Fig. 5. Widespread hemorrhaging and defective placental development in Blimp1 mutant embryos. (A,C) The heart is still beating in 9.5 dpc mutant embryos, and injection of India ink into the outflow tract outlines the major arterial system. The dorsal aorta is visible in both wild-type (A) and mutant (C) embryos. Compared with wild type, only the first branchial arch artery (1) is visible in the mutant. (G) By 10.5 dpc, Blimp1-deficient embryos show widespread hemorrhaging. Numerous small blood pools form beneath the surface ectoderm and blood accumulates in the caudal dorsal aorta. (B,D,F,H) Hematoxylin-Eosin-stained mid-sagittal sections of wild-type (B,F) and mutant (D,H) placentas at 9.5 and 10.5 dpc. At 9.5 dpc (B,D), all the major tissue components of the wild-type placenta (B) have differentiated correctly. However, at this stage, the mutant placenta (D) displays defects in elaboration of the labyrinthine region; the luminal spaces of the labyrinth are much reduced when compared with the wild type. This defect is further exacerbated 24 hours later (H), when very little villous branching of the fetal blood vessels is apparent. Both maternal and embryonic erythrocytes are present. ebc, embryonic blood cells; mbc, maternal blood cells; stc, spongiotrophoblast; la, labyrinthine; tgc, trophoblast giant cells; ys, yolk sac; al, allantois; cp, chorionic plate; am, amnion; da, dorsal aorta; 1, first branchial arch; 2, second branchial arch; 3, third branchial arch.