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Nuclear exclusion of Smad2 is a mechanism leading to loss of competence

Oliver H Grimm1, J B Gurdon

  • 1Wellcome Trust/Cancer Research UK Institute, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QR, UK.

Nature Cell Biology
|June 18, 2002
PubMed

Insights

Controlling developmental signalling duration is crucial. In Xenopus embryos, loss of mesodermal competence is linked to Smad2 nuclear accumulation, a process regulated by phosphorylation.

Area of Science:

  • Developmental Biology
  • Cell Signalling
  • Molecular Biology

Background:

  • Precise control of signalling duration is vital in embryonic development to prevent inappropriate cell fate changes.
  • Transforming growth factor-beta (TGF-beta) signalling plays a key role in mesoderm formation.
  • Loss of competence, the ability of cells to respond to signals, is a critical developmental process.

Purpose of the Study:

  • To investigate the mechanisms underlying the loss of competence during mesoderm formation in Xenopus laevis embryos.
  • To understand how transforming growth factor-beta (TGF-beta)-like signalling is temporally regulated.

Main Methods:

  • Analysis of mesodermal gene expression in response to activin (a TGF-beta-like molecule).
  • Studying the nuclear localization of Smad2, a key intracellular signal transducer.
  • Utilizing site-directed mutagenesis of Smad2 phosphorylation sites and overexpression studies.

Main Results:

  • Gastrula ectoderm initially responds to activin by expressing mesodermal genes but rapidly loses this competence.
  • Loss of mesodermal competence correlates with the failure of Smad2 to accumulate in the nucleus.
  • Mutating Smad2 phosphorylation sites prevents its nuclear accumulation and prolongs gene responsiveness.

Conclusions:

  • Restricting Smad2's subcellular localization is a key mechanism for the rapid loss of mesodermal competence.
  • This rapid regulation of signal transducer localization ensures an orderly sequence of developmental inductions.

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