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.Much of the adult Drosophila epidermis and some internal structures derive, at metamorphosis, from imaginal discs, which are present in larvae as convoluted inpocketings from the larval hypoderm. [Imaginal disc morphology and development are reviewed by Poodry (1).] In mature third-instar larvae each imaginal disc, although still largely undifferentiated, is stably determined to make a particular region of the adult (2, 3), and the cells within a particular part of a disc are specified to make a particular adult structure (4) (see Fig. 1). This precise specification of pattern within the disc appears to depend on intercellular interactions (6, 7). Clonal analysis has shown that discs are subdivided into compartments, defined by the observation that clones of genetically marked cells do not cross a compartment boundary into the territory of neighboring compartments (8). Genetic studies indicate that at least some of these compartments are units of gene action in the development of the epidermis (9, 10), although the relationship between compartments and the precise specification of pattern elements is not clear. We have studied the molecular basis of early disc development by using monoclonal antibodies to detect cell-surface antigens with heterogeneous distributions in larval discs before overt differentiation occurs. We previously described (5) the distribution of one such antigen, recognized by monoclonal antibody DK.1A4. Comparison of this antigen's distribution with a cell-lineage analysis of the mature wing imaginal disc (which makes the adult wing and associated mesothorax) showed that expression of the antigen correlated with the dorso-ventral lineage restriction (the border between dorsal and ventral compartments) in the epithelium. It was also clear that the expression of the antigen was not tightly linked to the type of adult structure that a disc cell was specified to differentiate, but seemed rather to depend on ...

Laminin, a basement membrane protein derived from the matrix of the Engelbreth-Holm-Swarm murine tumor, was nonenzymatically glycosylated in vitro in the presence of increasing glucose concentrations. The amount of glucose incorporated per laminin molecule was shown to be proportional to the molarity of glucose used. Nonenzymatic glycosylation resulted in formation of cross-links and alterations of the cruciform shape of laminin molecules; these alterations were dramatic when high concentrations of glucose were used. One of the functions of laminin, the process of self-assembly, was shown to be impaired after in vitro nonenzymatic glycosylation. Glucose incorporation resulted in a dramatic decrease of long-to-long laminin dimers, which normally form during the initial steps of assembly. Furthermore, nonenzymatic glycosylation of laminin reduced its ability to self-associate into complexes larger than dimers, as judged by turbidimetry. The observed decrease of maximal turbidity was proportional to the degree of nonenzymatic glycosylation. Aminoguanidine, which has been suggested to inhibit cross-link formation, was shown to restore to a large extent the shape of laminin, the percentage of long-to-long arm dimers, and the maximal turbidity when included in the mixtures of laminin and glucose. These data suggest that structural and functional alterations of laminin may be primarily due to formation of cross-links. Such modifications of laminin (along with our basement membrane components) may contribute to the morphological and physiological changes observed in basement membranes under diabetic conditions.

Abstract. Recent studies using solid-phase-binding assays and electron microscopy suggested the presence of a heparin-binding domain between the inner globule of a lateral short arm and the cross region of laminin. Using the information from the amino acid sequence of the B1 chain of laminin, several peptides were synthesized from areas with a low hydropathy index and a high density of lysines and/or arginines. One of these, peptide F-9 (RYVVLPRPVCFEKGMNYTVR), which is derived from the inner globular domain of the lateral short arm, demonstrated specific binding to heparin. This was tested in direct solid-phase binding assays by coating the peptide either on nitrocellulose or on polystyrene and in indirect competition assays where the peptide was in solution and either laminin or heparin was immobilized on a solid support. The binding of [3H]heparin to peptide F-9 was dramatically reduced when heparin but not other glycosaminoglycans other than heparin (dextran sulfate, dermatan sulfate) were used in competition assays. Modification of the free amino groups of peptide F-9 by acetylation abolished its ability to inhibit the binding of [3H]hepafin to laminin on polystyrene surfaces. Peptide F-9 promoted the adhesion of various cell lines (melanoma, fibrosarcoma, glioma, pheochromocytoma) and of aortic endothelial cells. Furthermore, when peptide F-9 was present in solution, it inhibited the adhesion of melanoma cells to laminin-coated substrates. These findings suggest that peptide F-9 defines a novel heparin-binding and cell adhesion-promoting site on laminin.

The nonenzymatic glycation of basement membrane proteins, such as fibronectin and type IV collagen, occurs in diabetes mellitus. These proteins are nonenzymatically glycated in vivo and can also be nonenzymatically glycated in vitro. After 12 days of incubation at 37 degrees C with 500 mM glucose, purified samples of human plasma fibronectin and native type IV collagen showed a 13.0- and 4.2-fold increase, respectively, in glycated amino acid levels in comparison to control samples incubated in the absence of glucose. Gelatin (denatured calfskin collagen) was glycated 22.3-fold under the same conditions. Scatchard analyses were performed on the binding of radiolabeled fibronectin to gelatin or type IV collagen. It was found that there is a 3-fold reduction in the affinity of fibronectin to type IV collagen due to the nonenzymatic glycation of fibronectin. The dissociation constant (KD) for the binding of control fibronectin to type IV collagen was 9.6 X 10(-7) M while the KD for glycated fibronectin and type IV collagen was 2.9 X 10(-6) M. This was similar to the 2.7-fold reduction in the affinity of fibronectin for gelatin found as a result of the nonenzymatic glycation of fibronectin (KD of 4.5 X 10(-7) M for the interaction of control fibronectin with gelatin vs. KD of 1.2 X 10(-6) M for the interaction of nonenzymatically glycated fibronectin with gelatin). The molecular association of control fibronectin or its glycated counterpart with [3H]heparin was also determined. Scatchard analyses of this interaction showed no difference between control fibronectin and glycated fibronectin in [3H]heparin binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract. We have previously identified three distinctive amino acid sequences from type IV collagen which specifically bound to heparin and also inhibited