Assessing acrosomal status of bovine sperm using fluoresceinated lectins

Binding of 12 lectins to bull sperm was analyzed to select a lectin that bound preferentially to the acrosomal region. Peanut agglutinin (PNA) and Pisum sativum agglutinin (PSA) were suitably specific for intracellular, acrosome-associated glycoconjugates. Peanut agglutinin exhibited almost no detectable binding to sperm surface receptors, but intense binding to the area of the acrosome anterior to the equatorial segment. In contrast, PSA bound intensely to anterior and equatorial acrosomal regions, and weakly to the other regions of the sperm. Acrosomal labeling by both lectins decreased when sperm were induced to acrosome-react with calcium ionophore. To determine if these lectins could be used to assess acrosomal status, we compared the percentage of acrosome-reacted sperm that were detected by staining with naphthol yellow and erythrosin B with the percentage that were detected by lectin labeling. The incidence of reacted sperm detected by PSA labeling was not significantly different from that detected by naphthol yellow/ erythrosin B (P = 0.46). The incidence of reacted sperm detected by PNA was correlated with the incidence detected by naphthol yellow/erythrosin B, but was significantly lower (P = 0.003). We conclude that labeling permeabilized sperm with fluoresceinated PSA can serve as a rapid assay for acrosomal status.