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#organizer genes

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frog development

Organizer genes include:

Spemann organizer transcriptome characterized by secreted antagonists and homeodomain transcription factors. Chordin and noggin are defining BMP antagonists co-expressed specifically in dorsal lip cells and required for dorsalization and neuralization. Goosecoid, FoxA4a and Lim1 are organizer transcription factors, Cerberus is additional antagonist. VegT and Vg1 are maternal vegetal determinants upstream of organizer induction, BMP and Activin are ventral signals antagonized by organizer, Xbra marks general mesoderm. Therefore classic organizer genes include chordin and noggin representing BMP

Ref: Balinsky, Introduction to Embryology: Organizer specific genes - chordin, noggin, goosecoid expression.

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frog development

Siamois and Twin are activated by:

Siamois and Twin are immediate early zygotic genes expressed in Nieuwkoop center downstream of Wnt pathway. Beta-catenin stabilized dorsally enters nucleus displacing Groucho corepressor from Tcf3, forming beta-catenin-Tcf3/Lef activation complex binding specific TCF sites in siamois and twin promoters. Their transcription suppressed by dominant-negative Tcf3 or beta-catenin depletion, superinduced by LiCl or Wnt mRNA. Noggin, Activin or BMP act later or downstream, so primary activator complex responsible for their initiation is beta-catenin-Tcf3 complex, initiating organizer cascade. This il

Ref: Gilbert, Developmental Biology 12th ed., Chapter 10: Siamois and Twin activation by beta-catenin-Tcf3.

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