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Fig. 7. Casanova activity is negatively regulated by the FGF-ERK signalling
pathway. Expression of sox17 (blue) in embryos at 30% epiboly
(A,B) or 50% epiboly (C-H). In C-E, FLDX used as lineage
marker was revealed by immunochemistry (red labelling). Embryos injected at
the 16-cell stage with RNA encoding Casanova-WT (A) or Casanova-S47A (B), each
at 10 ng/µl (see also Fig. S2 in the supplementary material). Mutation of
the putative phosphorylation site slightly increases Casanova activity.
Co-injection with fgf8 RNA at 10 ng/µl (C), CA-Ras RNA at 5
ng/µl (E) or ERK* RNA at 50 ng/µl (G) inhibits the ability of
Casanova-WT to induce sox17 (see Fig. S3 in the supplementary
material). However Casanova-S47A is insensitive to Fgf8 (D), CA-Ras (F) or
ERK* (H) overexpression. (I) RT-PCR analysis from three embryos
injected with cas RNA at 10 ng/µl alone or together with ERK2* RNA
at 50 ng/µl. (J) Differential activity of Casanova WT and Casanova
S47A, based on the percentage of embryos ectopically expressing sox17
(see Table 4). The activity of
exogenous Casanova-WT was compared with the activity of Casanova-S47A, treated
or not with MAPK, FGF inhibitors or an activated form of Erk2.
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