FIG. 9. Localization of solubilized zona pellucida proteins on live sperm. Alexa-labeled zona proteins and propidium iodide were added to live boar sperm. Alexa-zona proteins bound live, acrosome-intact sperm over the anterior head region concentrated over the acrosomal ridge (A). Addition of a 100-fold excess of unlabeled zona proteins displaced the signal (C). The Alexa-labeled control glycoprotein, transferrin, did not bind to live sperm indicated by the arrow in (E). Dead sperm stained with propidium iodide over the entire head are visible, since fluorescence images were captured using a filter set that allowed detection of both red and green fluorochromes simultaneously (A,C,E). Corresponding phase-contrast images are shown (B,D,F). [Adapted with permission from Burkin HR, Miller DJ 2000 Zona pellucida protein binding ability of porcine sperm during epididymal maturation and the acrosome reaction. Dev Biol 222:99–109. Copyright Academic Press.]