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To ensure genome stability, chromosomes need to undergo proper condensation into two linked sister chromatids from prophase to prometaphase, followed by equal segregation at anaphase. Emerging evidence has shown that persistent DNA entanglements connecting the sister chromatids lead to the formation of ultrafine anaphase bridges (UFBs). If UFBs are not resolved soon after anaphase, they can induce chromosome missegregation. PICH (PLK1-interacting checkpoint helicase) is a DNA translocase that localizes on chromosome arms, centromeres and UFBs. It plays multiple essential roles in mitotic chromosome organization and segregation. PICH also recruits other associated proteins to UFBs, and together they mediate UFB resolution. Here, the proposed mechanism behind PICH’s functions in chromosome organization and UFB resolution will be discussed. We summarize the regulation of PICH action at chromosome arms and centromeres, how PICH recognizes UFBs and recruits other UFB-associated factors, and finally how PICH promotes UFB resolution together with other DNA processing enzymes.

The mitotic index of the roots of pigeon pea can be the basis for determining the growth of pigeon pea. The purpose of this research was to determine the time of root cell division, to observe the mitotic phases, and to determine the mitotic index of pigeon pea root cells. The preparation of the pigeon pea was carried out for 4 days to grow the roots. The roots were cut off at 08.00, 08.15, and 08.30 WIT (Eastern Indonesian Time). The roots were cut 0.5-1cm. Carnoy’s solution was used as the fixative solution using the Squash technique. The prepared roots were then observed using an Olympus cx-22 microscope and an OptiLab camera with a magnification of 100x40. The data were descriptively analyzed to describe the images of mitotic phases and the mitotic index presentation in the root cells of pigeon pea. The results of this research showed that the cell division of the pigeon pea roots began at 08.00 WIT, which was marked by the presence of a lot of prophase. The next phases that appeared were prometaphase, metaphase, and anaphase which occurred from 08.15 to 08.30 with different numbers. The highest mitotic index occurred at 08.15, when most of the root cells underwent metaphase. This study succeeded in revealing that the optimum time for pigeon pea root cell division is 08.15 WIT. In the future, this research can help pigeon pea farmers in Southwest of Maluku to carry out vegetative reproduction which is closely related to this mitotic study.

Successful cell division relies on the timely removal of key cell cycle proteins such as securin. Securin inhibits separase, which cleaves the cohesin rings holding chromosomes together. Securin must be depleted before anaphase to ensure chromosome segregation occurs with anaphase. Here we find that in meiosis I, mouse oocytes contain an excess of securin over separase. We reveal a mechanism that promotes excess securin destruction in prometaphase I. Importantly, this mechanism relies on two phenylalanine residues within the separase-interacting segment (SIS) of securin that are only exposed when securin is not bound to separase. We suggest that these residues facilitate the removal of non-separase-bound securin ahead of metaphase, as inhibiting this period of destruction by mutating both residues causes the majority of oocytes to arrest in meiosis I. We further propose that cellular securin levels exceed the amount an oocyte is capable of removing in metaphase alone, such that the prometaphase destruction mechanism identified here is essential for correct meiotic progression in mouse oocytes., Securin inhibits the protease separase and must be removed before anaphase to ensure timely chromosome segregation. Here, the authors define a mechanism of securin destruction in prometaphase I in mouse oocytes and demonstrate its importance for successful meiotic progression.

Pre-metaphase stretch is a term first coined by the preeminent cell biologist Sally Hughes-Schrader in 1950 to describe an elongation of prometaphase chromosomes observed in the primary spermatocytes of phasmid insects and praying mantids. Research from many groups since Hughes-Schrader’s initial observation has revealed reasons for both how and why chromosomes might elongate prior to metaphase. In this review, we describe Hughes-Schrader’s initial findings and discuss how recent work illuminates and provides some mechanistic explanation for this long-ago observed phenomenon.

