A novel trans-complementation assay suggests full mammalian oocyte activation is coordinately initiated by multiple, submembrane sperm components. Biol Reprod 1999; 60: 747–755. [Medline] [CrossRef

To initiate normal embryonic development, an egg must re-ceive a signal to become activated at fertilization. We here re-port that the ability of demembranated sperm heads to activate is abolished after incubation over the range 20–448C and is sen-sitive to reducing agents. On the basis of this observation, we have developed a microinjection-based, trans-complementation assay in order to dissect the heat-inactivated sperm-borne oo-cyte-activating factor(s) (SOAF). We demonstrate that the failure of heat-inactivated sperm heads to activate an egg is rescued by coinjection with dithiothreitol-solubilized SOAF from demem-branated sperm heads. The solubilized SOAF (SOAFs) is trypsin sensitive and is liberated from demembranated heads in a tem-perature-dependent manner that inversely correlates with the ability of sperm heads to activate. This argues that SOAFs is a proteinaceous molecular species required to initiate activation. Injection of oocytes with mouse or hamster sperm cytosolic fac-tors, but not SOAFs alone, induced resumption of meiosis, fur-ther suggesting that these cytosolic factors and SOAF are dis-tinct. Collectively, these data strongly suggest that full mam-malian oocyte activation is initiated by the coordinated action of one or more heat-sensitive protein constituents of the peri-nuclear matrix and at least one heat-stable submembrane com-ponent