Failure to infect embryos after virus injection in mouse zygotes.

Background: The intracytoplasmic injection of sperm raises the problem that viral elements may be transported into the oocyte by the spermatozoon or the surrounding medium. It also raises questions about how the developing zygote will behave.

Methods: We used the murine model to microinject murine cytomegalovirus (MCMV) into the zygote ooplasm and followed the changes in these microinjected zygotes in vivo and in vitro over time.

Results: 80% of zygotes microinjected with viral suspension, and 80% injected with medium alone, survived. Although MCMV DNA was detected in 56% of injected embryos, up until the blastocyst stage, the mice born from these injected zygotes developed normally and did not contain MCMV DNA. When embryonic stem cells were co-incubated with MCMV and then transferred into healthy blastocysts, the offspring were normal and did not contain any MCMV DNA.

Conclusions: Our observations suggest that even if MCMV DNA persists from the zygote to the blastocyst stage, its presence has no detrimental effect on pre-implantation or post-implantation development.