Abstract

Cell-cell communication plays a key role in organ formation and patterning in multicellular animals and is carried out by a few evolutionarily conserved signaling pathways. The modes of action of these pathways share a number of general properties, or habits, that allow them to strongly activate target genes in a ligand-dependent manner in the proper cellular contexts. Recent studies have revealed that some developmental signaling pathways can also strongly repress genes in a ligand-dependent manner. These new findings raise the interesting possibility that this repressive mode of action is shared by many or most developmental signaling pathways.