Reproduction Abstracts

Embryo dormancy (embryo diapause) is a reproductive strategy used by ~100 different mammals to avoid the risk of exposing their offsprings to unfavourable environmental conditions by delaying embryo implantation. The blastocysts from domestic sheep, rabbit or cattle enter into diapause after being transfer into mouse uteri induced to have delayed implantation. The observation suggests that blastocysts from all mammals, including that of human, may have an ability to enter into diapause. The molecular mechanism of embryonic diapause in all species is not yet clear. Our previous data showed that the levels of let-7 were relatively high in diapause embryos compared to reactivated embryos by E₂ in mice. The embryos electroporated with let-7 can still be alive even after the culture for up to day 13. Delayed implantation model showed that the activated embryos changed into diapause state if these embryos were electroporated with let-7. Importantly, 12.5% of diapause embryos induced by let-7 in vivo developed to term after culture for 4 days (i.e. day 8). Microarray results showed that gene expression profiles were similar between let-7-treated and P₄-induced dormant embryos compared to D4 or E₂-activated embryos. Further analysis demonstrated that cell cycle and metabolism related genes were involved in the roles of let-7 in induction of embryo dormancy. In conclusion, let-7 has an important role in the induction of embryo dormancy in mice.