Figure 7. admp1 and admp2 act as prototypical BMP ligands but display divergent activities in specific contexts.

(a) Morphological phenotypes resulting from overexpression of admp1 and admp2. Overexpression of admp1 or admp2 at 1,000 μg ml⁻¹ completely radialized the embryos at gastrula stage. Note the presence of multiple spicule rudiments and the axial position of the gut in admp1 and admp2 overexpressing gastrulae. However, at pluteus stage, most embryos overexpressing admp1 or admp2 recovered a largely normal D/V axes and developed into normal pluteus. A fraction of these larvae displayed minor skeletal defects such as ectopic spicules elements. (b) Overexpression of admp2 suppressed formation of the ciliary band of SB431542 treated embryos and promoted growth and elongation of the skeleton resulting in a phenotype similar to that caused by overexpression of bmp2/4 or of bmp5/8. Overexpression of admp1 but not of admp2 in a chordin morpholino background caused 100% of the embryos to develop with a Nodal loss-of-function phenotype. (c) chordin expression is reduced in embryos overexpressing admp1 or in chordin morphants and eliminated in chordin morphants overexpressing admp1. (d) Both ADMP1 and ADMP2 promote pSmad1/5/8 signalling. pSmad1/5/8 antibody staining in control embryos and in embryos injected with admp1 or admp2 mRNAs. While the pSmad1/5/8 signal is restricted to the dorsal side of control embryos at mesenchyme blastula stage, overexpression of admp1 or of admp2 induces massive and strong phosphorylation of Smad1/5/8 in the whole ectoderm. In addition, overexpression of admp2, but not of admp1, induces strong pSmad1/5/8 in the primary mesenchymal cells. (e) Molecular analysis of admp1 or admp2 overexpressing embryos. At mesenchyme blastula stage, overexpression of admp1 or admp2 suppresses the expression of nodal and expands the expression of the dorsal marker genes smad6 and tbx2/3.admp1 overexpression also expands admp2 while overexpression of admp2 expands wnt5. Scale bar, 10 μm.