VISUALIZATION AND QUANTIFICATION OF GLYCOLIPID POLARITY DYNAMICS IN THE PLASMA-MEMBRANE OF THE MAMMALIAN SPERMATOZOON

Seminolipid (sulphogalactosylalkylacylglycerol), the glycolipid that i s specific for mammalian germ cells, is located exclusively in the out er leaflet of the sperm plasma membrane. In this study the lateral dis tribution of seminolipid on sperm heads has been investigated by indir ect immunofluorescence labelling and detection with digital imaging fl uorescence microscopy. In freshly ejaculated sperm cells this glycolip id was present primarily at the apical ridge subdomain of the plasma m embrane of the sperm head. After binding the sperm cells to zona-coate d coverslips seminolipid migrated, in 40 minutes, from the apical ridg e to the equatorial subdomain of the plasma membrane. A similar redist ribution of seminolipid was observed during capacitation of sperm cell s in vitro induced by Ca2+ or bovine serum albumin. Comparable migrati on of seminolipid was also found after prolonged storage of ejaculated sperm cells, albeit at a much slower rate. Addition of arylsulphatase A, an enzyme present in seminal plasma that desulphates seminolipid, significantly enhanced the migration of seminolipid during storage of sperm cells. Its breakdown product desulphoseminolipid (galactosylalky lacylglycerol) appeared highly specifically at the equatorial segment. The measured fluorescence intensity over the sperm head surface corre lated linearly with the spatial probe distribution as was checked by f luorescence lifetime imaging microscopy. This paper demonstrates and q uantifies for the first time the polarity of seminolipid on the surfac e of the sperm cell and the dynamic alterations that occur in this pol arity during post-ejaculatory events.