Fig. 3. Loss of BMP signaling in dorsal neural tube of Bmpr double knockout mice. (A) Immunostaining for phoshorylated-SMAD1 (phospho-SMAD1) in a normal embryo at 10.0 dpc. Immunoreactive cells are found in the roof plate and the adjacent dorsal neural tube (arrowhead). (B) Phospho-SMAD1 immunostaining in double mutant embryos demonstrates loss of immunoreactivity in the dorsal neural tube (arrowhead). A few phospho-SMAD1 positive cells remain in the roof plate (arrow). (C) Msx2 immunostaining in the dorsal neural tube of a 10.0 dpc normal embryo. (D) Msx2 immunostaining is intact at 10.0 dpc in Bmpr double knockout embryos. (E) Msx2 expression in the roof plate (arrowhead) and epidermal ectoderm of normal animals. (F) Msx2 expression is lost in the roof plate of mutant animals (arrowhead), although expression in the epidermal ectoderm is intact (arrow). (G) Bmp6 is expressed in the roof plate and immediately adjacent tissue at 10.5 dpc in normal embryos. (H) Bmp6 expression is intact in the Bmpr double knockout animals.