The transcription factor foxB mediates temporal loss of cellular competence for notochord induction in ascidian embryos

Hidehiko Hashimoto, Atsushi Enomoto, Gaku Kumano, Hiroki Nishida

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


In embryos of the ascidian Halocynthia roretzi, the competence of isolated presumptive notochord blastomeres to respond to fibroblast growth factor (FGF) for induction of the primary notochord decays by 1 hour after cleavage from the 32- to 64-cell stage. This study analyzes the molecular mechanisms responsible for this loss of competence and provides evidence for a novel mechanism. A forkhead family transcription factor, FoxB, plays a role in competence decay by preventing the induction of notochord-specific Brachyury (Bra) gene expression by the FGF/MAPK signaling pathway. Unlike the mechanisms reported previously in other animals, no component in the FGF signal transduction cascade appeared to be lost or inactivated at the time of competence loss. Knockdown of FoxB functions allowed the isolated cells to retain their competence for a longer period, and to respond to FGF with expression of Bra beyond the stage at which competence was normally lost. FoxB acts as a transcription repressor by directly binding to the cis-regulatory element of the Bra gene. Our results suggest that FoxB prevents ectopic induction of the notochord fate within the cells that assume a default nerve cord fate, after the stage when notochord induction has been completed. The merit of this system is that embryos can use the same FGF signaling cascade again for another purpose in the same cell lineage at later stages by keeping the signaling cascade itself available. Temporally and spatially regulated FoxB expression in nerve cord cells was promoted by the ZicN transcription factor and absence of FGF/MAPK signaling.

Original languageEnglish
Pages (from-to)2591-2600
Number of pages10
Issue number12
Publication statusPublished - 2011 Jun 15
Externally publishedYes


  • Ascidians
  • Competence
  • Embryonic induction
  • FGF
  • FoxB
  • Nerve cord
  • Notochord

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology


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