Stages Of Mitosis Research Articles

A novel immunofluorescence method to visualize microtubules in the antiparallel overlaps of microtubule-plus ends in the anaphase and telophase midzone

Cell division, in which duplicated chromosomes are separated into two daughter cells, is the most dynamic event during cell proliferation. Chromosome movement is powered mainly by microtubules, which vary in morphology and are organized into characteristic structures according to mitotic progression. During the later stages of mitosis, antiparallel microtubules form the spindle midzone, and the irregular formation of the midzone often leads to failure of cytokinesis, giving rise to the unequal segregation of chromosomes. However, it is difficult to analyze the morphology of these microtubules because microtubules in the antiparallel overlaps of microtubule-plus ends in the midzone are embedded in highly electron-dense matrices, impeding the access of anti-tubulin antibodies to their epitopes during immunofluorescence staining. Here, we developed a novel method to visualize selectively antiparallel microtubule overlaps in the midzone. When cells are air-dried before fixation, aligned α-tubulin staining is observed and colocalized with PRC1 in the center of the midzone of anaphase and telophase cells, suggesting that antiparallel microtubule overlaps can be visualized by this method. In air-dried cells, mCherry-α-tubulin fluorescence and β-tubulin staining show almost the same pattern as α-tubulin staining in the midzone, suggesting that the selective visualization of antiparallel microtubule overlaps in air-dried cells is not attributed to an alteration of the antigenicity of α-tubulin. Taxol treatment extends the microtubule filaments of the midzone in air-dried cells, and nocodazole treatment conversely decreases the number of microtubules, suggesting that unstable microtubules are depolymerized during the air-drying method. It is of note that the air-drying method enables the detection of the disruption of the midzone and premature midzone formation upon Aurora B and Plk1 inhibition, respectively. These results suggest that the air-drying method is suitable for visualizing microtubules in the antiparallel overlaps of microtubule-plus ends of the midzone and for detecting their effects on midzone formation.

Cytogenetic study on the invasive species Gmelinoides fasciatus in the ecosystem of the Gulf of Finland

The amphipod Gmelinoides fasciatus from Lake Baikal is an example of a species being introduced into a number of water bodies in Russia, including the water system of North-west Russia, to expand food reserves of commercial fish. The interest in this crustacean has been attributed to its successful adaptation and expanding habitat area in the region. In order to assess the role of genetic mechanisms in adaptation to new conditions the frequency of chromosomal aberrations (ChA) at anaphase and telophase stages of mitosis in G. fasciatus embryos from six local populations of Lake Baikal and two invasive populations of the Gulf of Finland, originating from natural habitats were studied in two sequential years. The average level of ChA varied slightly between 0.95% in the samples collected in Lake Baikal and 2.9% in those from the Gulf of Finland. A significant increase in the frequency of ChA was found at two sites in Lake Baikal in 2015 and at two locations in the Gulf of Finland in 2016. First information on G. fasciatus chromosome number and constitution acquired by means of molecular cytogenetic techniques is presented and discussed. The results enable us to suggest this amphipod as a sensitive model to study possible mechanisms of biological adaptation and at the same time as a natural bioindicator of the environmental state.

Abstract 1144: Dual inhibition of MEK1/2 and PLK1 specifically targets aggressive breast cancer cell population with CEP55 elevated expression

