Extracellular matrix and its receptors during development.

Extracellular matrix (ECM) components are essential for morphogenesis of virtually all tissues. The ECM interacts with the cell surface by binding to specific receptors. The first family of receptors for the ECM that was identified was the integrin family. Integrins are composed of an alpha and a beta-chain, both of which are single pass transmembrane proteins. In muscle cells the dystroglycan complex forms another important receptor system for ECM. It is a complex composed of many proteins. Recent studies have shown that dystroglycan is expressed by embryonic epithelial cells as well. The nature of constituents of the dystroglycan complex is well known for muscle, whereas the detailed composition of the dystroglycan complex in embryonic epithelium is not yet well known. We here review the evidence that binding of ECM to integrins and the dystroglycan complex could be essential for muscle and epithelial cell development and function. It is likely that integrins and the dystroglycan complex have distinct roles during development. It will be an interesting task to study the signal transduction pathways elicited by the interactions between ECM and the two receptor systems during muscle and epithelial morphogenesis.