BASEMENT MEMBRANE BIOSYNTHESIS

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Basement membranes are thin condensations of specialized extracellular matrix that underlie epithelia, surround muscle cells, and serve various physiological functions. Their pathobiological chemistry is important in several diseases, as well as in both aging and development. Their synthesis and remodelling are not understood. We showed that some major constituents of basement membranes are closely similar in man and Drosophila melanogaster, e.g. collagen IV and laminin, and identified a site in basement membrane collagen that is cut during remodelling. We established methodology for studying basement membrane formation in Drosophila, and in embryo cell cultures differentiating on known protein substrates. In the lethal mutant myospheroid, in which basement membranes detach, we found that this gene codes for a beta- integrin transmembrane connector. We demonstrated its pivotal role in myogenesis. In transgenic flies we interfered in the basement membrane synthesis of specific muscles by targeted expression of antisense RNA to collagen IV. We shall use such constructs to modulate the synthesis of known and new basement membrane components, to learn their role in the sequential deposition of basement membranes that we established. To learn the functions of domains of the laminin A chain that we sequenced, modified forms will be expressed in cell cultures and flies. We will study the roles of laminin and of basement membrane proteoglycan in the early stages of basement membrane formation, and of two new proteins in later specialization. We shall look for a crosslinker between laminin and collagen networks. Thus the combined study of isolated basement membrane components of differentiating cell cultures that use and make the components, and of the effects of modulating expression of these materials in whole animals, will help us to learn how basement membranes are made, modified, and rebuilt according to changing needs.