Fig. 7

Comparison of zebrafish follistatin, chordino, bmp2b, and bmp4 expression (A–G) revealed by in situ hybridization and interaction between follistatin and bmp4 (H). All embryos are of the 80% epiboly stage. The in situ probes used are indicated in the lower right corner. (A and B) follistatin expression, lateral view (A), dorsal view (B). (E and F) chordino expression, (E) lateral view, (F) dorsal view; while chordino is expressed in organizer-derived cells in the presumptive prechordal plate, follistatin is expressed in more posterior regions of the notochord anlage. The paraxial chordino and follistatin expression domains in epiblast and hypoblast, respectively, are almost congruent, as confirmed by anti-Ntl counterstaining, marking the notochord anlage and the germ ring as reference points (not shown). At slightly later stages, the paraxial chordino expression domain appears slightly larger than the follistatin domain, extending more into marginal regions (not shown). (C) bmp2b expression, lateral view; the dorsal extension in the ventral expression domain is indicated by an asterisk, the expression in dorsal marginal cells by an arrow. (G) follistatin and bmp2b expression, lateral view. (D) bmp4 expression, lateral view; the expression domain in the dorsal marginal cells is indicated by an arrow, the expression domain in the presumptive prechordal plate by an arrowhead. (H) bmp4 expression after overexpression of zebrafish follistatin, lateral view. The region with reduced bmp4 expression is delimited by two arrows.