhagen DK-2200, Denmark
| | | | - Heike Eckel
- Kinderwunschzentrum, Kasseler Landstraße 25A, Göttingen 37081, Germany
| | - Rüdiger Moltrecht
- Kinderwunschzentrum, Kasseler Landstraße 25A, Göttingen 37081, Germany
| | - Kay Elder
- Bourn Hall Clinic, High Street, Cambridge CB23 2TN, UK
| | - Eva R Hoffmann
- DNRF Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3, Copenhagen DK-2200, Denmark
| | - Melina Schuh
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany.
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14
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Abstract
Chromosome segregation errors in human oocytes lead to aneuploid embryos that cause infertility and birth defects. Here we provide an overview of the chromosome-segregation process in the mammalian oocyte, highlighting mechanistic differences between oocytes and somatic cells that render oocytes so prone to segregation error. These differences include the extremely large size of the oocyte cytoplasm, the unique geometry of meiosis-I chromosomes, idiosyncratic function of the spindle assembly checkpoint, and dramatically altered oocyte cell-cycle control and spindle assembly, as compared to typical somatic cells. We summarise recent work suggesting that aging leads to a further deterioration in fidelity of chromosome segregation by impacting multiple components of the chromosome-segregation machinery. In addition, we compare and contrast recent results from mouse and human oocytes, which exhibit overlapping defects to differing extents. We conclude that the striking propensity of the oocyte to mis-segregate chromosomes reflects the unique challenges faced by the spindle in a highly unusual cellular environment.
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Affiliation(s)
- Aleksandar I Mihajlović
- Centre Recherche CHUM and Department OBGYN, Université de Montreal, Montreal, Quebec, Canada
| | - Greg FitzHarris
- Centre Recherche CHUM and Department OBGYN, Université de Montreal, Montreal, Quebec, Canada.
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15
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Radonova L, Svobodova T, Skultety M, Mrkva O, Libichova L, Stein P, Anger M. ProTAME Arrest in Mammalian Oocytes and Embryos Does Not Require Spindle Assembly Checkpoint Activity. Int J Mol Sci 2019; 20:E4537. [PMID: 31540287 PMCID: PMC6770151 DOI: 10.3390/ijms20184537] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 09/06/2019] [Accepted: 09/11/2019] [Indexed: 11/16/2022] Open
Abstract
In both mitosis and meiosis, metaphase to anaphase transition requires the activity of a ubiquitin ligase known as anaphase promoting complex/cyclosome (APC/C). The activation of APC/C in metaphase is under the control of the checkpoint mechanism, called the spindle assembly checkpoint (SAC), which monitors the correct attachment of all kinetochores to the spindle. It has been shown previously in somatic cells that exposure to a small molecule inhibitor, prodrug tosyl-l-arginine methyl ester (proTAME), resulted in cell cycle arrest in metaphase, with low APC/C activity. Interestingly, some reports have also suggested that the activity of SAC is required for this arrest. We focused on the characterization of proTAME inhibition of cell cycle progression in mammalian oocytes and embryos. Our results show that mammalian oocytes and early cleavage embryos show dose-dependent metaphase arrest after exposure to proTAME. However, in comparison to the somatic cells, we show here that the proTAME-induced arrest in these cells does not require SAC activity. Our results revealed important differences between mammalian oocytes and early embryos and somatic cells in their requirements of SAC for APC/C inhibition. In comparison to the somatic cells, oocytes and embryos show much higher frequency of aneuploidy. Our results are therefore important for understanding chromosome segregation control mechanisms, which might contribute to the premature termination of development or severe developmental and mental disorders of newborns.
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Affiliation(s)
- Lenka Radonova
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
| | - Tereza Svobodova
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
| | - Michal Skultety
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
- Cellular Imaging Core Facility, Central European Institute CEITEC Masaryk University, 624 00 Brno, Czech Republic.
| | - Ondrej Mrkva
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
| | - Lenka Libichova
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
| | - Paula Stein
- National Institute of Environmental Health Sciences, NIH, Durham, NC 27709, USA.
| | - Martin Anger
- Central European Institute of Technology, Department of Genetics and Reproduction, Veterinary Research Institute, 621 00 Brno, Czech Republic.
