MALDI-TOF mass spectrometry as a simple tool to determine the phospholipid/glycolipid composition of sperm: pheasant spermatozoa as one selected example

Cellular membranes are composed of highly variable lipid molecules, mainly cholesterol and phospholipids (PLs). The cholesterol moiety and the saturation degree of the fatty acyl residues of PL determine the fluidity of the membrane, which is particularly important for sperm because they have to undergo characteristic membrane-dependent processes (acrosomal exocytosis and fusion with the oocyte). Glycolipids are an essential part of the membrane surface acting as key mediators in the interactions of sperm with components of the female genital tract. Although the lipid composition of many mammalian spermatozoa has already been determined, the lipid composition of avian spermatozoa has scarcely been investigated. Using spermatozoa extracts of the ring-necked pheasant (Phasianus colchicus) as a selected example, this work demonstrates that matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a simple and fast method to determine spermatozoal lipid compositions. The lipid compositions of pheasant spermatozoa have not yet been investigated. In addition to common membrane (primarily diacyl) PL (sphingomyelin, phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine), remarkable variation of different sulfoglycolipids (sulfogalactocerebrosides) was identified. This is in strong contrast to all other animal species investigated so far which nearly exclusively contain the sulfoglycolipid seminolipid (sulfogalactoalkylacylglycerol). We emphasize that the MALDI MS approach allows the characterization of sulfoglycolipids of sperm within a few minutes without the necessity for previous chromatographic separation.