Abstract Triple negative breast cancers (TNBCs), lacking the expression of ER, PR and HER2 amplification, are the most aggressive form of breast cancer (BC). Due to their heterogeneity influenced by high level of genomic instability and aneuploidy, treatment of TNBC patients is one of the biggest challenges faced in the clinics. CEP55, discovered first by our laboratory, is a key regulator of cytokinesis malfunction of which has been shown to cause multinucleation. Furthermore, ERK2/PLK1 critically regulates the functional role of CEP55 via phosphorylation of CEP55 at particular stages of mitosis, allowing it to localize to the midbody for accurate cytokinesis. Research has demonstrated association of CEP55 with various cancers especially BC as over-expression of CEP55 mRNA is associated with worse BC prognosis and poor survival. We hypothesized that, CEP55 regulates the fate of aneuploid cell population, which are highly dependent on mitotic genes for tumor progression among aggressive BC, thus can be targeted for therapy development. We have performed a series of in vitro studies demonstrating that depletion of CEP55 sensitizes cells to anti-mitotic drugs like PLK1 inhibitor (BI2536) and leads to unscheduled CDK1/Cyclin B activation and favor CDK1-Caspase 3-dependent mitotic catastrophe. We also demonstrate that ERK1/2 transcriptionally controls CEP55 mRNA and due to lack of a specific small molecule inhibitor against CEP55, inhibition of MEK1/2 using the small molecule inhibitor Selumetinib, can mimic depletion of CEP55 in vivo. Thus, we rationalized the usage of a MEK1/2 inhibitor in combination with a PLK1 inhibitor across a series of BC cell lines. We observed synthetic lethality among the aggressive hormone receptor negative cell lines, which expressed higher expression of CEP55 compared to normal like and hormone receptor positive BC cell lines with lower CEP55 level. The combination synergistically increased apoptosis of aneuploid population via premature entry of these cells into mitosis in the presence of antimitotic drugs due to exhaustion of CEP55. We have also validated this synergistic effect of MEK1/2 and PLK1 inhibition using xenograft models, results of which imitated the in vitro findings. Therefore, we propose a novel treatment strategy of MEK1/2-PLK1 dual combination for selectively targeting CEP55 over-expressing BC in the clinics. Citation Format: Debottam Sinha, Murugan Kalimutho, J. Alejandro Lopez, Kum Kum Khanna. Dual inhibition of MEK1/2 and PLK1 specifically targets aggressive breast cancer cell population with CEP55 elevated expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1144. doi:10.1158/1538-7445.AM2017-1144

Single-Cell RNA-Seq Analysis Maps Development of Human Germline Cells and Gonadal Niche Interactions

Human fetal germ cells (FGCs) are precursors to sperm and eggs and are crucial for maintenance of the species. However, the developmental trajectories and heterogeneity of human FGCs remain largely unknown. Here we performed single-cell RNA-seq analysis of over 2,000 FGCs and their gonadal niche cells in female and male human embryos spanning several developmental stages. We found that female FGCs undergo four distinct sequential phases characterized by mitosis, retinoic acid signaling, meiotic prophase, and oogenesis. Male FGCs develop through stages of migration, mitosis, and cell-cycle arrest. Individual embryos of both sexes simultaneously contain several subpopulations, highlighting the asynchronous and heterogeneous nature of FGC development. Moreover, we observed reciprocal signaling interactions between FGCs and their gonadal niche cells, including activation of the bone morphogenic protein (BMP) and Notch signaling pathways. Our work provides key insights into the crucial features of human FGCs during their highly ordered mitotic, meiotic, and gametogenetic processes invivo.

Slo3 Channel is Essential for Fertilized Egg Development by Controlling Critical Molecules for Mitosis

Slo3 channels are specially expressed in testis and sperms. Slo3 KO mice are male infertile but the mechanism remains elusive. In this abstract, we first use Ca2+ imaging method measured Ca2+ entry of wild type sperms and Slo3 KO mice sperms. We found that Ca2+ entry can be normally induced by high K+, cGMP and cAMP in all tested conditions in both capacitated or uncapacitated sperms. Thus, the male infertile phenotype cannot be explained by abnormal Ca2+ entry in fertilization process. Furthermore, in vitro fertilization indicated fertilized eggs with slo3 KO sperms can develop into two cell stage but cannot pass through this developing stage. In order to investigate the reason of stopping development, we performed micro-array analysis using testis tissues both from wild type mice and Slo3 KO mice. The results indicate that expression level of large numbers genes had been altered in Slo3 KO mice testis, not only in spermtocytes but also in steroli cells. Further analysis reviewed that critical gene is required for mitosis had been missed. In the meantime, we confirmed that fertilized eggs stayed in mitosis stage and cannot develop further. Thus, we concluded that Slo3 channels are essential for fertilized eggs development by controlling critical molecules in mitosis.

