La capacitation in vitro

Capacitation is a prerequisite for mammalian spermatozoa to fertilize oocytes. Lipids play a crucial role in the structural and functional organization of sperm plasma membrane. Lipid and membrane protein ordering changes dramatically during sperm capacitation but the resulting effects differ according to the regions of the sperm head. Lipids modifications are mainly characterized by a cholesterol efflux, dynamic cholesterol redistribution in particular in the apical zone of the head and also a phospholipids reorganization resulting to the scramblase activation. The existence of lipids ordered microdomains (lipid rafts) has been recently observed in sperm membranes. These lipid and membrane protein movements are believed to play a role in modulating signaling pathways mainly, the AMPc/PKA and ERK pathways. One of the early key events is the activation of adenylate cyclase by high levels of bicarbonate. All these pathways lead finally to the phosphorylation of Tyr-proteins. But capacitation seems to be more complex with the contribution of other kinases (from the PI3K/Akt pathway and phosphotyrosine kinases) towards the phosphorylation of other Ser/Thr and Tyr proteins. The reactive oxygen species (ROS) seem to be important in the control of mechanisms involved in capacitation.