Microtubules are highly strategic targets of cancer therapies. Small molecule antimitotic agents are so far the best chemotherapeutic medication in cancer treatment. However, the high rate of neuropathy and drug resistance limit their clinical usage. Inspired by the multicomponent-targeting feature of molecular self-assembly (MSA) overcoming drug resistance, we synthesized peptide-based rotor molecules that self-assemble in response to the surrounding environment to target the microtubule array. The MSAs self-adjust morphologically in response to the pH change and viscosity variations during Golgi-endosome trafficking, escape trafficking cargos, and eventually bind to the microtubule array physically in a nonspecific manner. Such unrefined nano-bio interactions suppress regional tubulin polymerization triggering atypical prometaphase--metaphase oscillations to inhibit various cancer cells proliferating without inducing obvious neurotoxicity. The MSA also exerts potent antiproliferative effects in the subcutaneous cervix cancer xenograft tumor model equivalent to Cisplatin, better than the classic antimitotic drug Taxol.

To improve the biological effects of the lead compound 5′-chloro-2,2′-dihydroxychalcone (Cl-DHC), bicyclic aromatic chalcones were designed, synthesized, and evaluated against androgen-independent prostate cancer (PCa) DU145 and PC-3 cell proliferation. Newly synthesized bi-naphthyl derivatives 2 and 3 suppressed the proliferation of these two cell lines and also taxane-resistant prostate cancer cell lines at a submicromolar level. The two compounds were 4–18 times more potent than the parent molecule Cl-DHC. A structure–activity relationship analysis revealed that the orientation of the 10π-electron ring-A naphthalene had a significant effect on the activity. Mode-of-action studies in KB-VIN cells demonstrated that 2 and 3 arrested cells in mitosis at prometaphase and metaphase followed by induction of sub-G1 accumulation. Thus, 2 and 3 have good potential as leads for continued development of treatments for cancers especially for not only androgen-independent PCa but also multidrug-resistant tumors.

Current evidence indicates that proliferating β-cells express lower levels of some functional cell identity genes, suggesting that proliferating cells are not optimally functional. Pdx1 is important for β-cell specification, function, and proliferation and is mutated in monogenic forms of diabetes. However, its regulation during the cell cycle is unknown. Here we examined Pdx1 protein expression in immortalized β-cells, maternal mouse islets during pregnancy, and mouse embryonic pancreas. We demonstrate that Pdx1 localization and protein levels are highly dynamic. In nonmitotic cells, Pdx1 is not observed in constitutive heterochromatin, nucleoli, or most areas containing repressive epigenetic marks. At prophase, Pdx1 is enriched around the chromosomes before Ki67 coating of the chromosome surface. Pdx1 uniformly localizes in the cytoplasm at prometaphase and becomes enriched around the chromosomes again at the end of cell division, before nuclear envelope formation. Cells in S phase have lower Pdx1 levels than cells at earlier cell cycle stages, and overexpression of Pdx1 in INS-1 cells prevents progression toward G2, suggesting that cell cycle–dependent regulation of Pdx1 is required for completion of mitosis. Together, we find that Pdx1 localization and protein levels are tightly regulated throughout the cell cycle. This dynamic regulation has implications for the dichotomous role of Pdx1 in β-cell function and proliferation.

Despite the huge amount of works devoted to the study of mitotic division, there is still a lot of unclear in its mechanisms. For example, insufficient attention has been paid to the processes of cell division in plant forms of different ploidy levels. The literature contains only fragmentary data on haploids in lower plants. This does not allow making any generalizations regarding mitosis in haploids of higher plants. This article presents the results of a cytological study of mitotically dividing cells of haploid maize plants. The article demonstrates the effectiveness of the well-known Chase method, based on the use of genetic markers and the ig mutation (indeterminate gametophyte) for obtaining and detecting haploids. An effective modification of a simple method of acetocarmine staining of cytological preparations is described. An essential result obtained is, in our opinion, the detection of a very brief moment in the state of chromosomes in a dividing cell of a haploid maize plant. This moment is characterized by the fact that the chromatids have already separated and turned into independent chromosomes, but have not yet begun their movement under the action of kinetochore microtubules. It is this feature that made it possible to designate this state as late prophase – early prometaphase of mitosis. An equally important feature of the detected moment is the unusual ordered arrangement of chromosomes, which lie parallel to each other close to each other along their entire length with the centromeres located on one line, which can be considered the equator of the fission spindle. The revealed fact allows us to assume that an essential role in the formation of such an arrangement of chromosomes is played by the bond of chromosomes with the equator of the nuclear membrane and their subsequent connection with the equator of the fission spindle.

