Fig. 8. A7.6 marker gene expression does not require Nodal signaling from b6.5. (A,B) In late 32-cell stage wild-type Ciona embryos, Nodal is expressed in endoderm/endomesoderm blastomeres (A) and in b6.5 (B). (C,D) In embryos treated with U0126 at early 32-cell stage, vegetal expression of Nodal is unaffected (C), whereas b6.5 expression is completely blocked (D). (E-H) Embryos grown in U0126 beginning at the 16-cell stage display variable changes in A7.6 marker gene expression. (I-K) Hand-like, FGF8 and Delta-like expression in A7.6 is not affected by U0126 inhibition. (L) MyTF expression in A7.6 partially requires MAPK signaling at the 16-cell stage, but not at the 32- to 64-cell stage. (M,N) Ectopic expression of Nodal in the vegetal hemisphere induces ectopic Snail expression in the A-line neural lineage. (O-Q) Ectopic Nodal expression does not induce A7.6 gene expression in A7.5 or other endoderm blastomere, but is able to induce Hand-like and Delta-like expression in the A-line neural lineage (O, arrow; P, arrowheads) or to induce ectopic MyTF expression in mesenchyme lineages (Q, arrow).