segregation errors
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Equal segregation of chromosomes during mitosis ensures euploidy of daughter cells. Defects in this process may result in an imbalance in the chromosomal composition and cellular transformation. Proteolytic and non-proteolytic ubiquitylation pathways ensure directionality and fidelity of mitotic progression but specific mitotic functions of deubiquitylating enzymes (DUBs) remain less studied. Here we describe the role of the DUB ubiquitin carboxyl-terminal hydrolase isozyme L3 (UCHL3) in the regulation of chromosome bi-orientation and segregation during mitosis. Downregulation or inhibition of UCHL3 leads to chromosome alignment defects during metaphase. Frequent segregation errors during anaphase are also observed upon inactivation of UCHL3. Mechanistically, UCHL3 interacts with and deubiquitylates Aurora B, the catalytic subunit of chromosome passenger complex (CPC), known to be critically involved in the regulation of chromosome alignment and segregation. UCHL3 does not regulate protein levels of Aurora B or the binding of Aurora B to other CPC subunits. Instead, UCHL3 promotes localization of Aurora B to kinetochores, suggesting its role in the error correction mechanism monitoring bi-orientation of chromosomes during metaphase. Thus, UCHL3 contributes to the regulation of faithful genome segregation and maintenance of euploidy in human cells.
- MeSH
- aurora kinasa B fyziologie MeSH
- HeLa buňky MeSH
- lidé MeSH
- mitóza * MeSH
- segregace chromozomů * MeSH
- thiolesterasa ubikvitinu fyziologie MeSH
- ubikvitinace MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Aneuploidy in human eggs is the leading cause of pregnancy loss and several genetic disorders such as Down syndrome. Most aneuploidy results from chromosome segregation errors during the meiotic divisions of an oocyte, the egg's progenitor cell. The basis for particularly error-prone chromosome segregation in human oocytes is not known. We analyzed meiosis in more than 100 live human oocytes and identified an error-prone chromosome-mediated spindle assembly mechanism as a major contributor to chromosome segregation defects. Human oocytes assembled a meiotic spindle independently of either centrosomes or other microtubule organizing centers. Instead, spindle assembly was mediated by chromosomes and the small guanosine triphosphatase Ran in a process requiring ~16 hours. This unusually long spindle assembly period was marked by intrinsic spindle instability and abnormal kinetochore-microtubule attachments, which favor chromosome segregation errors and provide a possible explanation for high rates of aneuploidy in human eggs. Copyright © 2015, American Association for the Advancement of Science.
- MeSH
- anafáze MeSH
- aneuploidie * MeSH
- aparát dělícího vřeténka * metabolismus MeSH
- kinetochory metabolismus MeSH
- kultivované buňky MeSH
- lidé MeSH
- meióza * MeSH
- myši MeSH
- oocyty * patologie MeSH
- organizační centrum mikrotubulů metabolismus MeSH
- proteiny asociované s mikrotubuly genetika metabolismus MeSH
- ran protein vázající GTP metabolismus MeSH
- segregace chromozomů * MeSH
- zelené fluorescenční proteiny genetika metabolismus MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- práce podpořená grantem MeSH
Mammalian female gametes frequently suffer from numerical chromosomal aberrations, the main cause of miscarriages and severe developmental defects. The underlying mechanisms responsible for the development of aneuploidy in oocytes are still not completely understood and remain a subject of extensive research. From studies focused on prevalence of aneuploidy in mouse oocytes, it has become obvious that reported rates of aneuploidy are strongly dependent on the method used for chromosome counting. In addition, it seems likely that differences between mouse strains could influence the frequency of aneuploidy as well; however, up till now, such a comparison has not been available. Therefore, in our study, we measured the levels of aneuploidy which has resulted from missegregation in meiosis I, in oocytes of three commonly used mouse strains-CD-1, C3H/HeJ, and C57BL/6. Our results revealed that, although the overall chromosomal numerical aberration rates were similar in all three strains, a different number of oocytes in each strain contained prematurely segregated sister chromatids (PSSC). This indicates that a predisposition for this type of chromosome segregation error in oocyte meiosis I is dependent on genetic background.
- MeSH
- aneuploidie MeSH
- chromatidy genetika MeSH
- meióza genetika MeSH
- myši inbrední C3H MeSH
- myši inbrední C57BL MeSH
- myši MeSH
- oocyty cytologie MeSH
- počet buněk MeSH
- polární tělísko metabolismus MeSH
- segregace chromozomů genetika MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The onset of an early development is, in mammals, characterized by profound changes of multiple aspects of cellular morphology and behavior. These are including, but not limited to, fertilization and the merging of parental genomes with a subsequent transition from the meiotic into the mitotic cycle, followed by global changes of chromatin epigenetic modifications, a gradual decrease in cell size and the initiation of gene expression from the newly formed embryonic genome. Some of these important, and sometimes also dramatic, changes are executed within the period during which the gene transcription is globally silenced or not progressed, and the regulation of most cellular activities, including those mentioned above, relies on controlled translation. It is known that the blastomeres within an early embryo are prone to chromosome segregation errors, which might, when affecting a significant proportion of a cell within the embryo, compromise its further development. In this review, we discuss how the absence of transcription affects the transition from the oocyte to the embryo and what impact global transcriptional silencing might have on the basic cell cycle and chromosome segregation controlling mechanisms.
