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At least 109 records · Page 6Linked to original sources
PubMed2003

The Medicago species A2-type cyclin is auxin regulated and involved in meristem formation but dispensable for endoreduplication-associated developmental programs.

Phytohormones as well as temporal and spatial regulation of the cell cycle play a key role in plant development. Here, we investigated the function and regulation of an alfalfa (Medicago sativa) A2-type cyclin in three distinct root developmental programs: in primary and secondary root development, nodule development, and nematode-elicited gall formation. Using transgenic plants carrying the Medsa;cycA2;2 promoter-beta-glucuronidase gene fusion, in combination with other techniques, cycA2;2 expression was localized in meristems and proliferating cells in the lateral root and nodule primordia. Rapid induction of cycA2;2 by Nod factors demonstrated that this gene is implicated in cell cycle activation of differentiated cells developing to nodule primordia. Surprisingly, cycA2;2 was repressed in the endoreduplicating, division-arrested cells both during nodule development and formation of giant cells in nematode-induced galls, indicating that CycA2;2 was dispensable for S-phase in endoreduplication cycles. Overexpression of cycA2;2 in transgenic plants corresponded to wild type protein levels and had no apparent phenotype. In contrast, antisense expression of cycA2;2 halted regeneration of somatic embryos, suggesting a role for CycA2;2 in the formation or activity of apical meristems. Expression of cycA2;2 was up-regulated by auxins, as expected from the presence of auxin response elements in the promoter. Moreover, auxin also affected the spatial expression pattern of this cyclin by shifting the cycA2;2 expression from the phloem to the xylem poles.

Animals↗
PubMed2005

Cyclin-dependent kinase inhibitors in maize endosperm and their potential role in endoreduplication.

Two maize (Zea mays) cyclin-dependent kinase (CDK) inhibitors, Zeama;KRP;1 and Zeama;KRP;2, were characterized and shown to be expressed in developing endosperm. Similar to the CDK inhibitors in Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum), the maize proteins contain a carboxy-terminal region related to the inhibitory domain of the mammalian Cip/Kip inhibitors. Zeama;KRP;1 is present in the endosperm between 7 and 21 d after pollination, a period that encompasses the onset of endoreduplication, while the Zeama;KRP;2 protein declines during this time. Nevertheless, Zeama;KRP;1 accounts for only part of the CDK inhibitory activity that peaks coincident with the endoreduplication phase of endosperm development. In vitro assays showed that Zeama;KRP;1 and Zeama;KRP;2 are able to inhibit endosperm Cdc2-related CKD activity that associates with p13(Suc1). They were also shown to specifically inhibit cyclin A1;3- and cyclin D5;1-associated CDK activities, but not cyclin B1;3/CDK. Overexpression of Zeama;KRP;1 in maize embryonic calli that ectopically expressed the wheat dwarf virus RepA protein, which counteracts retinoblastoma-related protein function, led to an additional round of DNA replication without nuclear division.

Amino Acid Sequence↗
PubMed2004

The plant-specific cyclin-dependent kinase CDKB1;1 and transcription factor E2Fa-DPa control the balance of mitotically dividing and endoreduplicating cells in Arabidopsis.

Transgenic Arabidopsis thaliana plants overproducing the E2Fa-DPa transcription factor have two distinct cell-specific phenotypes: some cells divide ectopically and others are stimulated to endocycle. The decision of cells to undergo extra mitotic divisions has been postulated to depend on the presence of a mitosis-inducing factor (MIF). Plants possess a unique class of cyclin-dependent kinases (CDKs; B-type) for which no ortholog is found in other kingdoms. The peak of CDKB1;1 activity around the G2-M boundary suggested that it might be part of the MIF. Plants that overexpressed a dominant negative allele of CDKB1;1 underwent enhanced endoreduplication, demonstrating that CDKB1;1 activity was required to inhibit the endocycle. Moreover, when the mutant CDKB1;1 allele was overexpressed in an E2Fa-DPa-overproducing background, it enhanced the endoreduplication phenotype, whereas the extra mitotic cell divisions normally induced by E2Fa-DPa were repressed. Surprisingly, CDKB1;1 transcription was controlled by the E2F pathway, as shown by its upregulation in E2Fa-DPa-overproducing plants and mutational analysis of the E2F binding site in the CDKB1;1 promoter. These findings illustrate a cross talking mechanism between the G1-S and G2-M transition points.

