Mitosis: A type of CELL NUCLEUS division by means of which the two daughter nuclei normally receive identical complements of the number of CHROMOSOMES of the somatic cells of the species.Spindle Apparatus: A microtubule structure that forms during CELL DIVISION. It consists of two SPINDLE POLES, and sets of MICROTUBULES that may include the astral microtubules, the polar microtubules, and the kinetochore microtubules.CDC2 Protein Kinase: Phosphoprotein with protein kinase activity that functions in the G2/M phase transition of the CELL CYCLE. It is the catalytic subunit of the MATURATION-PROMOTING FACTOR and complexes with both CYCLIN A and CYCLIN B in mammalian cells. The maximal activity of cyclin-dependent kinase 1 is achieved when it is fully dephosphorylated.Cell Cycle Proteins: Proteins that control the CELL DIVISION CYCLE. This family of proteins includes a wide variety of classes, including CYCLIN-DEPENDENT KINASES, mitogen-activated kinases, CYCLINS, and PHOSPHOPROTEIN PHOSPHATASES as well as their putative substrates such as chromatin-associated proteins, CYTOSKELETAL PROTEINS, and TRANSCRIPTION FACTORS.Interphase: The interval between two successive CELL DIVISIONS during which the CHROMOSOMES are not individually distinguishable. It is composed of the G phases (G1 PHASE; G0 PHASE; G2 PHASE) and S PHASE (when DNA replication occurs).Cell Cycle: The complex series of phenomena, occurring between the end of one CELL DIVISION and the end of the next, by which cellular material is duplicated and then divided between two daughter cells. The cell cycle includes INTERPHASE, which includes G0 PHASE; G1 PHASE; S PHASE; and G2 PHASE, and CELL DIVISION PHASE.Anaphase: The phase of cell nucleus division following METAPHASE, in which the CHROMATIDS separate and migrate to opposite poles of the spindle.Telophase: The final phase of cell nucleus division following ANAPHASE, in which two daughter nuclei are formed, the CYTOPLASM completes division, and the CHROMOSOMES lose their distinctness and are transformed into CHROMATIN threads.Kinetochores: Large multiprotein complexes that bind the centromeres of the chromosomes to the microtubules of the mitotic spindle during metaphase in the cell cycle.Microtubules: Slender, cylindrical filaments found in the cytoskeleton of plant and animal cells. They are composed of the protein TUBULIN and are influenced by TUBULIN MODULATORS.Chromosome Segregation: The orderly segregation of CHROMOSOMES during MEIOSIS or MITOSIS.Cyclin B: A cyclin subtype that is transported into the CELL NUCLEUS at the end of the G2 PHASE. It stimulates the G2/M phase transition by activating CDC2 PROTEIN KINASE.Centrosome: The cell center, consisting of a pair of CENTRIOLES surrounded by a cloud of amorphous material called the pericentriolar region. During interphase, the centrosome nucleates microtubule outgrowth. The centrosome duplicates and, during mitosis, separates to form the two poles of the mitotic spindle (MITOTIC SPINDLE APPARATUS).Metaphase: The phase of cell nucleus division following PROMETAPHASE, in which the CHROMOSOMES line up across the equatorial plane of the SPINDLE APPARATUS prior to separation.HeLa Cells: The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for VIRUS CULTIVATION and antitumor drug screening assays.Chromosomes: In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)G2 Phase: The period of the CELL CYCLE following DNA synthesis (S PHASE) and preceding M PHASE (cell division phase). The CHROMOSOMES are tetraploid in this point.Aurora Kinases: A family of highly conserved serine-threonine kinases that are involved in the regulation of MITOSIS. They are involved in many aspects of cell division, including centrosome duplication, SPINDLE APPARATUS formation, chromosome alignment, attachment to the spindle, checkpoint activation, and CYTOKINESIS.Nocodazole: Nocodazole is an antineoplastic agent which exerts its effect by depolymerizing microtubules.Protein-Serine-Threonine Kinases: A group of enzymes that catalyzes the phosphorylation of serine or threonine residues in proteins, with ATP or other nucleotides as phosphate donors.Cytokinesis: The process by which the CYTOPLASM of a cell is divided.Schizosaccharomyces: A genus of ascomycetous fungi of the family Schizosaccharomycetaceae, order Schizosaccharomycetales.Aurora Kinase B: An aurora kinase that is a component of the chromosomal passenger protein complex and is involved in the regulation of MITOSIS. It mediates proper CHROMOSOME SEGREGATION and contractile ring function during CYTOKINESIS.Centromere: The clear constricted portion of the chromosome at which the chromatids are joined and by which the chromosome is attached to the spindle during cell division.Nuclear Proteins: Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus.Anaphase-Promoting Complex-Cyclosome: An E3 ubiquitin ligase primarily involved in regulation of the metaphase-to-anaphase transition during MITOSIS through ubiquitination of specific CELL CYCLE PROTEINS. Enzyme activity is tightly regulated through subunits and cofactors, which modulate activation, inhibition, and substrate specificity. The anaphase-promoting complex, or APC-C, is also involved in tissue differentiation in the PLACENTA, CRYSTALLINE LENS, and SKELETAL MUSCLE, and in regulation of postmitotic NEURONAL PLASTICITY and excitability.Ubiquitin-Protein Ligase Complexes: Complexes of enzymes that catalyze the covalent attachment of UBIQUITIN to other proteins by forming a peptide bond between the C-terminal GLYCINE of UBIQUITIN and the alpha-amino groups of LYSINE residues in the protein. The complexes play an important role in mediating the selective-degradation of short-lived and abnormal proteins. The complex of enzymes can