- MeSH
- buněčný cyklus genetika MeSH
- chromatin genetika MeSH
- embryo savčí fyziologie MeSH
- embryonální vývoj genetika MeSH
- genetická transkripce genetika MeSH
- lidé MeSH
- segregace chromozomů genetika MeSH
- umlčování genů fyziologie MeSH
- vývojová regulace genové exprese genetika MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Aneuploidy in human eggs is the leading cause of pregnancy loss and Down's syndrome. Aneuploid eggs result from chromosome segregation errors when an egg develops from a progenitor cell, called an oocyte. The mechanisms that lead to an increase in aneuploidy with advanced maternal age are largely unclear. Here, we show that many sister kinetochores in human oocytes are separated and do not behave as a single functional unit during the first meiotic division. Having separated sister kinetochores allowed bivalents to rotate by 90 degrees on the spindle and increased the risk of merotelic kinetochore-microtubule attachments. Advanced maternal age led to an increase in sister kinetochore separation, rotated bivalents and merotelic attachments. Chromosome arm cohesion was weakened, and the fraction of bivalents that precociously dissociated into univalents was increased. Together, our data reveal multiple age-related changes in chromosome architecture that could explain why oocyte aneuploidy increases with advanced maternal age.
- MeSH
- aneuploidie * MeSH
- kinetochory * metabolismus MeSH
- lidé MeSH
- meióza * MeSH
- oocyty * fyziologie MeSH
- segregace chromozomů * MeSH
- věk matky MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
Receiving complete and undamaged genetic information is vital for the survival of daughter cells after chromosome segregation. The most critical steps in this process are accurate DNA replication during S phase and a faithful chromosome segregation during anaphase. Any errors in DNA replication or chromosome segregation have dire consequences, since cells arising after division might have either changed or incomplete genetic information. Accurate chromosome segregation during anaphase requires a protein complex called cohesin, which holds together sister chromatids. This complex unifies sister chromatids from their synthesis during S phase, until separation in anaphase. Upon entry into mitosis, the spindle apparatus is assembled, which eventually engages kinetochores of all chromosomes. Additionally, when kinetochores of sister chromatids assume amphitelic attachment to the spindle microtubules, cells are finally ready for the separation of sister chromatids. This is achieved by the enzymatic cleavage of cohesin subunits Scc1 or Rec8 by an enzyme called Separase. After cohesin cleavage, sister chromatids remain attached to the spindle apparatus and their poleward movement on the spindle is initiated. The removal of cohesion between sister chromatids is an irreversible step and therefore it must be synchronized with assembly of the spindle apparatus, since precocious separation of sister chromatids might lead into aneuploidy and tumorigenesis. In this review, we focus on recent discoveries concerning the regulation of Separase activity during the cell cycle.
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.
- MeSH
- aneuploidie MeSH
- chromozomy MeSH
- embryonální vývoj * genetika MeSH
- lidé MeSH
- savci genetika MeSH
- segregace chromozomů * MeSH
- velikost buňky MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Optimal culture conditions are essential for successful IVM of mammalian oocytes and for their further development into an embryo. In the present study we used live cell imaging microscopy to assess the effects of suboptimal culture temperature on various aspects of IVM, including duration of meiosis I, dynamics of polar body extrusion, chromosome congression, anaphase-promoting complex/cyclosome (APC/C) activation and aneuploidy. The data showed that even a small deviation from the optimal incubation temperature causes marked changes in the duration and synchronicity of meiosis, APC/C activity and the frequency of chromosome congression and segregation errors. In vitro manipulation and maturation of germ cells is widely used in both human and animal artificial reproduction techniques. Mammalian oocytes are naturally prone to chromosomal segregation errors, which are responsible for severe mental and developmental disorders. The data presented herein demonstrate that exposure of mouse oocytes to suboptimal temperature during manipulation and maturation could further increase the frequency of chromosome segregation defects in these cells.
- MeSH
- anafázi podporující komplex metabolismus MeSH
- aneuploidie * MeSH
- buněčné kultury metody MeSH
- chromozomální aberace * MeSH
- meióza fyziologie MeSH
- myši MeSH
- oocyty cytologie metabolismus MeSH
- segregace chromozomů * MeSH
- teplota * MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Chromosome segregation in mammalian oocytes is prone to errors causing aneuploidy with consequences such as precocious termination of development or severe developmental disorders. Aneuploidy also represents a serious problem in procedures utilizing mammalian gametes and early embryos in vitro. In our study, we focused on congression defects during meiosis I and observed whole nondisjoined bivalents in meiosis II as a direct consequence, together with a substantially delayed first polar body extrusion. We also show that the congression defects are accompanied by less stable attachments of the kinetochores. Our results describe a process by which congression defects directly contribute to aneuploidy.
- MeSH
- aneuploidie * MeSH
- časosběrné zobrazování metody MeSH
- kinetochory metabolismus MeSH
- konfokální mikroskopie MeSH
- meióza genetika MeSH
- mikrotubuly metabolismus MeSH
- myši inbrední C57BL MeSH
- myši MeSH
- nondisjunkce genetická * MeSH
- oocyty metabolismus MeSH
- segregace chromozomů genetika MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- myši MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.
