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MitosisClass of microtubulesHomologous chromosomesSpindle assemblyMitoticSpindlesKinetochoresOrganismsAnaphaseInitiatesCentersCentrosomeCytoplasmicNuclearAbnormalOrganizationAdditionallyOccursFateGenetic materialEnsuresYeastConsistsArrayCell divisionResultsOriginProcessFormConnectActivitiesFindComplexQuestionCells

Mitosis6

• During meiosis II, the cohesion between sister chromatids is released and they segregate from one another, as during mitosis. (wikipedia.org)
• Although the process of meiosis is related to the more general cell division process of mitosis, it differs in two important respects: Meiosis begins with a diploid cell, which contains two copies of each chromosome, termed homologs. (wikipedia.org)
• Moreover, the implication that the active form of Ran is concentrated in the vicinity of chromosomes suggests that these findings may resolve the long-standing question of how chromosomes can influence spindle assembly in the absence of microtubule-nucleating organelles (i.e., as in plant mitosis or mammalian meiosis). (silverchair.com)
• Remarkably, despite the high turnover of microtubules throughout mitosis 2 , the spindle maintains its bipolar structure with the chromosomes at its center and two poles that are separated by the plane of cell division. (nature.com)
• In human female primordial germ cells, the transition from mitosis to meiosis begins from the fetal stage. (bvsalud.org)
• This stage of mitosis is also an important one given that it's the stage at which the chromosomes start aligning at the central part of the cell so that they can be divided. (microscopemaster.com)

Class of microtubules1

• In all spindles, the microtubule cytoskeleton connects to chromosomes via a special class of microtubules called kinetochore microtubules (KMTs). (nature.com)

Homologous chromosomes4

• During this time, homologous chromosomes pair with each other and undergo genetic recombination, a programmed process in which DNA may be cut and then repaired, which allows them to exchange some of their genetic information. (wikipedia.org)
• A subset of recombination events results in crossovers, which create physical links known as chiasmata (singular: chiasma, for the Greek letter Chi (Χ)) between the homologous chromosomes. (wikipedia.org)
• In most organisms, these links can help direct each pair of homologous chromosomes to segregate away from each other during meiosis I, resulting in two haploid cells that have half the number of chromosomes as the parent cell. (wikipedia.org)
• In germ cells, meiosis is arrested at the diplotene stage of prophase in meiosis I (MI) after synapsis and recombination of homologous chromosomes, which cannot be segregated. (bvsalud.org)

Spindle assembly2

• While plants employ some evolutionarily conserved proteins to regulate spindle morphogenesis and remodeling, many essential spindle assembly factors found in vertebrates are either missing or not required for producing the plant bipolar microtubule array. (nsf.gov)
• Plant spindle assembly initiates with microtubule nucleation on the nuclear envelope followed by bipolarization into the prophase spindle. (nsf.gov)

Mitotic5

• The mitotic spindle ensures the faithful segregation of chromosomes. (nature.com)
• Here we combine the first large-scale serial electron tomography of whole mitotic spindles in early C. elegans embryos with live-cell imaging to reconstruct all microtubules in 3D and identify their plus- and minus-ends. (nature.com)
• The mitotic spindle is a dynamic microtubule-based apparatus that ensures the segregation of chromosomes during cell division. (nature.com)
• It is predicted that MCPH gene mutations may lead to the disease phenotype due to a disturbed mitotic spindle orientation, premature chromosomal condensation, signalling response as a result of damaged DNA, microtubule dynamics, transcriptional control or a few other hidden centrosomal mechanisms that can regulate the number of neurons produced by neuronal precursor cells. (biomedcentral.com)
• The role of microtubule pivoting in formation of complex structures such as microtubule bundles and mitotic spindles. (irb.hr)

Spindles3

• In this study, we find that a microtubule polymerase Mini spindles (Msps), the Drosophila homolog of XMAP215, is essential for maintenance of the oocyte specification. (bvsalud.org)
• In contrast to well-studied fungal and animal cells, plant cells assemble bipolar spindles that exhibit a great deal of plasticity in the absence of structurally defined microtubule-organizing centers like the centrosome. (nsf.gov)
• In the meiosis of many species, the process of chromosome segregation requires that bipolar spindles be formed without the aid of dedicated microtubule organizing centers, such as centrosomes. (nsf.gov)

Kinetochores2

• In the case of chromosomal origin, microtubules instead nucleate around chromosomes and only later attach to kinetochores, as observed in Xenopus cell-free extracts 13 . (nature.com)
• As they extend, some of the microtubules also attach and connect to the chromosomes at kinetochores allowing the separation to begin. (microscopemaster.com)

Organisms4

• This same pattern, but not the same number of chromosomes, occurs in all organisms that utilize meiosis. (wikipedia.org)
• Meiosis occurs in all sexually-reproducing single-celled and multicellular organisms (which are all eukaryotes), including animals, plants and fungi. (wikipedia.org)
• However, how KMTs bind to chromosomes varies substantially between organisms. (nature.com)
• Cytoskeletal microtubules ( MT s) have a multitude of functions including intracellular distribution of molecules and organelles, cell morphogenesis, as well as segregation of the genetic material and separation of the cytoplasm during cell division among eukaryotic organisms. (nsf.gov)

