In vivo expression of lacZ reporter in ASPP1 gene-trapped embryos. (A-D) ASPP1 was expressed in the yolk sac mesoderm and endothelial cells. (B) ASPP1 expression was also detected in the trophoblast. al indicates allantois; cv, cardinal vein; da, dorsal aorta; e, endocardium; tb, trophoblast; ys, yolk sac. Scale bars, 200 μm. Original magnifications: × 100 (A), × 40 (B), and × 25 (C).