Fig. 4. Ectopic expression of proepicardium (PE) marker genes in embryos implanted with the liver bud. (A) Schematic of the implantation procedure. Liver bud or lung bud was isolated from a quail donor and implanted ectopically in a host chick embryo. The host embryo was then cultured on an agar-albumen gel ventral side up. (B) A liver bud (arrow)-implanted embryo before whole-embryo culture. (C-J) In situ hybridization of liver bud-implanted embryos after 20 hours of whole-embryo culture. The embryos were stained for capsulin (C,D), Tbx18 (E,F), Pax2 (G,H) or Hex (I,J) transcripts. D,F,H and J are higher-magnification images of the boxed areas in C,E,G and I, respectively. Notice that ectopic expression of capsulin and Tbx18, but not of Pax2, is detectable at the site of implantation (arrows). The implant does not appear to affect endogenous expression for these markers in the intermediate mesoderm (im). (K-N) Lung bud-implanted embryos stained for capsulin (K,L) and Tbx18 (M,N). L and N are higher-magnification images of the boxed areas in K and M, respectively. No ectopic expression of these PE markers is detectable at implanted sites.