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Fig. 6. Xiro1 is upstream of Notch signaling in the specification of the
neural crest. Embryos were injected with 1 ng HDGR (A) mRNA, and
co-injected with 1 ng Hairy2A (B) or 1 ng Su(H)ankGR (C)
mRNA. A second set of experiments was performed by injecting two-cell embryos
in one blastomere with 0.25 ng Su(H)DBMGR (D) mRNA, and co-injecting
1 ng Hairy2A (E) or 0.7 ng Xmsx1GR (F) mRNA. Finally, a
third set of experiments was performed by injecting one blastomere of a
two-cell embryo with 1 ng of NICDGR (G) mRNA, and co-injecting 0.7 ng
of dnXmsxGR (H). The embryos were treated with dexomethasone at stage
12, and the expression of Xslug was analyzed by in situ hybridization
between stage 17 and 19. The injected side was visualized by alkaline
phosphatase-mediated FITC inmunodetection and is indicated by an arrowhead.
(A) Xslug expression was inhibited by HDGR. (B) The
inhibition of Xiro1 activity was rescued by co-injection of
Hairy2A, reaching 89% recovery of Xslug expression
(n=56). (C) A similar reversion of Xiro1 inhibition was
obtained by activating Notch signaling, 93% rescue of Xslug
expression was observed (n=47). (D) Xslug expression was
inhibited by Su(H)DBMGR. (E) The inhibition of the Notch signaling
could be rescued by co-expression of Hairy2A (92% rescue;
n=43). (F) The effect of inhibiting Notch signaling could be rescued
by co-expression of Xmsx1 (97% rescue; n=39). (G) Expansion
of Xslug expression by injecting 1 ng NICDGR. (H) The effect
of NICDGR was rescued by blocking msx1 activity with
dnXmsxGR, (92% rescue; n=45), whereas the effect of
NICDGR was not rescued by the co-injection of GFP mRNA (I; 0% rescue;
n=25).
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