Figure 5.

Severe vascular disorganization in the yolk sac membranes of mutant embryos in 129 Sv strain background. (A) E9.5. About 20% of the E9.5 mutants showed such pattern. (B) E11.5. Vascular patterns derived from +/− ES cell lines were identical to those shown in Figs. 3A and 4A and are not duplicated here. (C and D) Histological sections. About half of the E9.5 yolk sac membranes demonstrated disorganization. (C) Elongated endothelial linings and enlarged vascular lumen (compare with Fig. 4C). (D) Lumen enlargement appeared to be caused by merging of adjacent vessels. Arrows indicate sites of vascular merging. (Bars: A and B, 500 μm; C, 150 μm; and D, 75 μm.)