LacZ activation as revealed by histochemical X-gal staining.

(A) Whole embryo staining by X-gal. Yolk sac blood vessels were intensely stained. (B) Embryonic blood stained for X-gal showing that white cells (shown by arrows) are negative. (C, D) Plasma clots stained for benzidine, X-gal, and counterstained with hematoxylin. (C) One megakaryocytic colony is shown. Also present is a group of 3 benzidine-positive and X-gal-positive erythroid cells (arrows) and scattered white cells negative for X-gal. (D) Two megakaryocytic (m) colonies and 1 erythroid (e) colony (right upper corner) are seen, along with scattered white cells. Note the presence of positive and negative X-gal erythroid cells (arrows). (E) Spleen section with an X-gal-positive colony (CFU-S). (F) Red cells from a SCID/NOD mouse transplanted with FDG(+)/TER119(−) fetal liver cells at 5 weeks after transplantation. Note the larger size of X-gal(+) fetal red cells.