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Cell Death & Disease Feb 2023As a highly conserved and ubiquitously expressed serine/threonine kinase, p21-activated kinase 2 (PAK2) participates in diverse biologic events. However, its roles in...
As a highly conserved and ubiquitously expressed serine/threonine kinase, p21-activated kinase 2 (PAK2) participates in diverse biologic events. However, its roles in mouse oocyte meiotic maturation remain unclear. The present study revealed that mouse oocytes depleted of Pak2 were unable to completely progress through meiosis and that a majority were arrested at metaphase I. Pak2 depletion thus prompted MI arrest and induced meiotic chromosome alignment defects in mouse oocytes, in part due to a reduction in polo-like kinase (PLK1). We demonstrated that PAK2's interaction with PLK1 protected it from degradation by APC/C, and that it promoted meiotic progression and bipolar spindle formation. Our data collectively display critical functions for PAK2 in meiotic progression and chromosome alignment in mouse oocytes.
Topics: Animals; Mice; Cell Cycle Proteins; Chromosomes; Meiosis; Metaphase; Oocytes; p21-Activated Kinases; Spindle Apparatus
PubMed: 36813765
DOI: 10.1038/s41419-023-05585-7 -
Stem Cell Reports Nov 2020In vitro spermatogenesis has been achieved by culturing mouse embryonic stem cells (ESCs) together with a cell suspension of male juvenile gonad. However, for human...
In vitro spermatogenesis has been achieved by culturing mouse embryonic stem cells (ESCs) together with a cell suspension of male juvenile gonad. However, for human fertility treatment or preservation, patient-specific ESCs or juvenile gonad is not available. We therefore aim to achieve in vitro spermatogenesis using male germline stem cells (GSCs) without the use of juvenile gonad. GSCs, when cultured on immortalized Sertoli cells, were able to enter meiosis, reach the meiotic metaphase stages, and sporadically form spermatid-like cells. However, the in vitro-formed pachytene-like spermatocytes did not display full chromosome synapsis and did not form meiotic crossovers. Despite this, the meiotic checkpoints that usually eliminate such cells to prevent genomic instabilities from being transmitted to the offspring were not activated, allowing the cells to proceed to the meiotic metaphase stages. In vitro-generated spermatid-like cells should thus be thoroughly investigated before being considered for clinical use.
Topics: Animals; Cell Cycle Checkpoints; Cells, Cultured; Coculture Techniques; Germ Cells; In Vitro Techniques; Male; Meiosis; Metaphase; Mice; Mice, Inbred DBA; Microscopy, Fluorescence; Pachytene Stage; Sertoli Cells; Spermatids; Spermatogenesis; Stem Cells
PubMed: 33176123
DOI: 10.1016/j.stemcr.2020.10.006 -
Journal of Cell Science Jan 2021Errors in mitotic chromosome segregation can lead to DNA damage and aneuploidy, both hallmarks of cancer. To achieve synchronous error-free segregation, mitotic...
Errors in mitotic chromosome segregation can lead to DNA damage and aneuploidy, both hallmarks of cancer. To achieve synchronous error-free segregation, mitotic chromosomes must align at the metaphase plate with stable amphitelic attachments to microtubules emanating from opposing spindle poles. The astrin-kinastrin (astrin is also known as SPAG5 and kinastrin as SKAP) complex, also containing DYNLL1 and MYCBP, is a spindle and kinetochore protein complex with important roles in bipolar spindle formation, chromosome alignment and microtubule-kinetochore attachment. However, the molecular mechanisms by which astrin-kinastrin fulfils these diverse roles are not fully understood. Here, we characterise a direct interaction between astrin and the mitotic kinase Plk1. We identify the Plk1-binding site on astrin as well as four Plk1 phosphorylation sites on astrin. Regulation of astrin by Plk1 is dispensable for bipolar spindle formation and bulk chromosome congression, but promotes stable microtubule-kinetochore attachments and metaphase plate maintenance. It is known that Plk1 activity is required for effective microtubule-kinetochore attachment formation, and we suggest that astrin phosphorylation by Plk1 contributes to this process.