be broken down into three components that involve activation of ubiquitin (UBIQUITIN-ACTIVATING ENZYMES), conjugation of ubiquitin to the ligase complex (UBIQUITIN-CONJUGATING ENZYMES), and ligation of ubiquitin to the substrate protein (UBIQUITIN-PROTEIN LIGASES).Chromosomal Proteins, Non-Histone: Nucleoproteins, which in contrast to HISTONES, are acid insoluble. They are involved in chromosomal functions; e.g. they bind selectively to DNA, stimulate transcription resulting in tissue-specific RNA synthesis and undergo specific changes in response to various hormones or phytomitogens.Cyclin B1: A cyclin B subtype that colocalizes with MICROTUBULES during INTERPHASE and is transported into the CELL NUCLEUS at the end of the G2 PHASE.Mitosis Modulators: Agents that affect MITOSIS of CELLS.Phosphorylation: The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety.Schizosaccharomyces pombe Proteins: Proteins obtained from the species Schizosaccharomyces pombe. The function of specific proteins from this organism are the subject of intense scientific interest and have been used to derive basic understanding of the functioning similar proteins in higher eukaryotes.Cell Nucleus: Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (CELL NUCLEOLUS). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the ENDOPLASMIC RETICULUM. A cell may contain more than one nucleus. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Prophase: The first phase of cell nucleus division, in which the CHROMOSOMES become visible, the CELL NUCLEUS starts to lose its identity, the SPINDLE APPARATUS appears, and the CENTRIOLES migrate toward opposite poles.Microtubule-Associated Proteins: High molecular weight proteins found in the MICROTUBULES of the cytoskeletal system. Under certain conditions they are required for TUBULIN assembly into the microtubules and stabilize the assembled microtubules.Cell Nucleus Division: The process by which the CELL NUCLEUS is divided.Chromatids: Either of the two longitudinally adjacent threads formed when a eukaryotic chromosome replicates prior to mitosis. The chromatids are held together at the centromere. Sister chromatids are derived from the same chromosome. (Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Cell Division: The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.Tubulin: A microtubule subunit protein found in large quantities in mammalian brain. It has also been isolated from SPERM FLAGELLUM; CILIA; and other sources. Structurally, the protein is a dimer with a molecular weight of approximately 120,000 and a sedimentation coefficient of 5.8S. It binds to COLCHICINE; VINCRISTINE; and VINBLASTINE.cdc25 Phosphatases: A subclass of dual specificity phosphatases that play a role in the progression of the CELL CYCLE. They dephosphorylate and activate CYCLIN-DEPENDENT KINASES.Nuclear Envelope: The membrane system of the CELL NUCLEUS that surrounds the nucleoplasm. It consists of two concentric membranes separated by the perinuclear space. The structures of the envelope where it opens to the cytoplasm are called the nuclear pores (NUCLEAR PORE).Kinesin: A microtubule-associated mechanical adenosine triphosphatase, that uses the energy of ATP hydrolysis to move organelles along microtubules toward the plus end of the microtubule. The protein is found in squid axoplasm, optic lobes, and in bovine brain. Bovine kinesin is a heterotetramer composed of two heavy (120 kDa) and two light (62 kDa) chains. EC 3.6.1.-.Meiosis: A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells.Cdc20 Proteins: Highly conserved proteins that specifically bind to and activate the anaphase-promoting complex-cyclosome, promoting ubiquitination and proteolysis of cell-cycle-regulatory proteins. Cdc20 is essential for anaphase-promoting complex activity, initiation of anaphase, and cyclin proteolysis during mitosis.Mad2 Proteins: Mad2 is a component of the spindle-assembly checkpoint apparatus. It binds to and inhibits the Cdc20 activator subunit of the anaphase-promoting complex, preventing the onset of anaphase until all chromosomes are properly aligned at the metaphase plate. Mad2 is required for proper microtubule capture at KINETOCHORES.S Phase: Phase of the CELL CYCLE following G1 and preceding G2 when the entire DNA content of the nucleus is replicated. It is achieved by bidirectional replication at multiple sites along each chromosome.M Phase Cell Cycle Checkpoints: The cellular signaling system that halts the progression of cells through MITOSIS or MEIOSIS if a defect that will affect CHROMOSOME SEGREGATION is detected.Fungal Proteins: Proteins found in any species of fungus.Microscopy, Fluorescence: Microscopy of specimens stained with fluorescent dye (usually fluorescein isothiocyanate) or of naturally fluorescent materials, which emit light when exposed to ultraviolet or blue light. Immunofluorescence microscopy utilizes antibodies that are labeled with fluorescent dye.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Saccharomyces cerevisiae Proteins: Proteins obtained from the species SACCHAROMYCES CEREVISIAE. The function of specific proteins from this organism are the subject of intense scientific interest and have been used to derive basic understanding of the functioning similar proteins in higher eukaryotes.Centrioles: Self-replicating, short, fibrous, rod-shaped organelles. Each centriole is a short cylinder containing nine pairs of peripheral microtubules, arranged so as to form the wall of the cylinder.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.DNA Replication: The process by which a DNA molecule is duplicated.Cdh1 Proteins: Cdh1 is an activator of the anaphase-promoting complex-cyclosome, and is involved in substrate recognition. It associates with the complex in late MITOSIS from anaphase through G1 to regulate activity of CYCLIN-DEPENDENT KINASES and to prevent premature DNA replication.