Fig. 2. Unresponsiveness of the endoderm to the Nodal signal. (A,E) Schematic transverse sections of an E8.0 mouse embryo showing the strategy for culture with (A), or injection of (E), recombinant Nodal or Activin. Recombinant proteins added to the culture medium or injected into the right LPM are colored pink. (B-D) In situ hybridization for Nodal mRNA in embryos that were recovered at the one-somite stage and cultured in the absence (B) or presence of recombinant Nodal (C) or Activin (D) until they developed to the six-somite stage. (F-H) In situ hybridization for Nodal mRNA in embryos recovered at the one-somite stage, injected with medium containing bovine serum albumin (F), recombinant Nodal (G) or Activin (H), and cultured to the six-somite stage. Arrowheads indicate ectopic expression of Nodal in the right LPM. l, left; r, right. Scale bar: 200 µm.