Limits...
A mathematical model of mitotic exit in budding yeast: the role of Polo kinase.

Hancioglu B, Tyson JJ - PLoS ONE (2012)

Bottom Line: Entry into mitosis requires phosphorylation of many proteins targeted by mitotic Cdk, and exit from mitosis requires proteolysis of mitotic cyclins and dephosphorylation of their targeted proteins.The model captures the dynamics of this network in wild-type yeast cells and 110 mutant strains.The model clarifies the roles of Polo-like kinase (Cdc5) in the Cdc14 early anaphase release pathway and in the G-protein regulated mitotic exit network.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America. barish@rice.edu

ABSTRACT
Cell cycle progression in eukaryotes is regulated by periodic activation and inactivation of a family of cyclin-dependent kinases (Cdk's). Entry into mitosis requires phosphorylation of many proteins targeted by mitotic Cdk, and exit from mitosis requires proteolysis of mitotic cyclins and dephosphorylation of their targeted proteins. Mitotic exit in budding yeast is known to involve the interplay of mitotic kinases (Cdk and Polo kinases) and phosphatases (Cdc55/PP2A and Cdc14), as well as the action of the anaphase promoting complex (APC) in degrading specific proteins in anaphase and telophase. To understand the intricacies of this mechanism, we propose a mathematical model for the molecular events during mitotic exit in budding yeast. The model captures the dynamics of this network in wild-type yeast cells and 110 mutant strains. The model clarifies the roles of Polo-like kinase (Cdc5) in the Cdc14 early anaphase release pathway and in the G-protein regulated mitotic exit network.

Show MeSH

Related in: MedlinePlus

Mitotic progression of cells containing an ESP1 mutation.(A) In metaphase arrested cells at 23°C, overexpression of Esp1 induces Cdc14 release; however, cells do not exit from mitosis, and Cdh1 stays inactive. Cells are presimulated in metaphase arrest by Cdc20 deprivation, then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078), with the rate of Clb2 degradation at 23°C assumed to be half its basal value (kd,b2″ = 1.5). (B) Cdc14 release is dependent upon Cdc5 in nocodazole-arrested cells; when CDC5 is deleted, overexpressed Esp1 can no longer induce Cdc14 release. Cells are presimulated in metaphase arrest by nocodazole (N = 1) with no synthesis of Cdc5 (ks,polo = 0) and no initial Cdc5 proteins. Then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078). (C) When CLB5 is deleted, overexpressed Esp1 can induce ME. Reduction in Cdk activity by Clb5 deprivation allows for ME by increasing the phosphatase-to-kinase ratio, leading to activation of Cdh1. Simulation was done as in panel A, except that the synthesis rate of Clb2 was set to 80% of its basal value (ks,b2 = 0.024). (D) When Esp1 is inactive, Cdc14 cannot be released and the cell cannot exit from mitosis. It is assumed that separase is absent in esp1-2td mutant cells (ks,esp = 0). During the 120 min pre-simulation of Cdc20 block in metaphase, the rate of degradation of Esp1 was increased 10-fold, and the activity of Esp1 was lowered 10-fold. (effesp = 0.1, kd,esp = 0.028,). At t = 0, Cdc20 synthesis was induced, as usual.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3285609&req=5

pone-0030810-g009: Mitotic progression of cells containing an ESP1 mutation.(A) In metaphase arrested cells at 23°C, overexpression of Esp1 induces Cdc14 release; however, cells do not exit from mitosis, and Cdh1 stays inactive. Cells are presimulated in metaphase arrest by Cdc20 deprivation, then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078), with the rate of Clb2 degradation at 23°C assumed to be half its basal value (kd,b2″ = 1.5). (B) Cdc14 release is dependent upon Cdc5 in nocodazole-arrested cells; when CDC5 is deleted, overexpressed Esp1 can no longer induce Cdc14 release. Cells are presimulated in metaphase arrest by nocodazole (N = 1) with no synthesis of Cdc5 (ks,polo = 0) and no initial Cdc5 proteins. Then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078). (C) When CLB5 is deleted, overexpressed Esp1 can induce ME. Reduction in Cdk activity by Clb5 deprivation allows for ME by increasing the phosphatase-to-kinase ratio, leading to activation of Cdh1. Simulation was done as in panel A, except that the synthesis rate of Clb2 was set to 80% of its basal value (ks,b2 = 0.024). (D) When Esp1 is inactive, Cdc14 cannot be released and the cell cannot exit from mitosis. It is assumed that separase is absent in esp1-2td mutant cells (ks,esp = 0). During the 120 min pre-simulation of Cdc20 block in metaphase, the rate of degradation of Esp1 was increased 10-fold, and the activity of Esp1 was lowered 10-fold. (effesp = 0.1, kd,esp = 0.028,). At t = 0, Cdc20 synthesis was induced, as usual.

