Extracellular matrix (ECM) is in a dynamic state of synthesis and degradation, and small changes in the balance between these two processes will lead to selective accumulation or removal of its components, with resultant modulation of its composition. The composition and organization of ECM is an important determinant of cellular behavior in that it regulates cellular adhesion, cellular migration, cellular proliferation, and cellular differentiation.’,’Thus, it has been implicated in morphogenesis and more generally in embryogenesis, tissue repair, and normal as well as pathologic physiology. Study of the mechanisms underlying the elaboration of ECM and the regulation of its composition will lead to increased understanding of its role in these processes.

In recent years it has become apparent that a growth factor called transforming growth factor-j3 (TGF-j3) plays a pivotal role in control of ECM, regulating not only the synthesis and degradation of specific ECM components, but also the ability of cells to interact with molecules of the ECM via cell surface receptors called integrins (for an overview, see Refs. 3, 4). The multiple levels at which TGF-j3 acts to control