Fig. 4.

Normal bmp2/4 and chordin mRNA expression and pSmad1/5/8 activities during the periods before and after organizer formation. In each panel, the animal (ani.) and vegetal (veg.) views of the stained embryo are shown along with corresponding diagrams. The blastomeres showing gene expression are indicated in the diagrams, and those at the 60-cell stage are shown in supplementary figure S1a–d, Supplementary Material online (black asterisks in h and l). Note that although it could not be clearly discriminated in the figures, we confirmed bmp2/4 mRNA expression in 2q at the 16-cell stage (a) and in 1q¹² and its descendants at later stages (b–d); also, very weak but detectable pSmad1/5/8 activity could be observed in 16-cell embryos (i). In (k), the absence of pSmad1/5/8 staining in 1q² descendants (white asterisks) was caused by the active dividing of the cells, and we found that the signals were restored after cell division was completed. The carets in (c), (g), and (k) indicate that the 3Q macromeres were actually not distinguishable from each other based on morphology, despite 3D showing decreased chordin expression (g).