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Fig. 3. Effects of RA on Xlim-1 expression as visualized by wholemount
in situ hybridization. (A) Vegetal view of stage 10.25 embryo
(initial gastrula). Dorsal at the top. Xlim-1 expression in the dorsal
marginal zone is enhanced in the RA-treated embryo (RA; right
panel) compared to control (left). (B) Stage 11 (mid-gastrula).
Enhancement of Xlim-1 expression by RA is pronounced. (C) Lateral
view of stage 10.5/11 embryo. Dorsal to the right. In the untreated
embryo (left), dorsal mesoderm is stained but ventral mesoderm and
ectoderm are not; in the RA-treated embryo, ventral mesoderm and
dorsal ectoderm are also stained. The embryos were bisected for
photography. (D) Dorsal view of an RA-treated embryo at stage 12
(late gastrula). Forming notochord and anterior-lateral region are
stained, but presumptive somite region is not. (E) RA-treated embryo
at stage 14. Assignment of staining to neural plate (white arrow) and
lateral mesoderm (black arrow) was made on the basis of anterior
views (see panel G). The neural staining appears to be shifted
anteriorly compared to the control (Fig. 1B,D). (F) Lateral view at
stage 13. Anterior (An) is left and dorsal is up. The superficial
ectodermal layer is not obvious due to light printing. Filled triangles
indicate the anterior edge of staining. The stained region expands
more anteroventrally in the RA-treated embryo, and the
ventroposterior mesoderm is also stained. (G) Anterior views with
the plane of focus on the middle of embryo. Left, control embryo at
stage 13; right, RA-treated embryo at stage 12 (upper and lower parts
are from the same embryo at different exposures; embryo was
dissected for photography). The ectoderm region between the two
arrowheads is stained. (H) Dorsal view of stage 22 embryo; anterior
(An) is top. The pronephros (p) in the RA-treated embryo (right) is
enlarged compared with that in the control (left). (I) Ventral view of
RA-treated embryo; anterior is left. Xlim-1-positive tissue connects
left and right pronephroi at their anterior edge. (J) Stage 33/34. The
entire hindbrain-like region in the RA-treated embryo is stained
(left). In the control (right), staining is seen in the midbrain,
hindbrain, spinal cord, and more weakly, in the forebrain. Apparent
staining in the eyes is due to natural pigmentation. An, anterior; p,
pronephros; RA, retinoic acid-treated embryos.
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