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Fig. 7 Nodal-independent regulation of ntl is essential for tail formation. (A,B) Quantitative RT-PCR of ntl (red) and bra (blue) expression at 6 hpf. Absolute levels of wild-type ntl expression were 1.44 times greater than that of bra. (A) Embryos injected with Alk3* and wnt8 displayed an increase in ntl, but not bra expression. Injection of taram-d* produced an increase in both ntl and bra expression. (B) Injection of embryos with lefty and then Alk3* and wnt8 demonstrated that in the absence of nodal signalling BMP and Wnt signalling can activate the expression of ntl but not bra. (C) An embryo injected with an ntl morpholino and then further injected in the animal pole with bmp4 and wnt8 leads to a small ectopic mass (arrow) in 29% of embryos (n=77) (compare with Fig. 3C). (D) An MZoep embryo injected at the one-cell stage with an ntl MO. Loss of ntl function abolished the formation of somites within the tail region of MZoep embryos (arrowhead, compare with Fig. 3B).