Wnt signaling and transcriptional control of siamois in Xenopus embryos

Melinda J. Fan, Wolfram Grüning, Gerd Walz, Sergei Y. Sokol

Research output: Contribution to journalArticlepeer-review

84 Scopus citations


The Wnt-inducible homeobox gene Siamois is expressed in Xenopus embryos before gastrulation and is necessary for formation of the Spemann organizer. Here we show that 5'-flanking sequences of the Siamois coding region can specifically activate a heterologous reporter gene in dorsovegetal cells, thus mimicking Siamois's endogenous expression. A 245-bp DNA fragment is sufficient for activation by both Wnts and endogenous inducers. A dominant negative form of Xenopus T cell-specific factor 3 (XTCF-3) inhibited promoter activity, indicating that T cell-specific factor (TCF)/lymphocyte enhancer binding factor 1 (LEF-1) signaling is necessary for regulation of Siamois. Mutagenesis of two individual TCF sites in the -245 promoter revealed that the proximal, but not distal, site is necessary for dorsovegetal activation. These observations suggest that Siamois is directly regulated by TCFs during dorsoventral axis determination. Further deletion analysis identified a positive regulatory region that is required for dorsal activation, but not for Wnt inducibility, of the promoter. We also present evidence for autoregulation of Siamois transcription. Furthermore, the Siamois promoter was activated by Wut signaling in 293T tissue culture cells, demonstrating thai regulation of the promoter is functionally conserved.

Original languageEnglish
Pages (from-to)5626-5631
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number10
StatePublished - 12 May 1998
Externally publishedYes


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