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Fig. 6. Otx2 confers the ability to activate FoxE3 in response to Notch
signaling. (A-C'') Expression of Otx2 in the anterior
ectoderm detected by in situ hybridization. At the neural plate stages,
Otx2 is expressed in the anterior ectoderm including the presumptive
lens-fields, which are circled with white dotted lines in A. Arrows in B
indicate broad expression in the ectoderm that overlies the optic vesicles
(ov) and surrounds the cement gland primordium (cg). Arrows in C indicate the
border of ectodermal Otx2 expression. White lines in C indicate the
planes of transverse sections shown in C' and C''. Arrows in
C' and C'', respectively, indicate expression in the PLE overlying
the optic vesicle and in the ectoderm overlying the forebrain. (D-H)
Notch-Otx2 combination activates FoxE3 in the trunk ectoderm.
Xenopus embryos injected with the mRNAs indicated in each panel were
induced with Dex, and then subjected to lacZ staining and in situ
hybridization with FoxE3 probe. Ectopic FoxE3 expression was
not detected in embryos injected with mRNA encoding GR-Su(H)VP16 (1000 pg)
(D), Otx2-GR (250 pg) (E), or NICD (1000 pg) (G), whereas it was detected in
embryos injected with both GR-Su(H)VP16 (750 pg) and Otx2-GR (250 pg) (F), or
both NICD (750 pg) and Otx2-GR (250 pg) (H). Arrowheads in F and H indicate
ectopic FoxE3 expression. Arrows indicate endogenous FoxE3
expression in the PLE. The white line in F indicates the plane of the
transverse section shown in the inset. Black arrowheads in the inset indicate
the overlap of FoxE3 expression and nuclear lacZ staining in
the ectodermal cells, and white arrowheads indicate cells in the underlying
mesoderm layer showing nuclear lacZ staining but no FoxE3
expression. (I,J) The injected and uninjected sides,
respectively, of an embryo injected with mRNA encoding GR-Otx2-En (250 pg),
induced with Dex from stage 18, and then subjected to lacZ staining
and in situ hybridization with FoxE3 probe at stage 22. Arrows
indicate the PLE. (K) Transgenic experiments using Otx-Su(H) reporter
constructs. Numbers of embryos with GFP expression in the PLE and the total
number of normally (or near normally) developing embryos injected with the
constructs shown on the left are indicated on the right-hand side with
percentages of the GFP-positive cases. Gray and red boxes indicate Otx- and
Su(H)-binding motifs, respectively, in the constructs, and crosses indicate
base-substitution mutations introduced there. (L,L') A
representative transgenic embryo generated with Otx-Su(H)-βGFP. Black and
white arrows indicate GFP expression in the eye and spinal cord, respectively.
The white line indicates the plane of the transverse eye section shown in
L'. Black and white arrowheads indicate GFP expression in the PLE and
optic vesicle, respectively.
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