An early requirement for FGF signalling in the acquisition of neural cell fate in the chick embryo.
BACKGROUND
In Xenopus embryos, fibroblast growth factors (FGFs) and secreted inhibitors of bone morphogenetic protein (BMP)-mediated signalling have been implicated in neural induction. The precise roles, if any, that these factors play in neural induction in amniotes remains to be established.


RESULTS
To monitor the initial steps of neural induction in the chick embryo, we developed an in vitro assay of neural differentiation in epiblast cells. Using this assay, we found evidence that neural cell fate is specified in utero, before the generation of the primitive streak or Hensen's node. Early epiblast cells expressed both Bmp4 and Bmp7, but the expression of both genes was downregulated as cells acquired neural fate. During prestreak and gastrula stages, exposure of epiblast cells to BMP4 activity in vitro was sufficient to block the acquisition of neural fate and to promote the generation of epidermal cells. Fgf3 was also found to be expressed in the early epiblast, and ongoing FGF signalling in epiblast cells was required for acquisition of neural fate and for the suppression of Bmp4 and Bmp7 expression.


CONCLUSIONS
The onset of neural differentiation in the chick embryo occurs in utero, before the generation of Hensen's node. Fgf3, Bmp4 and Bmp7 are each expressed in prospective neural cells, and FGF signalling appears to be required for the repression of Bmp expression and for the acquisition of neural fate. Subsequent exposure of epiblast cells to BMPs, however, can prevent the generation of neural tissue and induce cells of epidermal character.
Wilson
S I
SI
Department of Microbiology, Umeå University, Umeå, S-901 87, Sweden.
Graziano
E
E
Harland
R
R
Jessell
T M
TM
Edlund
T
T
D000818:Animals; D015139:Blotting, Southern; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D002642:Chick Embryo; D046508:Culture Techniques; D015536:Down-Regulation; D051518:Fibroblast Growth Factor 3; D005346:Fibroblast Growth Factors / Q000494:pharmacology / Q000502:physiology*; D007150:Immunohistochemistry; D009417:Nerve Tissue / Q000196:embryology*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000494:pharmacology / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D029867:Xenopus Proteins
D019485:Bone Morphogenetic Proteins; C489198:FGF3 protein, Xenopus; D051518:Fibroblast Growth Factor 3; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D029867:Xenopus Proteins; D005346:Fibroblast Growth Factors