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Protein Kinases: A family of enzymes that catalyze the conversion of ATP and a protein to ADP and a phosphoprotein.G1 Phase: The period of the CELL CYCLE preceding DNA REPLICATION in S PHASE. Subphases of G1 include "competence" (to respond to growth factors), G1a (entry into G1), G1b (progression), and G1c (assembly). Progression through the G1 subphases is effected by limiting growth factors, nutrients, or inhibitors.Chromosomes, Human: Very long DNA molecules and associated proteins, HISTONES, and non-histone chromosomal proteins (CHROMOSOMAL PROTEINS, NON-HISTONE). Normally 46 chromosomes, including two sex chromosomes are found in the nucleus of human cells. They carry the hereditary information of the individual.RNA Interference: A gene silencing phenomenon whereby specific dsRNAs (RNA, DOUBLE-STRANDED) trigger the degradation of homologous mRNA (RNA, MESSENGER). The specific dsRNAs are processed into SMALL INTERFERING RNA (siRNA) which serves as a guide for cleavage of the homologous mRNA in the RNA-INDUCED SILENCING COMPLEX. DNA METHYLATION may also be triggered during this process.Xenopus Proteins: Proteins obtained from various species of Xenopus. Included here are proteins from the African clawed frog (XENOPUS LAEVIS). Many of these proteins have been the subject of scientific investigations in the area of MORPHOGENESIS and development.Chromatin: The material of CHROMOSOMES. It is a complex of DNA; HISTONES; and nonhistone proteins (CHROMOSOMAL PROTEINS, NON-HISTONE) found within the nucleus of a cell.Nuclear Matrix-Associated Proteins: A broad category of nuclear proteins that are components of or participate in the formation of the NUCLEAR MATRIX.Drosophila Proteins: Proteins that originate from insect species belonging to the genus DROSOPHILA. The proteins from the most intensely studied species of Drosophila, DROSOPHILA MELANOGASTER, are the subject of much interest in the area of MORPHOGENESIS and development.Mitotic Index: An expression of the number of mitoses found in a stated number of cells.Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome: A highly evolutionarily conserved subunit of the anaphase-promoting complex (APC-C) containing multiple 34-amino-acid tetratricopeptide repeats. These domains, also found in Apc subunits 6, 7, and 8, have been shown to mediate protein-protein interactions, suggesting that Apc3 may assist in coordinating the juxtaposition of the catalytic and substrate recognition module subunits relative to co-activators and APC-C inhibitors.Genes, cdc: Genes that code for proteins that regulate the CELL DIVISION CYCLE. These genes form a regulatory network that culminates in the onset of MITOSIS by activating the p34cdc2 protein (PROTEIN P34CDC2).Saccharomyces cerevisiae: A species of the genus SACCHAROMYCES, family Saccharomycetaceae, order Saccharomycetales, known as "baker's" or "brewer's" yeast. The dried form is used as a dietary supplement.Aurora Kinase A: An aurora kinase that localizes to the CENTROSOME during MITOSIS and is involved in centrosome regulation and formation of the MITOTIC SPINDLE. Aurora A overexpression in many malignant tumor types suggests that it may be directly involved in NEOPLASTIC CELL TRANSFORMATION.Cell Nucleolus: Within most types of eukaryotic CELL NUCLEUS, a distinct region, not delimited by a membrane, in which some species of rRNA (RNA, RIBOSOMAL) are synthesized and assembled into ribonucleoprotein subunits of ribosomes. In the nucleolus rRNA is transcribed from a nucleolar organizer, i.e., a group of tandemly repeated chromosomal genes which encode rRNA and which are transcribed by RNA polymerase I. (Singleton & Sainsbury, Dictionary of Microbiology & Molecular Biology, 2d ed)Fluorescent Antibody Technique: Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (FLUORESCENT ANTIBODY TECHNIQUE, DIRECT) or an indirect method, by formation of antigen-antibody complex which is then labeled with fluorescein-conjugated anti-immunoglobulin antibody (FLUORESCENT ANTIBODY TECHNIQUE, INDIRECT). The tissue is then examined by fluorescence microscopy.Potoroidae: A family of rat kangaroos found in and around Australia. Genera include Potorous and Bettongia.Recombinant Fusion Proteins: Recombinant proteins produced by the GENETIC TRANSLATION of fused genes formed by the combination of NUCLEIC ACID REGULATORY SEQUENCES of one or more genes with the protein coding sequences of one or more genes.Demecolcine: An alkaloid isolated from Colchicum autumnale L. and used as an antineoplastic.Cyclin A: A cyclin subtype that has specificity for CDC2 PROTEIN KINASE and CYCLIN-DEPENDENT KINASE 2. It plays a role in progression of the CELL CYCLE through G1/S and G2/M phase transitions.Cyclins: A large family of regulatory proteins that function as accessory subunits to a variety of CYCLIN-DEPENDENT KINASES. They generally function as ENZYME ACTIVATORS that drive the CELL CYCLE through transitions between phases. A subset of cyclins may also function as transcriptional regulators.Aspergillus nidulans: A species of imperfect fungi from which the antibiotic nidulin is obtained. Its teleomorph is Emericella nidulans.Xenopus: An aquatic genus of the family, Pipidae, occurring in Africa and distinguished by having black horny claws on three inner hind toes.Histones: Small chromosomal proteins (approx 12-20 kD) possessing an open, unfolded structure and attached to the DNA in cell nuclei by ionic linkages. Classification into the various types (designated histone I, histone II, etc.) is based on the relative amounts of arginine and lysine in each.Tubulin Modulators: Agents that interact with TUBULIN to inhibit or promote polymerization of MICROTUBULES.