scholarly journals Cyclins A and B associate with chromatin and the polar regions of spindles, respectively, and do not undergo complete degradation at anaphase in syncytial Drosophila embryos.

1992 ◽  
Vol 116 (4) ◽  
pp. 967-976 ◽  
Author(s):  
G Maldonado-Codina ◽  
D M Glover
Keyword(s):  
Metaphase Plate ◽  
Cyclin A ◽  
Cyclin B ◽  
Drosophila Embryo ◽  
Polar Regions ◽  
Surface Layers ◽  
Nuclear Envelope Breakdown ◽  
Apical Side ◽  
Punctate Staining ◽  
Drosophila Embryos

Maternally contributed cyclin A and B proteins are initially distributed uniformly throughout the syncytial Drosophila embryo. As dividing nuclei migrate to the cortex of the embryo, the A and B cyclins become concentrated in surface layers extending to depths of approximately 30-40 microns and 5-10 microns, respectively. The initiation of nuclear envelope breakdown, spindle formation, and the initial congression of the centromeric regions of the chromosomes onto the metaphase plate all take place within the surface layer occupied by cyclin B on the apical side of the blastoderm nuclei. Cyclin B is seen mainly, but not exclusively, in the vicinity of microtubules throughout the mitotic cycle. It is most conspicuous around the centrosomes. Cyclin A is present at its highest concentrations throughout the cytoplasm during the interphase periods of the blastoderm cycles, although weak punctate staining can also be detected in the nucleus. It associates with the condensing chromosomes during prophase, segregates into daughter nuclei in association with chromosomes during anaphase, to redistribute into the cytoplasm after telophase. In contrast to the cycles following cellularization, neither cyclin is completely degraded upon the metaphase-anaphase transition.

Cyclin A and B functions in the early Drosophila embryo

Development ◽  
1999 ◽  
Vol 126 (23) ◽  
pp. 5505-5513 ◽  
Author(s):  
L.A. Stiffler ◽  
J.Y. Ji ◽  
S. Trautmann ◽  
C. Trusty ◽  
G. Schubiger
Keyword(s):  
Cyclin A ◽  
Cyclin B ◽  
Drosophila Embryo ◽  
Late Prophase ◽  
Early Drosophila Embryo ◽  
Nuclear Events ◽  
The Relationship ◽  
Maternal Gene ◽  
Drosophila Embryos

In eukaryotes, mitotic cyclins localize differently in the cell and regulate different aspects of the cell cycle. We investigated the relationship between subcellular localization of cyclins A and B and their functions in syncytial preblastoderm Drosophila embryos. During early embryonic cycles, cyclin A was always concentrated in the nucleus and present at a low level in the cytoplasm. Cyclin B was predominantly cytoplasmic, and localized within nuclei only during late prophase. Also, cyclin B colocalized with metaphase but not anaphase spindle microtubules. We changed maternal gene doses of cyclins A and B to test their functions in preblastoderm embryos. We observed that increasing doses of cyclin B increased cyclin B-Cdk1 activity, which correlated with shorter microtubules and slower microtubule-dependent nuclear movements. This provides in vivo evidence that cyclin B-Cdk1 regulates microtubule dynamics. In addition, the overall duration of the early nuclear cycles was affected by cyclin A but not cyclin B levels. Taken together, our observations support the hypothesis that cyclin B regulates cytoskeletal changes while cyclin A regulates the nuclear cycles. Varying the relative levels of cyclins A and B uncoupled the cytoskeletal and nuclear events, so we speculate that a balance of cyclins is necessary for proper coordination during these embryonic cycles.

scholarly journals Cyclin A triggers Mitosis either via Greatwall or Cyclin B

2018 ◽  
Author(s):  
Nadia Hégarat ◽  
Adrijana Crncec ◽  
Maria F. Suarez Peredoa Rodri-guez ◽  
Fabio Echegaray Iturra ◽  
Yan Gu ◽  
...  
Keyword(s):  
Cyclin A ◽  
Cyclin B ◽  
Mitotic Progression ◽  
Nuclear Envelope Breakdown ◽  
Distinct Subset ◽  
Initial Activation ◽  
Greatwall Kinase ◽  
G2 Phase ◽  
Higher Eukaryotes ◽  
Complete Cell

