Visualization and quantification of glycolipid polarity dynamics in the plasmamembrane of the mammalian spermatozoon

Seminolipid (sulphogalactosylalkylacylglycerol), the glycolipidthat is specific for mammalian germ cells, is locatedexclusively in the outer leaflet of the sperm plasmamembrane. In this study the lateral distribution of seminolipidon sperm heads has been investigated by indirectimmunofluorescence labelling and detection with digitalimaging fluorescence microscopy. In freshly ejaculatedsperm cells this glycolipid was present primarily at theapical ridge subdomain of the plasma membrane of thesperm head. After binding the sperm cells to zona-coatedcoverslips seminolipid migrated, in 40 minutes, from theapical ridge to the equatorial subdomain of the plasmamembrane. A similar redistribution of seminolipid wasobserved during capacitation of sperm cells in vitroinduced by Ca2+ or bovine serum albumin. Comparablemigration of seminolipid was also found after prolongedstorage of ejaculated sperm cells, albeit at a much slowerrate. Addition of arylsulphatase A, an enzyme present inseminal plasma that desulphates seminolipid, significantlyenhanced the migration of seminolipid during storage ofsperm cells. Its breakdown product desulphoseminolipid(galactosylalkylacylglycerol) appeared highly specificallyat the equatorial segment. The measured fluorescenceintensity over the sperm head surface correlated linearlywith the spatial probe distribution as was checked by fluorescencelifetime imaging microscopy. This paper demonstratesand quantifies for the first time the polarity of seminolipidon the surface of the sperm cell and the dynamicalterations that occur in this polarity during post-ejaculatoryevents.