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16
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Griffin DK, Ogur C. Chromosomal analysis in IVF: just how useful is it? Reproduction 2018; 156:F29-F50. [PMID: 29945889 DOI: 10.1530/rep-17-0683] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 03/23/2018] [Indexed: 12/11/2022]
Abstract
Designed to minimize chances of genetically abnormal embryos, preimplantation genetic diagnosis (PGD) involves in vitro fertilization (IVF), embryo biopsy, diagnosis and selective embryo transfer. Preimplantation genetic testing for aneuploidy (PGT-A) aims to avoid miscarriage and live born trisomic offspring and to improve IVF success. Diagnostic approaches include fluorescence in situ hybridization (FISH) and more contemporary comprehensive chromosome screening (CCS) including array comparative genomic hybridization (aCGH), quantitative polymerase chain reaction (PCR), next-generation sequencing (NGS) and karyomapping. NGS has an improved dynamic range, and karyomapping can detect chromosomal and monogenic disorders simultaneously. Mosaicism (commonplace in human embryos) can arise by several mechanisms; those arising initially meiotically (but with a subsequent post-zygotic 'trisomy rescue' event) usually lead to adverse outcomes, whereas the extent to which mosaics that are initially chromosomally normal (but then arise purely post-zygotically) can lead to unaffected live births is uncertain. Polar body (PB) biopsy is the least common sampling method, having drawbacks including cost and inability to detect any paternal contribution. Historically, cleavage-stage (blastomere) biopsy has been the most popular; however, higher abnormality levels, mosaicism and potential for embryo damage have led to it being superseded by blastocyst (trophectoderm - TE) biopsy, which provides more cells for analysis. Improved biopsy, diagnosis and freeze-all strategies collectively have the potential to revolutionize PGT-A, and there is increasing evidence of their combined efficacy. Nonetheless, PGT-A continues to attract criticism, prompting questions of when we consider the evidence base sufficient to justify routine PGT-A? Basic biological research is essential to address unanswered questions concerning the chromosome complement of human embryos, and we thus entreat companies, governments and charities to fund more. This will benefit both IVF patients and prospective parents at risk of aneuploid offspring following natural conception. The aim of this review is to appraise the 'state of the art' in terms of PGT-A, including the controversial areas, and to suggest a practical 'way forward' in terms of future diagnosis and applied research.
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Affiliation(s)
- Darren K Griffin
- School of BiosciencesCentre for Interdisciplinary Studies of Reproduction, University of Kent, Canterbury, UK
| | - Cagri Ogur
- Bahceci Genetic Diagnosis Centerİstanbul, Turkey.,Department of BioengineeringYildiz Technical University, İstanbul, Turkey
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17
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Albertini DF. Making sense out of syngamy at the onset of mammalian development. J Assist Reprod Genet 2018; 35:1357-1358. [PMID: 30069851 DOI: 10.1007/s10815-018-1282-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
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18
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Greaney J, Wei Z, Homer H. Regulation of chromosome segregation in oocytes and the cellular basis for female meiotic errors. Hum Reprod Update 2017; 24:135-161. [PMID: 29244163 DOI: 10.1093/humupd/dmx035] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Revised: 09/12/2017] [Accepted: 11/26/2017] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Meiotic chromosome segregation in human oocytes is notoriously error-prone, especially with ageing. Such errors markedly reduce the reproductive chances of increasing numbers of women embarking on pregnancy later in life. However, understanding the basis for these errors is hampered by limited access to human oocytes. OBJECTIVE AND RATIONALE Important new discoveries have arisen from molecular analyses of human female recombination and aneuploidy along with high-resolution analyses of human oocyte maturation and mouse models. Here, we review these findings to provide a contemporary picture of the key players choreographing chromosome segregation in mammalian oocytes and the cellular basis for errors. SEARCH METHODS A search of PubMed was conducted using keywords including meiosis, oocytes, recombination, cohesion, cohesin complex, chromosome segregation, kinetochores, spindle, aneuploidy, meiotic cell cycle, spindle assembly checkpoint, anaphase-promoting complex, DNA damage, telomeres, mitochondria, female ageing and female fertility. We extracted papers focusing on mouse and human oocytes that best aligned with the themes of this review and that reported transformative and novel discoveries. OUTCOMES Meiosis incorporates two sequential rounds of chromosome segregation executed by a spindle whose component microtubules bind chromosomes via kinetochores. Cohesion mediated by the cohesin complex holds chromosomes together and should be resolved at the appropriate time, in a specific step-wise manner and in conjunction with meiotically programmed kinetochore behaviour. In women, the stage is set for meiotic error even before birth when female-specific crossover maturation inefficiency leads to the formation of at-risk recombination patterns. In adult life, multiple co-conspiring factors interact with at-risk crossovers to increase the likelihood of mis-segregation. Available evidence support that these factors include, but are not limited to, cohesion deterioration, uncoordinated sister kinetochore behaviour, erroneous microtubule attachments, spindle instability and structural chromosomal defects that impact centromeres and telomeres. Data from mice indicate that cohesin and centromere-specific histones are long-lived proteins in oocytes. Since these proteins are pivotal for chromosome segregation, but lack any obvious renewal pathway, their deterioration with age provides an appealing explanation for at least some of the problems in older oocytes. WIDER IMPLICATIONS Research in the mouse model has identified a number of candidate genes and pathways that are important for chromosome segregation in this species. However, many of these have not yet been investigated in human oocytes so it is uncertain at this stage to what extent they apply to women. The challenge for the future involves applying emerging knowledge of female meiotic molecular regulation towards improving clinical fertility management.
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Affiliation(s)
- Jessica Greaney
- Christopher Chen Oocyte Biology Research Laboratory, Centre for Clinical Research, Faculty of Medicine, The University of Queensland, Royal Brisbane & Women's Hospital Campus, Herston QLD 4029, Australia
| | - Zhe Wei
- Christopher Chen Oocyte Biology Research Laboratory, Centre for Clinical Research, Faculty of Medicine, The University of Queensland, Royal Brisbane & Women's Hospital Campus, Herston QLD 4029, Australia
| | - Hayden Homer
- Christopher Chen Oocyte Biology Research Laboratory, Centre for Clinical Research, Faculty of Medicine, The University of Queensland, Royal Brisbane & Women's Hospital Campus, Herston QLD 4029, Australia
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