Mentions: Overexpressed separase is sufficient to trigger Cdc14 release (simulated in Figure 9A) in cells arrested in metaphase by depletion of Cdc20 [17], [56], [57]. These authors used the attenuated GALS promoter to overexpress Esp1, which allows viability and ME at 30°C. Cdc14 release in overexpressed Esp1 depends on Cdc5 activity (simulated in Figure 9B). GALS-ESP1 cells do not exit from mitosis at 23°C as judged by cytokinesis and entry into the next cell cycle. Clb2 remains high because Cdc20 is inactive, and the Cdc14/Clb2 ratio may stay lower than the threshold to activate Cdh1. We are not exactly sure how temperature changes the phenotype. Temperature may alter the specific activity of Clb2/Cdk1 towards Cdh1, resulting in partially active Cdh1 at 23°C, which is unable to counteract all mitotic Cdk activity. In fact, when Cdk activity is reduced by deleting CLB5 (simulated in Figure 9C) in GAL-ESP1 cells, ME occurs in the absence of active Cdc20, as judged by cytokinesis and subsequent cell cycle [56]. In the simulation of GAL-ESP1 at 23°C, we reduce by one-half the degradation rate of Clb2, resulting in higher Clb2, which prevents cells from exiting mitosis.


A mathematical model of mitotic exit in budding yeast: the role of Polo kinase.

Hancioglu B, Tyson JJ - PLoS ONE (2012)

Mitotic progression of cells containing an ESP1 mutation.(A) In metaphase arrested cells at 23°C, overexpression of Esp1 induces Cdc14 release; however, cells do not exit from mitosis, and Cdh1 stays inactive. Cells are presimulated in metaphase arrest by Cdc20 deprivation, then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078), with the rate of Clb2 degradation at 23°C assumed to be half its basal value (kd,b2″ = 1.5). (B) Cdc14 release is dependent upon Cdc5 in nocodazole-arrested cells; when CDC5 is deleted, overexpressed Esp1 can no longer induce Cdc14 release. Cells are presimulated in metaphase arrest by nocodazole (N = 1) with no synthesis of Cdc5 (ks,polo = 0) and no initial Cdc5 proteins. Then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078). (C) When CLB5 is deleted, overexpressed Esp1 can induce ME. Reduction in Cdk activity by Clb5 deprivation allows for ME by increasing the phosphatase-to-kinase ratio, leading to activation of Cdh1. Simulation was done as in panel A, except that the synthesis rate of Clb2 was set to 80% of its basal value (ks,b2 = 0.024). (D) When Esp1 is inactive, Cdc14 cannot be released and the cell cannot exit from mitosis. It is assumed that separase is absent in esp1-2td mutant cells (ks,esp = 0). During the 120 min pre-simulation of Cdc20 block in metaphase, the rate of degradation of Esp1 was increased 10-fold, and the activity of Esp1 was lowered 10-fold. (effesp = 0.1, kd,esp = 0.028,). At t = 0, Cdc20 synthesis was induced, as usual.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3285609&req=5

