ANALYSIS OF IRRADIATION-INDUCED REPAIR FOCI IN MOUSE EMBRYONIC STEM CELLS
I.I. Suvorova,1,2,* V.A. Pospelov 1,2
1Institute of Cytology RAS, St. Petersburg, and 2 St.-Petersburg State University;
* e-mail: irsuvorov@yandex.ru
Somatic cells in response to DNA damage activate two important protective mechanisms: G1 checkpoint control and a program for recognizing and repairing
DNA defects (DDR signaling). Both mechanisms are triggered by the activation of common sensor kinases ATM and ATR, which in turn phosphorylate downstream targets.
Mouse embryonic stem cells (mESCs) lack of G1 checkpoint and undergo only temporary G2 delay after DNA damage.We have analyzed the ability
of mESCs to detect DNA damage and to form repair foci after irradiation. We showed irradiation-induced activation of ATM and ATR is followed by formation of
γH2AX foci colocalized with DNA repair proteins Rad51, DNA-PK and adapter protein 53BP1. Furthermore, we checked contribution of ATM/Chk2 and ATR/Chk1
cascades to cell cycle control and viability of mESCs after DNA da-mage. Inhibition of ATR/Chk1 cascade leads to accumulation of G1 phase cells, whereas
perturbation of ATM/Chk2 activity causes no such effect. Moreover, inhibition of ATR/Chk1 activity, but not ATM/Chk2, substantially augments the killing effect of ionizing
radiation on mESCs. In summary, our results indicate that mESCs are capable of recognizing DNA damage and forming repair foci, but their DDR signaling it seems to be distinct
from somatic cells and tightly connected with maintaining of pluripotency and self-renewal.
Key words: mousee mbryonic stem cells, DNA damage, ATM, ATR, γH2AX, DNA repair
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