G1 checkpoint establishment in vivo during embryonic liver development.

Xiao Wang,Chung Lo,Kwok Chan,Ronnie Tp Poon,Randy Yc Poon,Xiaoyan Ming,Vincent Ch Lui,Chris Norbury

doi:10.1186/1471-213x-14-23

Abstract

BackgroundThe DNA damage-mediated cell cycle checkpoint is an essential mechanism in the DNA damage response (DDR). During embryonic development, the characteristics of cell cycle and DNA damage checkpoint evolve from an extremely short G1 cell phase and lacking G1 checkpoint to lengthening G1 phase and the establishment of the G1 checkpoint. However, the regulatory mechanisms governing these transitions are not well understood. In this study, pregnant mice were exposed to ionizing radiation (IR) to induce DNA damage at different embryonic stages; the kinetics and mechanisms of the establishment of DNA damage-mediated G1 checkpoint in embryonic liver were investigated.ResultsWe found that the G2 cell cycle arrest was the first response to DNA damage in early developmental stages. Starting at E13.5/E15.5, IR mediated inhibition of the G1 to S phase transition became evident. Concomitantly, IR induced the robust expression of p21 and suppressed Cdk2/cyclin E activity, which might involve in the initiation of G1 checkpoint. The established G1 cell cycle checkpoint, in combination with an enhanced DNA repair capacity at E15.5, displayed biologically protective effects of repairing DNA double-strand breaks (DSBs) and reducing apoptosis in the short term as well as reducing chromosome deletion and breakage in the long term.ConclusionOur study is the first to demonstrate the establishment of the DNA damage-mediated G1 cell cycle checkpoint in liver cells during embryogenesis and its in vivo biological effects during embryonic liver development.

Highlights

The DNA damage-mediated cell cycle checkpoint is an essential mechanism in the DNA damage response (DDR)
G-banding and spectral karyotyping (SKY) analysis Pregnant mice were exposed to 0.5 Gy ionizing radiation (IR) at embryonic stages 11.5 and 15.5
The G1 checkpoint only appeared at the stage (E13.5/15.5) where IR induced high expression of p21, Figure 5 Low dose IR at E11.5 and E15.5 and its effects on chromosome abnormality in adult liver cells. (A & B) Pregnant mice were exposed to 0.5 Gy IR at embryonic stages 11.5 or 15.5, and the liver cells were isolated from the mice at adulthood (7 weeks old) and cultured

Summary

Introduction

The DNA damage-mediated cell cycle checkpoint is an essential mechanism in the DNA damage response (DDR). The DDR is a complex network that involves the control of cell cycle arrest, the activation of DNA repair machinery, the the DNA damage-mediated checkpoint is critical in DDR signaling, many of the regulatory components that govern this signaling pathway, in cells at the embryonic stage and during developmental processes, are not known. The cell cycle and the DNA damage checkpoint change over time, from an extremely short G1 cell cycle to maintain pluripotency, to lengthening the G1 phase during differentiation [4,5,6,7]; from lacking a G1 checkpoint [8,9,10] to the establishment of a G1 cell cycle arrest Both murine and human ES cells, as well as human embryonic carcinoma (EC) cells, are defective in the G1 checkpoint after DNA damage [8,9,10]. Differentiated EC cells show an increased G1 cell population but lack a G1 checkpoint, even though DDR protein activation appears to be normal [9]

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Results

Discussion

Conclusion