AbstractTwo mitotic Cyclins, A and B, exist in higher eukaryotes, but their specialised functions in mitosis are poorly understood. Using degron tags we analyse how acute depletion of these proteins affects mitosis. Loss of Cyclin A in G2-phase prevents the initial activation of Cdk1. Cells lacking Cyclin B can enter mitosis and phosphorylate most mitotic proteins, because of parallel PP2A:B55 phos-phatase inactivation by Greatwall kinase. The final barrier to mitotic establishment corresponds to nuclear envelope breakdown that requires a decisive shift in the balance of Cdk1 and PP2A:B55 activity. Beyond this point Cyclin B/Cdk1 is essential to phosphorylate a distinct subset mitotic Cdk1 substrates that are essential to complete cell division. Our results identify how Cyclin A, B and Greatwall coordinate mitotic progression by increasing levels of Cdk1-dependent substrate phos-phorylation.

scholarly journals Activation of the Xenopus cyclin degradation machinery by full-length cyclin A

1996 ◽  
Vol 109 (5) ◽  
pp. 1071-1079 ◽  
Author(s):  
C. Jones ◽  
C. Smythe
Keyword(s):  
Protein Synthesis ◽  
Dna Replication ◽  
Kinase Activity ◽  
Cyclin A ◽  
Cell Types ◽  
Cyclin B1 ◽  
Full Length ◽  
Cyclin B ◽  
Cdc2 Kinase ◽  
Nuclear Envelope Breakdown

The entry into mitosis is dependent on the activation of mitotic forms of cdc2 kinase. In many cell types, cyclin A-associated kinase activity peaks just prior to that of cyclin B, although the precise role of cyclin A-associated kinase in the entry into mitosis is still unclear. Previous work has suggested that while cyclin B is capable of triggering cyclin destruction in Xenopus cell-free systems, cyclin A-associated kinase is not able to support this function. Here we have expressed a full-length human cyclin A in Escherichia coli and purified the protein to homogeneity by virtue of an N-terminal histidine tag. We have found that when added to Xenopus cell-free extracts free of cyclin B and incapable of protein synthesis, the temporal pattern of cyclin A-associated cdc2 kinase activity showed distinct differences that were dependent on the concentration of cyclin A added. When cyclin A was added to a concentration that generated levels of cdc2 kinase activity capable of inducing nuclear envelope breakdown, the histone H1 kinase activity profile was bi-phasic, consisting of an activation phase followed by an inactivation phase. Inactivation was found to be due to cyclin destruction, which was prevented by mos protein. Cyclin destruction was followed by nuclear reassembly and an additional round of DNA replication, indicating that there is no protein synthesis requirement for DNA replication in this embryonic system. It has been suggested that the evolutionary recruitment of cyclin A into an S phase function may have necessitated the loss of an original mitotic ability to activate the cyclin destruction pathway. The results presented here indicate that cyclin A has not lost the ability to activate its own destruction and that cyclin A-mediated activation of the cyclin destruction pathway permitted destruction of cyclin B1 as well as cyclin A, indicating that there are not distinct cyclin A and cyclin B destruction pathways. Thus the ordered progression of the cell cycle requires the careful titration of cyclin. A concentration in order to avoid activation of the cyclin destruction pathway before sufficient active cyclin B/cdc2 kinase has accumulated.

Laser scanning confocal microscopic analysis of cytoskeletal and nuclear reorganization in live Drosophila embryos

1993 ◽  
Vol 51 ◽  
pp. 174-175
Author(s):  
William Theurkauf
Keyword(s):  
Laser Scanning ◽  
Microscopic Analysis ◽  
Large Cell ◽  
Early Embryo ◽  
Drosophila Embryo ◽  
Cortical Actin ◽  
Nuclear Reorganization ◽  
Cytoskeletal Elements ◽  
Microtubule Structure ◽  
Drosophila Embryos

Cell division in eucaryotes depends on coordinated changes in nuclear and cytoskeletal components. In Drosophila melanogaster embryos, the first 13 nuclear divisions occur without cytokinesis. During the final four divisions, nuclei divide in a uniform monolayer at the surface of the embryo. These surface divisions are accompanied by dramatic changes in cortical actin and microtubule structure (Karr and Alberts, 1986), and inhibitor studies indicate that these changes are essential to orderly mitosis (Zalokar and Erk, 1976). Because the early embryo is syncytial, fluorescent probes introduced by microinjection are incorporated in structures associated with all of the nuclei in the blastoderm. In addition, the nuclei divide synchronously every 10 to 20 min. These characteristics make the syncytial blastoderm embryo an excellent system for the analysis of mitotic reorganization of both nuclear and cytoskeletal elements. However, the Drosophila embryo is a large cell, and resolution of cytoskeletal filaments and nuclear structure is hampered by out-of focus signal.