Arabidopsis↗
PubMed2006

Increased level of polyploidy1, a conserved repressor of CYCLINA2 transcription, controls endoreduplication in Arabidopsis.

Endoreduplication is a type of cell cycle in which DNA replication continues without cell division. We have isolated several dominant mutants from Arabidopsis thaliana activation tagging lines by flow cytometry. One of the mutants, increased level of polyploidy1-1D (ilp1-1D), showed increased polyploidy in both light- and dark-grown hypocotyls. The corresponding gene of ilp1-1D encodes a protein homologous to the C-terminal region of mammalian GC binding factor. We demonstrate that this protein functions as a transcriptional repressor in vivo. The expression of all members of the CYCLINA2 (CYCA2) family was reduced in an ILP1 overexpressing line, and the mouse (Mus musculus) homolog of ILP1 repressed cyclin A2 expression in mouse NIH3T3 cells. T-DNA insertion mutants of ILP1 showed reduced polyploidy and upregulated all CYCA2 expression. Furthermore, loss of CYCA2;1 expression induces an increase in polyploidy in Arabidopsis. We demonstrate that this protein regulates endoreduplication through control of CYCA2 expression in Arabidopsis.

Amino Acid Sequence↗
PubMed2004

Tiny genomes and endoreduplication in Strepsiptera.

Using flow cytometry, the genome sizes of two species of Strepsiptera were studied: that of male Caenocholax fenyesi texensis Kathirithamby & Johnston (Myrmecolacidae) at 108 Mb, which is the smallest insect genome documented to date; and those of male and female Xenos vesparum Rossi (Stylopidae), which are 1C = 130 and 133 Mb, respectively. The genome sizes of the following were analysed for comparative purposes: (a) the Hessian fly, Mayetiola destructor (Say), which was previously reported to be the smallest among insects: the male measured at 1C = 121 Mb and the female at 1C = 158 Mb; and (b) the female parasitic, haplodiploid, microhymenopteran wasp, Trichogramma brassicae Bezdenko, which measured at 1C = 246 Mb. The hosts of the strepsipterans were also measured: male Solenopsis invicta Buren, the red imported fire ant (host of male C. f. texensis), which is 1C = 753.3 Mb, and female Polistes dominulus Christ, the paper wasp (host of X. vesparum), is 1C = 301.4 Mb. Endoreduplication (4C) of the genome of the thorax of the male strepsipteran, and higher levels of endoduplication (4, 8, 16C) in the body of the larger female was observed. In contrast, little or no endoreduplication was observed, either in the Hessian fly, or in the parasitic wasp.

Animals↗
PubMed2005

Retinoblastoma protein regulates cell proliferation, differentiation, and endoreduplication in plants.

Retinoblastoma protein (Rb) plays a key role in cell cycle control, cell differentiation, and apoptosis in animals. In this study, we used virus-induced gene silencing (VIGS) to investigate the cellular functions of Rb in higher plants. VIGS of NbRBR1, which encodes the Nicotiana benthamiana Rb homolog, resulted in growth retardation and abnormal organ development. At the cellular level, Rb suppression caused prolonged cell proliferation in tissues that are normally differentiated, which indicates that Rb is a negative regulator of plant cell division. Furthermore, differentiation of the epidermal pavement cells and trichomes was partially retarded, and stomatal clusters formed in the epidermis, likely due to uncontrolled cell division of stomata precursor cells. Rb suppression also caused extra DNA replication in endoreduplicating leaf cells, suggesting a role of Rb in the endocycle. These Rb phenotypes were accompanied by stimulated transcription of E2F and E2F-regulated S-phase genes. Thus, disruption of Rb function in plants leads to ectopic cell division in major organs that correlates with a delay in cell differentiation as well as increased endoreduplication, which indicates that Rb coordinates these processes in plant organ development.

Cell Differentiation↗
PubMed1964

DIPLOID AND ENDOREDUPLICATED CELLS: MEASUREMENTS OF DNA.

