FERTILIZATION AND DEVELOPMENT OF MOUSE OOCYTES INJECTED WITH ISOLATEDSPERM HEADS

To determine whether spermatozoa must be structurally intact before mi crosurgical injection into oocytes for normal fertilization, intact sp ermatozoa, as well as sperm heads separated from tails by sonication, were individually injected into oocytes. When whole spermatozoa were i njected immediately after their immobilization, the majority of the oo cytes were fertilized and developed normally. Sonication in the presen ce or absence of Triton X-100 decapitated more than 95% of spermatozoa . Although all decapitated spermatozoa were diagnosed as ''dead'' by l ive/dead sperm staining, separated sperm heads (nuclei) could particip ate in normal embryo development when injected into the oocytes. The a bility of isolated sperm heads (nuclei) to participate in normal embry o development was maintained under cryopreservation conditions that we re not suitable for the survival of plasma membrane-intact spermatozoa . These results indicate that 1) spermatozoa do not need to be structu rally intact for intracytoplasmic injection, 2) the plasma and acrosom al membranes and all tail components are not essential for normal embr yo development, at least in the mouse, and 3) the cryopreservation con ditions required for maintenance of the genetic integrity of sperm nuc lei are less stringent than those necessary for keeping plasma membran e-intact spermatozoa alive.