Kinetochore assembly and disassembly during mitotic entry and exit

2018 ◽  
Vol 52 ◽  
pp. 73-81 ◽  
Author(s):  
Masatoshi Hara ◽  
Tatsuo Fukagawa
Keyword(s):  
Entry And Exit ◽  
Mitotic Entry ◽  
Kinetochore Assembly

scholarly journals The nucleus serves as the pacemaker for the cell cycle

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Oshri Afanzar ◽  
Garrison K Buss ◽  
Tim Stearns ◽  
James E Ferrell
Keyword(s):  
Cell Cycle ◽  
Tubulin Polymerization ◽  
Entry And Exit ◽  
Mitotic Entry ◽  
Cellular Location ◽  
Phage Dna ◽  
Egg Extracts ◽  
The Waves

Mitosis is a dramatic process that affects all parts of the cell. It is driven by an oscillator whose various components are localized in the nucleus, centrosome, and cytoplasm. In principle, the cellular location with the fastest intrinsic rhythm should act as a pacemaker for the process. Here we traced the waves of tubulin polymerization and depolymerization that occur at mitotic entry and exit in Xenopus egg extracts back to their origins. We found that mitosis was commonly initiated at sperm-derived nuclei and their accompanying centrosomes. The cell cycle was ~20% faster at these initiation points than in the slowest regions of the extract. Nuclei produced from phage DNA, which did not possess centrosomes, also acted as trigger wave sources, but purified centrosomes in the absence of nuclei did not. We conclude that the nucleus accelerates mitotic entry and propose that it acts as a pacemaker for cell cycle.

scholarly journals Bistable, biphasic regulation of PP2A-B55 accounts for the dynamics of mitotic substrate phosphorylation

2020 ◽  
Author(s):  
Julia Kamenz ◽  
Lendert Gelens ◽  
James E. Ferrell
Keyword(s):  
Mitotic Exit ◽  
Cyclin Dependent Kinase ◽  
Entry And Exit ◽  
Bistable Switch ◽  
Mitotic Entry ◽  
Low Concentrations ◽  
M Phase ◽  
Egg Extracts ◽  
Substrate Phosphorylation ◽  
High Concentrations

SummaryThe phosphorylation of mitotic proteins is bistable, which contributes to the decisiveness of the transitions into and out of M phase. The bistability in substrate phosphorylation has been attributed to bistability in the activation of the cyclin-dependent kinase Cdk1. However, more recently it has been suggested that bistability also arises from positive feedback in the regulation of the Cdk1-counteracting phosphatase, PP2A-B55. Here, we demonstrate biochemically using Xenopus laevis egg extracts that the Cdk1-counteracting phosphatase PP2A-B55 functions as a bistable switch, even when the bistability of Cdk1 activation is suppressed. In addition, Cdk1 regulates PP2A-B55 in a biphasic manner; low concentrations of Cdk1 activate PP2A-B55 and high concentrations inactivate it. As a consequence of this incoherent feedforward regulation, PP2A-B55 activity rises concurrently with Cdk1 activity during interphase and suppresses substrate phosphorylation. PP2A-B55 activity is then sharply downregulated at the onset of mitosis. During mitotic exit Cdk1 activity initially falls with no obvious change in substrate phosphorylation; dephosphorylation then commences once PP2A-B55 spikes in activity. These findings suggest that changes in Cdk1 activity are permissive for mitotic entry and exit, but the changes in PP2A-B55 activity are the ultimate trigger.

scholarly journals Bistability of mitotic entry and exit switches during open mitosis in mammalian cells

BioEssays ◽  
2016 ◽  
Vol 38 (7) ◽  
pp. 627-643 ◽  
Author(s):  
Nadia Hégarat ◽  
Scott Rata ◽  
Helfrid Hochegger
Keyword(s):  
Mammalian Cells ◽  
Entry And Exit ◽  
Mitotic Entry

scholarly journals Mapping the invisible chromatin transactions of prophase chromosome remodelling

2021 ◽  
Author(s):  
Itaru SAMEJIMA ◽  
Christos Spanos ◽  
Kumiko Samejima ◽  
Juri Rappsilber ◽  
Georg Kustatscher ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Cell Entry ◽  
Mitotic Entry ◽  
Nuclear Envelope Breakdown ◽  
Kinetochore Assembly ◽  
Cytoplasmic Proteins ◽  
Chromatin Proteins ◽  
Polymerase I ◽  
Proteomic Map ◽  
Processing Factors

We have used a combination of chemical genetics, chromatin proteomics and imaging to map the earliest chromatin transactions during vertebrate cell entry into mitosis. Chicken DT40 CDK1as cells undergo synchronous mitotic entry within 15 minutes following release from a 1NM-PP1-induced arrest in late G2. In addition to changes in chromatin association with nuclear pores and the nuclear envelope, earliest prophase is dominated by changes in the association of ribonucleoproteins with chromatin, particularly in the nucleolus, where pre-rRNA processing factors leave chromatin significantly before RNA polymerase I. Nuclear envelope barrier function is lost early in prophase and cytoplasmic proteins begin to accumulate on the chromatin. As a result, outer kinetochore assembly appears complete by nuclear envelope breakdown (NEBD). Most interphase chromatin proteins remain associated with chromatin until NEBD, after which their levels drop sharply. An interactive proteomic map of chromatin transactions during mitotic entry is available as a resource at https://mitoChEP.bio.ed.ac.uk.

