Figure 5  In the Absence of BMP2 and BMP4, Osteogenesis Begins During Early Embryonic Development
(A–D) Sagittal sections of forelimb from E15.5 embryos. (A and B) Stained with toluidine blue. (A) Distal ulna from wild-type embryo, (B) distal ulna/radius from Bmp2C/C; Bmp4C/C; Prx1::cre embryo. Mineralized cartilage is shown by dark purple and osteoid is shown by light blue (red asterisk). (C and D) Humeri sections were hybridized with digoxigenin labeled riboprobe for ColI. (C) Section of wild-type humerus from E15.5 embryo, (D) from Bmp2C/C; Bmp4C/C; Prx1::cre E15.5 embryo.
(E–H) Sagittal sections of zeugopod from E17.5 embryos. (E and F) Stained with toluidine blue while G and H are stained for TRAP (brown stain, red arrow). (E and G) E17.5 proximal radius from wild-type embryo, (F and H) E17.5 proximal ulna/radius from Bmp2C/C; Bmp4C/C; Prx1::cre embryo. Although vascularization occurs in the absence of BMP2 and BMP4, few osteoclasts are observed in the mineralized cartilage in Bmp2C/C; Bmp4C/C; Prx1::cre mice. Please note all the panels other than (G) and (H) are photographed at ×20, while (G) and (H) were photographed at ×40.
(I and J) Sections of newborn proximal radius (I) from control animal and newborn proximal ulna/radius (J) from Bmp2C/C; Bmp4C/C; Prx1::cre animal were stained with toluidine blue. Red arrow shows the bone marrow cavity in (E) and (I). Note that bone collar (red *) forms at the right time and place in the absence of BMP2 and BMP4. Also note that since Bmp2C/C; Bmp4C/C; Prx1::cre mice occasionally have only one bone in zeugopod and the elbow joint is occasionally fused, it is difficult to distinguish between the ulna and the radius.