In prophase of meiosis I, homologous chromosomes pair and become connected by cross-overs. Chiasmata, the connections formed by cross-overs, enable the chromosome pair, called a bivalent, to attach as a single unit to the spindle. When the meiotic spindle forms in prometaphase, most bivalents are associated with one spindle pole and then go through a series of oscillations on the spindle, attaching to and detaching from microtubules until the partners of the bivalent become bioriented-attached to microtubules from opposite sides of the spindle. The conserved kinase, Mps1, is essential for the bivalents to be pulled by microtubules across the spindle in prometaphase. Here we show that MPS1 is needed for efficient triggering of the migration of microtubule-attached kinetochores toward the poles and promotes microtubule depolymerization. Our data support the model Mps1 acts at the kinetochore to coordinate the successful attachment of a microtubule and the triggering of microtubule depolymerization to then move the chromosome.

The process of chromosome congression and alignment is at the core of mitotic fidelity. In this review, we discuss distinct spatial routes that the chromosomes take to align during prometaphase, which are characterized by distinct biomolecular requirements. Peripheral polar chromosomes are an intriguing case as their alignment depends on the activity of kinetochore motors, polar ejection forces, and a transition from lateral to end-on attachments to microtubules, all of which can result in the delayed alignment of these chromosomes. Due to their undesirable position close to and often behind the spindle pole, these chromosomes may be particularly prone to the formation of erroneous kinetochore-microtubule interactions, such as merotelic attachments. To prevent such errors, the cell employs intricate mechanisms to preposition the spindle poles with respect to chromosomes, ensure the formation of end-on attachments in restricted spindle regions, repair faulty attachments by error correction mechanisms, and delay segregation by the spindle assembly checkpoint. Despite this protective machinery, there are several ways in which polar chromosomes can fail in alignment, mis-segregate, and lead to aneuploidy. In agreement with this, polar chromosomes are present in certain tumors and may even be involved in the process of tumorigenesis.

During mitosis, transcription of genomic DNA is dramatically reduced, before it is reactivated during nuclear reformation in anaphase/telophase. Many aspects of the underlying principles that mediate transcriptional memory and reactivation in the daughter cells remain unclear. Here, we used ChIP-seq on synchronized cells at different stages after mitosis to generate genome-wide maps of histone modifications. Combined with EU-RNA-seq and Hi-C analyses, we found that during prometaphase, promoters, enhancers, and insulators retain H3K4me3 and H3K4me1, while losing H3K27ac. Enhancers globally retaining mitotic H3K4me1 or locally retaining mitotic H3K27ac are associated with cell type-specific genes and their transcription factors for rapid transcriptional activation. As cells exit mitosis, promoters regain H3K27ac, which correlates with transcriptional reactivation. Insulators also gain H3K27ac and CCCTC-binding factor (CTCF) in anaphase/telophase. This increase of H3K27ac in anaphase/telophase is required for posttranscriptional activation and may play a role in the establishment of topologically associating domains (TADs). Together, our results suggest that the genome is reorganized in a sequential order, in which histone methylations occur first in prometaphase, histone acetylation, and CTCF in anaphase/telophase, transcription in cytokinesis, and long-range chromatin interactions in early G1. We thus provide insights into the histone modification landscape that allows faithful reestablishment of the transcriptional program and TADs during cell division.

The physical connections established by recombination are normally sufficient to ensure proper chromosome segregation during female Meiosis I. However, nonexchange chromosomes (such as the Muller F element or “dot” chromosome in D. melanogaster) can still segregate accurately because they remain connected by heterochromatic tethers. A recent study examined female meiosis in the closely related species D. melanogaster and D. simulans, and found a nearly twofold difference in the mean distance the obligately nonexchange dot chromosomes were separated during Prometaphase. That study proposed two speculative hypotheses for this difference, the first being the amount of heterochromatin in each species, and the second being the species’ differing tolerance for common inversions in natural populations. We tested these hypotheses by examining female meiosis in 12 additional Drosophila species. While neither hypothesis had significant support, we did see 10-fold variation in dot chromosome sizes, and fivefold variation in the frequency of chromosomes out on the spindle, which were both significantly correlated with chromosome separation distances. In addition to demonstrating that heterochromatin abundance changes chromosome behavior, this implies that the duration of Prometaphase chromosome movements must be proportional to the size of the F element in these species. Additionally, we examined D. willistoni, a species that lacks a free dot chromosome. We observed that chromosomes still moved out on the meiotic spindle, and the F element was always positioned closest to the spindle poles. This result is consistent with models where one role of the dot chromosomes is to help organize the meiotic spindle.

