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.