Decrease in the genotoxicity of metal-contaminated soils with biochar amendments.

Biochar amendments, i.e., the solid product of biomass pyrolysis, reduce soil metal availability, which may lower the toxicity of metal-contaminated soils. A direct link between the decrease in soil metal availability and improved plant development is however often difficult to establish, as biochar may induce undesirable side effects on plant growth, e.g., a modification to plant nutrition. In order to investigate toxicity processes at a cellular level, roots of Vicia faba were exposed for 7days to three metal-contaminated substrates and one control soil, amended with a 0 or 5% (w/w) addition of a wood-derived biochar. Exposure to pure biochar was also tested. Root tip cells were then observed to count the number of micronuclei as an estimation of DNA damage and the number of cells at mitosis stage. Results showed that biochar amendments led to a significant decrease in soil metal availability (Cd, Cu, Ni, Pb, and Zn) and to enhance root development on acidic substrates. The micronucleus frequency in root tip cells was positively correlated and the number of mitotic cells negatively, to the extractability of Zn in soils and to the concentration of Zn in secondary roots. Exposure to pure biochar caused a lower production of roots than most soil substrates, but led to the lowest number of observed micronuclei. In conclusion, biochar amendments can reduce the genotoxicity associated with the presence of metallic contaminants in soils, thereby potentially improving plant growth.

A Multi-Classifier System for Automatic Mitosis Detection in Breast Histopathology Images Using Deep Belief Networks.

Mitotic count is an important diagnostic factor in breast cancer grading and prognosis. Detection of mitosis in breast histopathology images is very challenging mainly due to diffused intensities along object boundary and shape variation in different stages of mitosis. This paper demonstrates an accurate technique for detecting the mitotic cells in Hematoxyline and Eosin stained images by step by step refinement of segmentation and classification stages. Krill Herd Algorithm-based localized active contour model precisely segments cell nuclei from background stroma. A deep belief network based multi-classifier system classifies the labeled cells into mitotic and nonmitotic groups. The proposed method has been evaluated on MITOS data set provided for MITOS-ATYPIA contest 2014 and also on clinical images obtained from Regional Cancer Centre (RCC), Thiruvananthapuram, which is a pioneer institute specifically for cancer diagnosis and research in India. The algorithm provides improved performance compared with other state–of–the-art techniques with average F-score of 84.29% for the MITOS data set and 75% for the clinical data set from RCC.

Design, Synthesis and Anti-tubulin Activity of Novel Dinitro Diphenyl Ether Derivatives as Potent Anticancer Agent

In this study, a series of Dinitrodiphenyl Ether derivatives (1b-5b) were synthesized and their biological activities were also evaluated as potential tubulin inhibitors. Among them, compound 3b (IC50=1.26 ± 0.84 μM) exhibited the most potent anti-proliferative activity of MCF-7 cancer cell line in vitro, which was comparable to that of colchicine (IC50=0.93 ± 0.46 μM) as reference. And it also showed the most potent growth inhibitory activity against tubulin (IC50=5.10 ± 0.81 μM), which was also compared with colchicine (IC50=3.42 ± 0.63 μM). Molecular docking simulation results demonstrated that 3b could bind to the colchicine binding site of tubulin and effectively inhibit tubulin polymerization. Moreover, the subsequent cell cycle arrest and apoptosis assay further confirmed that 3b could cause MCF-7 cell cycle arrest in the middle and later stages of mitosis and thus leading to cell apoptosis. To sum up, we recommend 3b as the best candidate of potential anti-cancer agent among these new compounds. Based on the preliminary results, compound 3b with potent inhibitory activity in tumor growth may be a potential anti-cancer agent.

Dynamics of Lamins B and A/C and Nucleoporin Nup160 during Meiotic Maturation in Mouse Oocytes

This study was aimed at elucidating the fate of three important nuclear envelope components – lamins B and A/C and nucleoporin Nup160, during meiotic maturation of mouse oocytes. These proteins were localized by epifluorescence and confocal microscopy using specific antibodies in oocytes at different stages from prophase I (germinal vesicle) to metaphase II. In immature germinal vesicle oocytes, all three proteins were detected at the nuclear periphery. In metaphase I and metaphase II, lamin B co-localized with the meiotic spindle, lamin A/C was found in a diffuse halo surrounding the spindle and to a lesser degree throughout the cytoplasm, and Nup160 was concentrated to the spindle poles. To our knowledge, this is the first report on nucleoporin localization in mammalian oocytes and the first successful detection of lamins in mature oocytes. While the distribution patterns of both lamins closely paralleled the respective stages of mitosis, Nup160 localization in metaphase oocytes corresponded to that in mitotic prometaphase rather than metaphase. The peculiar distribution of this nucleoporin in oocytes may reflect its role in meiosis-specific mechanisms of spindle assembly and its regulation.

Dual modified antiphospho (Ser10)-acetyl (Lys14)-histone H3 predominantly mark the pericentromeric chromatin during mitosis in monokinetic plants.

Epigenetic regulatory posttranslational histone modification marks not only function individually but also capable to act in combination as a unique pattern. A total of 16 plant species belonging to 11 genera of eight families (five dicots and three monocots) including land plants, epiphytes (orchids) and the holokinetic taxa (Drosera spp.) were analysed for chromosomal distribution of dual modified antiphospho (Ser10)-acetyl (K14)-histone H3 (H3S10phK14ac) to understand the combinatorial chromatin dynamics during mitotic cell division in plants. The anti-H3S10phK14ac evidently mark the pericentromeric chromatin on mitotic chromosomes of the plants excluding the holokinetic Drosera species, which revealed the immunolabelling of whole chromosomes all along the arms. The dual modified immunosignals were absent during early stages of mitosis, appeared intensively at metaphase and remained visible until late-anaphase/telophase however, labelled the whole chromosomes during meiotic metaphase I. Colocalization of anti-H3S10phK14ac with an onion's CENH3 antibody on mitotic chromosomes of Allium revealed the chromosomal location of anti-H3S10phK14ac in the region between signals for CENH3 detection. Overall analysis suggests that the unique localization of combinatorial histone modification mark at pericentromeric chromatin might have attributed through 'phospho-acetyl' cross talk that ultimately facilitate the sister chromatid cohesion at pericentromeres following condensation events in mitotic chromosomes. Here, we propose that dual modified H3S10phK14ac histone may serve as an additional cytogenetic landmark to identify pericentromeric chromatin during mitosis in plants. The plausible role of histone cross talk and future perspectives of combinatorial histone modification marks in plant cytogenetics with special reference to chromatin dynamics have been discussed.

Chromatin proteins and RNA are associated with DNA during all phases of mitosis.

Mitosis brings about major changes to chromosome and nuclear structure. We used recently developed proximity ligation assay-based techniques to investigate the association with DNA of chromatin-associated proteins and RNAs in Drosophila embryos during mitosis. All groups of tested proteins, histone-modifying and chromatin-remodeling proteins and methylated histones remained in close proximity to DNA during all phases of mitosis. We also found that RNA transcripts are associated with DNA during all stages of mitosis. Reduction of H3K27me3 levels or elimination of RNAs had no effect on the association of the components of PcG and TrxG complexes to DNA. Using a combination of proximity ligation assay-based techniques and super-resolution microscopy, we found that the number of protein–DNA and RNA–DNA foci undergoes significant reduction during mitosis, suggesting that mitosis may be accompanied by structural re-arrangement or compaction of specific chromatin domains.

