FGF7 and FGF10 directly induce the apical ectodermal ridge in chick embryos.
During vertebrate limb development, the apical ectodermal ridge (AER) plays a vital role in both limb initiation and distal outgrowth of the limb bud. In the early chick embryo the prelimb bud mesoderm induces the AER in the overlying ectoderm. However, the direct inducer of the AER remains unknown. Here we report that FGF7 and FGF10, members of the fibroblast growth factor family, are the best candidates for the direct inducer of the AER. FGF7 induces an ectopic AER in the flank ectoderm of the chick embryo in a different manner from FGF1, -2, and -4 and activates the expression of Fgf8, an AER marker gene, in a cultured flank ectoderm without the mesoderm. Remarkably, FGF7 and FGF10 applied in the back induced an ectopic AER in the dorsal median ectoderm. Our results suggest that FGF7 and FGF10 directly induce the AER in the ectoderm both of the flank and of the dorsal midline and that these two regions have the competence for AER induction. Formation of the AER of the dorsal median ectoderm in the chick embryo is likely to appear as a vestige of the dorsal fin of the ancestors.
Yonei-Tamura
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S
Biological Institute, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan. tam@biology.tohoku.ac.jp
Endo
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T
Yajima
H
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Ohuchi
H
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Ide
H
H
Tamura
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K
D000818:Animals; D002642:Chick Embryo; D004475:Ectoderm / Q000187:drug effects; D005121:Extremities / Q000196:embryology*; D051526:Fibroblast Growth Factor 10; D051523:Fibroblast Growth Factor 7; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000378:metabolism / Q000494:pharmacology*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D006133:Growth Substances / Q000494:pharmacology*; D017403:In Situ Hybridization; D012333:RNA, Messenger / Q000378:metabolism; D016378:Tissue Transplantation
D051526:Fibroblast Growth Factor 10; D006133:Growth Substances; D012333:RNA, Messenger; D051523:Fibroblast Growth Factor 7; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors