Concanavalin A binding sites on the surface of Drosophila melanogaster sperm: A fluorescence and ultrastructural study

The distribution of α-d-mannose/α-d-glucose terminal residues in the plasma membrane of Drosophila melanogaster spermatozoon has been investigated by fluorescence and electron microscopy using concanavalin A (Con A) labeling. The results indicate the presence of distinct domains on the sperm surface. Intense binding of Con A to the plasma membrane is highly restricted to the acrosomal region and to the endpiece of the tail. In the former, Con A receptors are not homogeneously distributed, suggesting the presence of microdomains in the acrosomal area. The main part of the tail contains very few Con A binding sites, which are confined to specific areas of the membrane. The sperm surface overlying the nucleus is completely negative. The labeling pattern is unchanged after storage in the female before fertilization. A preliminary analysis of the surface of mature oocytes using fluorochrome-conjugated horseradish peroxidase indicates that d-mannose binding molecules are specifically associated with the chorion of the micropyle anterior part, which might therefore be the site of a preliminary interaction between egg and spermatozoon.