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Fig. 4 ngn1 expression is regulated by Delta. (A,B) Embryos at the 3- somite stage co-injected with X-Delta-1 and β-gal RNA into one blastomere at the 2-cell stage. Embryos were stained for β-gal activity (turquoise) before in situ hybridisation with ngn1 antisense probe (purple). ngn1 expression (arrows) is strongly reduced or completely abolished in the injected side (turquoise). (C,D) Embryos at the 3- somite stage co-injected with the antimorphic X-Delta-1Stu and bgal RNA into one blastomere at the 2-cell stage. Expression of X-Delta- 1Stu results in up-regulation of ngn1 expression (purple, arrows) in the injected side (turquoise) in comparison to the uninjected control side. (A,C) Whole mounts in dorsal views onto the neural plate at the level of posterior hindbrain/anterior trunk; anterior up. B and D show flat preparation of different embryos from those in A and C, respectively; anterior up. Abbreviations: in, injected side; co, uninjected control side. Scale bar, 60 μm in A,C and 25 μm in B, D.