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Polyploidy: The chromosomal constitution of a cell containing multiples of the normal number of CHROMOSOMES; includes triploidy (symbol: 3N), tetraploidy (symbol: 4N), etc.Lamins: Nuclear matrix proteins that are structural components of the NUCLEAR LAMINA. They are found in most multicellular organisms.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.Green Fluorescent Proteins: Protein analogs and derivatives of the Aequorea victoria green fluorescent protein that emit light (FLUORESCENCE) when excited with ULTRAVIOLET RAYS. They are used in REPORTER GENES in doing GENETIC TECHNIQUES. Numerous mutants have been made to emit other colors or be sensitive to pH.Protamine Kinase: An aspect of protein kinase (EC 188.8.131.52) in which serine residues in protamines and histones are phosphorylated in the presence of ATP.CDC28 Protein Kinase, S cerevisiae: A protein kinase encoded by the Saccharomyces cerevisiae CDC28 gene and required for progression from the G1 PHASE to the S PHASE in the CELL CYCLE.Saccharomycetales: An order of fungi in the phylum Ascomycota that multiply by budding. They include the telomorphic ascomycetous yeasts which are found in a very wide range of habitats.Phosphoprotein Phosphatases: A group of enzymes removing the SERINE- or THREONINE-bound phosphate groups from a wide range of phosphoproteins, including a number of enzymes which have been phosphorylated under the action of a kinase. (Enzyme Nomenclature, 1992)DNA-Binding Proteins: Proteins which bind to DNA. The family includes proteins which bind to both double- and single-stranded DNA and also includes specific DNA binding proteins in serum which can be used as markers for malignant diseases.Securin: Securin is involved in the control of the metaphase-anaphase transition during MITOSIS. It promotes the onset of anaphase by blocking SEPARASE function and preventing proteolysis of cohesin and separation of sister CHROMATIDS. Overexpression of securin is associated with NEOPLASTIC CELL TRANSFORMATION and tumor formation.Cyclin-Dependent Kinases: Protein kinases that control cell cycle progression in all eukaryotes and require physical association with CYCLINS to achieve full enzymatic activity. Cyclin-dependent kinases are regulated by phosphorylation and dephosphorylation events.Drosophila: A genus of small, two-winged flies containing approximately 900 described species. These organisms are the most extensively studied of all genera from the standpoint of genetics and cytology.Embryo, Nonmammalian: The developmental entity of a fertilized egg (ZYGOTE) in animal species other than MAMMALS. For chickens, use CHICK EMBRYO.Dyneins: A family of multisubunit cytoskeletal motor proteins that use the energy of ATP hydrolysis to power a variety of cellular functions. Dyneins fall into two major classes based upon structural and functional criteria.Chromosomal Instability: An increased tendency to acquire CHROMOSOME ABERRATIONS when various processes involved in chromosome replication, repair, or segregation are dysfunctional.Nucleolus Organizer Region: The chromosome region which is active in nucleolus formation and which functions in the synthesis of ribosomal RNA.RNA, Small Interfering: Small double-stranded, non-protein coding RNAs (21-31 nucleotides) involved in GENE SILENCING functions, especially RNA INTERFERENCE (RNAi). Endogenously, siRNAs are generated from dsRNAs (RNA, DOUBLE-STRANDED) by the same ribonuclease, Dicer, that generates miRNAs (MICRORNAS). The perfect match of the siRNAs' antisense strand to their target RNAs mediates RNAi by siRNA-guided RNA cleavage. siRNAs fall into different classes including trans-acting siRNA (tasiRNA), repeat-associated RNA (rasiRNA), small-scan RNA (scnRNA), and Piwi protein-interacting RNA (piRNA) and have different specific gene silencing functions.Multiprotein Complexes: Macromolecular complexes formed from the association of defined protein subunits.Cytoplasm: The part of a cell that contains the CYTOSOL and small structures excluding the CELL NUCLEUS; MITOCHONDRIA; and large VACUOLES. (Glick, Glossary of Biochemistry and Molecular Biology, 1990)ran GTP-Binding Protein: A monomeric GTP-binding protein involved in nucleocytoplasmic transport of proteins into the nucleus and RNA into the cytoplasm. This enzyme was formerly listed as EC 184.108.40.206.Separase: Separase is a caspase-like cysteine protease, which plays a central role in triggering ANAPHASE by cleaving the SCC1/RAD21 subunit of the cohesin complex. Cohesin holds the sister CHROMATIDS together during METAPHASE and its cleavage results in chromosome segregation.Time Factors: Elements of limited time intervals, contributing to particular results or situations.DNA Damage: Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a MUTATION or a block of DNA REPLICATION. