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#Twin

2 public questions tagged with this topic.

frog development

Organizer induction requires cooperation between Siamois, Twin, and:

Formation of functional Spemann organizer requires integration of two vegetal signals: dorsal Wnt-beta-catenin via Siamois/Twin and Nodal-related TGF-beta via Smad2. Nodal ligands Xnr1,2,5 activated by VegT phosphorylate Smad2 which enters nucleus and cooperates with Siamois/Twin on enhancers of goosecoid, chordin and Cerberus. Chromatin immunoprecipitation shows Smad2/Siamois co-binding. Either pathway alone insufficient; blocking Smad2 with Cerberus-S or Siamois with dominant-negative abolishes organizer. Therefore cooperation between Siamois, Twin and Smad2 creates robust organizer inductio

Ref: Gilbert, Developmental Biology 12th ed., Chapter 10: Organizer induction by Siamois, Twin and Smad2 cooperation.

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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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