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FIG. 2. Xbra is essential for establishing and/or maintaining
animal/vegetal mesoderm polarity. (A) MAPK activation in
stage-11 embryos that had been injected in both the AB4 and CD4
blastomeres with 250 pg of Xbra-EnR RNA (total 1 ng). X-Gal
staining for the product of coinjected LacZ RNA (blue punctate
staining) marks the AB4 and CD4 descendants. MAPK activation
was detected with an antibody (diffuse purple staining). We conclude
that MAPK remains activated despite Xbra function being
blocked. (B) Close up of the marginal zone of the embryo shown in
(A). (Câ G) In situ hybridization for Xnr2 expression at stage 10.5.
The Spemann organizer is to the top for all embryos. (C) Control
(noninjected) embryo. (D) Embryo injected with 250 pg of Xbra-EnR
RNA into both the AB4 and CD4 blastomeres. Xnr2 expression was
expanded into the animal marginal zone of the embryo in comparison
to the control embryo (arrow). (E) Embryo injected with 1 ng of
Xbra RNA into both the CD4 blastomeres (total 2 ng of Xbra) at the
16-cell stage. Xnr2 expression was decreased in the descendents of
the injected blastomeres. LacZ staining (blue) indicates cells that
inherited the injected RNA. (F) Same treatment for the embryo as
in (E), except in this example Xnr2 expression is completely
eliminated in the injected cells. (G) Embryos were injected with
200 pg of XFD RNA into the AB3 and CD3 blastomeres (total 400
pg) on one side, and with 200 pg of XFD plus 1 ng of Xbra RNAs
into the other AB3 and CD3 (total 400 pg of XFD and 2 ng of Xbra)
blastomeres. Xnr2 expression is expanded into the animal marginal
zone on the side in which XFD RNA alone had been injected (left
side of the embryos in this picture, arrows), while the expression is
decreased or eliminated on the other side in which Xbra RNA had
been injected together with XFD RNA (right side of the embryos in
this picture, arrowheads). (H) Stage-11 embryo injected with 1 ng of
Xbra RNA into both the CD4 blastomeres (total 2 ng) at the 16-cell
stage. Immunostaining with an anti-activated MAPK antibody is
shown. Note that the gap between the domain of activated MAPK
(purple) and the blastopore lip still exists (arrow) (compare to A). |
