Figure 4.

Nodal rescues Bmp2-mediated suppression of APS gene expression. (A) Diagram of the experimental strategy. eGFP alone, or eGFP with experimental transgene expression vectors, was introduced into the APS region of WT E6.5 embryos. After 14 h culture, transgenic embryos were sorted by location of GFP expression (distal or proximal). Two-colored WMISH was used to detect ectopic gene expression (light blue) and endogenous APS gene expression (purple). eGFP expression (green arrowheads) in neither the distal (B1) nor the proximal epiblast (B2) alters Foxa2 expression. Foxa2 expression is inhibited by ectopic Bmp2 in the distal epiblast (C1) but not in the proximal epiblast (C2). Co-expression of Bmp2 and Nodal either distally (D1) or proximally (D2) does not affect Foxa2 expression. (E and F) Summary of the effects of transgene expression on Foxa2 and Gsc expression. The numbers of embryos with normal (red) or reduced expression (blue) are indicated. Asterisks denote a significant difference (P < 0.001) by Student's t-test between the indicated categories.