Bone morphogenetic protein antagonism of Spemann's organizer is independent of Wnt signaling

The Xenopus homeobox gene twin is involved in the Wnt-mediated induction of Spemann's organizer. Additionally, several lines of evidence indicate that bone morphogenetic proteins (BMPs) play a role in repressing the formation of the organizer by antagonizing the expression of genes involved in organ izer establishment. In order to determine at what level BMPs exert their ef fect, we measured the activity of different genes expressed within the orga nizer region. We report that BMP signaling can antagonize the induction of the dorsal-specific gene goosecoid but is unable to affect Wnt signaling at the level of twin. These results suggest that the antagonistic activities of BMPs in organizer formation occur postzygotically, independent of twin r egulation, and that Wnt-like dorsal determinant signaling pathways do not c rosstalk with BMPs. (C) 1999 Academic Press.