Related cell-surface antigens expressed with positional specificity in Drosophila imaginal discs

We have isolated three classes of monoclonal antibodies against Drosophila cell-surface antigens that are expressed with positional specificity in imaginal discs. Comparison of immunofluorescence patterns with the wing-disc fate map reveals that expression of the antigens is not directly related to the specific type of cuticular structure that a cell will make upon differentiation but depends on the position of the cell in the undifferentiated disc epithelium. On mature wing discs, each class of position-specific (PS) antibody binds nonuniformly with respect to the dorso-ventral compartment boundary, with PS1 antibodies binding primarily to dorsal cells and PS2 antibodies, to ventral cells. Antibodies of the different PS classes extract similar but nonidentical sets of large glycoproteins from cell lysates, and antibodies of the most general class, PS3, recognize the PS1 and PS2 antigens in addition to PS3-specific components. Thus, the distributions and molecular characteristics of the PS antigens suggest that the molecules are structurally and functionally related to one another.