The Anaphase Promoting Complex/Cyclosome (APC/C) is a ubiquitin ligase that initiates anaphase and mitotic exit. The APC/C is activated by Cdc20 and inhibited by the mitotic checkpoint complex (MCC), which delays mitotic exit when the spindle assembly checkpoint (SAC) is activated. We previously identified apcin as a small molecule ligand of Cdc20 that inhibits APC/CCdc20 and prolongs mitosis. Here we find that apcin paradoxically shortens mitosis when SAC activity is high. These opposing effects of apcin arise from targeting a common binding site in Cdc20 required for both substrate ubiquitination and MCC-dependent APC/C inhibition. Furthermore, we found that apcin cooperates with p31comet to relieve MCC-dependent inhibition of APC/C. Apcin therefore causes either net APC/C inhibition, prolonging mitosis when SAC activity is low, or net APC/C activation, shortening mitosis when SAC activity is high, demonstrating that a small molecule can produce opposing biological effects depending on regulatory context.

E2F8 is a transcriptional repressor that antagonizes the canonical cell cycle transcription factor E2F1. Despite the importance of this atypical E2F family member in cell cycle, apoptosis and cancer, we lack a complete description of the mechanisms that control its dynamics. To address this question, we developed a complementary set of static and dynamic cell-free systems of human origin, which recapitulate inter-mitotic and G1 phases, and a full transition from pro-metaphase to G1. This revealed an interlocking molecular switch controlling E2F8 degradation at mitotic exit, involving dephosphorylation of Cdk1 sites in E2F8 and the activation of APC/CCdh1, but not APC/CCdc20. Further, we revealed a differential stability of E2F8, accounting for its accumulation in late G1 while APC/CCdh1 is still active and suggesting a key role for APC/C in controlling G1-S transcription. Finally, we identified SCF-Cyclin F as the ubiquitin ligase controlling E2F8 in G2-phase. Altogether, our data provide new insights into the regulation of E2F8 throughout the cell cycle, illuminating an extensive coordination between phosphorylation, ubiquitination and transcription in promoting orderly cell cycle progression.

Nanoscale electrostatics plays important roles in aster (spindle) assembly and motion, nuclear envelope breakdown and reassembly, and in force generation at kinetochores, poles, and chromosome arms for prometaphase, metaphase, and anaphase—A chromosome motions during mitosis. A large body of experimental evidence also suggests a role for electrostatics as the trigger for mitosis, which is considered here particularly in the context of cancer. Cancer cells are characterized by impaired intercellular electrical communication and adhesive contact as well as a loss of contact inhibition, conditions associated with increased cell surface negativity relative to their normal counterparts. Dividing cells have also been associated with lower transmembrane potentials and altered intracellular ionic concentrations. Here we propose that cancer cells are distinguished by abnormal trans- and intramembrane electric potentials, leading to the loss of active Na+/K+ plasma membrane pumping, increased intracellular concentrations of sodium and other ions, and alkaline nucleo-cytoplasmic pH, all of which are associated with and integral to carcinogenesis.

This paper describes an easy method to enrich the harvest of adherent mammalian cells at each stage of mitosis (from prometaphase to cytokinesis) by combining Eg5 inhibition using dimethylenastron (DMA) with mitotic shake-off, followed by timed release from the drug.

