The translational repressor 4E-BP mediates hypoxia-induced defects in myotome cells

Area of Science:

• Developmental Biology
• Molecular Biology
• Cellular Biology

Background:

• Oxygen availability critically influences cell growth, proliferation, differentiation, and survival.
• The molecular mechanisms by which embryonic cells maintain viability under hypoxia are not well understood.

Purpose of the Study:

• To investigate the effects of hypoxia on Xenopus embryogenesis.
• To elucidate the molecular mechanisms underlying cellular responses to hypoxia, particularly concerning muscle development.

Main Methods:

• Xenopus embryos were exposed to hypoxic conditions.
• Analysis of developmental delay, cell apoptosis, somitogenesis, mitotic cell counts, and muscle-specific protein accumulation.
• Investigation of MyoD and MRF4 transcription factor expression.
• Assessment of Akt phosphorylation and 4E-binding protein (4E-BP) levels.
• Pharmacological inhibition of PI3-kinase and mTOR.
• Overexpression of a non-phosphorylatable 4E-BP mutant.

Main Results:

• Hypoxia induced significant developmental delay and apoptosis in Xenopus embryos.
• Hypoxia affected mitotic cell numbers and muscle protein accumulation in somites but not somitogenesis or key transcription factors (MyoD, MRF4).
• Hypoxia decreased Akt phosphorylation and increased 4E-BP, which associated with eIF4E. PI3-kinase or mTOR inhibition mimicked this 4E-BP accumulation.
• Overexpression of non-phosphorylatable 4E-BP recapitulated hypoxia-induced defects in mitotic cells and muscle protein accumulation.

Conclusions:

• Hypoxia triggers developmental defects in Xenopus embryos, impacting muscle development.
• The translational repressor 4E-BP is a crucial mediator of hypoxia's effects, promoting cap-independent translation over cap-dependent translation.
• These findings highlight 4E-BP's central role in cellular responses to hypoxia and muscle development.