Fig. 6. Contribution of Cripto null mutant cells to prechordal mesoderm, notochord and foregut endoderm in chimeric embryos. (A-L) Analysis of Rosa26/+; Cripto^lacZ/del +/+ chimeras generated by morula aggregation; whole-mount embryos were stained for ß-galactosidase activity, and cryosections were counterstained with Nuclear Fast Red. (A-E) Medium-grade Rosa26/+; Cripto^lacZ/del +/+ chimera at the late head-fold stage. Transverse sections (B,D) show random distribution of marked Cripto mutant cells in the headfolds and allantois; high-power views (C,E) show contribution of marked Cripto mutant cells to the prechordal plate and notochordal plate. (F-J) Medium-high-grade Rosa26/+; Cripto^lacZ/del +/+ chimera at 9.5 dpc. Marked Cripto mutant cells contribute with high efficiency to all tissues examined (G,I); high-power views (H,J) show contribution of marked Cripto mutant cells to the notochord, floor plate and foregut endoderm. (K,L) High-grade Rosa26/+; Cripto^lacZ/del +/+ chimera with abnormal morphology; note the presence of mesoderm (arrow in L). (M-O) Analysis of medium-grade chimera generated by blastocyst injection of marked Cripto^lacZ/del ES cells. Mutant cells contribute efficiently to the prechordal plate, anterior diencephalic ventral midline and foregut endoderm. Scale bars: 100 µm. advm, anterior diencephalic ventral midline; al, allantois; fg, foregut endoderm; fp, floor plate; hf, headfolds; nc, notochord; np, notochordal plate; pp, prechordal plate.