Sperm membrane dynamics assessed by changes in lectin fluorescence before and after capacitation.

Sperm capacitation is correlated with acquisition of fertilizing ability, and the molecular events underlying this process are only beginning to be understood. A number of membrane changes associated with capacitation have been documented. In this study we used lectin probes to identify changes in glycoprotein localization as a result of capacitation of mouse sperm. Eight lectins (LEA, PSA, PNA, AAA, UEA-1, WGA, STA, and TPA) stained regions of the mouse sperm head, tail, or both. No changes in tail staining patterns were detected when sperm were incubated under capacitating conditions. In contrast, 7 of 8 lectins tested showed clear shifts in staining patterns in the sperm head as a result of incubation under capacitating conditions. When staining patterns were quantified, a distinct heterogeneity within the sperm population was observed. Each lectin displayed 3 distinct staining patterns in both uncapacitated and capacitated sperm samples. The least common pattern represented the acrosome-reacted (AR) pattern, as independently assessed by lectin staining of ionophoretreated sperm that were >95% AR as judged by Coomassie staining. However, a reciprocal shift in the two predominant staining patterns was correlated with capacitation and suggests that changes in distribution of cell surface proteins during capacitation constitute part of the molecular changes which result in changes in sperm function acquired during this process.