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The deployment of a cell's genetic program in a multicellular organism must be tightly controlled for the sake of the organism as a whole. Over the past 20 years the transforming growth factor‐β (TGF‐β) family of secretory polypeptides has emerged as a major source of signals exerting this type of control. This family includes various forms of TGF‐β, the bone morphogenetic proteins (BMPs), the Nodals, the Activins, the anti‐Müllerian hormone, and many other structurally related factors in vertebrates, insects and nematodes (Massagué, 1998). Produced by diverse cell types, these factors regulate cell migration, adhesion, multiplication, differentiation and death throughout the life span of the organism. Many of these responses result from changes in the expression of key target genes. Hence, transcriptional control by the TGF‐β family has become a subject of intense investigation in recent years. The present …