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Fig. 5. Conditional activation of ß-catenin in Pax2+
cells expands the otic placode at the expense of epidermis. (A)
Whole-mount in situ hybridization of otic and epidermal markers in
ß-catenin cAct embryos. Expression of the early otic markers Pax2,
Pax8 and Dlx5 are upregulated in ectoderm lateral to the otic
cup (arrows) at E8.75, while the epidermal marker Foxi2 is
downregulated at E9.5. The broken line indicates the outline of the
Foxi2- placodal domain. Markers of the mid-hindbrain
boundary (asterisk) are also expanded in cAct embryos. (B) Expansion of
the placodal domain without an increase in cell division in cAct embryos. The
ectoderm lateral to the otic cup is thickened from E8.75 in cAct embryos and
ß-catenin protein (red) is expressed strongly in the placodal epithelium.
By E9.5, the placodal epithelium fails to close in cAct embryos, forming a
grossly enlarged placode extending ventrally to the level of the pharynx, with
accumulated ß-catenin and ectopic invaginating regions (asterisk).
(C) The average number of pH3-positive cells is not significantly
increased in cAct placodal epithelium. Numbers are normalized to the length of
the apical surface of the placode (see Materials and methods). Scale bars: 100
µm.
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