Mice homozygous for fII^WE complete embryonic development but uniformly experience fatal postnatal bleeding events. (A-C) Representative examples of fII^WE/WE homozygous neonates. Note that most of the fII^WE/WE postnatal animals displayed appreciable abdominal hemorrhage. In addition, subcutaneous bleeding events in the head and neck region were also routinely observed. (D-F) Representative examples of fII^WT/WT, fII^WT/WE, and fII^WE/WE embryos, respectively, collected at E18.5. Each animal was alive at the time of harvest, macroscopically normal, and free of overt hemorrhage. (G-V) Microscopic analysis revealing a normal pattern of development with no signs of hemorrhage in any organ system of fII^WE/WE offspring at E18.5. Note that hematoxylin/eosin–stained sections prepared from embryonic brain (G-J), heart (K-N), lung (O,Q), liver (P, R), small intestine (S,U), and pancreas (T,V) were virtually indistinguishable in wild-type offspring (panels G, H, K, L, O, P, S, T) and homozygous fII^WE/WE offspring (panels I, J, M,N, Q, R, U, V). The heart ventricle and atrium are annotated by vtl and atm, respectively. The scale bar indicates 100 μm.