Specification of epibranchial placodes in zebrafish.
In all vertebrates, the neurogenic placodes are transient ectodermal thickenings that give rise to sensory neurons of the cranial ganglia. Epibranchial (EB) placodes generate neurons of the distal facial, glossopharyngeal and vagal ganglia, which convey sensation from the viscera, including pharyngeal endoderm structures, to the CNS. Recent studies have implicated signals from pharyngeal endoderm in the initiation of neurogenesis from EB placodes; however, the signals underlying the formation of placodes are unknown. Here, we show that zebrafish embryos mutant for fgf3 and fgf8 do not express early EB placode markers, including foxi1 and pax2a. Mosaic analysis demonstrates that placodal cells must directly receive Fgf signals during a specific crucial period of development. Transplantation experiments and mutant analysis reveal that cephalic mesoderm is the source of Fgf signals. Finally, both Fgf3 and Fgf8 are sufficient to induce foxi1-positive placodal precursors in wild-type as well as Fgf3-plus Fgf8-depleted embryos. We propose a model in which mesoderm-derived Fgf3 and Fgf8 signals establish both the EB placodes and the development of the pharyngeal endoderm, the subsequent interaction of which promotes neurogenesis. The coordinated interplay between craniofacial tissues would thus assure proper spatial and temporal interactions in the shaping of the vertebrate head.
Nechiporuk
Alexei
A
Department of Biological Structure, University of Washington, Seattle, WA 98195-7420, USA.
Linbo
Tor
T
Poss
Kenneth D
KD
Raible
David W
DW
D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001934:Branchial Region / Q000196:embryology* / Q000378:metabolism; D051518:Fibroblast Growth Factor 3 / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008959:Models, Neurological; D009154:Mutation; D020319:Oligodeoxyribonucleotides, Antisense / Q000235:genetics; D051762:PAX2 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
D051518:Fibroblast Growth Factor 3; D051858:Forkhead Transcription Factors; D020319:Oligodeoxyribonucleotides, Antisense; D051762:PAX2 Transcription Factor; D029961:Zebrafish Proteins; C489200:fgf3 protein, zebrafish; C517774:fgf8a protein, zebrafish; C472802:foxi1 protein, zebrafish; C497320:pax2a protein, zebrafish; D005346:Fibroblast Growth Factors