Two-wavelength microspectrophotometry has shown that endoreduplicated cells in an x-irradiated culture of human leukocytes contained about twice as much DNA as diploid cells from the same culture. This supports the assumption that endoreduplicated cells represent a form of polyploidy.

Chromosomes↗
PubMed1998

Effects of p21(Cip1/Waf1) at both the G1/S and the G2/M cell cycle transitions: pRb is a critical determinant in blocking DNA replication and in preventing endoreduplication.

It has been proposed that the functions of the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27Kip1 are limited to cell cycle control at the G1/S-phase transition and in the maintenance of cellular quiescence. To test the validity of this hypothesis, p21 was expressed in a diverse panel of cell lines, thus isolating the effects of p21 activity from the pleiotropic effects of upstream signaling pathways that normally induce p21 expression. The data show that at physiological levels of accumulation, p21, in addition to its role in negatively regulating the G1/S transition, contributes to regulation of the G2/M transition. Both G1- and G2-arrested cells were observed in all cell types, with different preponderances. Preponderant G1 arrest in response to p21 expression correlated with the presence of functional pRb. G2 arrest was more prominent in pRb-negative cells. The arrest distribution did not correlate with the p53 status, and proliferating-cell nuclear antigen (PCNA) binding activity of p21 did not appear to be involved, since p27, which lacks a PCNA binding domain, produced similar arrest distributions [corrected], DNA endoreduplication occurred in pRb-negative but not in pRb-positive cells, suggesting that functional pRb is necessary to prevent DNA replication in p21 G2-arrested cells. These results suggest that the primary target of the Cip/Kip family of inhibitors leading to efficient G1 arrest as well as to blockade of DNA replication from either G1 or G2 phase is the pRb regulatory system. Finally, the tendency of Rb-negative cells to undergo endoreduplication cycles when p21 is expressed may have negative implications in the therapy of Rb-negative cancers with genotoxic agents that activate the p53/p21 pathway.

Cyclin-Dependent Kinase Inhibitor p21↗
PubMed1979

Induction of high frequencies of endoreduplication in mammalian cell cultures with 33258 Hoechst and rubidazone.

Cells of the mouse L strain and the Chinese hamster CHO line were treated with 33258 Hoechst, rubidazone, and a combination of these. Recovering cell populations following the drug removal exhibited a high frequency (20--50%) of metaphases with diplochromosomes (endoreduplication), especially in the combination treatment series (up to more than 70% in the L strain). Such a procedure should be useful in probing the mechanisms of the endoreduplication process.

Animals↗
PubMed2003

Chromatin of endoreduplicated pavement cells has greater range of movement than that of diploid guard cells in Arabidopsis thaliana.

In the current model of chromatin organization in the interphase cell nucleus, chromosomes are organized into territories. Although constrained diffusion of chromatin in interphase cells has been confirmed in all cell types examined, little is known about chromatin dynamics in plant interphase cells. In this work, we measured for the first time interphase chromatin dynamics in plants using the green-fluorescent-protein-mediated chromatin-tagging system. Moreover, we compared the dynamics of diploid guard cells and endoreduplicated pavement cells. The movement of tagged loci in live seedlings shows constrained behavior in both types of nuclei. However, we found that the apparent confinement area for tagged loci in pavement cells is over 6 times larger than it is in guard cells. These findings suggest that chromatin is anchored to some component of the nucleus and that this might be responsible for the different dynamics of chromatin diffusion between diploid cells and endoreduplicated cells.

Arabidopsis↗
PubMed1993

Mitosis of rotenone-induced endoreduplication in Chinese hamster cells.

Endoreduplication was induced by rotenone with an extremely high frequency (approximately 90% of all the metaphases) in cultured Chinese hamster cells. Endoreduplicated cells were fixed without colchicine or hypotonic treatment, and chromosomal configurations were examined in various mitotic stages. The two sister chromosomes of each diplochromosome at late prophase were widely separated except the centromeric region, but they became gradually paired along the total length as the cell cycle progressed to metaphase. The anaphase cells underwent multipolar division, resulting in three or four aneuploid daughter cells. Indirect immunofluorescence staining using anti-beta tubulin antibody revealed tripolar or tetrapolar spindles and unusual equatorial plates.

Animals↗
PubMed1982

DNA polymerase beta involvement in DNA endoreduplication in rat giant trophoblast cells.

DNA synthesis in vitro was studied in rat giant trophoblast nuclei from parietal yolk sacs at Day 13 of development. These nuclei synthesize DNA by a series of endoreduplications in the absence of mitosis. Although the nuclei contain DNA polymerase alpha and beta activities, polymerase alpha activity is not expressed since DNA synthesis is insensitive to aphidicolin. In contrast, N-ethylmaleimide and the DNA polymerase beta inhibitors, 50 mM potassium phosphate, and 2',3'-dideoxythymidine triphosphate inhibit DNA synthesis in isolated nuclei to a degree identical with that seen with partially purified trophoblast DNA polymerase beta, suggesting that polymerase beta is the major polymerase activity in Day 13 trophoblast nuclei. DNA synthesis by these nuclei is dependent on ATP and inhibited by novobiocin and has been shown to be replicative rather than repair-type synthesis, since the newly synthesized DNA is contiguous with DNA replicated in vivo in the presence of a bromodeoxyuridine density label. The results suggest that DNA endoreduplication in these nuclei is being carried out by DNA polymerase beta.

Animals↗
PubMed2005

Histone H4 post-translational modifications in chordate mitotic and endoreduplicative cell cycles.

Histone post-translational modifications mark distinct structural and functional chromatin states but little is known of their involvement in the progression of different cell cycle types across phylogeny. We compared temporal and spatial dynamics of histone H4 post-translational modifications during both mitotic and endoreduplicative cycles of the urochordate, Oikopleura dioica, and proliferating mammalian cells. Endocycling cells showed no signs of chromosome condensation or entry into mitosis. They exhibited an evolution of replication patterns indicative of reduced chromatin compartmentalization relative to proliferating mammalian cells. In the latter cells, published cell cycle profiles of histone H4 acetylated at lysine 16 (H4AcK16) or dimethylated at lysine 20 (H4Me2K20) are disputed. Our results, using different, widely used H4AcK16 antibodies, revealed significant antibody-specific discrepancies in spatial and temporal cell cycle regulation of this modification, with repercussions for interpretation of previous immunofluorescence and immunoprecipitation data based on these reagents. On the other hand, three different antibodies to H4Me2K20 revealed similar cell cycle profiles of this modification that were conserved throughout the mitotic cell cycle in urochordate and mammalian cells, with accumulation at mitosis and a decrease during S-phase. H4Me2K20 also cycled in endocycles, indicating that dynamics of this modification are not strictly constrained by the mitotic phase of the cell cycle and suggesting additional roles during G- and S-phase progression. This article contains Supplementary Material available at http://www.mrw.interscience.wiley.com/suppmat/0730-2312/suppmat/2005/95/spada.html.

Acetylation↗
PubMed1994

Ki-S1 and PCNA expression in erythroid precursors and megakaryocytes--a comparative study on proliferative and endoreduplicative activity in reactive and neoplastic bone marrow lesions.

The monoclonal antibody Ki-S1 reacts with a cell proliferation-associated nuclear antigen which is expressed in the G1 through G2/M phases of the cell cycle and is resistant to formalin fixation. We have studied Ki-S1 and PCNA (PC10) immunostaining of erythroid precursors (proliferative activity) and megakaryocytes (endoreduplicative activity) in bone marrow trephine biopsies in a variety of reactive and neoplastic lesions using double immunohistochemistry to identify both cell lineages. A significant increase in Ki-S1 labelling compared with PCNA positivity was found in all conditions studied. In particular, specimens derived from secondary polycythaemia (SP), polycythaemia vera (P. vera), and primary osteomyelofibrosis (OMF), and from splenic tissue with myeloid metaplasia (MM), revealed a disproportionally high labelling index of erythropoiesis, which was not present in chronic myelogenous leukaemia (CML), AIDS, and autoimmune (idiopathic) thrombocytopenia (ITP). Enhancement of Ki-S1 (PCNA) staining in SP and P. vera is in keeping with the relevant increase in erythroid precursor proliferation, but in OMF and MM there is overexpression of both proliferation markers, possibly due to secondary folic acid deficiency, which is known to cause a block in the S-phase of the cell cycle. A significant correlation was observed between the sizes of megakaryocytes and their nuclei with Ki-S1 (and also PCNA) staining. Ki-S1 (and PCNA) labelling of predominantly smaller elements of this lineage supports a hypothesis that the phases of the cell cycle have different durations in the various steps of polyploidization, with a prolongation of G1/G2 at higher ploidy levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens, Neoplasm↗
PubMed2002