Mutations affecting the cytoskeletal organization of syncytial Drosophila embryos

Development ◽  
1993 ◽  
Vol 118 (4) ◽  
pp. 1245-1254 ◽  
Author(s):  
W. Sullivan ◽  
P. Fogarty ◽  
W. Theurkauf
Keyword(s):  
Mitotic Division ◽  
P Element ◽  
Drosophila Embryo ◽  
Nuclear Movement ◽  
Microtubule Organization ◽  
Cytoskeletal Organization ◽  
New Genes ◽  
Movement Organization ◽  
Cytoplasmic Organization ◽  
Drosophila Embryos

Cytoplasmic organization, nuclear migration, and nuclear division in the early syncytial Drosophila embryo are all modulated by the cytoskeleton. In an attempt to identify genes involved in cytoskeletal functions, we have examined a collection of maternal-effect lethal mutations induced by single P-element transposition for those that cause defects in nuclear movement, organization, or morphology during the syncytial embryonic divisions. We describe three mutations, grapes, scrambled, and nuclear-fallout, which define three previously uncharacterized genes. Females homozygous for these mutations produce embryos that exhibit extensive mitotic division errors only after the nuclei migrate to the surface. Analysis of the microfilament and microtubule organization in embryos derived from these newly identified mutations reveal disruptions in the cortical cytoskeleton. Each of the three mutations disrupts the actin-based pseudocleavage furrows and the cellularization furrows in a distinct fashion. In addition to identifying new genes involved in cytoskeletal organization, these mutations provide insights into cytoskeletal function during early Drosophila embryogenesis.

The Polo-like kinase Plx1 is a component of the MPF amplification loop at the G2/M-phase transition of the cell cycle in Xenopus eggs

1998 ◽  
Vol 111 (12) ◽  
pp. 1751-1757 ◽  
Author(s):  
A. Abrieu ◽  
T. Brassac ◽  
S. Galas ◽  
D. Fisher ◽  
J.C. Labbe ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Cycle ◽  
Cyclin A ◽  
Cyclin B ◽  
Cdc2 Kinase ◽  
C Terminus ◽  
M Phase ◽  
Egg Extracts ◽  
Amplification Loop

We have investigated whether Plx1, a kinase recently shown to phosphorylate cdc25c in vitro, is required for activation of cdc25c at the G2/M-phase transition of the cell cycle in Xenopus. Using immunodepletion or the mere addition of an antibody against the C terminus of Plx1, which suppressed its activation (not its activity) at G2/M, we show that Plx1 activity is required for activation of cyclin B-cdc2 kinase in both interphase egg extracts receiving recombinant cyclin B, and cycling extracts that spontaneously oscillate between interphase and mitosis. Furthermore, a positive feedback loop allows cyclin B-cdc2 kinase to activate Plx1 at the G2/M-phase transition. In contrast, activation of cyclin A-cdc2 kinase does not require Plx1 activity, and cyclin A-cdc2 kinase fails to activate Plx1 and its consequence, cdc25c activation in cycling extracts.

Maize meiotic spindles assemble around chromatin and do not require paired chromosomes

1998 ◽  
Vol 111 (23) ◽  
pp. 3507-3515 ◽  
Author(s):  
A. Chan ◽  
W.Z. Cande
Keyword(s):  
Nuclear Envelope ◽  
Higher Plants ◽  
Metaphase Plate ◽  
Meiotic Spindle ◽  
Wild Type ◽  
Homologous Chromosomes ◽  
Nuclear Envelope Breakdown ◽  
Meiotic Spindles ◽  
Meiotic Mutations ◽  
Bipolar Spindles

To understand how the meiotic spindle is formed and maintained in higher plants, we studied the organization of microtubule arrays in wild-type maize meiocytes and three maize meiotic mutants, desynaptic1 (dsy1), desynaptic2 (dsy2), and absence of first division (afd). All three meiotic mutations have abnormal chromosome pairing and produce univalents by diakinesis. Using these three mutants, we investigated how the absence of paired homologous chromosomes affects the assembly and maintenance of the meiotic spindle. Before nuclear envelope breakdown, in wild-type meiocytes, there were no bipolar microtubule arrays. Instead, these structures formed after nuclear envelope breakdown and were associated with the chromosomes. The presence of univalent chromosomes in dsy1, dsy2, and afd meiocytes and of unpaired sister chromatids in the afd meiocytes did not affect the formation of bipolar spindles. However, alignment of chromosomes on the metaphase plate and subsequent anaphase chromosome segregation were perturbed. We propose a model for spindle formation in maize meiocytes in which microtubules initially appear around the chromosomes during prometaphase and then the microtubules self-organize. However, this process does not require paired kinetochores to establish spindle bipolarity.

