Fig. 4

Fig. 4 Overexpression of dominant negative bmpr2a and bmpr2b block BMP signalling in vivo. Unless otherwise stated, bmpr2a-Δic and bmpr2b-Δic mRNA were injected at 100 ng/μl. (A) Smad-dependent BMP signalling upon overexpression of full length or truncated bmpr2a and bmpr2b mRNA in embryos. Injection of 200 ng/μl of bmpr2a-Δic or bmpr2b-Δic mRNA efficiently blocked endogenous BRE-Luciferase activity in embryos at 70% epiboly. Injection of mRNA encoding tBR, a Xenopus dominant negative ALK3, was injected as a control. (B–D) Gata1 expression at 12 somites in wild type (B), bmpr2a-Δic (C) and bmpr2b-Δic (D) injected embryos. (E) At the 4-somite stage, pax2 is expressed in the midbrain–hindbrain boundary (mhb), otic placodes (ot) and pronephric (ventral) mesoderm (p), while myoD is expressed in the presomitic (axial) mesoderm (m) in wild type embryos. Embryos injected with bmpr2a-Δic (F) or bmpr2b-Δic (G) showed an expanded pax2 expression in the mhb domain concomitant with a strong reduction of pax2 expression in the otic placodes. (H) Expression of myoD in the somites of a wild type 14-somite stage embryo (lateral view, anterior to the right). Overexpression of bmpr2a-Δic (I) or bmpr2b-Δic (J) in 14-somite stage embryos. Note that the myoD expression is ventrally expanded, surrounding the most posterior end of the defective axis; the most anterior somites do not seem to be affected. RLU - Relative Luciferase Units.