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Fig. 5. Ubiquitous activation of FGF signaling inhibits A7.6 group gene
expression. (A) The constitutively active form of FGFR
(torso-FGFR) is expressed under the ZicL enhancer.
Brachyury is ectopically expressed in A-line neural blastomeres,
consistent with ectopic activation of the MAPK pathway. Some ectopic
Ci-Bra expression is also observed in the muscle and mesenchyme.
(B) Ci-Bra expression in wild-type Ciona embryo.
(C-F'') Embryos injected at the 1-cell stage with
torso-FGFR mRNA. Expression of A7.6 group genes is modestly reduced.
To demonstrate the variable degree of reduction, embryos with no expression
(C,D,F), weak expression (C',D',E,F') and wild-type
expression levels (C'',D'',E',F'') are shown together
with the number of embryos affected. In addition to A7.6, there are three
instead of two Delta-like-positive blastomere cells (E'')
consistently observed in injected embryos [in wild-type embryos,
Delta-like expression in A7.8 is highly variable and only seen in
20% of the embryos (Hudson and Yasuo,
2006), suggesting that MAPK usually activates Delta-like
in these cells].
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