THE SPEMANN ORGANIZER SIGNAL NOGGIN BINDS AND INACTIVATES BONE MORPHOGENETIC PROTEIN-4

Signals released by the Spemann organizer of the amphibian gastrula ca n directly induce neural tissue from ectoderm and can dorsalize ventra l mesoderm to form muscle. The secreted polypeptide noggin mimics thes e activities and is expressed at the appropriate time and place to par ticipate in the organizer signal. Neural induction and mesoderm dorsal ization are antagonized by bone morphogenetic proteins (BMPs), which i nduce epidermis and ventral mesoderm instead. Here we report that nogg in protein binds BMP4 with high affinity and can abolish BMP4 activity by blocking binding to cognate cell-surface receptors. These data sug gest that noggin secreted by the organizer patterns the embryo by inte rrupting BMP signaling.