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Fig. 7 Synergistic regulation of spt and tbx6 by spt and ntl. Expression of tbx6 (A-D; bud, 10 h.p.f.) and spt (E-H; 95% epiboly, 9.5 h.p.f.). In ntl- embryos expression of tbx6 (B) and spt (F) are similar to WT (A,E) except for broadening of the non-expressing notochord domain (Melby et al., 1997). In addition, spt is no longer prominently expressed by adaxial cells. In spt- embryos, expression of both tbx6 (C) and spt (G) are very weak or absent from hypoblast cells but remain detectable in the tail bud epiblast (*). In spt-;ntl- embryos, expression of tbx6 (D) is entirely undetectable, and spt (H) is only barely detected (arrow).