Mutations in Citron Kinase Cause Recessive Microlissencephaly with Multinucleated Neurons

Primary microcephaly is a neurodevelopmental disorder that is caused by a reduction in brain size as a result of defects in the proliferation of neural progenitor cells during development. Mutations in genes encoding proteins that localize to the mitotic spindle and centrosomes have been implicated in the pathogenicity of primary microcephaly. In contrast, the contractile ring and midbody required for cytokinesis, the final stage of mitosis, have not previously been implicated by human genetics in the molecular mechanisms of this phenotype. Citron kinase (CIT) is a multi-domain protein that localizes to the cleavage furrow and midbody of mitotic cells, where it is required for the completion of cytokinesis. Rodent models of Cit deficiency highlighted the role of this gene in neurogenesis and microcephaly over a decade ago. Here, we identify recessively inherited pathogenic variants in CIT as the genetic basis of severe microcephaly and neonatal death. We present postmortem data showing that CIT is critical to building a normally sized human brain. Consistent with cytokinesis defects attributed to CIT, multinucleated neurons were observed throughout the cerebral cortex and cerebellum of an affected proband, expanding our understanding of mechanisms attributed to primary microcephaly.

Abstract 3008: Preclinical characterization of AMG 900, a pan-aurora kinase inhibitor, alone and in combination with taxanes in ovarian cancer

Abstract BACKGROUND: Aurora kinases (AK) A and B play essential roles in multiple stages of mitosis and are frequently overexpressed in a subset of human cancers, including ovarian cancer (OC). AMG 900, a potent and highly selective small molecule inhibitor of AKs, showed promising single-agent activity in heavily pretreated patients with advanced OC in a Phase 1b clinical trial. In this study, we report the preclinical effects of AMG 900 in a panel of well-characterized human cancer cell lines representing clinically-relevant OC subtypes. METHODS: The anti-proliferative effects of AMG 900 were evaluated using a 5-day cell count assay. Cell lines were classified as sensitive to AMG 900 when lethality was > 15% at 10 nM. Molecular markers were profiled including TP53 mutation status, AURKA, CCNE1, MYC copy number, and p53, p21 and cyclin E1 protein by reverse phase protein array. Flow cytometry and imaging methods were used to evaluate the mechanism of action of AMG 900 alone and in combination with chemotherapy. The combination of AMG 900 plus docetaxel was evaluated in an IGROV-1 ovarian endometrioid carcinoma xenograft model. RESULTS: One third of the cell lines (11 of 35) were classified as sensitive to AMG 900 and showed enrichment for TP53 mutations and serous OC subtype. However, 10 of 24 resistant cell lines harbored TP53 mutations, indicating that TP53 mutational status alone was not sufficient for predicting AMG 900 sensitivity. Inhibition of AK activity by AMG 900 in OC cells resulted in aborted cell division leading to polyploidy and cell death (suggestive of aurora-B dominant phenotype). Re-plating of remnant cells after AMG 900 treatment showed an attenuation of cell regrowth, where TP53mut IGROV-1 cells showed minimal regrowth compared to TP53wt OVCAR-5 cells. AMG 900 inhibited proliferation at low nanomolar concentrations in the majority of OC cell lines and enhanced the effects of paclitaxel, carboplatin, and doxorubicin in IGROV-1 cells. In tumor-bearing mice, administration of AMG 900 at 7.5 mg/kg (PO) for two days per week or docetaxel at 10 mg/kg (IP) weekly for four cycles significantly inhibited the growth of IGROV-1 tumor xenografts (P < .0001 vs. vehicle alone). Notably, co-administration of AMG 900 with docetaxel enhanced efficacy and induced a delay in tumor regrowth compared to docetaxel alone. Single-agent-treated mice showed minimal body weight loss (BWL), whereas combination-treated mice showed moderate BWL (average < 10%) that was largely reversible (2 of 12 animals removed due to toxicity). CONCLUSIONS: AMG 900 alone or in combination with chemotherapy such as paclitaxel may be a promising clinical strategy to treat patients with ovarian cancer. Citation Format: Ondrej Kalous, Dylan Conklin, Kanthinh Manivong, William Wayne, Kelly Hanestad, Jude Canon, Robert Loberg, Gregory Friberg, Erick Gamelin, Florian D. Vogl, Gloria Juan, Angela Coxon, Dennis Slamon, Richard Finn, Marc Payton. Preclinical characterization of AMG 900, a pan-aurora kinase inhibitor, alone and in combination with taxanes in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3008.

