Tissue-specific modulation of a set of related cell surface antigens in Drosophila

To be integrated correctly into the developing organism, cells need to interact with an environment that includes neighbouring cells, the extracellular matrix and soluble factors. These interactions probably require specific recognition events mediated by cell-surface molecules, and evidence has accumulated for the presence of such molecules in several organisms (see, for example, refs 1-6). In Drosophila, a family of cell-surface glycoprotein complexes, the position-specific (PS) antigens, may be involved in such processes^7-11. PS antigens show spatially restricted distributions on imaginai disks that vary during development; their expression on any particular cell correlates with the position of that cell in the developing disk epithelium rather than with its ultimate differentiation. In contrast to the situation in disks, however, immuno-fluorescence revealed few regional restrictions of PS-antigen expression on other larval tissues^7,11. If the PS antigens have a general role in morphogenesis, then widespread regional variation in their distributions might be expected. We now report that, by using polyacrylamide gel electrophoresis (PAGE), a technique that gives higher resolution than immunofluorescence, we detect an increase in both the concentration and the diversity of the complexes during embryogenesis, beginning at gastrulation. Further, each larval and adult tissue examined carries its own characteristic set of complexes. This tissue- and region-specific diversity is achieved by combining different members of a set of related components with a glycoprotein common to all the complexes.