PARTHENOGENETIC ACTIVATION OF PORCINE OOCYTES WITH GUANOSINE-5'-0-(3'-THIOTRIPHOSPHATE)

A possible mechanism by which sperm activate oocytes may involve a G p rotein-mediated signal-transducing pathway. Artificial stimulation of G proteins leads to events very similar to those at fertilization in o ocytes of several species. Here we report the effects of activation of a G protein with guanosine-5'-O-(3'-thiotriphosphate) (GTP-gamma-S), a hydrolysis-resistant analog of guanosine triphosphate (GTP), in porc ine oocytes. Mature oocytes were injected with 1 mM GTP-gamma-S. In re sponse to injection, oocytes underwent changes normally occurring at f ertilization, i.e., cortical granule exocytosis, changes in the protei n synthetic profile, pronuclear formation, and development to the blas tocyst stage. Guanosine-5'-O-(2-thiodiphosphate) (GDP-beta-S; a metabo lically stable analog of guanosine diphosphate [GDP] that inactivates the G protein) and the carrier medium (CM; medium in which the injecte d compounds were dissolved) were significantly less effective in oocyt e activation. It is suggested that porcine oocytes contain the compone nts of a G protein-mediated signaling pathway that might function in o ocyte activation at fertilization.