Fig. 5. Ectopic induction of Wt1 expression by the liver bud as shown by immunohistochemistry. (A) A chick embryo implanted with a quail liver bud (arrow) at stage 13; (B) after 20 hours of whole-embryo culture. (C-F) Transverse sections of the embryo shown in B at the level of the implant. The sections were stained with anti-Wt1 (C,D) or anti-Pax2 (E,F) antibody (green). The sections were also stained with a quail-specific QCPN antibody (red) and DAPI (blue; for counterstaining). D and F are high-magnification images of the boxed regions in C and E, respectively. Bona fide expression of Wt1 and Pax2 was detected in the intermediate mesoderm and dorsal mesothelium (asterisks). Wt1 (arrowheads in D), but not Pax2 (F), was detected ectopically in the ventrolateral lining of the body cavity. The signal was observed in the nuclei of the host-derived cells adjacent to the QCPN-positive donor tissue. (G-L) Embryos implanted with the liver at a more-posterior level, showing that ectopic Wt1 expression becomes detectable far form the intermediate mesoderm prior to the completion of the lateral body folding. im, intermediate mesoderm; nt, neural tube.