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First published online 20 October 2004
doi: 10.1242/dev.01449

Development 131, 5613-5626 (2004)
Published by The Company of Biologists 2004
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Negative regulation of Smad2 by PIASy is required for proper Xenopus mesoderm formation

Maki Daniels1, Kazuya Shimizu2,*, Aaron M. Zorn2,{dagger} and Shin-ichi Ohnuma1,{ddagger}

1 Department of Oncology, The Hutchison/MRC Research Centre, University of Cambridge, Hills Road, Cambridge CB2 2XZ, UK
2 Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK

{ddagger} Author for correspondence (e-mail: so218{at}cam.ac.uk)

Accepted 10 September 2004

Mesoderm induction and patterning are primarily regulated by the concentration of locally expressed morphogens such as members of the TGFß superfamily. Smad2 functions as a transcription factor to regulate expression of mesodermal genes downstream of such morphogens. We have identified Xenopus PIASy (XPIASy), a member of the PIAS family, by yeast two-hybrid screening using Xenopus Smad2 (XSmad2) as a bait. During mesoderm induction, XPIASy is expressed in the animal half of embryos with a ventral high-dorsal low gradient at the marginal zone. XPIASy expression is positively and negatively regulated by activities of the XSmad2 and Wnt pathways, respectively. Interestingly, inhibition of XPIASy by morpholinos induces elongation of animal caps with induction of mesoderm genes even in the absence of their morphogen-mediated activation. In addition, their introduction into the ventral marginal zone results in a secondary axis formation. Gain-of-function analysis revealed that XPIASy inhibits mesoderm induction by specific and direct downregulation of XSmad2 transcriptional activity. These observations indicate that XPIASy functions as an essential negative regulator of the XSmad2 pathway to ensure proper mesoderm induction at the appropriate time and in the appropriate region, and suggest that both the initial step of morphogen-mediated activation of the XSmad2 pathway and regulation of the final downstream transcription step have crucial roles in mesoderm induction and patterning.

Key words: Smad2, Mesoderm induction, PIASy, Xenopus






© The Company of Biologists Ltd 2004