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (PYRIMIDINE DIMERS) or interstrand crosslinking. Damage can often be repaired (DNA REPAIR). If the damage is extensive, it can induce APOPTOSIS.Genes, Fungal: The functional hereditary units of FUNGI.Protein Transport: The process of moving proteins from one cellular compartment (including extracellular) to another by various sorting and transport mechanisms such as gated transport, protein translocation, and vesicular transport.Ovum: A mature haploid female germ cell extruded from the OVARY at OVULATION.Nuclear Pore: An opening through the NUCLEAR ENVELOPE formed by the nuclear pore complex which transports nuclear proteins or RNA into or out of the CELL NUCLEUS and which, under some conditions, acts as an ion channel.Maturation-Promoting Factor: Protein kinase that drives both the mitotic and meiotic cycles in all eukaryotic organisms. In meiosis it induces immature oocytes to undergo meiotic maturation. In mitosis it has a role in the G2/M phase transition. Once activated by CYCLINS; MPF directly phosphorylates some of the proteins involved in nuclear envelope breakdown, chromosome condensation, spindle assembly, and the degradation of cyclins. The catalytic subunit of MPF is PROTEIN P34CDC2.Drosophila melanogaster: A species of fruit fly much used in genetics because of the large size of its chromosomes.Lamin Type B: A subclass of ubiquitously-expressed lamins having an acidic isoelectric point. They are found to remain bound to nuclear membranes during mitosis.Microtubule Proteins: Proteins found in the microtubules.Microscopy, Video: Microscopy in which television cameras are used to brighten magnified images that are otherwise too dark to be seen with the naked eye. It is used frequently in TELEPATHOLOGY.Apc6 Subunit, Anaphase-Promoting Complex-Cyclosome: A highly conserved subunit of the anaphase-promoting complex (APC-C) containing multiple 34 amino acid tetratricopeptide repeats. These domains, also found in Apc3, Apc7, and Apc8, have been shown to mediate protein-protein interactions, suggesting that Apc6 may assist in coordinating the juxtaposition of the catalytic and substrate recognition module subunits relative to coactivators and APC-C inhibitors.Dipodomys: A genus of the family Heteromyidae which contains 22 species. Their physiology is adapted for the conservation of water, and they seldom drink water. They are found in arid or desert habitats and travel by hopping on their hind limbs.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Cell Cycle Checkpoints: Regulatory signaling systems that control the progression through the CELL CYCLE. They ensure that the cell has completed, in the correct order and without mistakes, all the processes required to replicate the GENOME and CYTOPLASM, and divide them equally between two daughter cells. If cells sense they have not completed these processes or that the environment does not have the nutrients and growth hormones in place to proceed, then the cells are restrained (or "arrested") until the processes are completed and growth conditions are suitable.Colchicine: A major alkaloid from Colchicum autumnale L. and found also in other Colchicum species. Its primary therapeutic use is in the treatment of gout, but it has been used also in the therapy of familial Mediterranean fever (PERIODIC DISEASE).DNA: A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Oocytes: Female germ cells derived from OOGONIA and termed OOCYTES when they enter MEIOSIS. The primary oocytes begin meiosis but are arrested at the diplotene state until OVULATION at PUBERTY to give rise to haploid secondary oocytes or ova (OVUM).Aneuploidy: The chromosomal constitution of cells which deviate from the normal by the addition or subtraction of CHROMOSOMES, chromosome pairs, or chromosome fragments. In a normally diploid cell (DIPLOIDY) the loss of a chromosome pair is termed nullisomy (symbol: 2N-2), the loss of a single chromosome is MONOSOMY (symbol: 2N-1), the addition of a chromosome pair is tetrasomy (symbol: 2N+2), the addition of a single chromosome is TRISOMY (symbol: 2N+1).Cell Line, Tumor: A cell line derived from cultured tumor cells.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Benomyl: A systemic agricultural fungicide used for control of certain fungal diseases of stone fruit.PhosphoproteinsCyclin A2: A widely-expressed cyclin A subtype that functions during the G1/S and G2/M transitions of the CELL CYCLE.Time-Lapse Imaging: Recording serial images of a process at regular intervals spaced out over a longer period of time than the time in which the recordings will be played back.Antimitotic Agents: Agents that arrest cells in MITOSIS, most notably TUBULIN MODULATORS.Geminin: Geminin inhibits DNA replication by preventing the incorporation of MCM complex into pre-replication complex. It is absent during G1 phase of the CELL CYCLE and accumulates through S, G2,and M phases. It is degraded at the metaphase-anaphase transition by the ANAPHASE-PROMOTING COMPLEX-CYCLOSOME.Cell Extracts: Preparations of cell constituents or subcellular materials, isolates, or substances.Ligases: A class of enzymes that catalyze the formation of a bond between two substrate molecules, coupled with the hydrolysis of a pyrophosphate bond in ATP or a similar energy donor. (Dorland, 28th ed) EC 6.Luminescent Proteins: Proteins which are involved in the phenomenon of light emission in living systems. Included are the "enzymatic" and "non-enzymatic" types of system with or without the presence of oxygen or co-factors.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Ubiquitin-Protein Ligases: A diverse class of enzymes that interact with UBIQUITIN-CONJUGATING ENZYMES and ubiquitination-specific protein substrates. Each member of this enzyme group has its own distinct specificity for a substrate and ubiquitin-conjugating enzyme. Ubiquitin-protein ligases exist as both monomeric proteins multiprotein complexes.Aphidicolin: An antiviral antibiotic produced by Cephalosporium aphidicola and other fungi. It inhibits the growth of eukaryotic cells and certain animal viruses by selectively inhibiting the cellular replication of DNA polymerase II or the viral-induced DNA polymerases. The drug may be useful for controlling excessive cell proliferation in patients with cancer, psoriasis or other dermatitis with little or no adverse effect upon non-multiplying cells.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.
