Dynamics in the membrane organization of the mammalian sperm cell and functionality in fertilization

The capacitation process of sperm cells involves complex changes in the com position and orientation of molecules at the surface of the sperm cell. Her e we focus on the lipid architecture in the sperm plasma membrane and demon strate that the sperm plasma membrane is not static but is an extremely dyn amic structure. Advanced fluoroscopic techniques enabled continuous monitor ing of lipid organization in living cells and extremely rapid lipid movemen ts were observed, The orientation of lipids in the sperm plasma membrane ch anged under capacitative treatments, was found to be sensitive for temperat ure and also changed upon binding of sperm cells to the zona pellucida. The changes in membrane properties coincided with an activation of protein kin ases resulting in tyrosine phosphorylation of specific plasma membrane prot eins. The detected membrane changes relate to intrinsic membrane properties such as fluidity, permeability, adhesiveness and fusibility, We think that these results may provide a physiological basis for new assays, able to di scriminate between functional and non-physiological sperm cells.