SNAP-25 IS ESSENTIAL FOR CORTICAL GRANULE EXOCYTOSIS IN MOUSE EGGS

Synaptosome-associated protein of 25 kDa (SNAP-25) has been shown to p lay an important role in Ca2+ dependent exocytosis in neurons and endo crine cells. During fertilization, sperm-egg fusion induces cytosolic Ca2+ mobilization and subsequently Ca2+-dependent cortical granule ICG ) exocytosis in eggs. However, it is not yet clear whether SNAP-25 is involved in this process. In this study, rye determined the expression and function of SNAP-25 in mouse eggs. mRNA and SNAP-25 were detected in metaphase II (MII) mouse eggs by RT-PCR and immunoblot analysis, r espectively. Next, to determine the function of SNAP-25, we evaluated the change in CG exocytosis with a membrane dye, tetramethylammonium-1 ,6-diphenyl-1,3,5-hexatriene, after microinjection of a botulinum neur otoxin A (BoNT/A), which selectively cleaves SNAP-25 in MH eggs. Sperm -induced CG exocytosis was significantly inhibited in the BoNT/A-treat ed eggs. The inhibition was attenuated by coinjection of SNAP-25. Thes e results suggest that SNAP-25 may be involved in Ca2+-dependent CG ex ocytosis during fertilization in mouse eggs.