Fig. 5. Phenotypic abnormalities in Tsg^-/-;Bmp7^-/- and Tsg^+/–;Bmp7^-/- compound mutants in the mouse. (A) Wild-type embryo 10.5 dpc. (B) Side view of a Bmp7^-/-,Tsg^-/- mutant with sirenomelia; the hindlimb buds are fused into a single bud (arrow). (C) Ventral view of a severely affected Tsg^+/–;Bmp7^-/- mutant embryo with heart edema and underdeveloped anterior and posterior structures. (D-G') Histological analyses of the posterior region of 9.5 dpc wild-type and Tsg^-/-;Bmp7^-/- embryos. (D,D') Side view of the embryos indicating the level of sections in E-G'. The posterior arterial system is drawn schematically and superimposed; the dorsal aorta (da) curves ventrally in the tailbud, forming the recurved distal aorta (rda), from which the umbilical artery (ua) originates. (E-G') Transverse serial sections of embryos shown in D and D' stained with Hematoxylin and Eosin. (E,E') Section at the level of the right and left hindlimb buds (rhb, lhb) showing the absence of the rda, fusion of the hindlimb buds (hb) and a single coelomic cavity (cc) in the mutant. (F,F') More posterior sections showing a decreased diameter of the tail at the level of the aortic curvature. (G,G') Section at the tip of the tail showing fewer tailbud mesoderm cells and a normal neural plate in the mutant. hg, hindgut; lhb, left hindlimb bud; n, node; nt, neural tube; rhb, right hindlimb bud; s, somite; tbm, tail bud mesoderm; ua, umbilical artery; va, vitelline artery.