Hindbrain-derived Wnt and Fgf signals cooperate to specify the otic placode in Xenopus.
Induction of the otic placode, the rudiment of the inner ear, is believed to depend on signals derived from surrounding tissues, the head mesoderm and the prospective hindbrain. Here we report the first attempt to define the specific contribution of the neuroectoderm to this inductive process in Xenopus. To this end we tested the ability of segments of the neural plate (NP), isolated from different axial levels, to induce the otic marker Pax8 when recombined with blastula stage animal caps. We found that one single domain of the NP, corresponding to the prospective anterior hindbrain, had Pax8-inducing activity in this assay. Surprisingly, more than half of these recombinants formed otic vesicle-like structures. Lineage tracing experiments indicate that these vesicle-like structures are entirely derived from the animal cap and express several pan-otic markers. Pax8 activation in these recombinants requires active Fgf and canonical Wnt signaling, as interference with either pathway blocks Pax8 induction. Furthermore, we demonstrate that Fgf and canonical Wnt signaling cooperate to activate Pax8 expression in isolated animal caps. We propose that in the absence of mesoderm cues the combined activity of hindbrain-derived Wnt and Fgf signals specifies the otic placode in Xenopus, and promotes its morphogenesis into an otocyst.
Park
Byung-Yong
BY
Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104, USA.
Saint-Jeannet
Jean-Pierre
JP
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D007758:Ear, Inner / Q000196:embryology* / Q000378:metabolism; D004625:Embryo, Nonmammalian; D004627:Embryonic Induction; D005346:Fibroblast Growth Factors / Q000502:physiology*; D008648:Mesoderm / Q000166:cytology / Q000502:physiology; D009024:Morphogenesis / Q000502:physiology; D054258:Neural Plate / Q000196:embryology; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000502:physiology; D012249:Rhombencephalon / Q000378:metabolism*; D015398:Signal Transduction; D051153:Wnt Proteins / Q000502:physiology*; D014981:Xenopus / Q000196:embryology* / Q000378:metabolism; D029867:Xenopus Proteins / Q000502:physiology
D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors; C499500:Pax8 protein, Xenopus; D051153:Wnt Proteins; D029867:Xenopus Proteins; D005346:Fibroblast Growth Factors