Bookmarking: Bookmarking (also "gene bookmarking" or "mitotic bookmarking") refers to a potential mechanism of transmission of gene expression programs through cell division.Spindle apparatus: In cell biology, the spindle apparatus refers to the subcellular structure of eukaryotic cells that separates chromosomes between daughter cells during cell division. It is also referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell.Start point (yeast): The Start checkpoint is a major cell cycle checkpoint in yeast. The Start checkpoint ensures irreversible cell-cycle entry even if conditions later become unfavorable.AnaphaseKinetochore: The kinetochore is the protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart.Microtubule: Microtubules ([+ tube] + [are a component of the [[cytoskeleton], found throughout the [[cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres and are highly dynamic.Immortal DNA strand hypothesis: The immortal DNA strand hypothesis was proposed in 1975 by John Cairns as a mechanism for adult stem cells to minimize mutations in their genomes.Cairns, J.Clb 5,6 (Cdk1): Clb5 and Clb6 are B-type, S-phase cyclins in yeast that assist in cell cycle regulation.Morgan, DO (2007) 'The Cell Cycle: Principles of Control, Oxford University Press Clb5 and Clb6 bind and activate Cdk1, and high levels of these cyclins are required for entering S-phase.Centrosome cycle: Centrosomes are the major microtubule organizing center (MTOC) in mammalian cells. Failure of centrosome regulation can cause mistakes in chromosome segregation and is associated with aneuploidy.Metaphase: Metaphase (from the Greek μετά, "adjacent" and φάσις, "stage") is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase. These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells.Premature chromosome condensation: Premature chromosome condensation (PCC) occurs in eukaryotic organisms when mitotic cells fuse with interphase cells. Chromatin, a substance that contains genetic material such as DNA, is normally found in a loose bundle inside a cell's nucleus.Aurora inhibitorNocodazoleSerine/threonine-specific protein kinaseCytokinesis: Cytokinesis (from the Greek κύτος, "container" and κίνησις, "motion") is the process during cell division in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It usually initiates during the early stages of mitosis, and sometimes meiosis, splitting a mitotic cell in two, to ensure that chromosome number is maintained from one generation to the next.Schizosaccharomyces pombe: Schizosaccharomyces pombe, also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped.CentromereAPC/C activator protein CDH1: Cdh1 is one of the substrate adaptor protein of the anaphase-promoting complex (APC) in the budding yeast Saccharomyces cerevisiae. Functioning as an activator of the APC/C, Cdh1 regulates the activity and substrate specificity of this ubiquitin E3-ligase.Chromo shadow domain: In molecular biology, the chromo shadow domain is a protein domain which is distantly related to the chromodomain. It is always found in association with a chromodomain.Hyperphosphorylation: Hyperphosphorylation occurs when a biochemical with multiple phosphorylation sites is fully saturated. Hyperphosphorylation is one of the signalling mechanisms used by the cell to regulate mitosis.Establishment of sister chromatid cohesion: Sister chromatid cohesion refers to the process by which sister chromatids are paired and held together during certain phases of the cell cycle. Establishment of sister chromatid cohesion is the process by which chromatin-associated cohesin protein becomes competent to physically bind together the sister chromatids.MinC: The MinC protein is one of three proteins encoded by the minB operon and which is required to generate pole to pole oscillations prior to bacterial cell division as a means of specifying the midzone of the cell. This function is achieved by preventing the formation of the divisome Z-ring around the poles.Tubulin: Tubulin ([+ -in]) in [[molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoskeleton.KASH domains: KASH domains are conserved C-terminal protein regions less than ~30 amino acids. KASH is an acronym for Klarsicht, ANC-1, Syne Homology.KinesinTotal internal reflection fluorescence microscope: A total internal reflection fluorescence microscope (TIRFM) is a type of microscope with which a thin region of a specimen, usually less than 200 nm can be observed.Coles PhillipsSilent mutation: Silent mutations are mutations in DNA that do not significantly alter the phenotype of the organism in which they occur. Silent mutations can occur in non-coding regions (outside of genes or within introns), or they may occur within exons.Pericentriolar material: Pericentriolar material (PCM, sometimes also called pericentriolar matrix) is an amorphous mass of protein which makes up the part of the animal centrosome that surrounds the two centrioles. The PCM contains proteins responsible for microtubule nucleation and anchoring including γ-tubulin, pericentrin and ninein.Protein primary structure: The primary structure of a peptide or protein is the linear sequence of its amino acid structural units, and partly comprises its overall biomolecular structure. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end.DNA re-replication: DNA re-replication (or simply rereplication) is an undesirable and possibly fatal occurrence in eukaryotic cells in which the genome is replicated more than once per cell cycle. Rereplication is believed to lead to genomic instability and has been implicated in the pathologies of a variety of human cancers.Kinome: In molecular biology, the kinome of an organism is the set of protein kinases in its genome. Kinases are enzymes that catalyze phosphorylation reactions (of amino acids) and fall into several groups and families, e.RNAi-Based Identification System and interference of Specific Cancer Cells: A “classifier” was created to classify cells by identifying specific characteristics of Cervical Cancer. These characteristics were consistent with HeLa cells, which served as the target cell line for cell death.Bivalent chromatin: Bivalent chromatin are segments of DNA, bound to histone proteins, that have both repressing and activating epigenetic regulators in the same region. These regulators work to enhance or silence the expression of genes.BESS domain: In molecular biology, the BESS domain is a protein domain which has been named after the three proteins that originally defined the domain: BEAF (Boundary element associated factor 32), Suvar(3)7 and Stonewall ). The BESS domain is 40 amino acid residues long and is predicted to be composed of three alpha helices, as such it might be related to the myb/SANT HTH domain.Zuotin: Z-DNA binding protein 1, also known as Zuotin, is a Saccharomyces cerevisiae yeast gene.Nucleolus: The nucleolus (; plural nucleoli ) is the largest structure in the nucleus of eukaryotic cells, where it primarily serves as the site of ribosome synthesis and assembly. Nucleoli also have other important functions like assembly of signal recognition particles and playing a role in the cell's response to stress.DemecolcineCyclin: Cyclins are a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes.NEK8: Serine/threonine-protein kinase Nek8, also known as never in mitosis A-related kinase 8, is an enzyme that in humans is encoded by the NEK8 gene.Histone octamer: A histone octamer is the eight protein complex found at the center of a nucleosome core particle. It consists of two copies of each of the four core histone proteins (H2A, H2B, H3 and H4).Matrix model: == Mathematics and physics ==PaleopolyploidyLamin: Nuclear lamins, also known as Class V intermediate filaments, are fibrous proteins providing structural function and transcriptional regulation in the cell nucleus. Nuclear lamins interact with membrane-associated proteins to form the nuclear lamina on the interior of the nuclear envelope.Proximity ligation assay: Proximity ligation assay (in situ PLA) is a technology that extends the capabilities of traditional immunoassays to include direct detection of proteins, protein interactions and modifications with high specificity and sensitivity. Protein targets can be readily detected and localized with single molecule resolution and objectively quantified in unmodified cells and tissues.Synapto-pHluorin: Synapto-pHluorin is a genetically encoded optical indicator of vesicle release and recycling. It is used in neuroscience to study transmitter release.Protein serine/threonine phosphatase: Protein serine/threonine phosphatase (PSP) is a form of phosphoprotein phosphatase that acts upon serine/threonine residues.DNA-binding proteinCyclin-dependent kinase complex: A cyclin-dependent kinase complex (CDKC, cyclin-CDK) is a protein complex formed by the association of an inactive catalytic subunit of a protein kinase, cyclin-dependent kinase (CDK), with a regulatory subunit, cyclin.Malumbres M, Barbacid M.Drosophila embryogenesis: Drosophila embryogenesis, the process by which Drosophila (fruit fly) embryos form, is a favorite model system for geneticists and developmental biologists studying embryogenesis. The small size, short generation time, and large brood size make it ideal for genetic studies.Janin PlotRibosomal DNACondensin: Condensins are large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis.
