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Quantitative Analysis of Protein Expression to Study Lineage Specification in Mouse Preimplantation Embryos
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Deficiency in the response to DNA double-strand breaks in mouse early preimplantation embryos

Masashi Yukawa1, Shoji Oda, Hiroshi Mitani

  • 1Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan.

Biochemical and Biophysical Research Communications
|May 15, 2007
PubMed

Insights

Early mouse embryos exhibit hypersensitivity to DNA damage due to insufficient G2/M checkpoint and DNA repair mechanisms. Specifically, phosphorylated H2AX (gamma-H2AX) is notably absent in one- and two-cell embryos following gamma-irradiation.

Area of Science:

  • Developmental Biology
  • Molecular Biology
  • Radiation Biology

Background:

  • DNA double-strand breaks (DSBs) are critical DNA lesions induced by environmental factors like ionizing radiation.
  • Cell cycle checkpoints, involving phosphorylated H2AX (gamma-H2AX), are essential for halting cell division until DSBs are repaired.
  • Mouse preimplantation embryos are particularly sensitive to ionizing radiation, with zygotes arresting at the G2 phase.

Purpose of the Study:

  • To investigate the G2/M checkpoint and DNA repair responses to DNA damage in mouse preimplantation embryos.
  • To elucidate the mechanisms underlying the hypersensitivity of early mouse embryos to gamma-irradiation.

Main Methods:

  • Induction of DSBs in mouse embryos (one- to two-cell stages) using gamma-irradiation.
  • Analysis of cell cycle progression, cleavage delay, and developmental arrest using microscopy.
  • Immunocytochemical detection of phosphorylated H2AX (gamma-H2AX), phosphorylated ATM, and DNA-PKcs.

Main Results:

  • Gamma-irradiated one- and two-cell embryos showed delayed cleavage and developmental arrest before the blastocyst stage.
  • Phosphorylated H2AX (gamma-H2AX) was not detected in one- and two-cell embryos post-irradiation, but was present in later stages.
  • While ATM and DNA-PKcs were detected, their presence did not correlate with gamma-H2AX formation in early-stage embryos.

Conclusions:

  • The G2/M checkpoint and DNA repair mechanisms are functionally deficient in one- and two-cell mouse embryos, explaining their radiosensitivity.
  • The absence of gamma-H2AX in early-stage embryos suggests regulation by factors other than ATM and DNA-PKcs.
  • These findings highlight critical developmental windows of DNA damage response vulnerability in mammalian embryogenesis.

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