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Figure 3
The early phenotype fetuses. (A) The mutant fetus is severely retarded (left) compared with the control littermate (right). (B) The unfused allantois (arrow) can be seen as a balloon-shaped sac next to a mutant fetus. (C and D) At fetal day 8.5, the control fetus (C) has completed the turning process and shows a successful fusion of the chorionic and allantoic membranes with penetration of embryonic vessels into the chorionic plate (c in insert of C). The mutant fetus (D) is also well into the turning process, but still has an unfused allantois (a in insert of D), despite being beyond the 7–10 somite stage when fusion normally takes place. (E and F) No fetal blood cells were distinguished in the mutant placenta (F), whereas the labyrinth layer of the control placenta (E) contained both nucleated fetal blood cells (arrow) and anucleated maternal blood cells (asterisk). (G) A single layer of cytokeratin-positive trophoblast giant cells lined the mutant placenta (arrowheads in G and F). (H) These giant trophoblast cells were observed by TUNEL assay to be undergoing apoptosis (arrowheads). (I) Staining of the placenta of a control mouse with a type XIII collagen antibody. Strong type XIII collagen staining is seen in the ectoplacental cone (arrowheads and e in insert), which is formed after fusion of the chorion and allantois. No difference in the staining pattern of the placenta of mutant mice surviving the initial chorioallantoic fusion could be observed (data not shown). The insert shows the same area stained by hematoxylin–eosin where the distinct structures of the ectoplacental cone (e) and the labyrinth layer of the placenta (l) can be appreciated. hd, head; h, heart; t, tail; c, chorionic plate; a, allantois; e, ectoplacental cone; l, labyrinth layer. Bars: 1.5 mm (A and B), 50  m (C and D) and 20 m (E–I).
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