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Fig. 3. Initiation of mkp3 expression by maternal ß-catenin. (A)
mkp3 is not expressed maternally but is initiated at the high stage
at 3.3 hpf, as determined by RT-PCR; ß-actin and Histone H4 serve as
loading controls. (B) Activity of the MAPK pathway in the early zebrafish
embryo as visualized by staining with anti-phospho MAPK, is detected from the
oblong stage onwards. (C,D) Both fgf3 and fgf8 are first
expressed in the prospective organizer region at the oblong stage. (E,F)
Immunohistochemical staining of MAPK-p shows it to be localized to the
prospective organizer side of the oblong stage embryo (arrow in F), but not at
512 cell stage (E). (G-J) Expression of XFD does not inhibit the initiation of
mkp3 expression at the high stage (G,H), but is effective at the dome
stage (I,J). (K-N) High stage. mkp3 expression is expanded by
activating the ß-catenin pathway through LiCl treatment (compare L with
K), and by ectopic expression of an activated form of ß-catenin (N),
whereas expression of a dominant-negative version of TCF3 suppresses the
induction of mkp3 (M). (O-R) Sphere stage. The initial expression of
mkp3 is abolished in the ich mutant (compare O with P). (Q)
Activation of mkp3 by FGF genes is independent of ß-catenin, as
ectopic expression of fgf8 in ich mutants can still activate
mkp3. (R) Expression of mkp3 is unaffected in boz
mutants, an organizer-defective mutant downstream of the maternal
ß-catenin pathway. Arrowhead in N indicates ectopic mkp3
expression.
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