Fig. 7. Addition of exogenous Cripto alters the differentiation of chick node/head process mesoderm explants. (A,E) Schematic drawings showing regions dissected at HH stage 4^--4 (A) and HH stage 5 (E). (B-D,J-L) Explants of HH stage 4 Hensen's node cultured in vitro for 20 hours in the presence of 293T cell conditioned medium, either untransfected (B-D) or transfected with Cripto (J-L). Gsc-expressing prechordal mesoderm and Hex-expressing anterior endoderm differentiate with or without Cripto (B,C,J,K). 3B9-expressing notochord cells differentiate in control cultures (D) but not in explants exposed to Cripto (L). (F-I,M-P) Explants of HH stage 5 posterior head process mesoderm cultured in vitro for 20 hours (F-H,N-P) or 4 hours (I,M). Control cultures express 3B9 (H) and Fgf10 (M) but not Gsc or Hex (F,G,M). Explants exposed to Cripto protein express Gsc and Hex (I,N,O), but downregulate 3B9 and Fgf10 (M,P). Explant cultures (H,P) were counterstained with DAPI. (Q,U) Schematic drawings showing bead implant at HH stage 4 (Q) and level of sections analyzed at HH stage 9 (U). (R-T,V-X) Serial adjacent sections of HH stage 9 embryos, in which control beads (R-T) or Cripto-soaked beads (V-X) were placed adjacent to Hensen's node at HH stage 4. Axial mesoderm cells of control embryos display notochord properties, expressing 3B9 and Shh, but not Gsc (R-T). Axial mesoderm cells of Cripto-exposed embryos display prechordal mesoderm properties, expressing Shh and Gsc, but not 3B9 (V-X). (Y-BB) Explants of HH stage 5 head process mesoderm cultured in vitro for 20 hours. Control cultures and cultures exposed to SB-431542 express 3B9 (Y,AA). Cripto prevents expression of 3B9 (Z). The Cripto-mediated loss of 3B9 is abolished by treatment with SB-431542 (BB).