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Fig. 6. Foxi1 mediates Fgf response in the EB placodes. foxi1 mutant
embryos and their wild-type sibs were processed for in-situ hybridization with
phox2a and phox2b (A), pea3 (B) and modified
Richardson's stain (C). All whole-mount panels show lateral views. Anterior is
left. (A) When compared with their wild-type sibs (left), phox2a
expression is absent in the facial, glossopharyngeal and small vagal ganglia,
while it is significantly reduced in the large vagal ganglion (arrow) in the
foxi1 mutants (right). By contrast, phox2b is still
expressed in all EB ganglia, albeit at lower levels (arrows). (B) Optical
sections through the facial placode (presumptive facial placode is outlined by
a dashed circle). Note significant reduction of pea3 expression in
the facial placode of the foxi1 mutant embryo (right), while other
pea3 expression domains are unaffected. (C) Histological analysis of
the transverse sections through the head region revealed the presence of
columnar epithelium (marked by arrowheads; compare with the ectoderm
immediately proximal to the facial placode, left panel), indicating presence
of placodes in the foxi1 mutants. Scale bars: 50 µm. mhb,
midhindbrain boundary; nc, chondrogenic neural crest of the first and second
arches; o, otic vesicle. Other abbreviations are as in
Fig. 1.
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