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Fig. 4 Overlapping and complementary expression of T-box genes in the early mesoderm. (A-C) Sections through lateral germ ring at midgastrulation (8.5 h.p.f.); arrows mark limits of expression in epiblast (e) and hypoblast (h). (A) spt and (B) tbx6 are expressed in epiblast cells closest to the margin, and broadly in the hypoblast. (C) ntl expression is expressed only near the margin in both the epiblast and hypoblast. (D-F) Posterior views of 4-6-somite embryos (12 h.p.f., dorsal uppermost). (D) spt and (E) tbx6 are co-expressed in the region of the tail bud epiblast (*) where involution occurs (Kanki and Ho, 1997) and in the underlying hypoblast and segmental plate (S), but only spt is prominently expressed in adaxial cells (arrows in D). (F) ntl is expressed more broadly in the tail bud epiblast (*); ntl expression in the hypoblast is restricted to the notochord (arrow).