Topics: Alcian Blue; Cell Cycle Proteins; Chromosome Segregation; HeLa Cells; Humans; Kinetochores; Metaphase; Microtubule-Associated Proteins; Microtubules; Mitosis; Phenazines; Phenothiazines; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Resorcinols; Spindle Apparatus; Polo-Like Kinase 1
PubMed: 33288550
DOI: 10.1242/jcs.251025 -
Fertility and Sterility Dec 2019To establish which meiotic checkpoints are activated in males with severe spermatogenic impairment to improve phenotypic characterization of meiotic defects. (Observational Study)
Observational Study
OBJECTIVE
To establish which meiotic checkpoints are activated in males with severe spermatogenic impairment to improve phenotypic characterization of meiotic defects.
DESIGN
Retrospective observational study.
SETTING
University medical center research laboratory and andrology clinic.
PATIENT(S)
Forty-eight patients with confirmed spermatogenic impairment (Johnsen scores 3-6) and 15 controls (Johnsen score 10).
INTERVENTION(S)
None.
MAIN OUTCOME MEASURE(S)
Quantitative assessment of immunofluorescent analyses of specific markers to determine meiotic entry, chromosome pairing, progression of DNA double-strand break repair, crossover formation, formation of meiotic metaphases, metaphase arrest, and spermatid formation, resulting in a novel classification of human meiotic arrest types.
RESULT(S)
Complete metaphase arrest was observed most frequently (27%), and the patients with the highest frequency of apoptotic metaphases also displayed a reduction in crossover number. Incomplete metaphase arrest was observed in 17% of the patients. Only four patients (8%) displayed a failure to complete meiotic chromosome pairing leading to pachytene arrest. Two new types of meiotic arrest were defined: premetaphase and postmetaphase arrest (15% and 13%, respectively).
CONCLUSION(S)
Meiotic arrest in men occurs most frequently at meiotic metaphase. This arrest can be incomplete, resulting in low numbers of spermatids, and often occurs in association with reduced crossover frequency. The phenotyping approach described here provides mechanistic insights to help identify candidate infertility genes and to assess genotype-phenotype correlations in individual cases.
Topics: Apoptosis; Azoospermia; Chromosome Pairing; DNA Breaks, Double-Stranded; Humans; Male; Metaphase; Pachytene Stage; Retrospective Studies; Spermatogenesis; Spermatozoa; Testis
PubMed: 31767154
DOI: 10.1016/j.fertnstert.2019.08.004 -
Nature Communications Apr 2019During mitosis, tension develops across the centromere as a result of spindle-based forces. Metaphase tension may be critical in preventing mitotic chromosome...
During mitosis, tension develops across the centromere as a result of spindle-based forces. Metaphase tension may be critical in preventing mitotic chromosome segregation errors, however, the nature of force transmission at the centromere and the role of centromere mechanics in controlling metaphase tension remains unknown. We combined quantitative, biophysical microscopy with computational analysis to elucidate the mechanics of the centromere in unperturbed, mitotic human cells. We discovered that the mechanical stiffness of the human centromere matures during mitotic progression, which leads to amplified centromere tension specifically at metaphase. Centromere mechanical maturation is disrupted across multiple aneuploid cell lines, leading to a weak metaphase tension signal. Further, increasing deficiencies in centromere mechanical maturation are correlated with rising frequencies of lagging, merotelic chromosomes in anaphase, leading to segregation defects at telophase. Thus, we reveal a centromere maturation process that may be critical to the fidelity of chromosome segregation during mitosis.
Topics: Aneuploidy; Cell Line, Tumor; Centromere; Chromosome Segregation; HeLa Cells; Humans; Metaphase; Mitosis; Models, Biological; Spindle Apparatus
PubMed: 30988289
DOI: 10.1038/s41467-019-09578-z -
ELife Jul 2022During cell division, kinetochore microtubules (KMTs) provide a physical linkage between the chromosomes and the rest of the spindle. KMTs in mammalian cells are...
During cell division, kinetochore microtubules (KMTs) provide a physical linkage between the chromosomes and the rest of the spindle. KMTs in mammalian cells are organized into bundles, so-called kinetochore-fibers (k-fibers), but the ultrastructure of these fibers is currently not well characterized. Here, we show by large-scale electron tomography that each k-fiber in HeLa cells in metaphase is composed of approximately nine KMTs, only half of which reach the spindle pole. Our comprehensive reconstructions allowed us to analyze the three-dimensional (3D) morphology of k-fibers and their surrounding MTs in detail. We found that k-fibers exhibit remarkable variation in circumference and KMT density along their length, with the pole-proximal side showing a broadening. Extending our structural analysis then to other MTs in the spindle, we further observed that the association of KMTs with non-KMTs predominantly occurs in the spindle pole regions. Our 3D reconstructions have implications for KMT growth and k-fiber self-organization models as covered in a parallel publication applying complementary live-cell imaging in combination with biophysical modeling (Conway et al., 2022). Finally, we also introduce a new visualization tool allowing an interactive display of our 3D spindle data that will serve as a resource for further structural studies on mitosis in human cells.
Topics: Animals; Chromosomes; HeLa Cells; Humans; Kinetochores; Mammals; Metaphase; Microtubules; Spindle Apparatus
PubMed: 35894209
DOI: 10.7554/eLife.75459 -
Cell Reports Aug 2022Chromosome alignment at the spindle equator promotes proper chromosome segregation and depends on pulling forces exerted at kinetochore fiber tips together with polar...
Chromosome alignment at the spindle equator promotes proper chromosome segregation and depends on pulling forces exerted at kinetochore fiber tips together with polar ejection forces. However, kinetochore fibers are also subjected to forces driving their poleward flux. Here we introduce a flux-driven centering model that relies on flux generated by forces within the overlaps of bridging and kinetochore fibers. This centering mechanism works so that the longer kinetochore fiber fluxes faster than the shorter one, moving the kinetochores toward the center. We develop speckle microscopy in human spindles and confirm the key prediction that kinetochore fiber flux is length dependent. Kinetochores are better centered when overlaps are shorter and the kinetochore fiber flux slower than the bridging fiber flux. We identify Kif18A and Kif4A as overlap and flux regulators and NuMA as a fiber coupler. Thus, length-dependent sliding forces exerted by the bridging fiber onto kinetochore fibers support chromosome alignment.
Topics: Anaphase; Cell Cycle Proteins; Chromosome Segregation; Chromosomes; Humans; Kinesins; Kinetochores; Metaphase; Microtubules; Spindle Apparatus
PubMed: 35926461
DOI: 10.1016/j.celrep.2022.111169 -
International Journal of Molecular... Jan 2021The combination of in vitro maturation (IVM) techniques and oocyte vitrification (OV) could increase the number of useful oocytes in different types of patients. IVM and... (Randomized Controlled Trial)
Randomized Controlled Trial
The combination of in vitro maturation (IVM) techniques and oocyte vitrification (OV) could increase the number of useful oocytes in different types of patients. IVM and subsequent OV is the most widely used clinical strategy. Would the results improve if we reverse the order of the techniques? Here, we evaluated survival, in vitro maturation, time to extrude the first polar body (PB), and the metaphase plate configuration of human prophase I (GV) oocytes before or after their vitrification. Specific, 195 GV oocytes from 104 patients subjected to controlled ovarian stimulation cycles were included. We stablished three experimental groups: GV oocytes vitrified and IVM (Group GV-Vit), GV oocytes IVM and vitrified at MII stage (Group MII-Vit), and GV oocytes IVM (Group not-Vit). All of them were in vitro matured for a maximum of 48 h and fixed to study the metaphase plate by confocal microscopy. According to our results, the vitrification of immature oocytes and their subsequent maturation presented similar survival, maturation, and metaphase plate conformation rates, but a significantly higher percentage of normal spindle than the standard strategy. Additionally, the extension of IVM time to 48 h did not seem to negatively affect the oocyte metaphase plate configuration.
Topics: Cell Survival; Chromosomes, Human; Cryopreservation; Female; Humans; In Vitro Oocyte Maturation Techniques; Metaphase; Oocytes; Spindle Apparatus; Time Factors; Vitrification
PubMed: 33498768
DOI: 10.3390/ijms22031125 -
Fertility and Sterility Apr 2023To evaluate whether metaphase I (MI) oocytes completing maturation in vitro to metaphase II ("MI-MII oocytes") have similar developmental competence as the sibling...
OBJECTIVE
To evaluate whether metaphase I (MI) oocytes completing maturation in vitro to metaphase II ("MI-MII oocytes") have similar developmental competence as the sibling metaphase II (MII) oocytes that reached maturity in vivo.
