Foregut organ specification requires prolonged contact with the cardiac-lateral plate mesoderm. (A) Diagram of the experimental design. Ventral explants were cultured with (+Meso) or without mesoderm (−Meso) during the indicated time points and assayed by in situ hybridization at stage NF37. (B) Summary of experimental results showing the percentage of explants with mesoderm removed at different times expressing liver (nr1h5), lung/thyroid (nkx2.1) and pancreas (pdx1 or ptf1a) markers at stage NF37, n > 20 explants for each condition and each probe. (C) Representative explants cultured from stage NF16 to NF37 with or without mesoderm and corresponding whole embryo controls assayed by in situ hybridization with the indicated markers. Endodermal (gjb1) or mesodermal (foxf1 and tnni3) specific markers demonstrated clean separation of the tissues.