pone-0030810-g009: Mitotic progression of cells containing an ESP1 mutation.(A) In metaphase arrested cells at 23°C, overexpression of Esp1 induces Cdc14 release; however, cells do not exit from mitosis, and Cdh1 stays inactive. Cells are presimulated in metaphase arrest by Cdc20 deprivation, then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078), with the rate of Clb2 degradation at 23°C assumed to be half its basal value (kd,b2″ = 1.5). (B) Cdc14 release is dependent upon Cdc5 in nocodazole-arrested cells; when CDC5 is deleted, overexpressed Esp1 can no longer induce Cdc14 release. Cells are presimulated in metaphase arrest by nocodazole (N = 1) with no synthesis of Cdc5 (ks,polo = 0) and no initial Cdc5 proteins. Then at t = 0 the rate of synthesis of Esp1 is increased 60-fold (ks,esp = 0.078). (C) When CLB5 is deleted, overexpressed Esp1 can induce ME. Reduction in Cdk activity by Clb5 deprivation allows for ME by increasing the phosphatase-to-kinase ratio, leading to activation of Cdh1. Simulation was done as in panel A, except that the synthesis rate of Clb2 was set to 80% of its basal value (ks,b2 = 0.024). (D) When Esp1 is inactive, Cdc14 cannot be released and the cell cannot exit from mitosis. It is assumed that separase is absent in esp1-2td mutant cells (ks,esp = 0). During the 120 min pre-simulation of Cdc20 block in metaphase, the rate of degradation of Esp1 was increased 10-fold, and the activity of Esp1 was lowered 10-fold. (effesp = 0.1, kd,esp = 0.028,). At t = 0, Cdc20 synthesis was induced, as usual.
Mentions: Overexpressed separase is sufficient to trigger Cdc14 release (simulated in Figure 9A) in cells arrested in metaphase by depletion of Cdc20 [17], [56], [57]. These authors used the attenuated GALS promoter to overexpress Esp1, which allows viability and ME at 30°C. Cdc14 release in overexpressed Esp1 depends on Cdc5 activity (simulated in Figure 9B). GALS-ESP1 cells do not exit from mitosis at 23°C as judged by cytokinesis and entry into the next cell cycle. Clb2 remains high because Cdc20 is inactive, and the Cdc14/Clb2 ratio may stay lower than the threshold to activate Cdh1. We are not exactly sure how temperature changes the phenotype. Temperature may alter the specific activity of Clb2/Cdk1 towards Cdh1, resulting in partially active Cdh1 at 23°C, which is unable to counteract all mitotic Cdk activity. In fact, when Cdk activity is reduced by deleting CLB5 (simulated in Figure 9C) in GAL-ESP1 cells, ME occurs in the absence of active Cdc20, as judged by cytokinesis and subsequent cell cycle [56]. In the simulation of GAL-ESP1 at 23°C, we reduce by one-half the degradation rate of Clb2, resulting in higher Clb2, which prevents cells from exiting mitosis.

Bottom Line: Entry into mitosis requires phosphorylation of many proteins targeted by mitotic Cdk, and exit from mitosis requires proteolysis of mitotic cyclins and dephosphorylation of their targeted proteins.The model captures the dynamics of this network in wild-type yeast cells and 110 mutant strains.The model clarifies the roles of Polo-like kinase (Cdc5) in the Cdc14 early anaphase release pathway and in the G-protein regulated mitotic exit network.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America. barish@rice.edu

ABSTRACT
Cell cycle progression in eukaryotes is regulated by periodic activation and inactivation of a family of cyclin-dependent kinases (Cdk's). Entry into mitosis requires phosphorylation of many proteins targeted by mitotic Cdk, and exit from mitosis requires proteolysis of mitotic cyclins and dephosphorylation of their targeted proteins. Mitotic exit in budding yeast is known to involve the interplay of mitotic kinases (Cdk and Polo kinases) and phosphatases (Cdc55/PP2A and Cdc14), as well as the action of the anaphase promoting complex (APC) in degrading specific proteins in anaphase and telophase. To understand the intricacies of this mechanism, we propose a mathematical model for the molecular events during mitotic exit in budding yeast. The model captures the dynamics of this network in wild-type yeast cells and 110 mutant strains. The model clarifies the roles of Polo-like kinase (Cdc5) in the Cdc14 early anaphase release pathway and in the G-protein regulated mitotic exit network.

Show MeSH
Related in: MedlinePlus