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Study of the DNA Damage Checkpoint using Xenopus Egg Extracts
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Study of the DNA Damage Checkpoint using Xenopus Egg Extracts

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The midblastula transition in Xenopus embryos activates multiple pathways to prevent apoptosis in response to DNA

C V Finkielstein1, A L Lewellyn, J L Maller

  • 1Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, CO 80262, USA.

Proceedings of the National Academy of Sciences of the United States of America
|February 7, 2001
PubMed

Insights

Xenopus embryos irradiated after the midblastula transition (MBT) activate Akt/protein kinase B, preventing apoptosis. This survival mechanism involves xBcl-2/xBax changes and G1/S arrest via p27(Xic1) to allow DNA repair.

Area of Science:

  • Developmental Biology
  • Cellular Biology
  • Molecular Biology

Background:

  • Apoptosis, or programmed cell death, is crucial for development and tissue homeostasis.
  • Xenopus embryos exhibit differential responses to DNA damage, with apoptosis occurring only after irradiation before the midblastula transition (MBT).

Purpose of the Study:

  • To investigate the molecular mechanisms underlying the differential apoptotic response to DNA damage in Xenopus embryos.
  • To identify the signaling pathways and regulatory proteins involved in preventing apoptosis after the MBT.

Main Methods:

  • Irradiation of Xenopus embryos at different developmental stages (pre- and post-MBT).
  • Analysis of protein activation (Akt/protein kinase B) and interactions (xBcl-2/xBax oligomerization and homodimerization).
  • Assessment of cell cycle progression and expression of cell cycle regulators (p27(Xic1), cyclin D/Cdk4, cyclin A/Cdk2).

Main Results:

  • Akt/protein kinase B activation and mediation of an antiapoptotic signal were observed exclusively in post-MBT embryos.
  • Post-MBT embryos showed increased xBcl-2/xBax oligomerization and decreased xBax homodimerization, conferring protection against apoptosis.
  • A survival mechanism involving G1 phase arrest was identified, mediated by increased p27(Xic1) expression, which inhibits cyclin D/Cdk4 and cyclin A/Cdk2 complexes.

Conclusions:

  • The DNA damage response is integrated into the midblastula transition (MBT) in Xenopus development.
  • Multiple molecular mechanisms cooperate to prevent apoptosis and promote cell survival in post-MBT Xenopus embryos, including Akt activation and cell cycle arrest for DNA repair.

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