scholarly journals Nuclear Localization of Cyclin B1 Controls Mitotic Entry After DNA Damage

1998 ◽  
Vol 141 (4) ◽  
pp. 875-885 ◽  
Author(s):  
Pei Jin ◽  
Stephen Hardy ◽  
David O. Morgan
Keyword(s):  
Dna Damage ◽  
Normal Growth ◽  
Subcellular Location ◽  
Cyclin B1 ◽  
Growth Conditions ◽  
Human Cells ◽  
Entry And Exit ◽  
Nuclear Targeting ◽  
G2 Arrest ◽  
Mitotic Entry

Mitosis in human cells is initiated by the protein kinase Cdc2-cyclin B1, which is activated at the end of G2 by dephosphorylation of two inhibitory residues, Thr14 and Tyr15. The G2 arrest that occurs after DNA damage is due in part to stabilization of phosphorylation at these sites. We explored the possibility that entry into mitosis is also regulated by the subcellular location of Cdc2-cyclin B1, which is suddenly imported into the nucleus at the end of G2. We measured the timing of mitosis in HeLa cells expressing a constitutively nuclear cyclin B1 mutant. Parallel studies were performed with cells expressing Cdc2AF, a Cdc2 mutant that cannot be phosphorylated at inhibitory sites. Whereas nuclear cyclin B1 and Cdc2AF each had little effect under normal growth conditions, together they induced a striking premature mitotic phenotype. Nuclear targeting of cyclin B1 was particularly effective in cells arrested in G2 by DNA damage, where it greatly reduced the damage-induced G2 arrest. Expression of nuclear cyclin B1 and Cdc2AF also resulted in significant defects in the exit from mitosis. Thus, nuclear targeting of cyclin B1 and dephosphorylation of Cdc2 both contribute to the control of mitotic entry and exit in human cells.

Meiotic CENP-C is a shepherd: bridging the space between the centromere and the kinetochore in time and space

2020 ◽  
Vol 64 (2) ◽  
pp. 251-261
Author(s):  
Jessica E. Fellmeth ◽  
Kim S. McKim
Keyword(s):  
Chromosome Segregation ◽  
New Technologies ◽  
Early Prophase ◽  
Unique Role ◽  
Kinetochore Assembly ◽  
M Phase ◽  
In Vivo Analysis ◽  
Meiosis I

Abstract While many of the proteins involved in the mitotic centromere and kinetochore are conserved in meiosis, they often gain a novel function due to the unique needs of homolog segregation during meiosis I (MI). CENP-C is a critical component of the centromere for kinetochore assembly in mitosis. Recent work, however, has highlighted the unique features of meiotic CENP-C. Centromere establishment and stability require CENP-C loading at the centromere for CENP-A function. Pre-meiotic loading of proteins necessary for homolog recombination as well as cohesion also rely on CENP-C, as do the main scaffolding components of the kinetochore. Much of this work relies on new technologies that enable in vivo analysis of meiosis like never before. Here, we strive to highlight the unique role of this highly conserved centromere protein that loads on to centromeres prior to M-phase onset, but continues to perform critical functions through chromosome segregation. CENP-C is not merely a structural link between the centromere and the kinetochore, but also a functional one joining the processes of early prophase homolog synapsis to late metaphase kinetochore assembly and signaling.

Business processes in the insurance company: The method of operation through separating the key areas of activities

2020 ◽  
Vol 23 (11) ◽  
pp. 1269-1290
Author(s):  
A.A. Turgaeva
Keyword(s):  
Business Process ◽  
Business Processes ◽  
Systems Approach ◽  
Insurance Company ◽  
Entry And Exit ◽  
Control Procedures ◽  
Selection Of

Subject. This article analyzes the business processes in the insurance company, using the method of their operation with the selection of key areas of activity. Objectives. The article aims to describe certain business processes in insurance, highlighting participants, lines of activity, and the sequence of procedures. It analyzes the business process Settlement of Losses, which is one of the significant business processes in the insurance company. Methods. For the study, I used the methods of induction and deduction, analogy, and the systems approach. Results. Based on the analysis and description of business processes in the insurance company and the identification of key elements and steps in terms of the effectiveness of decisions, the article identifies the checkpoints of Entry and Exit, activity direction, and resources of the Settlement of Losses process. Conclusions. The application of the categories that split business processes makes it possible to develop step regulation for all processes and acceptable control procedures for different operations. The presented checkpoints at different steps of the business process will help identify weaknesses and eliminate them by re-checking the point.

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