During mitosis, the cell forms a spindle that equally segregates chromosomes into two daughter cells. Soon after nuclear envelope breakdown (NEB), kinetochores on chromosomes are captured by microtubules nucleated at the spindle pole. Some chromosomes immediately find themselves in the area between two spindle poles, yet approximately 7 out of 46 chromosomes, termed polar chromosomes, are positioned behind the pole at NEB in human cells. These polar chromosomes first approach the spindle pole with the help of kinetochore dynein and subsequently undergo CENP-E mediated sliding towards the equator [1, 2]. However, the mechanism of their passage across the polar region and its importance for faithful cell division remain unknown. Here we show that polar chromosomes are particularly prone to missegregation when the checkpoint is weakened. These chromosomes stall behind the pole and acquire speed similar to non- polar chromosomes once they reach the spindle body, indicating that the centrosome creates a physical barrier for chromosome movement in this area. To test this hypothesis, we removed one centrosome using centrinone, which indeed resolved the observed delay in the congression of polar chromosomes and suggested that they must have an additional and distinct mechanism of congression. Imaging of EB3, a microtubule plus end marker, revealed that astral microtubules attached to kinetochores of polar chromosomes pivot around the spindle pole and thereby transport polar chromosomes towards the spindle body. The angle that the kinetochores of these chromosomes form with the spindle axis changed during the period of rapid spindle elongation, indicating a role of centrosome separation in this process. By using different kinesin-5 (Eg5) inhibitors to perturb the sliding of antiparallel microtubules and consequently stop or reverse spindle elongation, we confirmed that pivoting occurs due to a hydrodynamic drag force created by centrosome movement. Stimulated emission depletion (STED) imaging of astral microtubules and Mad2, a marker for absent or immature end-on attachments, showed that during pivoting, both kinetochores of a polar chromosome typically attach to a single microtubule laterally, with more complex attachments observed less frequently. Altogether, we propose a model in which pivoting of microtubules around the spindle pole, driven by spindle elongation, promotes the movement of polar chromosomes towards the spindle body and consequently their proper congression to the spindle equator. [1] Barisic et al. Kinetochore motors drive congression of peripheral polar chromosomes by overcoming random arm-ejection forces. Nat Cell Biol, 16(12): 1249-1256 (2014) [2] Kapoor et al. Chromosomes can congress to the metaphase plate before biorientation. Science, 311(5759): 388-391 (2006)

To ensure faithful mitosis, chromosomes located at different nuclear positions during nuclear envelope breakdown need to properly congress to the metaphase plate. The most unfavorably positioned chromosomes are polar chromosomes, which are located behind the spindle pole at nuclear envelope breakdown and make up approximately 7 out 46 chromosomes in human cells. These chromosomes first need to approach the spindle pole from the back and at a later point slide towards the metaphase plate in a motor- dependent manner. However, the mechanism of their passage across the polar region and its importance for faithful mitosis remain unknown. Here we show, by using live-cell confocal microscopy with high spatial and temporal resolution, that polar chromosomes are the last to reach the metaphase plate. They also stall behind the pole, indicating that the centrosome creates a physical barrier to their movement. To test this hypothesis, we removed one centrosome using centrinone, which indeed resolved the observed delay in the congression of polar chromosomes, suggesting the existence of an additional and distinct mechanism of congression in a polar region. By imaging the microtubule plus end marker EB3, we reveal that this mechanism is based on pivoting of astral microtubules with attached chromosomes around the spindle pole. The angle that the kinetochores of these chromosomes form with the spindle axis changed during the period of rapid spindle elongation, indicating a role of centrosome separation in this process. By using different kinesin-5 (Eg5) inhibitors to either stop or reverse spindle elongation, we confirmed that pivoting occurs due to a hydrodynamic drag force created by centrosome movement. Superresolution STED microscopy of astral microtubules and Mad2, a marker of unstable attachments, revealed that polar chromosomes are mostly laterally attached to one astral microtubule emanating from the pole behind which they are situated, with other more complex attachments observed less frequently. Finally, we show that polar chromosomes are prone to misalignment and cause aneuploidy in 62% of cases when the spindle checkpoint is weakened, highlighting their importance in faithful chromosome segregation. Altogether, we propose a model in which pivoting of microtubules around the spindle pole, driven by spindle elongation, promotes the movement of polar chromosomes towards the spindle body and consequently their proper congression to the spindle equator.

Background The World Health Organization (WHO) proposed COVID-19 vaccination as an emergent and important method to end the COVID-19 pandemic. Since China started vaccination programs in December 2020, vaccination has spread to provinces and municipalities nationwide. Previous research has focused on people's vaccination willingness and its influencing factors but has not examined vaccination behavior. We examine the effectiveness of psychosocial factors in predicting vaccination behavior. Methods A cross-sectional online survey was performed among Chinese adults on 8 May and 4 June 2021. The statistical analysis of the data included univariate analysis, receiver operator characteristics (ROC) analysis and ordinal multiclassification logistic regression model analysis. Results Of the 1300 respondents, 761 (58.5%) were vaccinated. Univariate analysis showed that a high education level and good subjective health status were protective factors for vaccination behavior, while suffering from chronic diseases was a risk factor. ROC analysis showed that subjective health status (AUC = 0.625, 95% CI: 0.594–0.656, P Conclusion Our study found a simple and effective marker, subjective health status, that can predict vaccination behavior. This finding can guide future epidemic prevention work.

