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Dev Biol 2008 Dec 01;3241:108-21. doi: 10.1016/j.ydbio.2008.09.009.
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Hindbrain-derived Wnt and Fgf signals cooperate to specify the otic placode in Xenopus.

Park BY , Saint-Jeannet JP .

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.

PubMed ID: 18831968
PMC ID: PMC2605947
Article link: Dev Biol
Grant support: [+]

Species referenced: Xenopus
Genes referenced: ctnnb1 egr2 fgf3 fgf8 nptx2 otx2 pax8 sox9 wnt1 wnt8a
Morpholinos: ctnnb1 MO1 fgf3 MO1 fgf8 MO1 wnt1 MO1 wnt8a MO1

Article Images: [+] show captions
References [+] :
Ahrens, Tissues and signals involved in the induction of placodal Six1 expression in Xenopus laevis. 2005, Pubmed, Xenbase