ROLES OF HETEROTRIMERIC AND MONOMERIC G-PROTEINS IN SPERM-INDUCED ACTIVATION OF MOUSE EGGS

Results of several lines of experimentation suggest that sperm-induced egg activation has several features in common with G protein-coupled receptor signal transduction mechanisms, We report that microinjection of GDP beta S into metaphase II-arrested mouse eggs blocks sperm-indu ced egg activation, Since GDP beta S inactivates both heterotrimeric a nd monomeric classes of G proteins, the involvement of members of each of these families in sperm-induced egg activation was evaluated, Neit her pertussis toxin treatment of eggs nor microinjection of eggs with inhibitory antibodies toward G alpha(q) blocked sperm-induced egg acti vation, Nevertheless, microinjection of phosducin, a protein that bind s tightly to free G protein beta gamma subunits, specifically inhibite d second polar body emission, the fertilization evoked decrease of H1 kinase activity and pronucleus formation, Microinjection of phosducin, however, did not inhibit the fertilization-induced modifications of t he zona pellucida and microinjection of beta gamma(t) did not result i n egg activation in the absence of sperm, Inactivation of the monomeri c Rho family of G proteins with C3 transferase from Clostridium botuli num inhibited emission of the second polar body and cleavage to the 2- cell stage, but did not affect the modifications of the zona pellucida or pronucleus formation, Microinjection of Ras(val12), which is a con stitutively active form of Ras, did not result in egg activation in th e absence of sperm, Moreover, microinjection of either an anti-Ras neu tralizing antibody (Y13-259) or a dominant negative form of Ras (Ras(T )) did not affect events of sperm-induced egg activation, In contrast, microinjection of Ras(T) inhibited embryo cleavage to the 2-cell stag e, These results suggest that both heterotrimeric and monomeric G prot eins are involved in various aspects of sperm-induced egg activation.