The chromokinesin KIF22 generates forces that contribute to mitotic chromosome congression and alignment. Mutations in the α2 helix of the motor domain of KIF22 have been identified in patients with abnormal skeletal development, and we report the identification of a patient with a novel mutation in the KIF22 tail. We demonstrate that pathogenic mutations do not result in a loss of KIF22’s functions in early mitosis. Instead, mutations disrupt chromosome segregation in anaphase, resulting in reduced proliferation, abnormal daughter cell nuclear morphology, and, in a subset of cells, cytokinesis failure. This phenotype could be explained by a failure of KIF22 to inactivate in anaphase. Consistent with this model, constitutive activation of the motor via a known site of phosphoregulation in the tail phenocopied the effects of pathogenic mutations. These results suggest the motor domain α2 helix may be an important site for regulation of KIF22 activity at the metaphase to anaphase transition. In support of this conclusion, mimicking phosphorylation of α2 helix residue T158 also prevents inactivation of KIF22 in anaphase. These findings demonstrate the importance of both the head and tail of the motor in regulating the activity of KIF22 and offer insight into the cellular consequences of preventing KIF22 inactivation and disrupting force balance in anaphase.

Tightly controlled fluctuations in kinase and phosphatase activity play important roles in regulating M-Phase transitions. Protein Phosphatase 1 (PP1) is one of these phosphatases, with oscillations in PP1 activity driving mitotic M-Phase. Evidence from a variety of experimental systems also points to roles in meiosis. Here we report that PP1 is important for M-Phase transitions through mouse oocyte meiosis. We employed a unique small-molecule approach to inhibit or activate PP1 at distinct phases of mouse oocyte meiosis. These studies show that temporal control of PP1 activity is essential for G2/M transition, metaphase I/anaphase I transition, and the formation of a normal metaphase II oocyte. Our data also reveal that inappropriate activation of PP1 is more deleterious at G2/M transition than at prometaphase I-to-metaphase I, and that an active pool of PP1 during prometaphase is vital for metaphase I/anaphase I transition and metaphase II chromosome alignment. Taken together, these results establish that loss of oscillations in PP1 activity causes a range of severe meiotic defects, pointing to essential roles for PP1 in female fertility, and more broadly, M-Phase regulation.Summary statementAltering the normal cyclical activity of the phosphatase PP1 in oocytes causes a range of severe meiotic defects, pointing to essential roles for PP1 in M-Phase entry, progression, and exit.

Mitotic kinesin-like protein 2 (MKLP2) is a motor protein with a well-established function in promoting cytokinesis. However, our results with siRNAs targeting MKLP2 and small molecule inhibitors of MKLP2 (MKLP2i) suggested a function earlier in mitosis, prior to anaphase. In this study we provide direct evidence that MKLP2 facilitates chromosome congression in prometaphase. We employed live imaging to observe HeLa cells with fluorescently tagged histones treated with MKLP2i and discovered a pronounced chromosome congression defect. We show that MKLP2 is essential for pole-based error correction as inhibited cells had a significant increase in unstable kinetochore-microtubule attachments due to impaired error correction of syntelic attachments. We propose that MKLP2 mediates kinetochore microtubule attachment stability by regulating Aurora Kinase activity and a downstream target, pHEC1 (Ser 55). Lastly, we show that MKLP2 inhibition results in aneuploidy, confirming that MKLP2 safeguards cells against chromosomal instability.SummarySchrock et al. demonstrate that the mitotic kinesin, MKLP2, is required for congression of chromosomes located near the spindle poles. They show that MKLP2 inhibition causes elevated active Aurora Kinase A, unstable microtubule kinetochore attachments, and impaired syntelic error correction.

