Sustained interactive Wnt and FGF signaling is required to maintain isthmic identity.
Fibroblast growth factor 8 (FGF8) is expressed at the mid-hindbrain boundary and is an important signal emanating from the isthmic organizer. Wnt1 is expressed in the caudal midbrain juxtaposed to Fgf8 expression and has been implicated in its regulation. In this study, we examine the requirement for continuous Wnt signaling in the maintenance of Fgf8 expression at the isthmus. We demonstrate that prior to HH10, ongoing Wnt signaling is required to maintain the normal pattern of isthmic Fgf8 expression in ovo. Similarly, in explant assays, sustained Wnt signaling is essential to maintain Fgf8 expression in rhombomere 1. The mechanism by which Wnt signaling regulates isthmic Fgf8 expression is likely to be a maintenance response rather than an inductive effect. Finally, we show that Wnt maintenance of Fgf8 expression is dependent upon positive feedback by FGF signaling itself, and that rhombomere 1 does not receive instructive cues from the posterior hindbrain. In summary, these findings establish that a sustained reciprocal interaction between Wnt and FGF signaling is essential to maintain isthmic identity.
Canning
Claire A
CA
Centre for Molecular Medicine, 61 Biopolis Drive, Singapore 138673, Singapore. claire@cmm.a-star.edu.sg
Lee
Lily
L
Irving
Carol
C
Mason
Ivor
I
Jones
C Michael
CM
D000818:Animals; D002642:Chick Embryo; D051524:Fibroblast Growth Factor 8 / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008156:Luciferases; D008636:Mesencephalon / Q000196:embryology*; D012249:Rhombencephalon / Q000196:embryology*; D015398:Signal Transduction / Q000502:physiology*; D051155:Wnt1 Protein / Q000378:metabolism*
D051155:Wnt1 Protein; D051524:Fibroblast Growth Factor 8; D008156:Luciferases