Electrical-assisted microinjection for analysis of fertilization and cell division in mammalian oocytes and early embryos

Microinjection is an essential approach in the study of mammalian oocytes and early embryos, and is useful for the introduction of many molecules and reagents. Whereas microinjection into germinal vesicle stage oocytes is relatively simple using various microinjection setups, metaphase-II mouse eggs are notoriously fragile, and nondamaging microinjection can be difficult to achieve. Here we describe a microinjection method that is based on electrophysiology, which vastly reduces microinjection damage, especially in metaphase-II eggs. When optimized, this approach allows for over 90% oocyte survival, increasing confidence in experimental results.