Glycoconjugates of the surface of the spermatozoa of Drosophila melanogaster: a qualitative and quantitative study

The important roles played by glycoconjugates in the recognition of gametes and in fertilization are well documented. In the present study, the nature and distribution of carbohydrate residues of the plasma membrane of spermatozoa of Drosophila melanogaster were characterized by use of FITC-conjugated lectins as probes. The plasma membrane bound agglutinins from Concanavalia ensiformis (Con A) and Pisum sativum (PSA), native and succinylated agglutinins from wheat germ (WGA and s-WGA), the A(4) isoform of agglutinin-I from Griffonia simplicifolia (GSA-I A(4)), and, to a lesser extent, the lectins from Dolichus biflorus (DBA), Lotus tetragonolobus (LTA), and Glycine maximus (SBA). Each lectin gave a specific pattern of binding. The extent of binding of Con A, WGA, s-WGA, and GSA-I A(4) over the acrosomal region was greater than over nonacrosomal regions, indicating the concentration of alpha-mannose/alpha-glucose, beta-N-acetylglucosamine, and alpha-N-acetylgalactosamine residues in this area of the plasma membrane. The surface of the sperm failed to react with lectins from Ricinus communis (RCA-I), Limulus polyphemus (LPA), and Limax flavus (LFA) and with the B-4 isoform of agglutinin-I from Griffonia simplicifolia-I (GSA-I B-4) The plasma membrane over the nucleus did not react with any of the lectins tested. Quantitative analysis of binding of Con A, s-WGA, and GSA-I A(4) to spermatozoa showed that only Con A bound consistently to the sperm surface, showing high affinity for the acrosomal area of the plasma membrane. The other lectins tested bound only to limited and variably sized fractions of the total population of sperm. Therefore, only residues of alpha-mannose/alpha-glucose are a constitutive component of the plasma membrane, and they are characteristic of the acrosomal area. Con A can be used as a marker of the acrosome portion of sperm from Drosophila for visualization and assessment of acrosome status; labelling with FITC-conjugated Con A provides a simple and reliable method for visualization of the acrosome of Drosophila sperm that is otherwise detectable only by ultrastructural examination.