In contrast to CAV2 and GM3, the other two proteins analyzed, IZUMO and FLOT2, can still be detected by immunofluorescence in acrosome-reacted sperm, although they showed a different localization compared with the one originally displayed in nonreacted cells. In intact sperm, IZUMO was restricted to the dorsal portion of the sperm head; after the acrosome reaction, it distributed to a new region opposite to the anterior acrosome, including part of the postacrosomal region. Different IZUMO staining patterns have been previously observed [50] , but their connection with antigen relocation due to the acrosome reaction has not been analyzed in detail. Concerning FLOT2, the staining formerly observed in the midpiece did not change with the acrosome reaction, but the signal located in the apical portion of the head extended along the acrosomal domain, revealing the presence of FLOT2 in the equatorial segment in cells that underwent the acrosome reaction. In addition to FLOT2, several proteins that have been reported to relocate after the acrosome reaction such as SPAM1, CRISP1, and IZUMO are present in the light buoyant DRM fractions [51] [52] [53] . This common feature suggests that changes in localization could be related to these membrane substructures rather than to a specific aspect of the individual proteins.