News archives


OCTOBER - DECEMBER 17

JULY - SEPTEMBER 17

APRIL - JUNE 17

JANUARY - MARCH 17

OCTOBER - DECEMBER 16

JULY - SEPTEMBER 16

APRIL - JUNE 16

JANUARY - MARCH 16

OCTOBER - DECEMBER 15

JULY - SEPTEMBER 15

APRIL - JUNE 15

JANUARY - MARCH 15

OCTOBER - DECEMBER 14

JULY - SEPTEMBER 14

APRIL - JUNE 14

JANUARY - MARCH 14

OCTOBER - DECEMBER 13

JULY - SEPTEMBER 13

APRIL - JUNE 13

JANUARY - MARCH 13

OCTOBER - DECEMBER 12

JULY - SEPTEMBER 12

APRIL - JUNE 12

JANUARY - MARCH 12

OCTOBER - DECEMBER 11

JULY - SEPTEMBER 11

APRIL - JUNE 11

JANUARY - MARCH 11

OCTOBER - DECEMBER 10

JULY - SEPTEMBER 10

APRIL - JUNE 10

JANUARY - MARCH 10

OCTOBER - DECEMBER 09

JULY - SEPTEMBER 09

APRIL - JUNE 09

JANUARY - MARCH 09

OCTOBER - DECEMBER 08

JULY - SEPTEMBER 08

APRIL - JUNE 08

JANUARY - MARCH 08

OCTOBER - DECEMBER 07

JULY - SEPTEMBER 07

APRIL - JUNE 07

JANUARY - MARCH 07

 
  current news   Press   selected story    
     
  10 January 2013  
 

Congratulations to IMCB’s recent PhD graduate

 
 




PhD Graduate: Wei Theng POH
                        under the A*STAR-Dundee Partnership Programme (ADP)

Thesis Title: The role of Cdc7 and cyclin-dependent kinases in DNA replication and S phase

Abstract

In the cell cycle, DNA replication takes place during S phase to faithfully duplicate a cell’s genetic material. In eukaryotes, S phase onset involves the initiation of numerous licensed replication origins across the genome. Initiation of DNA replication from licensed origins requires two protein kinases: cyclin-dependent kinase (Cdk) and Cdc7. Although S phase-Cdk activity has been intensively studied, relatively little is known about how Cdc7 is regulated. PHA-767491, a small molecule inhibitor of Cdc7, was first characterised and used to dissect the role of Cdc7 in regulating S phase progression in Xenopus egg extracts. Cdc7 is not rate limiting for the progression of the replication timing programme once its essential function has been executed, unlike Cdk whose activity is required throughout S phase. Protein Phosphatase 1 (PP1) was identified as a modulator of Cdc7 activity in egg extracts. It rapidly reverses Cdc7-dependent phosphorylation of chromatin-bound Mcm4 and likely functionally lowers Cdc7 activity during an etoposide-induced checkpoint response. This provides a novel mechanism for regulating Cdc7 by counteracting its activity on essential replication substrates in the event of replicative stress. In the second part of this work, S phase entry and progression was examined in mouse embryonic fibroblasts lacking both Cdk1 and Cdk2, which provide S phase-Cdk activity in metazoans. Contrary to expectations, Cdk1/Cdk2 double knockout cells can enter S phase in the absence of detectable S phase-Cdk activity. S phase progression, however, was inefficient. Cdc6 and cyclin E1 proteins were found to accumulate in high levels in these cells, although the exact function(s) and mechanism(s) for these observations remain to be elucidated.

 

 
 


 
 


Figure legend

a) The cell cycle is driven by the successive activation of cyclin-dependent kinases (Cdk). In eukaryotes, S phase onset requires the activity of two protein kinases: cyclin-dependent kinase and Cdc7 (Dbf4/Drf1-dependent kinase).

b) Cdk1/Cdk2 double knockout cells can enter S phase. However, S phase progression is inefficient.

c) Events occurring during S phase are shown at an early-replicating (left) and a late-replicating origin (right): Mcm2-7 at both origins are phosphorylated by Cdc7, which in turn is reversed by PP1. Cdk substrates for initiation are recruited preferentially to the early-replicating origin. Checkpoint kinases activated in response to etoposide promote PP1 chromatin association to reverse Cdc7 activity and independently inhibit Cdk activity.

Supervisors:
Dr. Philipp Kaldis
(IMCB, A*STAR)
Professor J. Julian Blow
(Centre for Gene Regulation and Expression, University of Dundee)

For more information on Philipp KALDIS's Lab, please click here.

For more information on J. Julian BLOW's Lab, please click here.