Recent progress towards understanding the roles of the basement membrane in development.

A brief description of the structure of basement membranes is presented including results of immunocytochemical investigations. A number of developmental events are considered in which the basement membrane has been implicated in the regulation of morphogenesis. One of the clearest developmental functions appears to be the maintenance of the lobular morphology of glandular epithelia, where the basement membrane supplies a supportive scaffold. The contributions of the glycoproteins laminin and fibronectin to basement membrane function are discussed with reference to potential roles for this structure as a substratum for morphogenetic cell migrations and as a mediator of inductive interactions in embryogenesis. Examples used to illustrate these proposals include the mesodermal migrations of gastrulation, kidney tubule morphogenesis, and limb bud development. Evidence from these and other sources lend support to current view for an active and changing role for the basement membrane in the epithelial-mesenchymal interactions of embryonic development.