Fig. 4. Summary of CNS transformations caused by the loss of Cdx function. Summary diagrams showing the hindbrain and spinal cord transformation seen in wild-type (A,C) and cdx1a/cdx4-deficient (B,D) zebrafish embryos with (A,B) or without (C,D) an intact retinoic acid signaling pathway. Diagrams of 20-somite, stage-matched embryos are based on Figs 2 and 3. Rhombomeres are color coded according to their identity; the location of the third somite, the normal position of the hindbrain-spinal cord transition in wild-type embryos, is indicated by an arrowhead. Dorsal views, anterior to the left. Scale bar: 100 µm.