Transgene expression in mouse embryos.

(A) Wild-type (wt) and transgenic (TG) embryos from E6.5 through E11.5 were collected and assayed in situ for PLAP enzymatic activity (blue staining). Embryos from E9.5 to E11.5 are shown with yolk sac (left column) and without yolk sac (right column). a indicates allantois; br, brain; e, embryo proper; ey, eye; fl, fetal liver; h, heart; lb, limb bud; n, notochord; p, placenta; t, tail; ys, yolk sac. Filled arrowheads point to blood islands or blood vessels in the yolk sac. Magnification × 10-20. (B) Paraffin sections at E7.5 and E9.5 show transgene expression in blood islands or blood vessels of the yolk sac. Annotations are as in panel A. Magnification × 200.