(1/11754) Analysis of the effects of food and of digestive secretions on the small intestine of the rat. 1. Mucosal morphology and epithelial replacement.
A modified Roux-en-Y repositioning of rat small intestine was performed so that the proximal segment of bowel (A) received only bile and pancreastic secretions, the second (B) received food direct from the stomach, and these two segments drained into a third (C). Four to five weeks after operation, cell production was assessed by injection of vincristine into operated, sham-operated and unoperated rats, and counts of blocked metaphases were made on isolated microdissected crypts. Villus height, crypt depth, and the number of crypts per villus (crypt/villus ratio) were also measured. Most of segment A showed no significant differences from sham-operated intestine, although the normal proximo-distal gradient of villus height was abolished. At the distal end (near the anastomosis with segments B and C), crypt depth and cell production were increased. The villus height gradient in segment B was also abolished, although crypt depth and cell production were significantly increased, especially at the proximal end. Crypt/villus ratio was also increased. Segment C showed all the characteristics of small bowel promoted to a more proximal position: increased villus height, crypt depth and cell production. Increased crypt/villus ratio was also observed. These results are discussed in terms of the role of food and of digestive secretions in the control of mucosal morphology and epithelial replacement. (+info)
(2/11754) Functions of cyclin A1 in the cell cycle and its interactions with transcription factor E2F-1 and the Rb family of proteins.
Human cyclin A1, a newly discovered cyclin, is expressed in testis and is thought to function in the meiotic cell cycle. Here, we show that the expression of human cyclin A1 and cyclin A1-associated kinase activities was regulated during the mitotic cell cycle. In the osteosarcoma cell line MG63, cyclin A1 mRNA and protein were present at very low levels in cells at the G0 phase. They increased during the progression of the cell cycle and reached the highest levels in the S and G2/M phases. Furthermore, the cyclin A1-associated histone H1 kinase activity peaked at the G2/M phase. We report that cyclin A1 could bind to important cell cycle regulators: the Rb family of proteins, the transcription factor E2F-1, and the p21 family of proteins. The in vitro interaction of cyclin A1 with E2F-1 was greatly enhanced when cyclin A1 was complexed with CDK2. Associations of cyclin A1 with Rb and E2F-1 were observed in vivo in several cell lines. When cyclin A1 was coexpressed with CDK2 in sf9 insect cells, the CDK2-cyclin A1 complex had kinase activities for histone H1, E2F-1, and the Rb family of proteins. Our results suggest that the Rb family of proteins and E2F-1 may be important targets for phosphorylation by the cyclin A1-associated kinase. Cyclin A1 may function in the mitotic cell cycle in certain cells. (+info)
(3/11754) Thyroid hormone effects on Krox-24 transcription in the post-natal mouse brain are developmentally regulated but are not correlated with mitosis.
Krox-24 (NGFI-A, Egr-1) is an immediate-early gene encoding a zinc finger transcription factor. As Krox-24 is expressed in brain areas showing post-natal neurogenesis during a thyroid hormone (T3)-sensitive period, we followed T3 effects on Krox-24 expression in newborn mice. We analysed whether regulation was associated with changes in mitotic activity in the subventricular zone and the cerebellum. In vivo T3-dependent Krox-24 transcription was studied by polyethylenimine-based gene transfer. T3 increased transcription from the Krox-24 promoter in both areas studied at post-natal day 2, but was without effect at day 6. An intact thyroid hormone response element (TRE) in the Krox-24 promoter was necessary for these inductions. These stage-dependent effects were also seen in endogenous Krox-24 mRNA levels: activation at day 2 and no effect at day 6. Moreover, similar results were obtained by examining beta-galactosidase expression in heterozygous mice in which one allele of the Krox-24 gene was disrupted with an inframe Lac-Z insertion. However, bromodeoxyuridine incorporation showed mitosis to continue through to day 6. We conclude first, that T3 activates Krox-24 transcription during early post-natal mitosis but that this effect is extinguished as development proceeds and second, loss of T3-dependent Krox-24 expression is not correlated with loss of mitotic activity. (+info)
(4/11754) Diverse developing mouse lineages exhibit high-level c-Myb expression in immature cells and loss of expression upon differentiation.
