Glycoconjugate expression during Drosophila embryogenesis.

Glycoproteins and other glycoconjugates present on the surface of many cell types have been identified and assigned various functions. The extent of variation possible in complex glycan structures and the heterogeneity of glycoconjugate expression between two apparently similar cells has been demonstrated previously by using plant lectins to survey developmental biological models. To examine the array and extent of glycoconjugate roles in embryonic Drosophila neurogenesis, we have used plant lectins to characterize lectin receptor molecules present on the neuronal and non-neuronal cell surfaces during critical stages in axonogenesis and axon fascicle development. A collection of lectins representing a variety of hapten monocarbohydrate specificities uncovered a complex expression pattern in many glycan structures. D-Galactose-specific lectins, Bauhina purpura agglutinin (BPA) and Arachis hypogea agglutinin (peanut agglutinin, PNA), and a D-galactose/N-acetylgalactosamine-specific lectin, Glycine max agglutinin (soybean agglutinin, SBA), all recognized the surface of most cultured neurons and their axons. In the intact embryo, only the PNA and BPA receptors were found on neurons of the central and peripheral nervous systems, while SBA recognized cells of structures other than the nervous system. All three lectins recognize a high molecular weight glycoprotein when used to precipitate lectin receptor from culture homogenates. Results suggest the presence of lectin receptor glycoproteins at temporally and spatially important positions within the embryo and in culture. These glycoproteins may provide functions critical in establishing the final phenotypes of specific cells through either axon guidance/target acquisition or morphogenic adhesive events.