PLASMA-MEMBRANE BLOCK TO SPERM ENTRY OCCURS IN MOUSE EGGS UPON PARTHENOGENETIC ACTIVATION

The ability of parthenogenetically activated mouse eggs to establish a plasma membrane (PM) block to sperm penetration was studied. Zona-fre e eggs preloaded with Hoechst 33342 were activated by exposure to etha nol or OAG (1-oleoyl-2-acetyl-sn-glycerol) and inseminated after diffe rent periods. Eggs challenged with sperm at 30- or 60-min postactivati on displayed a fertilization frequency significantly lower than that o f control eggs. Conversely, when insemination was carried out at 120-m in postactivation, the proportion of fertilized eggs was equivalent to that observed in the control group. Moreover, we report that when the eggs were induced to resume meiosis without any notable loss of CGs ( egg exposure to OAG at 100 mu M external Ca2+ or to heat shock), a nor mal ability to be penetrated was recorded at 30-min postactivation. Si milar behaviour was exhibited by eggs that underwent a CG exocytosis c lose to that triggered by sperm in absence of nuclear activation (micr oinjection of inositol 1,4,5-trisphosphate into the egg at 1 mu M cyto solic concentration). Present data support the conclusion that parthen ogenetically activated mouse eggs are capable of a transitory PM block response that requires both CG exocytosis and meiosis resumption to o ccur. (C) 1994 Wiley-Liss, Inc.