DESIGN
Retrospective cohort study.
SETTING
Academic medical center.
PATIENT(S)
A total of 1,124 intracytoplasmic sperm injection (ICSI) cycles from 800 patients at a single academic center between April 2016 and December 2020 with at least 1 MII oocyte immediately after retrieval and at least 1 sibling "MI-MII oocyte" that was retrieved as MI and matured to MII in culture before ICSI were included in the study.
INTERVENTION(S)
None.
MAIN OUTCOME MEASURE(S)
A total of 7,865 MII and 2,369 sibling MI-MII oocytes retrieved from the same individuals were compared for the fertilization and blastocyst formation rates. For patients who underwent single euploid blastocyst transfers (n = 406), the clinical pregnancy, spontaneous pregnancy loss, and live birth rates were compared between the 2 groups.
RESULT(S)
The fertilization rate was significantly higher in MII oocytes than in delayed matured MI-MII oocytes (75.9% vs. 56.1%). Similarly, the blastocyst formation rate was higher in embryos derived from MII oocytes than in those from MI-MII oocytes (53.8% vs. 23.9%). The percentage of euploid embryos derived from MII oocytes was significantly higher than that of those from MI-MII oocytes (49.2% vs. 34.7%). Paired comparison of sibling oocytes within the same cycle showed higher developmental competence of the MII oocytes than that of MI-MII oocytes. However, the pregnancy, spontaneous pregnancy loss, and live birth rates after a single euploid blastocyst transfer showed no statistically significant difference between the 2 groups (MII vs. MI-MII group, 65.7% vs. 74.1%, 6.4% vs. 5.0%, and 61.5% vs. 70.0%, respectively).
CONCLUSION(S)
Compared with oocytes that matured in vivo and were retrieved as MII, the oocytes that were retrieved as MI and matured to MII in vitro before ICSI showed lower developmental competence, including lower fertilization, blastocyst formation, and euploidy rates. However, euploid blastocysts from either cohort resulted in similar live birth rates, indicating that the MI oocytes with delayed maturation can still be useful even though the overall developmental competence was lower than that of their in vivo matured counterparts.
Topics: Pregnancy; Female; Humans; Male; Abortion, Spontaneous; Retrospective Studies; Metaphase; Semen; Oocytes; Fertilization in Vitro
PubMed: 36567036
DOI: 10.1016/j.fertnstert.2022.12.033 -
Nucleic Acids Research Sep 2019DNA damage-induced cell cycle checkpoints serve as surveillance mechanisms to maintain genomic stability, and are regulated by ATM/ATR-mediated signaling pathways that...
DNA damage-induced cell cycle checkpoints serve as surveillance mechanisms to maintain genomic stability, and are regulated by ATM/ATR-mediated signaling pathways that are conserved from yeast to humans. Trypanosoma brucei, an early divergent microbial eukaryote, lacks key components of the conventional DNA damage-induced G2/M cell cycle checkpoint and the spindle assembly checkpoint, and nothing is known about how T. brucei controls its cell cycle checkpoints. Here we discover a kinetochore-based, DNA damage-induced metaphase checkpoint in T. brucei. MMS-induced DNA damage triggers a metaphase arrest by modulating the abundance of the outer kinetochore protein KKIP5 in an Aurora B kinase- and kinetochore-dependent, but ATM/ATR-independent manner. Overexpression of KKIP5 arrests cells at metaphase through stabilizing the mitotic cyclin CYC6 and the cohesin subunit SCC1, mimicking DNA damage-induced metaphase arrest, whereas depletion of KKIP5 alleviates the DNA damage-induced metaphase arrest and causes chromosome mis-segregation and aneuploidy. These findings suggest that trypanosomes employ a novel DNA damage-induced metaphase checkpoint to maintain genomic integrity.
Topics: Ataxia Telangiectasia Mutated Proteins; Cell Cycle Checkpoints; Cell Cycle Proteins; Chromosomal Proteins, Non-Histone; Cyclins; DNA Damage; Genome, Protozoan; Genomic Instability; Humans; Kinetochores; Metaphase; Protozoan Proteins; Trypanosoma; Trypanosoma brucei brucei; Cohesins
PubMed: 31147720
DOI: 10.1093/nar/gkz476