Abstract 3592: BaP induces chromosome missegregation through mitotic spindle defects in normal lung epithelial cells

Abstract Lung cancer remains the leading cause of cancer related deaths in the United States. Cancer results from an accumulation of multiple genetic events leading to genomic instability that is a crucial early event in carcinogenesis. Aneuploidy is the most frequently identified genomic abnormality in cancer. We have previously reported a significantly higher level of aneuploidy in smokers who developed lung cancer as compared to smoker controls. Benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is a pulmonary carcinogen and one of 60 different carcinogens found in tobacco smoke. In this study, we hypothesize that B(a)P disrupts mitotic spindle assembly that impairs the fidelity of mitosis leading to chromosome missegregation and aneuploidy. To test our hypothesis, we use confocal imaging in combination with traditional molecular biology techniques to dissect the precise mechanism by which B[a]P induces chromosome missegregation and aneuploidy. Mitotic spindle defects in the form of chromosome lags and bridges, monopolar and multipolar spindles, were assessed in normal lung epithelial cells after treatment with 10μM B[a]P for 6 hrs. Spindle defects were assessed at 24, 48, 72 and 96 hours after treatment. Immunofluorescence revealed abnormal mitosis in the prometaphase through the telophase stage of mitosis. Our result show that B[a]P exposure induced abnormal spindles in the form of monopolar (14%) and multipolar (4%) spindles. High resolution confocal images further revealed that B[a]P exposure led to misoriented mitotic spindles with an abnormal spindle angle [-380] relative to normal plane [180]. Chromosome lagging at both metaphase (17%) and anaphase (9%) has also been recorded in response to B[a]P exposure, observations that result from defects in the mitotic apparatus and kinetochores. Furthermore, we assessed the extent of B[a]P induced genetic instability [in the form of double strand DNA breaks] using gama-H2AX in order to elucidate the underlying mechanism associated with accumulated genetic damage and chromosome missegregation. Our data indicate that B[a]P results in accumulation of mitotic abnormalities and gama-H2AX foci (22%) peaks at 48 hr compared to other time points. Taken together, our data show that B[a]P potently induces mitotic abnormalities by disrupting kinetochore microtubules. The induction of mitotic abnormalities by B[a]P leading to chromosome missegregation and aneuploidy, would unravel a novel targetable molecular mechanism of cigarette smoke induced lung tumorigenesis. Citation Format: Jose T. Thaiparambil, Randa El-Zein. BaP induces chromosome missegregation through mitotic spindle defects in normal lung epithelial cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3592.

Effect of the Aquatic Plant Hydrella vorticellata as a Fertilizer on Seed Germination and some Chemical and Cytogenetics Parameters in the cell of Hordeum vulgare and Vicia faba

The present study is concerned with studying the effect of aquatic plant Hydrella vorticellata with the concentration of 10 and 20 gm/2 K gm soil on percentage and growth rate of germinating seeds of Hordeum vulgare and Vicia faba. More overs, the quantitative amount of NPK in both tested plants and Hydrella vorticellata, are estimated as an organic fertilizer. It has also been find the total number of root cells, the number of dividing cells, and stages of mitosis. The study reveales, that there are no significant differences between the concentration of hydrella used in germination percentage, growth rate, wet and dry weight. While there are differences in the plants containing NPK. The number of cells dividing stages and number of dividing cells are increased significantly.

