Lipid Rafts: Keys to Sperm Maturation, Fertilization, and Early Embryogenesis
Figure 1
Schematic of lipid rafts in gamete formation, function, fertilization, and early embryogenesis. (a) Sperm mature, gaining motility and fertilizing abilities, during epididymis transit. The extracellular factors, epididymosome and HE1, dynamically change the components of the sperm plasma membrane. (GPI, glycosylphoshphatidylinositol; SM, sphingomyelin; PFA, polyunsaturated membranous fatty acids). (b) Ejaculated sperm are temporally bound to SVS2 (decapacitation). SVS2 binds to GM1 of the sperm head in the uterus, resulting in the inhibition of the fertilizing ability of sperm. Subsequently, the sperm that migrate to the oviduct undergo capacitation. Capacitation causes an efflux of cholesterol and GM1 from the plasma membrane and an increase of membrane fluidity and protein tyrosine phosphorylation (PTP). (c) Sperm recognize and adhere to UpIII/UpIb of Xenopus oocyte and fuse with CD9/CD81 of murine oocyte plasma membrane. These molecules are enriched in lipid rafts, and oocytes treated with cyclodextrin prevent the sperm from fertilization. (d) In early embryogenesis, SSEAs are colocalized with cholesterol and GM1 plays an important role in the compaction of an embryo, leading to the decision of cell fate and its pluripotency.
