Fig. 4. Brachyury expression during gastrulation (between 6.0 and 7.5 d.p.c.) as determined by in situ hybridisation; position of the AMC is indicated by asterisks. Bars and letters indicate position of sagittal sections shown in Fig. 5. (A,B) Stage 2, Brachyury-expressing cells lie singly at first (A) and a little later in a coherent patch (B) in the PGE. (C,D) Strong Brachyury expression in the emerging (C) and definitive (D) primitive streak at stage 3. (E) Early stage 4 with lack of Brachyury expression in the anterior half of the primitive streak (anterior to arrow) but distinct expression in the primordium of Hensen’s node (h). (F) Late stage 4 with node fully formed and strong Brachyury expression along the entire primitive streak. Arrow as in E. (G,H) Stage 5 and 6 with Brachyury expression also in notochordal process (n). Scale bars: 130 µm in A-D; 160 µm in E-G; 290 µm in H.