Production of mouse offspring from inactivated spermatozoa using horse PLCζ mRNA

Improving artificial oocyte activation is essential for assisted reproduction or animal biotechnology that can obtain healthy offspring with a high success rate. Here, we examined whether intracytoplasmic injection of equine sperm-specific phospholipase C zeta (ePLCzeta) mRNA, the PLCzeta with the strongest oocyte activation potential in mammals, could improve the mouse oocyte activation rate and subsequent embryonic development using inactivated spermatozoa. mRNA of mouse PLCzeta (mPLCzeta) or ePLCzeta were injected into mouse oocytes to determine the optimal mRNA concentration to maximize the oocyte activation rate and developmental rate of parthenogenetic embryos in vitro. Full-term development was examined using NaOH-treated inactive spermatozoa using the optimal activation method. We found that the most optimal ePLCzeta mRNA concentration was 0.1 ng/microl for mouse oocyte activation, which was ten times stronger than mPLCzeta mRNA. The concentration did not affect parthenogenetic embryo development in vitro. Relatively normal blastocysts were obtained with the same developmental rate (52-53% or 48-51%, respectively) when inactive spermatozoa were injected into activated oocytes using ePLCzeta or mPLCzeta mRNA injection. However, the birth rate after embryo transfer was slightly but significantly decreased in oocytes activated by ePLCzeta mRNA (24%) compared to mPLCzeta mRNA (37%) or strontium treatment (40%) activation. These results suggest that the higher activation rate does not always correlate the higher birth rate, and some mechanisms might exist in the oocyte activation process that could affect the later developmental stages like full-term development.