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Fig. 5. Autonomous requirement of Cdx factors in the zebrafish CNS for hindbrain
and spinal cord specification. Expression analysis of the r5/6 marker
val (red staining) in clones of cdx1a/cdx4-deficient cells
transplanted into wild-type hosts (A-E) or wild-type cells transplanted
into cdx1a/cdx4-deficient host embryos (F-J) (transplanted
cells in green). (A,B) cdx1a/cdx4-deficient cells can incorporate
into the wild-type host CNS at all axial levels. The boxed regions are shown
at higher magnification in C-E. (C) cdx1a/cdx4-deficient cells are
evenly distributed in hindbrain and spinal cord regions of the CNS, only
expressing val when located in the r5/6 territory (white arrowhead
compared with black arrowhead). (D,E) cdx1a/cdx4-deficient cells
located in the caudal spinal cord tend to form clusters of cells that express
val (n=8). Surrounding wild-type cells do not express this
marker. Isolated cells also express this gene (arrowheads). (F,H)
cdx1a/cdx4-deficient embryos show ectopic val expression in
the posterior CNS despite the presence of wild-type cells in the paraxial
mesoderm (n=2). (G) Incorporation of wild-type cells throughout the
CNS of cdx1a/cdx4-deficient hosts. The boxed regions are shown at
higher magnification in I and J. (I) Uniform distribution of wild-type cells
in the hindbrain and surrounding regions of cdx1a/cdx4-deficient host
embryos. Cells located within the r5/6 region express the marker val
(white arrowheads compared with black arrowheads). (J) In the posterior CNS,
most wild-type cells segregate in clusters that fail to express val
(black arrowhead). When in isolation, wild-type cells express val
(white arrowheads, n=5). Confocal 3 µm sections of dorsal
flat-mounted embryos, anterior to the left. Scale bars: in G, 100 µm for
A,B,F,G; in J, 100 µm for C-E,H-J.
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