The c-myb gene encodes a sequence specific transactivator that is required for fetal hematopoiesis, but its potential role in other tissues is less clear because of the early fetal demise of mice with targeted deletions of the c-myb gene and incomplete of knowledge about c-myb's expression pattern. In the hematopoietic system, c-Myb protein acts on target genes whose expression is restricted to individual lineages, despite Myb's presence and role in multiple immature lineages. This suggests that c-Myb actions within different cell type-specific contexts are strongly affected by combinatorial interactions. To consider the possibility of similar c-Myb actions could extend into non-hematopoietic systems in other cell and tissue compartments, we characterized c-myb expression in developing and adult mice using in situ hybridization and correlated this with stage-specific differentiation and mitotic activity. Diverse tissues exhibited strong c-myb expression during development, notably tooth buds, the thyroid primordium, developing trachea and proximal branching airway epithelium, hair follicles, hematopoietic cells, and gastrointestinal crypt epithelial cells. The latter three of these all maintained high expression into adulthood, but with characteristic restriction to immature cell lineages prior to their terminal differentiation. In all sites, during fetal and adult stages, loss of c-Myb expression correlated strikingly with the initiation of terminal differentiation, but not the loss of mitotic activity. Based on these data, we hypothesize that c-Myb's function during cellular differentiation is both an activator of immature gene expression and a suppressor of terminal differentiation in diverse lineages. (+info)
(5/11754) The postnatal development of the alimentary canal in the opossum. I. Oesophagus.
The oesophageal epithelium of the newborn opossum generally is two to three cells in depth and in some regions appears pseudostratified. By the 9th postnatal day the epithelium shows two distinct strata. Ciliated cells and occasional goblet cells also are observed within the epithelium during this stage and in subsequent stages. Cilia persist in the oesophagus of the adult opossum, but are restricted to the depths of the transverse folds found in the distal part of the organ. The epithelium covering the transverse folds of the adult likewise has an immature appearance. By 4-5 cm (ca. 20 days), the epithelium has assumed a more mature appearance and is of greater depth. This and later stages show three basic strata: a germinal layer, a spinous layer and, adjacent to the lumen, a flattened layer of cells that retain their nuclei. The epithelium throughout the postnatal period and in the adult does not undergo complete keratinization. The oesophageal glands begin as outgrowths from the epithelium just prior to 4-5 cm (ca. 20 days). The glands continue their development throughout the remainder of the postnatal period. The secretory units of the oesophageal glands of the the major portion of the secretory elements, and a light, rounded cell type which is less numerous and which occupies the terminal portions of the secretory units. Secretory material of the former appears complex, consisting of both neutral and acid glycoproteins. The secretory product of the light cell type is unknown at present. Both cell types are encompassed by myoepithelial cells. The relationship of the mitotic sequences to the observations made by microscopic examination of the developing oesophagus is discussed. (+info)
(6/11754) Changes in the total number of neuroglia, mitotic cells and necrotic cells in the anterior limb of the mouse anterior commissure following hypoxic stress.
The effects of hypoxic stress (390 mmHg) on the total number of glia, cell division, and cell death in the anterior limb of the anterior commissure were studied. There was a significant (P less than 0-01) fall in the total number of glia following exposure to hypoxia at 390 mmHg for two days. No significant change was observed in the total number of glia between the hypoxic and recovery group one week after return to sea level (ca. 760 mmHg). No change was observed in the number of mitotic figures in the control, hypoxic or recovery groups, but significant falls were observed in the mean number of necrotic cells between both the control and hypoxic groups (P less than 0-05) and the hypoxic and recovery groups (P less than 0-012). The decrease in necrotic cells may be due to a large number of elderly and effete cells, which would normally have undergone degeneration over a period of weeks, dying rapidly after the onset of hypoxia, thus temporarily reducing the daily cell death rate. (+info)
(7/11754) The preprophase band: possible involvement in the formation of the cell wall.
Numerous vesicles were observed among the microtubules of the "preprophase" band in prophase cells from root tips of Allium cepa. The content of these vesicles looks similar to the matrix of adjacent cell walls, and these vesicles often appear to be involved in exocytosis. In addition, the cell walls perpendicular to the plane of (beneath) the preprophase band are often differentially thickened compared to the walls lying parallel to the plane of the band. Our interpretation of these observations is that the preprophase band may direct or channel vesicles containing precursors of the cell wall to localized regions of wall synthesis. The incorporation of constituents of the cell wall into a narrow region defined by the position of the preprophase band may be a mechanism that ensures unidirecitonal growth of meristematic cells. (+info)
(8/11754) Arsenic targets tubulins to induce apoptosis in myeloid leukemia cells.
Arsenic exhibits a differential toxicity to cancer cells. At a high concentration (>5 microM), As2O3 causes acute necrosis in various cell lines. At a lower concentration (0.5-5 microm), it induces myeloid cell maturation and an arrest in metaphase, leading to apoptosis. As2O3-treated cells have features found with both tubulin-assembling enhancers (Taxol) and inhibitors (colchicine). Prior treatment of monomeric tubulin with As2O3 markedly inhibits GTP-induced polymerization and microtubule formation in vitro but does not destabilize GTP-induced tubulin polymers. Cross-inhibition experiments indicate that As2O3 is a noncompetitive inhibitor of GTP binding to tubulin. These observations correlate with the three-dimensional structure of beta-tubulin and suggest that the cross-linking of two vicinal cysteine residues (Cys-12 and Cys-213) by trivalent arsenic inactivates the GTP binding site. Furthermore, exogenous GTP can prevent As2O3-induced mitotic arrest. (+info)