Positioning adjacent pair-rule stripes in the posterior Drosophila embryo

Development ◽  
1994 ◽  
Vol 120 (10) ◽  
pp. 2945-2955 ◽  
Author(s):  
J.A. Langeland ◽  
S.F. Attai ◽  
K. Vorwerk ◽  
S.B. Carroll
Keyword(s):  
Binding Sites ◽  
Drosophila Embryo ◽  
Regulatory Sequences ◽  
Posterior Border ◽  
Adjacent Pair ◽  
Gap Gene ◽  
Competitive Mechanism ◽  
Pair Rule ◽  
Drosophila Embryos ◽  
Do So

We present a genetic and molecular analysis of two hairy (h) pair-rule stripes in order to determine how gradients of gap proteins position adjacent stripes of gene expression in the posterior of Drosophila embryos. We have delimited regulatory sequences critical for the expression of h stripes 5 and 6 to 302 bp and 526 bp fragments, respectively, and assayed the expression of stripe-specific reporter constructs in several gap mutant backgrounds. We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border. Interestingly, Kruppel (Kr) limits the anterior expression limits of both stripes and is the only gap gene to do so, indicating that stripes 5 and 6 may be coordinately positioned by the Kr repressor. In contrast to these very similar cases of spatial repression, stripes 5 and 6 appear to be activated by different mechanisms. Stripe 6 is critically dependent upon knirps (kni) for activation, while stripe 5 likely requires a combination of activating proteins (gap and non-gap). To begin a mechanistic understanding of stripe formation, we locate binding sites for the Kr protein in both stripe enhancers. The stripe 6 enhancer contains higher affinity Kr-binding sites than the stripe 5 enhancer, which may allow for the two stripes to be repressed at different Kr protein concentration thresholds. We also demonstrate that the kni activator binds to the stripe 6 enhancer and present evidence for a competitive mechanism of Kr repression of stripe 6.

scholarly journals SGK phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation at the meiotic G2/M transition

2019 ◽  
Vol 218 (11) ◽  
pp. 3597-3611 ◽  
Author(s):  
Daisaku Hiraoka ◽  
Enako Hosoda ◽  
Kazuyoshi Chiba ◽  
Takeo Kishimoto
Keyword(s):  
Somatic Cell ◽  
Cyclin A ◽  
Pi3k Pathway ◽  
Cyclin B ◽  
Hormonal Stimulation ◽  
Oocyte Meiosis ◽  
M Phase ◽  
Mitosis And Meiosis ◽  
Cell Mitosis ◽  
Stimulation Of

The kinase cyclin B–Cdk1 complex is a master regulator of M-phase in both mitosis and meiosis. At the G2/M transition, cyclin B–Cdk1 activation is initiated by a trigger that reverses the balance of activities between Cdc25 and Wee1/Myt1 and is further accelerated by autoregulatory loops. In somatic cell mitosis, this trigger was recently proposed to be the cyclin A–Cdk1/Plk1 axis. However, in the oocyte meiotic G2/M transition, in which hormonal stimuli induce cyclin B–Cdk1 activation, cyclin A–Cdk1 is nonessential and hence the trigger remains elusive. Here, we show that SGK directly phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation in starfish oocytes. Upon hormonal stimulation of the meiotic G2/M transition, SGK is activated by cooperation between the Gβγ-PI3K pathway and an unidentified pathway downstream of Gβγ, called the atypical Gβγ pathway. These findings identify the trigger in oocyte meiosis and provide insights into the role and activation of SGK.

scholarly journals Both cyclin A delta 60 and B delta 97 are stable and arrest cells in M-phase, but only cyclin B delta 97 turns on cyclin destruction.

1991 ◽  
Vol 10 (13) ◽  
pp. 4311-4320 ◽  
Author(s):  
F.C. Luca ◽  
E.K. Shibuya ◽  
C.E. Dohrmann ◽  
J.V. Ruderman
Keyword(s):  
Cyclin A ◽  
Cyclin B ◽  
M Phase
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