Embryonic lethality of a homozygous Mfrn1 deletion. (A) PCR analysis of the offspring from the breeding of Mfrn1^+/− with Mfrn1^+/− mice. These littermates were genotyped at E9.5. In this particular litter, 1 animal was wild-type, 6 were heterozygous, and 1 was homozygous for the Mfrn1 deletion. PCR was done using primers F, R3, and R4, as indicated in the legend to Figure 1. (B) Western blot of whole embryos probed with antibodies against Mfrn1, Mfrn2, and tubulin using peroxidase-conjugated goat anti–rabbit IgG or goat anti–mouse IgG. (C-H) Stereomicroscopy of E9.5 embryos from Mfrn1^+/− × Mfrn1^+/− breeding. Panels C, E, and G are the Mfrn1^+/− mouse; panels D, F, and H are the Mfrn1^−/− mouse. Panels C and D show embryos kept in the yolk sac, panels E and F show embryos without their yolk sac, and panels G and H are enlarged images from panels E and F. The Mfrn1^−/− mouse is deprived of hemoglobin, as shown by the lack of RBCs in vasculature of the yolk sac (ys) in panel D compared with panel C, and by the hemoglobinization of the heart and the common atrial chamber of the heart (h) in panels F and H compared with Mfrn1^+/− mice panels E and G.