Anaphase3

• Of note, compared to fungal and animal systems, relatively little is known about how plant cells remodel the spindle microtubule array during anaphase. (nsf.gov)
• For this reason, cytokinesis cannot occur during metaphase and therefore has to wait until the separation of chromosomes start (during anaphase). (microscopemaster.com)
• While some studies attribute the onset of anaphase chromosomes, this is attributed to the activities of the spindle by other studies. (microscopemaster.com)

Initiates1

• Regardless, it's the separation of chromosomes and the consequent creation of a cleavage furrow between the chromosomes that initiates cytoplasm division. (microscopemaster.com)

Centers2

• Although many key factors contributing to MT nucleation and organization are well conserved in different kingdoms, the centrosome, representing the most prominent microtubule organizing centers ( MTOC s), disappeared during plant evolution as angiosperms lack the structure. (nsf.gov)
• In higher plants, microtubule organizing centers (centrosome) is absent. (microscopemaster.com)

Centrosome2

• Indeed, by quantitatively analysing several models of microtubule growth, we conclude that minus-ends of KMTs have selectively detached and depolymerized from the centrosome. (nature.com)
• Here, centrioles, contained in the centrosome , are responsible for the production of microtubules that form the central fibers. (microscopemaster.com)

Cytoplasmic1

• In Drosophila melanogaster, 16 interconnected cells form a germline cyst, where one cell differentiates into an oocyte, while the rest become nurse cells that supply the oocyte with mRNAs, proteins, and organelles through intercellular cytoplasmic bridges named ring canals via microtubule-based transport. (bvsalud.org)

Nuclear2

• Instead, Ran and its associated proteins shift their focus from nuclear transport to the regulation of microtubule dynamics. (silverchair.com)
• To provide a comprehensive understanding of the recently uncovered regulatory network involved in oocyte development and maturation, the progress of the cellular and molecular mechanisms of oocyte nuclear maturation including meiosis arrest and meiosis resumption is summarized. (bvsalud.org)

Abnormal1

• Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. (wikipedia.org)

Organization1

• Recent findings by several groups have shown that the GTP-bound form of Ran is necessary for the nucleation and organization of microtubule structures during M phase. (silverchair.com)

Additionally1

• Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. (wikipedia.org)

Occurs1

• During estrus phase in animals or the menstrual cycle in humans, the resumption of meiosis occurs in certain oocytes due to a surge of luteinizing hormone (LH) levels. (bvsalud.org)

Fate1

• Thus, the Msps-dynein duo creates a positive feedback loop, ensuring oocyte fate maintenance by promoting high microtubule polymerization activity in the oocyte, and enhancing dynein-dependent nurse cell-to-oocyte transport. (bvsalud.org)

Genetic material1

• However, during metaphase, genetic material first condenses into chromosomes which makes them visible. (microscopemaster.com)

Ensures1

• This is important because it ensures that as the cell continues to separate, each of the new daughter cells receives an equal number of chromosomes. (microscopemaster.com)

Yeast1

• In budding yeast, single continuous KMTs span the full pole-to-chromosome distance 6 . (nature.com)

Consists2

• Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. (wikipedia.org)
• These are also known as central spindle and consists of an array of microtubules. (microscopemaster.com)

Array1

• Once they are produced, the array of microtubules extend to different directions within the cytoplasm forming the spindle. (microscopemaster.com)

Cell division1

• In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. (wikipedia.org)

Results2

• In toto , our results show that the connection between centrosomes and chromosomes is mediated by an anchoring into the entire spindle network and that any direct connections through KMTs are few and likely very transient. (nature.com)
• At the cell equator, these factors stimulate the recruitment of formins which in turn results in the nucleation of actin filaments as well as myosin localization. (microscopemaster.com)

Origin1

• For example, diploid human cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes (46 total), half of maternal origin and half of paternal origin. (wikipedia.org)

Process1

• Here, it's worth noting that cytokinesis is a tightly coordinated process that follows the separation of chromosomes. (microscopemaster.com)

Form2

• Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. (wikipedia.org)
• From here, microtubules that form the fibers radiate to the cell cortex located at the inner part of the cell membrane . (microscopemaster.com)

Connect1

• If the role of KMTs is to mediate forces between chromosomes and spindle poles, they need to somehow connect to the centrosomes. (nature.com)

Activities1

• It is intriguing what proteins are associated with plant‐specific MTOC s and how plant cells activate or inactivate MT nucleation activities in spatiotemporally regulated manners. (nsf.gov)

Find1

• While our light microscopy and mutant studies show that microtubules are nucleated from the centrosomes, we find only a few KMTs directly connected to the centrosomes. (nature.com)

Complex1

• MT ‐dependent MT nucleation is particularly noticeable in plant cells because it accounts for the primary source of MT generation for assembling spindle, phragmoplast, and cortical arrays when the γ‐tubulin ring complex is anchored and activated by the augmin complex. (nsf.gov)

Question1

• A related question is the site of KMT nucleation. (nature.com)

Cells2

• It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome (haploid). (wikipedia.org)
• Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a cell with two copies of each chromosome again, the zygote. (wikipedia.org)