Patterning through differential endoreduplication in epithelial organogenesis of the chordate, Oikopleura dioica.

The contributions that control of cell proliferation and cell growth make to developmental regulation of organ and body size remain poorly explored, particularly with respect to endocycles in polyploid tissues. The epithelium of the marine chordate Oikopleura dioica is composed of a fixed number of cells grouped in territories according to gene-specific expression and nuclear sizes and shapes. As the animal grows 10-fold during the life cycle, epithelial cells increase in size differentially as a function of their spatial position. We show that this cellular pattern reflected differences in ploidy levels ranging from 34 to 1,300 C. The diverse ploidy levels in defined cellular fields resulted both from different timing of entry into endocycles and from cell-specific regulation of endocycle lengths. Throughout the life cycle, differential cell size and ploidy increases were accompanied by field-specific profiles of progressive reductions in G-phase duration. Endocycles were asynchronous among cells of a given epithelial territory, but at the resolution of individual cells, both DNA replication timing and ploidy levels were bilaterally symmetric. The transparent, accessible, oikoplastic epithelium is a model of choice for the study of endoreduplication in the context of pattern formation and growth.

Animals↗
PubMed1993

Chromosomal breakage, endomitosis, endoreduplication, and hypersensitivity toward radiomimetric and alkylating agents: a possible new autosomal recessive mutation in a girl with craniosynostosis and microcephaly.

A high frequency of spontaneous chromosomal breakage, endomitosis, endoreduplication and hypersensitivity toward both the alkylating agent Trenimon and the radiomimetric drug bleomycin was observed in phytohemagglutinin-stimulated peripheral lymphocytes from a girl with craniosynostosis, microcephaly, ptosis, bird-like facies, and moderate mental retardation. We also observed abnormal chromosomal spiralization and some aspects of abnormal cellular division. Several fruitless attempts were made to establish a cell line. The parents were consanguineous, supporting the existence of a new, rare, autosomal, recessive condition in man. The mutation might involve a gene involved in DNA repair and/or regulation of the mitotic cycle.

Adult↗
PubMed2003

Endoreduplication in conjunction with tumor progression in an aneuploid laryngeal squamous cell carcinoma.

We report the case of a 58-year-old man who presented with a squamous cell carcinoma pT1a G2 of the left vocal cord. Six months after histologically verified complete resection, the patient experienced an endolaryngeal and extralaryngeal local recurrence pT4 pN2b G2. We applied DNA flow cytometry (FCM) and comparative genomic hybridization (CGH) on both primary and recurrent tumor. The primary tumor and the endolaryngeal compartment of the relapse was an aneuploid cell clone with a FCM DNA index of 1.42 and 1.44, respectively. The extralaryngeal compartment showed a shift featuring a DNA index of 2.78. In the primary tumor and in both compartments of the recurrence there was an identical pattern of complex chromosomal imbalances as detected in CGH (CGH karyotype: rev ish enh [8q24.2-q24.3, 10q26.1-q26.3, 11q24-q25, 12q24.2-q23.33,X], dim [4q, 13q14.3-q31], amp[1p36.1-p36.2]). Hence, the recurrence was not associated with further gains and losses of chromosomal material. However, in the anterior part of the recurrence, the aneuploid tumor cell genome had completely doubled, obviously due to endoreduplication. Immunohistochemical analysis of several cell-cycle regulators revealed altered expression of checkpoint proteins, pointing to a complex disturbance in cell-cycle regulation.

Aneuploidy↗