Hindbrain expansion and spinal cord reduction or loss in zebrafish embryos lacking Cdx function. Distribution of hindbrain and spinal cord cell populations in wild-type embryos (A-E) and in cdx4-(F-J), cdx1a- (K-O) and cdx1a/cdx4-(P-T) deficient embryos. (A,F,K,P) Distribution of isl1:GFP-positive vagal motor neurons (green) in relation to adjacent somites (s, red) at 50 hours post-fertilization (hpf). (B,G,L,Q) Distribution of RMO44-immunopositive reticulospinal neurons at 50 hpf. The region occupied by T reticular interneurons is indicated with a bracket. r2 Mauthner neurons are also indicated (Ma). (C,H,M,R) Distribution of spinal motor neurons visualized with an anti-acetylated Tubulin antibody (n, green) in relation to adjacent somites (s, red) at 72 hpf. Axons of the first spinal motor neuron pool are indicated with arrowheads. (D,I,N,S) Distribution of olig2-expressing spinal cord oligodendrocytes (purple) with respect to krx20-expressing r3 and r5 (red) at the 20-somite stage (19 hpf). Distances between r5 and the rostral-most olig2-positive cells are indicated by arrowheads. Forebrain was removed for mounting purposes except in S, where it was retained to show that the in situ hybridization worked in these embryos. (E,J,O,T) Distribution of spinal cord isl1-positive (purple) motor neurons and Rohon-Beard sensory neurons as compared with krx20 expression in r3 and r5 (red) at 20 hpf. The position of r5 (large arrowheads), the most-rostral spinal motor neurons (arrows) and Rohon-Beard sensory neurons (small arrowhead) are indicated. For each condition, a minimum of 40 embryos from five independent experiments were analyzed. A,B,F,G,K,L,Q, dorsal view; K, oblique view; remaining embryos, lateral view. Scale bars: 100 µm for each column, except in K, for A,F,K.
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