Abstract
Replication stress, a major cause of genome instability in cycling cells, is mainly prevented by the ATR‐dependent replication stress response pathway in somatic cells. However, the replication stress response pathway in embryonic stem cells (ESCs) may be different due to alterations in cell cycle phase length. The transcription factor MYBL2, which is implicated in cell cycle regulation, is expressed a hundred to a thousand‐fold more in ESCs compared with somatic cells. Here we show that MYBL2 activates ATM and suppresses replication stress in ESCs. Consequently, loss of MYBL2 or inhibition of ATM or Mre11 in ESCs results in replication fork slowing, increased fork stalling and elevated origin firing. Additionally, we demonstrate that inhibition of CDC7 activity rescues replication stress induced by MYBL2 loss and ATM inhibition, suggesting that uncontrolled new origin firing may underlie the replication stress phenotype resulting from loss/inhibition of MYBL2 and ATM. Overall, our study proposes that in addition to ATR, a MYBL2‐MRN‐ATM replication stress response pathway functions in ESCs to control DNA replication initiation and prevent genome instability.
SYNOPSIS
While in somatic cells the replication stress response is controlled by ATR, in ESCs it is coordinated by both ATM and ATR, and the stem cell‐specific transcription factor MYBL2 promotes the ATM‐dependent response.
Loss of MYBL2 compromises the replication stress response in ESCs and is epistatic with the loss of ATM or the inhibition of the nuclease activity of Mre11 and the kinase activity of CHK2.
Loss of MYBL2 compromises ATM activation, and the subsequent activation of Chk1‐dependent DNA damage checkpoint pathways.
Suppressing CDC7 (but not CDK) activity overcomes the replication stress observed in ESCs lacking MYBL2 or ATM activity.
While in somatic cells the replication stress response is controlled by ATR, in ESCs it is coordinated by both ATM and ATR, and the stem cell‐specific transcription factor MYBL2 promotes the ATM‐dependent response.