Detection of RNA-DNA association by a proximity ligation-based method

We describe a proximity ligation assay (PLA)-based method of assessing association of DNA and RNA in single cells during the cell cycle. Pulse-labeling of DNA with EdU and RNA with BrU and testing their close proximity by PLA demonstrates that RNA synthesis in individual cells resumes about 30–45 min after DNA replication. Consistent with this conclusion, RNA Pol II phosphorylated at Ser2 of its CTD is detected at the same time as RNA transcripts on nascent DNA. Our results also show that RNA is associated with DNA foci during all stages of mitosis.

Entangled but Finicky Ingression Protein Complexes for Successful Cytokinesis

Cytokinesis is the final stage of mitosis that leads to the physical separation of two daughter cells and comprises a...

Autophagic flux is highly active in early mitosis and differentially regulated throughout the cell cycle.

Mitosis is a fast process that involves dramatic cellular remodeling and has a high energy demand. Whether autophagy is active or inactive during the early stages of mitosis in a naturally dividing cell is still debated. Here we aimed to use multiple assays to resolve this apparent discrepancy. Although the LC3 puncta number was reduced in mitosis, the four different cell lines we tested all have active autophagic flux in both interphase and mitosis. In addition, the autophagic flux was highly active in nocodazole-induced, double-thymidine synchronization released as well as naturally occurring mitosis in HeLa cells. Multiple autophagy proteins are upregulated in mitosis and the increased Beclin-1 level likely contributes to the active autophagic flux in early mitosis. It is interesting that although the autophagic flux is active throughout the cell cycle, early mitosis and S phase have relatively higher autophagic flux than G1 and late G2 phases, which might be helpful to degrade the damaged organelles and provide energy during S phase and mitosis.

The final cut: cell polarity meets cytokinesis at the bud neck in S. cerevisiae.

Cell division is a fundamental but complex process that gives rise to two daughter cells. It includes an ordered set of events, altogether called “the cell cycle”, that culminate with cytokinesis, the final stage of mitosis leading to the physical separation of the two daughter cells. Symmetric cell division equally partitions cellular components between the two daughter cells, which are therefore identical to one another and often share the same fate. In many cases, however, cell division is asymmetrical and generates two daughter cells that differ in specific protein inheritance, cell size, or developmental potential. The budding yeast Saccharomyces cerevisiae has proven to be an excellent system to investigate the molecular mechanisms governing asymmetric cell division and cytokinesis. Budding yeast is highly polarized during the cell cycle and divides asymmetrically, producing two cells with distinct sizes and fates. Many components of the machinery establishing cell polarization during budding are relocalized to the division site (i.e., the bud neck) for cytokinesis. In this review we recapitulate how budding yeast cells undergo polarized processes at the bud neck for cell division.

Cell division study in ‘pollen mother cells’ and ‘pollen grains’ of in vivo and ex vitro plants in Drimiopsis botryoides

The various normal and abnormal stages of meiosis and pollen mitosis of Drimiopsis botryoides are described, and a comparison between naturally propagated in vivo and tissue culture derived ex vitro plants in respect to their cytological behaviour presented. We also describe the floral morphology and investigate the relationship between the floral developmental stages and the progression of microgametogenesis. In total, 33 bivalents are observed in diakinesis, which indicate the diploid number 2n = 66 and this number is cross-checked by a haploid set of n = 33 chromosomes in pollen mitosis. Only 6.8% and 4.9% meiotic abnormalities were recorded on in vivo and ex vitro plants, respectively, which led to the formation of non-viable pollen. Finally, the microspores have to develop into tri-cellular male gametophyte. Only 0.2% pollen grains are found with a micro-nucleus. Though the higher pollen viability was recorded on both in vivo (89.3 ± 4.1%) and ex vitro (92.1 ± 4.6%) plants, but surprisingly the pollen germination rate is extremely low with 13.6 ± 1.74% and 21.3 ± 1.55%, respectively. The present study obviously enriches the cytological database of D. botryoides and may help future research on androgenesis and genetic improvement.