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Fig. 1. Expression of the neuronal differentiation marker N-tubulin, in stage 16 neural plate (A), stage 27 (B,C,D) and stage 31 (E,F) tadpole Xenopus embryos. (A-D) Embryos analysed for N-tubulin expression shown in whole mount; (E,F) N-tubulin staining in sections. (A,C) Hybridised with En-2, which is a marker for the midbrain-hindbrain boundary and is shown with an arrow. (A-C) Frontal views; (D) side view of the head. Neuronal differentiation takes place at the neural plate stage and is confined to three stripes on either side of the dorsal midline. Note that the expression of N-tubulin is not detected anterior to En-2 at the neural plate stage. In contrast, N-tubulin expression can be detected in the forebrain, starting at later tadpole stages (stage 27) when it is localised to the epiphysis (black arrow), ventral postoptic diencephalon (white arrow) and olfactory placodes (white arrowhead; see also Hartenstein, 1993). At stage 31, N-tubulin expression is abundant posteriorly (F) as well as anteriorly (E). (E) A section through the forebrain (fb), including olfactory placodes (op); (F) a section through the hindbrain (hb) at the level of the otocysts (ot). |