Induction of meiosis requires exogenous signals that activate internal gene regulatory networks. Meiotic commitment ensures the irreversible continuation of meiosis, even upon withdrawal of the meiosis inducing signals. Budding yeast cells have a unique property in that cells enter meiosis when starved, but if given nutrient-rich medium prior to the commitment point, they exit meiosis and enter mitosis. After the meiotic commitment point in prometaphase I, cells remain in meiosis even with addition of nutrients. Despite the importance of meiotic commitment in ensuring the production of gametes, only a few genes involved in the commitment process are known. We performed a genome-scale screen in budding yeast and discovered new regulators of meiotic commitment including Bcy1, which is involved in nutrient sensing, the meiosis-specific kinase Ime2, Polo kinase Cdc5, and the 14-3-3 proteins Bmh1 and Bmh2. Importantly, we found that Bmh1 and Bmh2 are involved in multiple processes throughout meiosis including the maintenance of the middle meiosis transcription factor Ndt80, activation of Cdc5, and interaction with an RNA-binding protein Pes4, which is important for regulating the timing of translation of several mRNAs in meiosis II. This study identifies a meiotic commitment regulatory network with the 14-3-3 proteins functioning as central regulators.

Copyright © 2021 The Author(s). Ki-67 is highly expressed in proliferating cells, a characteristic that made the protein a very important proliferation marker widely used in the clinic. However, the molecular functions and properties of Ki-67 remained quite obscure for a long time. Only recently important discoveries have shed some light on its function and shown that Ki-67 has a major role in the formation of mitotic chromosome periphery compartment, it is associated with protein phosphatase one (PP1) and regulates chromatin function in interphase and mitosis. In this review, we discuss the role of Ki-67 during cell division. Specifically, we focus on the importance of Ki-67 in chromosome individualisation at mitotic entry (prometaphase) and its contribution to chromosome clustering and nuclear remodelling during mitotic exit. Wellcome Trust. Investigator award 210742/Z/18/Z (Chromatin Re-Organisation at the Transition from Mitosis to G1: How Phospho-Switches Regulate the Process in Space and Time); Brunel University London (CHMLS scholarship).

The spindle assembly checkpoint (SAC) is critical for sensing defective microtubule-kinetochore attachments and tension across the kinetochore and functions to arrest cells in prometaphase to allow time to repair any errors before proceeding into anaphase. Dysregulation of the SAC leads to chromosome segregation errors that have been linked to human diseases like cancer. Although much has been learned about the composition of the SAC and the factors that regulate its activity, the proximity associations of core SAC components have not been explored in a systematic manner. Here, we have taken a BioID2-proximity-labeling proteomic approach to define the proximity protein environment for each of the five core SAC proteins BUB1, BUB3, BUBR1, MAD1L1, and MAD2L1 in mitotic-enriched populations of cells where the SAC is active. These five protein association maps were integrated to generate a SAC proximity protein network that contains multiple layers of information related to core SAC protein complexes, protein-protein interactions, and proximity associations. Our analysis validated many known SAC complexes and protein-protein interactions. Additionally, it uncovered new protein associations, including the ELYS-MAD1L1 interaction that we have validated, which lend insight into the functioning of core SAC proteins and highlight future areas of investigation to better understand the SAC.

The knowledge with reference to the grapevine tapetum has been centered on its anatomy/morphology and hardly anything at all is known about its mitotic activity throughout the microsporogenesis. The aim of this study was to ascertain the mitotic activity in tapetal cells of some grapevines (Vitis L.) broadening knowledge about this tissue and simultaneously corroborating the viability of its use as an alternative tissue for further cytogenetic studies. Young buds of 12 grapevine varieties at different meiotic stages were squashed and tapetal cells a prometaphase/metaphase scored in each meiotic stage. Mitotic activity was observed since the beginning of microsporogenesis, where it was more intense, decreasing toward tetrad. Polyploid tapetal cells arose through endomitosis while the microsporogenesis advanced. Two types of polyploid cells were evidenced, those with two or more individualized diploid chromosome groups and those with only one polyploid group. The percentage of diploid cells and of polyploid cells with two or more individualized diploid groups was higher during the first stage of microsporogenesis, though decreasing and giving way to cells with one large polyploid group as microsporogenesis moved toward tetrad. The nucleolus number was scored at interphase at different stages. Two and four nucleoli prevailed in tapetal cells at all stages except at tetrad where one large nucleolus was seen. The results showed that despite of the squashing technique applied, grapevine tapetum has a substantial amount of cells with mitotic activity with a satisfactory chromosome spreading therefore establishing an interesting alternative and promising tissue for later cytomolecular studies.