Development and loss of the ability of mouse oolemma to fuse with spermatozoa

To further our knowledge on the mechanisms and molecules involved in mouse sperm-oocyte plasma membrane interaction, experiments were carried out to determine the stage during oogenesis at which an oocyte acquires the capacity to fuse with acrosome-reacted sperm. Zona-free oocytes 10 microns in diameter do not fuse with sperm. Oolemma fusibility is first acquired when the oocyte reaches about 20 microns in diameter. Fusibility is maintained even after fertilisation has occurred and is lost completely by the 4-cell stage.