In early vertebrate development, mesoderm induction is a crucial event regulated by several factors including the activin, BMP and FGF signaling pathways. While the requirement of FGF in Nodal/activin-induced mesoderm formation has been reported, the fate of the tissue modulated by these signals is not fully understood. Here, we examined the fate of tissues when exogenous activin was added and FGF signaling was inhibited in animal cap explants of Xenopus embryos. Activin-induced dorsal mesoderm was converted to ventral mesoderm by inhibition of FGF signaling. We also found that inhibiting FGF signaling in the dorsal marginal zone, in vegetal-animal cap conjugates or in the presence of the activin signaling component Smad2, converted dorsal mesoderm to ventral mesoderm. The expression and promoter activities of a BMP responsive molecule, PV.1 and a Spemann organizer, noggin, were investigated while FGF signaling was inhibited. PV.1 expression increased, while noggin decreased. In addition, inhibiting BMP-4 signaling abolished ventral mesoderm formation induced by exogenous activin and FGF inhibition. Taken together, these results suggest that the formation of dorso-ventral mesoderm in early Xenopus embryos is regulated by a combination of FGF, activin and BMP signaling.
Bibliographical noteFunding Information:
We thank Dr. Makoto Asashima (Dept. of Life Science, University of Tokyo) for the activin protein. This research was supported by the Basic Science Research Program ( KRF-2005-C00115 and KRF-2005-015-C00390 ) and by the Priority Research Centers Program ( 2010-0029642 ) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology .
- Bone morphogenetic protein-4
- Fibroblast growthfactor
- Mesoderm formation